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- CHAPTER 7- 
SYNTHESIS AND ANTITUMOR ACTIVITY 
OF ELLIPTICINE ALKALOIDS 
AND RELATED COMPOUNDS 
GORDON W. GRIBBLE 
Deparhnent of Chemistry 
Dartmouth College 
Hanover, New Hampshire 03755 
I. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
11. Occurrence and Structural Determination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
IV. Synthesis of Olivacine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
V. Synthesis of Modified Ellipticine Derivatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
111. Synthesis of Ellipticine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
A. Synthesis of Substituted Ellipticines . . . . . . . . . . . . . . . . . . . 
C. Synthesis of Azaellipticines . . . . . . . . . . . . . . . . . . . . . 
D. Synthesis of Nonlinear Pyridocarbazoles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
F. Synthesis of Tricyclic Analogs . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . 
B. Synthesis of Isoellipticines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
E. Synthesis of Oxazolopyridocarbazoles . . . . . . . . . . . . . . . . . . 
H. Synthesis of Ellipticine Conjugates . . . . . . . . . . . . . . . . . . 
I. Synthesis of Miscellaneous Analogs . . . . . . . . . . 
VI. Biological Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
VII. Antitumor Activity in . . . . . . . . . . . . . . . . . 
IX. Mutagenicity . . . . . . . . . . . . . . 
VIII. Mechanism of Action . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
X. Metabolism and Microbial Transformation . . . . . . . . . . . . . . . . . . . . 
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
XIII. Clinical Trials .................... 
XIV. Conclusion 
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 
239 
240 
242 
250 
254 
255 
266 
27 1 
274 
219 
283 
29 1 
294 
300 
305 
307 
31 I 
325 
325 
328 
340 
340 
343 
343 
I. Introduction 
This chapter deals with the synthesis and biological properties of the relatively 
small family of pyrido[4,3-b]carbazole alkaloids, exemplified by ellipticine (l), 
9-methoxyellipticine (2), 9-hydroxyellipticine (3), and olivacine (4), and of the 
much larger number of structural analogs that have been synthesized and studied 
239 THE ALKALOIDS, VOL. 39 
Copyright 0 1990 by Academic Press, Inc. 
All rights of reproduclion in any form reserved. 
240 GORDON W. GRIBBLE 
following the initial discovery of the antitumor properties of these alkaloids (1- 
5) . Indeed, although synthetic activity in this area has been intense and constant 
in the 30-year period since the original isolation of these alkaloids (6,7), the 
introduction into the cancer clinic of 9-methoxyellipticine lactate in 1969 (8) 
and, especially, "elliptinium" (2-methyl-9-hydroxyellipticinium acetate) (5) in 
1977 (9) has triggered an explosion of activity, both in the synthesis of pyridocar- 
bazoles and related ring systems and in their biological evaluation. Thus, even 
though this area was comprehensively reviewed by Suffness and Cordell (10) in 
Volume 25 of this treatise [with coverage through December 1984 and some 
additional references to April 1985, and including much unpublished data from 
the National Cancer Institute (NCI)], the wealth of new material justifies the 
present review. This chapter covers the literature from 1985 through most of 
1989. In addition to the excellent Suffness and Cordell review (lo), there are 
several other important articles that provide coverage of the synthesis andlor 
biological profile of the ellipticine alkaloids (11-21). Owing to the large number 
of pyridocarbazole structural variants to be discussed, the Chemical Abstracts 
pyridocarbazole numbering system (l), rather than the alkaloid biogenetic path- 
way numbering system, is used throughout this chapter. 
11. Occurrence and Structural Determination 
Ellipticine (1) and 9-methoxyellipticine (2) have been isolated from Ochrosia 
acurninata stems (22) and from in vitro callus cultures derived from the stems of 
Ochrosia elliptica (23,24). It is found that the in vitro production of these 
alkaloids can be increased by cloning small cell aggregates. 
A noteworthy development is the isolation and characterization of the first 
1 R = H 
2 R=OCH3 
3 R = O H 
7. ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 24 1 
naturally occurring bisellipticine alkaloid, strellidimine (8), from the African tree 
Strychnos dinklugei Gilg. (Loganiaceae) (Scheme 1) (25). it is evident that this 
optically inactive alkaloid is formed in vivo by the coupling of 9-hydroxyellip- 
ticine (3) and 3,4-dihydroellipticine (7), both of which are present in S. dinklugei 
(26). This biogenesis was demonstrated by the biomimetic synthesis of 8 shown 
in Scheme 1. Oxidation of 3 to the ellipticine quinone imine 6 with horseradish 
peroxidase (HRP) and hydrogen peroxide in the presence of 7 gave strellidimine 
(8) in quantitative yield (25). 
A method for the separation of ellipticine (l), 9-methoxyellipticine (2), and 9- 
hydroxyellipticine (3) using cellulose adsorption chromatography (thin layer or 
paper) has been developed (27). The technique involves a solvent system consist- 
ing of a 50 : 50 mixture of 1.3 M ammonium sulfate and 96% acetic acid, 
followed by iodine vapor detection. 
An X-ray crystal structure of 9-methoxy-l l-demethylellipticine (9) (28) re- 
veals little difference in geometry from that previously observed in ellipticine and 
its derivatives (29,30). Thus, the absence of a methyl group at C-11 and the 
presence of the 9-methoxyl substituent does not alter the pyrido[4,3-b]carbazole 
structure. An X-ray crystal structure study of the charge-transfer complex formed 
between 9-methoxyellipticine (2) and 7,7,8,8-tetracyano-p-quinodimethane 
yJ--& + Q-@ pH 7.4 * 
30 rnin 
- 100% 0 0 
CH3 
H 
CH3 
7 6 
SCHEME 1. Structure and biomimetic synthesis of strellidirnine (8) (25) 
242 GORDON W. GRIBBLE 
(TCNQ) (10) reveals a stacking sequence between electron acceptor (10) and 
electron donor (2) as follows: 10-2-2-10 (31). 
In what, it is hoped, will be the final word on the NMR chemical shift 
assignments of 9-methoxyellipticine (2), Commenges and Rao (32) have revised 
several of the I3C-NMR assignments published earlier by Sainsbury and co- 
workers (33). In the present work, a combination of two-dimensional (2D) NMR 
techniques ('H-IH homonuclear and 'H- 13C heteronuclear chemical shift cor- 
relations, including long-range 'JCH determinations) and the reinvestigation of 
model compounds(5-methoxyindole and 1,4-dimethylcarbazole) has required the 
reassignment of C-4, C-5, C-7, C-8, C-10, C-lOa, C-lob, C-11, and C-1 la of 9- 
methoxyellipticine (2). The full set of 'H and I3C chemical shifts is given in 
Scheme 2. 
111. Synthesis of Ellipticine 
In addition to the reviews cited earlier (10-14,16,19), several other reviews 
covering the previous synthetic efforts toward ellipticine are available (34-37). 
This section deals with new synthetic approaches to the ellipticine skeleton only; 
123.3 
7.89 3.27 9.69 153.1 123.6 
7.20 8.41 
CH, H 
2.77 7.91 
11.2 7.49 
137.3 
107.8 
SCHEME 2. 'H- and I3C-NMR chemical shifts of 9-methoxyellipticine (2) in parts per million 
downfield from tetramethylsilane in (methyl sulfoxide)-d6 (32). 
7. ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 243 
derivatives of ellipticine as well as variations of the pyrido[4,3-b]carbazole ring 
system are covered in Section V. 
Differding and Ghosez (38) have reported a novel and highly convergent 
construction of the 6H-pyrido[4,3-b]carbazole ring system, involving, as the key 
step,an intramolecular Diels-Alder cycloaddition of a vinylketenimine (18 --., 
19) (Scheme 3). Piperidone 11 was converted to the unsaturated ester 12 by an 
Emmons-Wadsworth reaction, and then deconjugation and saponification gave 
acid 14. Conversion to acid chloride 15 and acylation of aniline 16 gave the 
amide 17. In situ formation of the vinylketenimine 18 was accomplished with 
triphenylphosphine dibromide to yield, after the facile Diels-Alder cycloaddi- 
tion, tetracycle 20 after tautomerism of the initially formed 19. Reduction of the 
ester group in 20 gave the (unnamed) alkaloid 21 which had been previously 
converted to ellipticine (1) by dehydrogenation/demethylation (39). The overall 
yield of 1 from 11 is 5%, although the final step obviously reduces the overall 
yield drastically. Surprisingly, this strategy-wherein more than one ring of the 
final tetracycle is formed in a single step-apparently has not been previously 
pursued in the construction of pyridocarbazoles. 
Miyake and co-workers (40) have published a synthesis of ellipticine that 
features a novel reductive phenylation of nitroarenes (41) (Scheme 4). Nitration 
of 5,g-dimethyl- 1,2,3,4-tetrahydroisoquinoline (22) gave an inseparable mixture 
of nitro compounds 23. Treatment of this mixture with iron pentacarbonyl and 
triflic acid in the presence of benzene gave a 2 : 1 mixture of amines 24 and 25. 
Separation of these isomers and diazotization of each with nitrous acid, conver- 
sion to the azide, and thermolysis yielded ellipticine (1) and “isoellipticine” (27) 
(5,l I-dimethyl- 10H-pyrido[3,4-b]carbazole), respectively, following Pd/C de- 
hydrogenation of the initially formed nitrene insertion product (e.g., 26). The 
overall yield of ellipticine is 9%. 
Ketcha and Gribble (42) have adapted the earlier Saulnier-Gribble synthesis 
(43) of isoellipticine quinone to the synthesis of ellipticine quinone 33 and hence 
to ellipticine (Scheme 5). A refinement of the earlier 3-lithioindole technology 
(43) involves the direct Friedel-Crafts acylation of 1 -( phenylsulfony1)indole 
(31) to introduce the 3-acyl group. Thus, the inherent regioselectivity of 3,4- 
pyridinedicarboxylic anhydride (28) (cinchomeronic anhydride) was reversed by 
conversion of the known ester acid 29 to acid chloride 30. Acylation of indole 31 
with 30 gave keto ester 32. Final closure to quinone 33 was accomplished using 
tandem in situ carbonyl protection and deprotonation at C-2, followed by 
cyclization. Since quinone 33 had been previously converted to ellipticine by 
Joule and co-workers (44), this work represents a formal synthesis of 1, in 13% 
overall yield from anhydride 28. The identical protocol applied to keto acid 34, 
obtained via Friedel-Crafts acylation of 1-( phenylsulfony1)indole (31) with 
pyridine anhydride 28, provided isoellipticine quinone 36 and, hence, isoellip- 
ticine (27) in 13% overall yield from the N-protected indole 31 (42) (Scheme 6). 
H3C COZCH, 
1. LDA 
THF -68°C 1 h 
I A -4 2. NHiCl ( E10)2POCH(CH3)C02Me NaH €120 
75% 
6 
CH3 
1 1 
I -100% 
12 13 
CH3 
I 
CH3 
H3cYC02H 
1N KOH 
2 h 60°C 
75% I 
14 
CH3 
C 
I 
I 
17 
CH3 
HzNn 
16 MeO,C-CaC * 
Ei3N 
1. HCI 
CHpClp 
2. (CH,),C =C(CI)NMe, 
CHzCIz 
20°C 
P h3 P Br2 
t 
ET3N CH2CIp 
A 2.5 h 
75% 
I 
15 
CH3 
__c 
50% 
COZCH, 
I 
~ c H 3 LiAIH4 COZCH, - 
/ AICl3 
I / N H € 1 2 0 
CH3 CH3 A 1.25 h 
71 Yo 19 20 
10% Pd/C 
H3c?F) 
t l 
*0cH3 / / 36% 
CH3 
21 
SCHEME 3. Differding-Ghosez synthesis of ellipticine (1) (38). 
7. ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 245 
i H 3 
2 2 
I 2. ” N$02 NaN3 
WAC / / 10% Pd/C A 
46‘70 
1- 
H 
CH3 
26 
CH3 
23 
CH3 
25 (22%) 
SCHEME 4. Miyake et al. synthesis of ellipticine (1) and isoellipticine (27) (40). 
Ketcha and Gribble (42) have also used this methodology to convert phthalic 
anhydride (37) to the benzo[b]carbazole quinone 38. 
In two papers, Miller and co-workers (45,46) have extended their intra- 
molecular ring B cyclization strategy (47) to the use of aryl nitrenes in the 
synthesis of pyridocarbazoles. Thus, in the first paper, isoquinoline azide 39 was 
heated at 180-200°C to afford ellipticine (1) as the minor product (20%) 
(Scheme 7). The major product was the isomeric pyrido[3,4-~]carbazole 40 
(60%). This result is consistent with the relative nucleophilicities of C-6 and C-8 
of isoquinoline. The isomeric azido isoquinoline 41 exhibited comparable re- 
gioselectivity in the cyclization of the corresponding nitrene to yield isoellip- 
ticine (27) as the minor product (Scheme 7). 
246 GORDON W. GRIBBLE 
0% 7 
0 0 
37 38 
The second paper (46) describes an improvement in the nitrene strategy by 
merely switching the location of the azide group to the C-6 position of the 
isoquinoline ring (Scheme 8). Using their previously developed isoquinoline 
synthesis (48), Miller and Dugar prepared 47 in several steps from acetanilide 43 
via indene 46. A Suzuki reaction with 47 gave the requisite amine 48, which, 
upon diazotization and trapping, afforded azide 49. Heating 49 gave ellipticine 
(1) in excellent yield and in 41% overall yield from 43. 
2 8 
C0ZCH3 
&cocl 
30 
1. NaOMe C0ZCH3 
MeOH THF 
-70°C + rt - - 
2. aqHCI PhH A 
73% 
AICl3 CH2C12 
25°C 
50% 
. _ 
29 
78% 
0 COZCH, 
QCTJfyl I 
SOZPh 
32 
1. LiN(Me)CH2CH2NMe2 THF -75°C 2 h *fJ--& - 1 1. CHBLi 
2. (TMS)*NLi 2. NaBH4 
THF -75'C+rt 
0 94% 
33 
47% 
SCHEME 5 . Ketcha-Gribble synthesis of ellipticine quinone 33 and ellipticine (1) (42). 
0 COZH 
07 + O*N - 25°C 2 h @ J J N I 
SOzPh 69% S0,Ph 
31 2 8 34 
0 COZEt 
1. LiN(Me)CHzCHzNMez 
M F -75°C 2 h OTMN 2. (TMS)2NLi EtOH pTsOH PhH 
A 3days 
* 
I THF -75°C + rt 
75% SOzPh 
37% 
35 
3 6 2 7 
SCHEME 6. Ketcha-Grihhle synthesis of isoellipticine quinone 36 and isoellipticine (27) (42). 
0 / 180 dodecane - 200°C (20%) 1+fJ--QH3 0-w 
N 
\ CH3 
39 40 (60%) 
dodecane w 2 7 + 07gH3 
CH3 1 . 3 \ N 
4 1 42 
SCHEME 7. Miller et al. synthesis of ellipticine (1) and isoellipticine (27) (45). 
248 GORDON W. GRIBBLE 
1. Br2, l2 cat 
CH2C12 rt 
____) 
2. CH3COCI 
Et3N THF 
CH3 rt 
94% 
- @ 
1. CICH2CH2C02H 
CS2 AIC13 
2. AIC13, NaCl 
AcHN 180°C H2N 
CH3 3. 2NHCI 
43 44 A 
84% 
1. 0 3 -78°C 
MeOH CH2CI2 
t 
2. (CH&S NaHC03 
3. NH40H 
AcHN 
CH3 3. Ac20 NaOAc CH3 4. 2N HCI A 
85% 
Bf* 
1. NaBH4 MeOH 
0°C E rt 
2. 40%H2SO4 
THF A 
AcHN 
75% 46 
Br* 45 
1. NaN02 
Br@ PhB(OH)2 
PhH A 
dil HCI 0°C t 
/ 2. NaN3 
H2N 85% 
\ / Pd(PPh3)4 (cat) \ 
H2N 
CH3 2M Na2C03 CH3 
47 99% 48 
180°C 
- 1 
96% CH3 
49 
SCHEME 8. Miller-Dug= synthesis of ellipticine (1) (46). 
Zee and Su (49) have modified the original Woodward et al. (7) synthesis 
of ellipticine, as improved by Sainsbury and Schinazi (50) and Berman and 
Carlsson (51), to achieve a convenient and reasonably efficient synthesis of 
ellipticine (1) (Scheme 9). Bergman’s improved method (51) was used to prepare 
3-vinylindole 53, which, after catalytic hydrogenation to 54, was reductively 
acetylated directly to afford 2-acetyl- 1,2-dihydroellipticine (55). Hydrolysis and 
aromatization completed the synthesis of ellipticine (1) in 12% overall yield from 
indole (50). 
7. ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 249 
CH3 
I CH3 I 
< 1 torr 
H 10h H 50% 
81% 
5 0 51 52 
Zn Ac20 
A 48 YO 2 h 
- 
o : - i N H 
HZ 20psi CH30H 5‘X0 Pd’c, 6 h 0 7 - i N H 
53 90% 54 
CH3 
I 
10% H2S04 
____t 
CH30H air 
A 6 h 
68% 
SCHEME 9. Zee-Su synthesis of ellipticine (1) (49). 
May and Moody (52) have reported a full account of their Diels-Alder 
cycloaddition route to ellipticine (1) and isoellipticine (27) (Scheme 10). Conver- 
sion of indole (50) to 3-indole-2-propionic acid (56) with lactic acid was fol- 
lowed by a Plieninger cyclization to the pyranoindole 57. Reaction of 57 with 
3,4-pyridyne (59), as generated from triazene 58, afforded equal amounts of 
ellipticine (1) and isoellipticine (27). Although theoverall yield of 1 from indole 
is only 3%, the sequence involves only three steps. 
In an effort to overcome the lack of regioselectivity in the cycloaddition of 3,4- 
pyridyne (59) with dienes, such as 57 (Scheme lo), or furo[3,4-b]indoles (e.g., 
60) (53), Davis and Gribble (54) have utilized unsaturated lactams 61 and 62 as 
250 GORDON W. GRIBBLE 
lactic acid 
250°C 
32% 
50 
59 10 
@--j---jCOzH - BF3 Et20 07- 
H 43% H 
56 57 
CH3 
‘ N / 0 N 
H H 
CH3 CH3 
1 (20%) 27 (20%) 
58 
SCHEME 10. May-Moody synthesis of ellipticine (1) and isoellipticine (27) (52) 
3,4-pyridyne surrogates (Scheme 11). Work with model dienophiles and a fron- 
tier molecular orbital analysis of furo[3,4-b]indole 60 led to the prediction that 
the “ellipticine orientation” would obtain (54). Thus, the dimethylfuroindole 60, 
prepared from 3-ethylindole as previously described (53), was treated with un- 
saturated lactam 61 (prepared from 8-valerolactam in three steps) in the presence 
of trimethylsilyl triflate to give lactam 63 as a single product. Difficulty in 
removing the benzyl group forced these workers to synthesize the p-methoxy- 
benzyl analog 62. The Diels-Alder cycloaddition reaction yielded the adduct 64, 
which was converted to ellipticine (1) by reduction and dehydrogenation. Con- 
trol experiments with mixtures of 1 and isoellipticine (27) revealed that the 
Diels-Alder cycloaddition leading to 64 was at least 99% regioselective. How- 
ever, the overall yield of l from 60 thus far is a disappointing 18%, owing to the 
difficulty in manipulating the D ring. 
IV. Synthesis of Olivacine 
As we see in later sections, olivacine (4), the oft forgotten cousin of ellip- 
ticine, is receiving renewed attention as the search for improved antitumor 
pyridocarbazoles continues. Nevertheless, the number of new synthetic routes to 
olivacine is few. 
7. ELLIPTICINE 
60 
ALKALOIDS AND RELATED COMPOUNDS 25 1 
0 
2. aqNaHC03 
61 R = PhCH2 (76%) 
62 R = p-CH3OPhCH2 (88%) 
CH3 0 
1 . LiAIH4 
THF 
2. PdIC 
decalin A 
20% 
63 R = P h C H 2 
64 R = p-CH30PhCH2 
SCHEME 1 1 . Davis-Gribble synthesis of ellipticine (1) (54) 
Using Husson’s method (39), Maftouh and co-workers (55) have described 
syntheses of 7-hydroxy- (71) and 9-hydroxyolivacine (73). Thus, 7-methoxyin- 
dole (65) was condensed with enamine ketal66 (prepared from the correspond- 
ing pyridine 67) to give carbazole 68 (Scheme 12). Standard ring D construction 
involving a Bischler-Napieralski cyclization (39) gave the tetrahydroolivacine 
derivative 69. Dehydrogenation and demethylation completed the synthesis of 
71. In identical fashion, the synthesis of 9-hydroxyolivacine (73) was accom- 
plished (55) by the demethylation of the alkaloid 9-methoxyolivacine (72), which 
had been previously synthesized by Besselievre and Husson (39). 
Using the Cranwell-Saxton synthesis (56) of ellipticine, as modified by Birch 
et al. ( 5 3 , Sainsbury and co-workers (58), have described a new 3-acylcarbazole 
synthesis and its application to a synthesis of olivacine (4) (Scheme 13). Reaction 
of gramine (74) with the appropriate biscyano ketone gave 75. Cyclization in 
acetic acid afforded 76, which, upon treatment with hot silica gel, underwent 
dehydrocyanation and tautomerization to give cyanocarbazole 77. Reduction to 
aldehyde 78 was followed by imine 79 formation. The addition of methyllithium 
and p-toluenesulfonyl chloride gave carbazole acetal80. Ring D was crafted by 
the standard hydrogen chloride ring closure. The final dephenylsulfonylation was 
performed with sodium to give olivacine (4). Surprisingly, sulfonamide 81 was 
very stable in acid, but, more importantly, no cyclization to the alternative 
pyrido[3,6c]carbazole 82 was detected. Although the methyl ketone 83 could be 
easily prepared from nitrile 77, condensation of the latter with amino 
1. CH31 
65 
50% HOAc 
A 
56 h 
CH&N 
A 
2. NaBH4 
81% OCH, I 
66 
82% 
67 
t 1. Ac20 pyr 
l h rt 65% 
* 
\ / 2. POC13 
CHC13 
CH3 A 1 0 h 
OCH3 
68 3. NaBH4 
CH30H CHCl3 
WHCH3 
39% 
7H3 y 3 
9 - - g C H 3 A 24h 9-q H / / 
OCH, CH3 22% OCH, CH3 
69 70 
48% HBr 
A l h 
- 
70% 
OH CH3 
71 
SCHEME 12. Maftouh et al. synthesis of 7-hydroxyolivacine (71) (55) 
cH30n-- - 48% HBr ""n-- 
/ / A l h ' N / / 
H 
' N 
H 
CH3 
70 '/o CH3 
7 2 73 
252 
o - q c : N 250°C silica gel 0--qCN 5 
94% 
CH3 
55% 
76 77 
SCHEME 13. Synthesis of olivacine (4) by Sainsbury and co-workers (58). 
254 GORDON W . GRIBBLE 
r OH 1 
oq 85 ' 
NaBH4 
EtOH 
A 
57% 
- 
I -Njl' H , 2. LiBHEt3 -1 00°C 
L 86 J 
SCHEME 14. Gribble-Obaza-Nutaitis synthesis of olivacine (4) (60). 
acetaldehyde acetal to the olivacine precursor 84, in contrast to a prior report 
(59), could not be effected (58). 
In unpublished work, Gribble and Obaza-Nutaitis (60) have adapted the Saul- 
nier-Gribble ellipticine synthesis (61) to the synthesis of olivacine (Scheme 14). 
Keto lactam 85, available from indole in four steps (71% yield) (61), was treated 
sequentially with methyllithium and lithium triethylborohydride to give diol 86, 
which, without isolation, was reduced with sodium borohydride to give l-de- 
methylolivacine (87). This had been previously converted to olivacine (4) by 
Kutney and co-workers (62). The success of this synthesis of 87 was due to the 
fact that Saulnier and Gribble (63) had previously established that the ketone 
carbonyl of keto lactam 85 is more reactive than the lactam carbonyl group. 
V. Synthesis of Modified Ellipticine Derivatives 
Most of the new synthetic work on ellipticine in the late 1980s has dealt with 
modified ellipticine derivatives. Several French groups have made enormous 
strides in the design and synthesis of ellipticine analogs. The material in this 
section is divided into nine areas: A. Synthesis of Substituted Ellipticines; B. 
Synthesis of Isoellipticines; C. Synthesis of Azaellipticines; D. Synthesis of 
Nonlinear Pyridocarbazoles; E. Synthesis of Oxazolopyridocarbazoles; F. Syn- 
7. ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 255 
thesis of Tricyclic Analogs; G. Synthesis of Bispyridocarbazoles; H. Synthesis of 
Ellipticine Conjugates; and I. Synthesis of Miscellaneous Analogs. 
A. SYNTHESIS OF SUBSTITUTED ELLIPTICINES 
Although direct substitution on the ellipticine nucleus is rare, a number of 
important such developments have been reported since 1984. Pandit and co- 
workers (64,65) have achieved excellent success in the important introduction of 
a hydroxyl group into the C-9 position of the pyrido[4,3-b]carbazole nucleus 
(Scheme 15). Thus, 6-methylellipticine (88), prepared from 1 in 81% yield 
CH3COCI 
8 8 
CICH20CHC12 
AIC$ 0°C 3h 
CH2C12 91% 96% 
CH3 CH3 
89 
0 CH3 
CH3 CH, 
91 90 
93 9 2 
SCHEME 15. C-9 hydroxylation of 6-methylellipticine (88) by Pandit and co-workers (64,65). 
256 GORDON W. GRIBBLE 
[NaH, dimethylformamide (DMF), CH,I], undergoes electrophilic nitration (89), 
Friedel-Crafts acylation (90), and alkylation (91) at the C-9 position. Although 
attempts to effect a Baeyer-Villiger oxidation of ketone 90 were successful, the 
route was laborious since oxidation to amine oxide 92 preceded oxidation of the 
methyl ketone 90. However, a Dakin reaction of aldehyde 91 gave 9-hydroxy-6- 
methylellipticine (93) in excellent yield. It remains to be seen if this meth- 
odology can be extended to an N-unsubstituted ellipticine. 
In attempting to functionalize the C-1 1 position of ellipticine-in the reason- 
able belief that it resembles electronically the C-2 methyl group of 2-methyl- 
pyridine N-oxide-Pandit and group (66,67) prepared 6-methylellipticine N- 
oxide (94) (Scheme 16). However, treatment of 94 with acetic anhydride led not 
to the anticipated 97 but rather to pyridones 95 and 96, in what represents a new 
functionalization of the C-1 position. However, the fact that the C-11 methyl 
group is in potential conjugation with the pyridine nitrogen allowed Pandit and 
co-workers(66,67) to deprotonate selectively this position with lithium di- 
isopropylamide (LDA), and, after quenching 98 with formaldehyde, they were 
able to prepare several novel glycosides (e.g., 99-101) (Scheme 17). 
Honda and team (68-70) at the Suntory Institute have reported a simple 
synthesis of N-2 ellipticine glycosides (e.g., 104) (Scheme 18), which have high 
water solubility and extraordinary antitumor activity (see Section XI). A key 
feature in the preparation of these quaternary glycosides is the use of cadmium 
carbonate, which seems to enhance the remarkable 1 ,2'-trans stereoselectivity 
of the condensation step. 
88 rn-CPBA nT@Ro- Ac20 
CH2Cl2 rt / / NaOAc A 
75% 40% 
CH, CH, 
9 4 
0 
II 
95 R = H 
96 R=COCH3 
97 
SCHEME 16. C-l functionalization of 6-methylellipticine (88) by Pandit and co-workers (66,67). 
7. ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 257 
1 
CH3 CH3 
1. AcO& AcO OAc OAc 
- 
CH, CH3 
98 
P HCHO Q)--& 
56% / / 
CH3 CH, 
/"%OH q - - OH I 
/ / 
CH, CH3 
9 9 ' 25% 
CH, CH3 CH, CH, 
100 101 
SCHEME 17. Synthesis of ellipticine glycosides (99-101) by Pandit and co-workers (66,67). 
Werbel and co-workers (71) have synthesized several N-6 (88, 105-109) and 
some N-2 (110, 111) amino and alkyl derivatives of ellipticine (1) by straightfor- 
ward alkylation methods. Paoletti and co-workers (72) have reported the syn- 
thesis of a variety of 1 -amino-substituted 9-methoxyellipticines (Scheme 19) in a 
continuing study of the antitumor properties of these compounds. The starting 1- 
258 GORDON W. GRIBBLE 
102 103 
104 
SCHEME 18. Honda er al. synthesis of quaternary ellipticine glycosides (e.g., 104) (69). 
chloroellipticine (112) is available from the corresponding pyridone by treatment 
with phosphorus oxychloride (73). The subsequent reactions with amines or 
ammonia were typically carried out neat. The 1-amino substituted 9-hy- 
droxyellipticine derivatives were synthesized by starting with the 9-benzyloxy 
derivative 119 as shown below for the preparation of 120 (72). 
Bisagni and co-workers (74) have synthesized the 1-chloroellipticine 126 in 
unique fashion (Scheme 20). Condensation of the readily available aldehyde 122 
with lithiated chloropyridine 124 gave alcohol 125. Ionic hydrogenation and 
cyclization afforded 126 in 35% yield from aldehyde 122. This route is much 
shorter than an 1 1-step procedure reported earlier (75). 
1. NaH 
X- 
DMF 
rt 0.5 h RX 
Et3N 
H DM F MeOH 
R CH3 tt 17h rt CH3 
2.5 - 55% 20 - 100% 
110 R=CH3,X= l 
111 R = CHzCHzNEtz, X = Br 88 R=CH3 
105 R = (CH&NMez 
106 R = CHZCH~N(CH~CHZ)~O 
107 R = CH2CH2N(CH2)5 
108 R = CH2CHzNEtz 
109 R = CH2CONEt2 
7. ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 259 
H H 
CH, CH, 
114 
120°C 
7 days 150°C 3days 
CH3 CI 
112 
23 - 54% 
CH, NHR 
H H 
CH, CH, 
11 5 R = CH2CHzCH3 118 
116 R = CHzCH(CH3)z 
117 R = CH2CHzCH(CH& 
SCHEME 19. Synthesis of 1-amino-substituted 9-methoxyellipticines 113-118 by Paoletti and co- 
workers (72). 
Gansser ef al. (76) have employed a Cranwell-Saxton synthesis (56) to pre- 
pare 9-(dimethylamino)ellipticine (130) from 5-(dimethy1amino)indole (127) 
(Scheme 21). To avoid formylation of the carbazole N-9 position, it was neces- 
sary to use the hydrochloride of 128. However, the yield of the desired aldehyde 
129 was still very poor (3%) as formylation at C-5 was a side reaction. Finally, 
the Dalton modification ( I ) was used to form the D ring. Gansser and co-workers 
260 GORDON W. GRIBBLE 
CH, CI 
1. H2NCH2CH2CH(CH& 
90°C 2days 
* 
2. H2 Pd/C 
EtOH 60°C 24h 
45% 
1 1 9 
H 
CH3 
1 2 0 
cH3073-- DMF A I 
CH3 > - I 87% CH, 121 1 2 2 
LDA 
P Co ' THF -70°C 
0 
CH3 CH, 
123 1 2 4 
OH Cl CI 
1. Et3SiHKF3C02H * c H 3 0 0 y @ 
2. 50%H2S04 / / 
4 h 60°C 
54% CH, CH, 
125 1 2 6 
SCHEME 20. Bisagni et al. synthesis of 1-chloropyridocarbazole 126 (74). 
7. ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 26 1 MezNa~ + i5 B h ’ E t 2 0 MezNf& . - - CH3 
1. HCI EtOH - * 
dioxane / 2. DMF PCCI~ 
9% H 
1 2 8 
A 5h H 
CH3 CH3 39% 
1 2 7 
aT-cHo 1. H2NCH&H(OEt)z *MezNQT& / / 
2h A 
CH3 
2. H3W4 165°C 
130 30 rnin 
CH3 
1 2 9 
SCHEME 21. Gansser et al. synthesis of 9-dimethylaminoellipticine (130) (76) 
(77) have also reported a synthesis of 8-methoxyellipticine (134) using Miller’s 
strategy (47) (Scheme 22), although both the Goldberg coupling leading to 131 
and the final pyrolysis proceeded in very poor yields. The Gansser group (78) 
also described the synthesis of 9-methoxy-4-hydroxy-1,2,3,4-tetrahydroellip- 
ticine (137) (Scheme 23) using the Cranwell-Saxton method (56). Thus, the 
Dalton intermediate 135 ( I ) , which was prepared from 6-methoxy- 1,4-di- 
methylcarbazole in two steps, was reduced with sodium borohydride and 
cyclized with mild acid to give a mixture of 137 and the imine 138. 
Gribble and Saulnier (79) have extended their ellipticine synthesis (43) to the 
synthesis of 9-methoxyellipticine (2) (Scheme 24). One of the key features of this 
approach is the regioselective nucleophilic addition to the C-4 carbonyl group of 
pyridine anhydride 28. The other noteworthy transformation is the conversion of 
keto lactam 142 to the diol 143 with methyllithium, a process that presumably 
involves cleavage of the initial adduct to a methyl ketone which undergoes 
cyclization at the C-3 position of the indolyl anion. Reduction of 143 with 
sodium borohydride completes the synthesis of 2, in 47% overall yield from 5- 
methoxyindole (139). Gribble and students (80) have also used this method to 
synthesize 8-methoxyellipticine (134), 9-fluoroellipticine (144), and the pre- 
viously unknown 7,8,9,10-tetrafluorellipticine (145), each from the appropriate 
indole. 
In an improvement of the earlier use of keto lactam 85 to synthesize the 
alkaloid 17-oxoellipticine (148) (63) [alkaloid numbering ( S I ) ] , Obaza-Nutaitis 
and Gribble (82) have found that vinyllithium is an excellent alternative to the 
more conventional acyl anion equivalents (Scheme 25). Thus, the addition to 
N2H4 RaNi NaN02 - 
95% EtOH CH,O / / aq HOAc 
* 
H 
CH3 
88% 
132 
7H3 
500°C 
CH30 30/0 CH30 
H 
CH3 
134 
133 
SCHEME 22. Gansser et al. synthesis of 8-rnethoxyellipticine (134) (77). 
- 
CH3 OEt CH3 OEt 
H 
88% 
135 136 
6N HCI cH300-& H :H30n-& / 
EtOH ' N / \ N 
H H 
CH3 OH CH3 
28 h 
137 (59%) 138 (28%) 
SCHEME 23. Martin-Onraet er al. synthesis of 9-methoxy-4-hydroxy- I ,2,3,4-tetrahydroellipticine 
(137) (78). 
7. ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 263 
cH30Q- 
H 
139 
L ~ - 
aq MeOH 
A 5 h 
l O O ~ / O 
c H 3 0 7 3 - - J - + 3 g 3 0 7 3 - 4 - -1 MeLi 00°C 
98% 
0 ’ 
COZH 
N 
\ 
141 
142 
cH30QN@ HO CH3 Na; cH3073,--....- - 
aq EtOH ’ / I I 
H 
CH3 HO CH3 
143 2 
75% from 142 
SCHEME 24. Gribble-Saulnier synthesis of 9-methoxyellipticine (2) (79). 
keto lactam 85, sequentially, of vinyllithium and methyllithium gave, after re- 
duction of the intermediate diol 146, vinyl ellipticine 147. The cleavage of the 
vinyl group was surprisingly difficult but was finally achieved with chromic acid 
and a dispersing agent. 
Ross and Archer (83,84) have also synthesized 17-oxoellipticine (148) 
(Scheme 26). Using the Weller-Ford methodology (85), these workers prepared 
ester 149 and, in a clever maneuver, effected debenzylation via the Krohnke 
264 GORDON W. GRIBBLE 
N 
% 8 5 \ 
1. H,C=CHLi 
M F -100°C - 
2. CH3Li 
-1 00°C 4 rt 
3h 
Q);p OH 
146 
NaBH4 
EtOH 
A 23h 
- 
78% from 85 
SCHEME 25. Obaza-Nutaitis-Gribble synthesis of 17-oxoellipticine (148) (82). 
aldehyde synthesis (86) to afford ellipticine ester 150. Subsequent standard ma- 
nipulation of the carbomethoxy group gave 17-oxoellipticine (148). Reaction of 
alcohol 152 with methyl isocyanate (MIC) gave carbamate 153, which has 
important antitumor activity (see Section VII). 
Archer and co-workers (84) have used the original Stillwell ellipticine syn- 
thesis (83,as later exploited by Gouyette et al. (88) to prepare the simple 9- 
hydroxy-6H-pyrido[4,3-b]carbazole (158) (Scheme 27). N-Benzyl-4-piperidone 
was converted via enamine 154 to the enone 155. Hydrogenation gave a mixture 
of cis- and trans-ketones 156 which were separately converted to indole 157 by 
Fischer indolization. Some of the nonlinear pyrido[3,4-~]carbazole (1 7%) was 
formed from the cis-ketone. Dehydrogenation and demethylation gave the de- 
sired 158. 
Using their earlier developed methodology (89), which is similar to that de- 
scribed by Weller and Ford (85) but developed independently, Pandit and co- 
workers (90) have synthesized the 3-methyl derivatives of 6-methylellipticine 
and l-demethyl-6-methylolivacine, 165 and 166, respectively (Scheme 28). 
Acylation of indole ester 159 with 6-methylnicotinoyl chloride hydrochloride 
(160) in hot sulfolane gave keto ester 161. Alkylation and cyclization gave 
dihydropyridine 162, which was oxidized with N-benzylacridinium bromide to 
give salt 163. Reductive debenzylation gave the key intermediate ketone 164. 
Conversion of 164 to the ellipticine derivative 165 was accomplished by the 
addition of methylmagnesium iodide, followed by hydroxide-induced decarbox- 
7. ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 265 
1. BrCH, 
acetone 24 h 92% CH2C6H,NO2 
/ 2. NaOCH3 / / Br- 
C02CH3 
QpJ$TJ 
CO2CH3 
149 150 
80% 
LiAIH4 
* 
* ) -& \ 5 h 25°C H / / THF l h rl 56% from 150 
O N e N ( C H 3 1 2 - 
NaOCH3 CH30H 
C02CH, 
151 
MIC 
rl 3days 
CHZOCNHCH, 
II 61% 
CH20H 
152 
153 0 
148 
CHCb 
A 3.5 h 
79% 
SCHEME 26. Ross-Archer synthesis of 17-oxoellipticine (148) and carbamate 153 (83). 
ylation-dehydration. The olivacine derivative 166 was prepared by the reduction 
of 164 with Red-Al. 
Using the Birth modification (57) of the Cranwell-Saxton (56) methodology, 
Narasimhan and Dhavale (91) have described a synthesis of 6-methyl-1 l-de- 
methylellipticine (171) (Scheme 29). Carbazole aldehyde 167 underwent the 
usual condensation to give imine 168. Direct cyclization of 168 with phosphoric 
acid gave a mixture of 171 and 172, although only the former could be obtained 
in pure form (by repeated crystallization). However, reduction of 168 to 169, 
followed by tosylation and cyclization, gave 171 exclusively. 
Sainsbury er al. (92) have also employed the Cranwell-Saxton strategy (56) to 
prepare ring A- and ring D-substituted 9-methoxyellipticine derivatives. The 
synthesis of amine derivative 177 was accomplished as shown in Scheme 30. An 
266 GORDON W. GRIBBLE 
(p-ph 
154 
1. q( 
- 
dioxane 
A 17h 
A l h 
2. H 2 0 
0 L U P h 
155 
H2 5% RtVA1203 
* 
95% EtOH 
4h 
C H 3 0 0 N H N H 2 HCI * cH30n7qn Ph 
EtOH rt 24 h 
H 38% (cis) H H 
157 61% (trans) 
0 
156 
___) I 
Ph20 
H 52% H 
A 2h 
158 73% 
SCHEME 27. Archer et al. synthesis of 9-hydroxy-6H-pyrido[4,3-b]carbazole (158) (84). 
aza Cope rearrangement afforded mainly the desired 174. Some C-3 ally1 product 
(24%) was obtained along with 7% of the hydrogen chloride addition product. 
This could be converted to 174 on treatment with sodium hydride (DMF, O°C, 
86%). Palladium-catalyzed double-bond isomerization, followed by ozonolysis, 
gave the aldehyde 175. A Wadsworth-Emmons olefination, followed by for- 
mylation, gave aldehyde 176. Hydrogenation of the unsaturated amide, followed 
by the standard ring D formation and amide reduction, gave the target 177. In 
related chemistry Sainsbury et al. (92) prepared 178, but ring D formation was 
thwarted, giving instead the unusual dimer 179. Attempts by this group (92) to 
prepare C-3-substituted ellipticines by the modified Cranwell-Saxton approach 
were foiled by the decomposition of the side chain during the Pomeranz-Fritsch 
reaction. 
B. SYNTHESIS OF ISOELLIPTICINES 
By “isoellipticine,” we refer to a derivative in which the pyridine nitrogen is 
in a different ring D position. Compared to the other structural variations de- 
scribed in later sections, the isoellipticines have received little attention. A few 
7. ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 267 
n 0 
___) 
CH3 
90-1OO"c 
CH3 CH3 CH3 CH3 
159 160 161 
74% 
Br- 
, 'N-Ph 'Ph 
V"/ 
+ I 
w 
CH3CN rt 
CH3 
rt - sD$cA I H3C CO2Et 95% 
1. PhCH2Br 
90°C 30min 
2. Et3N EtOAc 
H3C 
162 54% 
' ' CH3 CH3 
CH3 CH3 CH3 CH3 
165 166 
SCHEME 28. Synthesis of 3,6-dimethylellipticine (165) and I-demethyl-3,6-dimethylolivacine 
(166) by Pandit and co-workers (90). 
new syntheses of the so-called isoellipticine (27) have already been noted. A 
short synthesis of 4-hydroxy-2,5,11 -trimethyl-6H-pyrido[3,2-b]carbazole (183) 
has been published by Viossat et al. (93) (Scheme 31). An X-ray crystal struc- 
ture reveals that the lactam structure 182 exists in the solid state but the hy- 
droxypyridine form (183) predominates in solution. 
Using their earlier methodology to synthesize ellipticine (l), Gribble and 
268 GORDON W. GRIBBLE 
mcHo / HzNCHZCH(0Me)z PhH A 2 h * T L C H 3 F 20 rnin \ 
CH, CH, OCH, 45% 
86% 
I I 
CH, CH3 
167 
F N 
I I 
CH3 CH3 CH, CH, 
171 \ 6NHC' 172 
dioxane 
1o-2o0c 
38% 20h \ 
aq THF 
OCH, PTsCl OCH, 
CH, CH, OCH, CH, CH, OCH, 83% 
170 169 
SCHEME 29. Narasimhan-Dhavale synthesis of 6-methyl-1 I -demethylellipticine (171) (91). 
students (94) developed a synthesis of the lOH-pyrid0[2,3-b]carbazole ring sys- 
tem (Scheme 32). Once again, excellent, if not complete, regioselective acyla- 
tion of 2-lithioindole 184 with pyridine anhydride 185 was attained. The subse- 
quent conversion to keto lactam 186 and the addition of methyllithium, followed 
by reduction, gave 187, in 60% overall yield from indole. The 7- and 8-methoxyl 
derivatives of 187 were similarly prepared. 
The 5H-pyrido[4,3-b]benzoV]indole ring system (e.g., 192) represents an- 
other type of isoellipticine, and its synthesis has been explored by Bisagni and 
co-workers (95) (Scheme 33). Azaindole 188 was elaborated by means of con- 
ventional lithiation methodology to alcohol 189. A sequence of dehydration, 
hydrogenation, and chlorination gave 190. Either Vilsmeier-Haack conversion 
to aldehyde 191 and polyphosphoric acid (PPA) cyclization to the desired ring 
system 192 or direct cyclization to 192 completed the synthesis. The side chain 
amines were introduced by heating the components neat to provide 193-195. 
The methoxyl derivatives 196 and 197 were also synthesized (95). 
Bisagni and team (96) have also reported a synthesis of the related 5H- 
pyrido[4,3-b]benzo~indolo-6,ll-quinone ring system (e.g., 200) (Scheme 34). 
Using a modification of the Watanabe-Snieckus synthesis (97) of ellipticine, the 
7. ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 269 
NaH DMF - - 
90°C + II 
7 h 
N 
H 50°C 6 h 
62% 92% 
CH3 
173 
" 174 
1. PdCl2 CH3CN PhH c H 3 o w 
t 
50°C 24h 
89% 
2.03 -20°C CHO CH3 
MeOH CHgI2 
79% 175 
1.NaH DMF 
(E10)2POCH2CONEt2 
24h rt 98% 
t 
2. TFAA 
lmkhzole 
CHSN A 3.5h 
3. aq NaOH 
EtOH A 15min 
83% 
1. H2NCH2CH(OMe)2 
c H 3 0 ~ c H 0 HZ zl 'd lc :H30p CHo 2.H2 80°C Pt02 mlsieve c 
latrn rt EtOH latrn 
CH3 4 h II H CH3 82% 
90% / 
A 176 
0 NEt, 
~ONEI, 3.pTsCl pyr 
24h rl 
85% 
1.HCI doxane 
100% 3h 
56% 
OCH3 2. BH3 Me2S 
H THF A 75min 
OCH, 3.6MHCI 
I 
CONEt, 
51 % 
'NEt2 
SCHEME 30. Sainsbury et al. synthesis of ring A-substituted 9-methoxyellipticine (177) (92) 
French group condensed indole aldehyde 198 with the appropriate metalated 
aromatic to give, after spontaneous oxidation of semiquinone 199, the desired 
quinone 200. Conventional amination yielded the target compounds (e .g . , 201). 
Many such derivatives were prepared by Bisagni and co-workers (96), including 
the disubstituted compounds 202 and 203. 
270 GORDON W. GRIBBLE 
1. rrBuLi 
M F -78°C CH,O 
53% 
2. pTsCI 
ww3 
CH, OCH, aq MF CH3 OCH3 
178 78% 
f CH3 
OCH, - 5M HCI 
dioxane 
ti 12h 
179 
NHz CH3COCH2C02C2H5 Q QNycH3 
C02C2H5 
to1 \ N / 
H 
8 h A H 
180 181 
CH, CH, 
Ph20- 
A 
65% from 180 
CH3 0 
H 
CH3 OH 
182 183 
SCHEME 31. Viossat et al. synthesis of 4-hydroxy-2,5,1 l-trimethyl-6H-pyrido[3,2-b]carbazole 
(183) (93). 
7. ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 27 1 
LDA 07 I THF - 
SOZPh 
31 
0-J Li 
S02Ph 
184 
0 
O R 0 185 
-1 00°C 
83% 
A c ~ O 
H3C OH 
2 eq MeLi 
@ J o -1oo"c-trt * 
NaBH4 
EtOH 
A 
96% from 185 
187 
SCHEME 32. Gribble et al. synthesis of the lOH-pyrido[2,3-b]carbazole ring system (e.g., 187) 
(94). 
c. SYNTHESIS OF AZAELLIPTICINES 
The importance of azaellipticines is illustrated by the fact that 204 (BD-40) is 
undergoing clinical trials (20,98). Using their new 1-chloroellipticine synthesis 
(Scheme 20), Bisagni et al. (74) have described an extremely concise route to 10- 
chloro-5,6-dimethyl-5~-pyrido[3',4':4,5]pyrrolo[2,3-g]isoquinoline (208) and 
the side-chain amine derivatives 209-211 (Scheme 35). Formylation of 1 -methyl 
-5-azaindole (205), followed by reaction with the lithiochloropyridine 124, gave 
CH, CH, CH, CH, 
(23%) (53%) 
SCHEME 33. Synthesis of the SH-pyrid0[4,3-b]benzov]indole ring system (192) by Bisagni and 
co-workers (95). 
Et,N(CH2)3HN 
N J - w o c H 3 / / 
' N 
I 
CH3 CH, Ph 
196 197 
272 
L i f i H , 
EI2NOC OCH, 
POCI, 
DMF 
1004: 2h 
94% 
- 
I 
CH, 
198 
E1,NOC OCH, 
OLi OCH, OLi OCH, 
OCH, 
OH OCH, 
CH, 0 CH, 0 
199 200 
201 
SCHEME 34. Synthesis of the SH-pyrido[4,3-b]benzov]indolo-6,1 I-quinone ring system ( e . g . , 
200) by Bisagni and co-workers (96). 
EtzN(CH2)JiN 
&-7& 
CH, 0 NH(CHz),NEt, 
202 
NH(CH,),NEt, 
fJ-7@ 
CH3 0 NH(CHz),NEtz 
203 
273 
274 GORDON W. GRIBBLE 
NH(CH,),NEt2 
I 
204 ("BD-40") 
alcohol 207. Reduction and acid-induced cyclization gave 208 in 28% overall 
yield from aldehyde 206. Displacement of chloride occurred upon heating 208 
neat with the appropriate diamine to give 209-211. 
D. SYNTHESIS OF NONLINEAR PYRIDOCARBAZOLES 
An obvious structural modification of ellipticine is the fusion of the pyridine 
ring to the a or c bond of carbazole. Indeed, pursuit of this idea has led to the 
1. Hexamethylenetetramine 
TFA A 3 h NaJ 2. 3NHCI 59% 
205 
. . 
I A 3 h 
CH3 72% 
1 
CH3 
206 
OH CI 
1. Et3SiH 
TFA 
2. 50%H2SO4 
24h rt 
48% 
CH3 CH3 
207 208 
RNH2 ~ NaT@ 209 210 R R=(CH2)3N(CH3)2 = (CH2)3N(C2H5)2 
21 1 R = (CH2)3NHC2H5 140 - 160°C / / 
5-48h 
44 - 89% 
CH3 CH, 
SCHEME 35. Bisagni er al. synthesis of I-amino-substituted 9-azaellipticines 209-211 (74). 
7. ELLIPTICINE ALKALOIDS A N D RELATED COMPOUNDS 275 
H H 
21 2 
CH,O 
N-NH 
N 21 3 
N 
10% P&C 
decalin 
A 6 h 
* 
\ 14 - 20% 
=- cH30=% N 
H2S04 
HOAc 
A 15min 
42 - 50% 
214 
cH30y-qJq) 1 \ \ 3 4 
2 'N 215 1N , 
216 3N 
217 4N 
48% HBr 
120°C 5h 
27 - 40% 
40°C 
- . 
NCH, 221 1N 
222 3N 
223 4N 
f 
Ho=% '\ 
N 218 1N 
219 3N 
220 4N 
SCHEME 36. Lescot et al. synthesis of 11H-pyrido[a]carbazoles (215-223) (100) 
276 GORDON W. GRIBBLE 
discovery of the clinically active drug “ditercalinium” (212) (99), a bis-7H- 
pyrido[4,3-c]carbazole derivative. 
Lescot and co-workers (100) have described two routes to the 11H- 
pyrido[a]carbazoles. In the first (Scheme 36), a Fischer indole cyclization of the 
naphthylhydrazone 213, followed by dehydrogenation, gave the fully aromatic 
pyrido[a]carbazoles 215-217. Methylation or demethylation completed the 
preparation of the desired target compounds. A different route was used to 
synthesize the 5-methyl-2-aza derivatives 226 and 227 (Scheme 37) (100). Con- 
densation of aldehyde 224 with 4-ethylpyridine gave the vinylindole 225. De- 
acylation and a variation of the Snieckus pyrido[c]carbazole synthesis (101) gave 
the desired compounds 226 and 227. 
Roques and co-workers (102) have described a general route to the 7H- 
pyrido[c]carbazole ring system (Schemes 38 and 39). The preparation of the 5- 
methyl isomer 233 was performed by first converting 5-methoxy-2-indole car- 
boxylic acid (228) to aldehyde 229. Condensation with 4-ethylpyridine and a 
Snieckus oxidative photocyclization (101) of the heterocyclic stibene 230 gave 
231 in low yield. A somewhat better procedure utilized the methiodide of 4- 
ethylpyridine in the coupling step, although photocyclization of 232 was still 
poor. The 6-methyl derivatives (238-241) were prepared by converting iso- 
gramine methiodide 234 to nitrile 235 (Scheme 39) (102). Aldol condensation 
with the three isomeric pyridine aldehydes afforded the expected products 236. 
Photocyclization proceeded in much higher yields than before (Scheme 38) to 
‘ ~ - J C H o + cb A 18h 
Ac 
224 225 
H 21 - 25% 
aq NaOH 
15rnin rt 
EtOH 95% EtOH 
11 -14% 
226 R = H 
227 R=CH3 
90 - 94% 
SCHEME 37. Lescot el al. synthesis of the 5-methyl-1 1H-pyrido[3,4-a]carbazole ring system 
(226, 227) (ZOO). 
SOCI2 
A 4 h LiAIH4 
cH30Q-1 - Et20 THF 
A 1.5 h 
C02H EtoH 
H 89% H 
228 98% 
CrO3 c H 3 0 Q - ~ CHO AC20 A 
H rt 19h H 60h 
60% 229 10% 
95% EtOH 
I 28% H 
Ac 
230 231 
' I- 
CHO H3C'+ I- Et20 N 0 9""""' piperidine *cH3073--3cH3 
rt 21h H 
cH3073-7- 
H 
229 63% 232 
CH3 ' I- 
hv 
EtOH 
14% H 
- 
233 
SCHEME 38. Synthesis of the 5-methyl-7H-pyrido[4,3-c]carbazole ring system (e.g., 231, 233) 
by Roques and co-workers (102). 
278 GORDON W . GRIBBLE 
KCN * 
N(CH3)3 -cH3073--L CH30H CN NaOCH3 CH30H 
20% l h 
A 18h H 
cH3073---&+ 
H I- 
234 67% 235 
51 - 70"/0 
- 
95% EtOH 
31 - 75% CN 
237 
CN 
236 
NaN02 
H20 HBr RaNi 
NH3 HMPT II 30rnin 
lobar 3.5 h 
- H2 
59 - 83% 
57 - 95% 
I 
CH,Br 
H2 
RaNi 
latrn 4 h 
CH30H 
20 - 52% 
2 N 
238 1-aza 
239 2-aza 
240 3-aza 
241 4-aza 
SCHEME 39. Synthesis of the 6-methyl-7H-pyrido[c]carbazole ring system (e .g . , 238-241) by 
Roques and co-workers (102). 
S0,Ph 
242 
hv 12 
69% 
7. ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 279 
NaH THF 
PhO2S 
244 
TH2P(olPh, 
COCO2CH3 
’243 
rt 16h 
Mn02 
A 6 h 
CHC13 
MeOH 24h 
52% 
79% 
LiAIH4 
M F 0°C 20min 
95% 
4 
COZCH, 
H 
245 
&OH 
246 
CHO 
248 
H2 10% Pd/C 
CH3W 
3atm 2 h 
80% 
’. I 
CH20CNHCH3 
I I 
62% 
Ph3P = CH, 
DMSO 
r l 16h 
65% 
247 0 
249 
I 
CH=CH2 
SCHEME 40. Synthesis of the 7H-pyrido[4,3-c]carbazole ring system (e.g., 247, 249) by Archer 
and co-workers (103). 
280 GORDON W. GRIBBLE 
give the tetracyclic nitriles 237. Reduction, diazotization, and debromination 
gave the desired 1-, 2-, 3-, and 4-aza derivatives (238-241). 
Archer and co-workers (103) have also employed the Snieckus oxidative pho- 
tocyclization in the key step of their synthesis of the 7H-pyrido[4,3-c]carbazole 
ring system (Scheme 40). Thus, a Wittig condensation between pyruvate 242 and 
pyridine 243 gave the unsaturated ester 244. Photocyclization gave the 
tetracyclic ester 245. Reduction and reaction with methyl isocyanate led to 
carbamate 247. Oxidation of alcohol 246 to aldehyde 248, followed by a stan- 
dard one-carbon homologation, gave the desired ethyl derivative 249. These 
chemists also synthesized the 10-methoxyl derivative of each compound. 
In an extension of their earlier work on the use of furo[3,4-b]indoles to 
construct ellipticine (Scheme l l ) , Gribble and Saulnier (79) have utilized an 
intramolecular Diels-Alder reaction to prepare 6-methylbenzo[c]carbazole (255) 
as a model for the 6-methylpyrido[c]carbazole ring system (Scheme 41). Addi- 
tion of the unsaturated Grignard reagent 251 to aldehyde 250 gave alcohol 252. 
The usual C-2 functionalization, oxidation, and cyclization furnished 
furo[3,4-b]indole 253. This underwent a smooth intramolecular Diels-Alder 
cycloaddition to give 254. Hydrolysis and dehydrogenation furnished the target 
compound 255. 
E. SYNTHESIS OF OXAZOLOPYRIDOCARBAZOLES 
As seen in Section VIII, the facile oxidation of 9-hydroxyellipticine (3) and 
elliptinium (5) to the corresponding quinone imines (6 and 256, respectively) 
with the enzyme HRP and H,O, may represent an important facet of the mecha- 
nism of antitumoraction of these compounds. In the presence of amino acids, the 
quinone imine 256 formed adducts that were assigned structures 257 (104,105). 
However, numerous discrepancies between the expected and observed chemical 
and physical behavior led the original group (106) and, independently, Potier and 
co-workers (107) to reassign these amino acid adducts as having the ox- 
azolopyridocarbazole structure 258. For example, the mass spectra of these 
adducts displayed parent ion peaks that were 46 mass units lower than expected 
for structure 257, and the infrared “carbonyl” band at 1670 cm-1 seemed 
dubious (107). The adducts did not react with acetic anhydride, did not undergo 
electrochemical oxidation, but, unlike 9-hydroxyellipticine (3), were strongly 
fluorescent in water (106). Moreover, the ‘H- and 13C-NMR data seemed more 
consistent with the oxazole structure 258. Finally, quinone imine 256 reacted 
with alanine and ethylamine to give the same adduct 258 (R = CH,) (106)! 
Potier and co-workers (107,208) have proposed a mechanism for this reaction 
leading to the oxazolopyridocarbazole structure (Scheme 42). Potier and co- 
workers (107,108) have also demonstrated that this oxidation and interception 
with amines can be performed using manganese dioxide as the oxidant and 
7. ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 28 1 
MgBr_ 
7 
251 
-1 00% . . 
I 
SOZPh 
250 
.. 
I 
SO2Ph 
252 
OH 
1. MnO;! 
2. TFA 
* 
CH2C12 A 
36%0 
1. t-BuLi 
2. CH3CHO 
94% PhOZS OH 
I 
Ph02S 6H3 
253 
1. NaOH 
2. DDQ 
41% 
- - 
H I 
CH3 
255 
SCHEME 4 1. Gribble-Saulnier synthesis of 6-methylbenzo[c]carbazole (255) (79). 
simple carbazoles (e.g., 259) as the substrate (Scheme 43). In the absence of a 
trap, quinone imine 260 was isolated in nearly quantitative yield. 
Meunier and co-workers (109) also studied the oxidation of elliptinium (5) in 
the presence of aminocarboxylic acids with HRP/H,O, as a preparative route to 
the novel oxazolopyridocarbazole acids 267. Photooxidation of 5 in the presence 
of leucine also gives the oxazopyridocarbazole adduct (110). Archer and col- 
leagues (84) used this facile oxidation-amine trapping protocol to prepare ox- 
azole 268. 
282 GORDON W. GRIBBLE 
HOW ,CH, peroxidase horse radish (HRP) 
/ / H2Q 
CH3 CH3 
amino acids 
‘ N 
H 
5 256 
CO,H 
U 
II 
SCHEME 42. Reassignment of ellipticine quinone amino acid adduct 258 and proposed mecha- 
nism of formation by Potier and co-workers (107). 
7. ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 283 
R 
F. SYNTHESIS OF TRICYCLIC ANALOGS 
In an unquestioned tour de force, Bisagni and co-workers (111-113,115- 
I 17) have published an extensive account of the syntheses and biological prop- 
erties of a series of novel tricyclic analogs in which the C ring of ellipticine 
or 9-azaellipticine has been deleted to give y-carbolines or 5H-pyrido- 
[3’,4’:4,5]pyrrolo[3,2-~]pyridines, respectively. Bisagni’s first approach to the 
diazacarbazole ring system (SH-pyrido[3’,4’:4,5]pyrrolo[3,2-c]pyridine) in- 
volved the buildup and cyclization of the pyridine ring onto an azaindole 
(Scheme 44) (111). Metalation of indole 269, followed by quenching with 
acetaldehyde, gave alcohol 270. Oxidation and an Emmons-Wadsworth reaction 
gave acid 272, after saponification. Formation of acyl azide 273 was followed by 
thermolysis to effect cyclization of the isocyanate to the indole C-3 position, to 
give pyridone 274. Subsequent manipulation gave the target molecules 275 and 
277. Similar chemistry starting with N-methylindole 188 afforded 278. 
Bisagni’s second approach to these tricyclic molecules involved a Fischer 
indolization strategy (Scheme 45) (112) and was improved over the previous 
synthesis (Scheme 44). Hydrazinolysis of hydroxypyridone 279 followed by 
condensation with N-acetylpiperidone gave hydrazone 280. The subsequent 
Fischer cyclization was accomplished in refluxing diphenyl ether. Dehydrogena- 
tion and chlorination gave the target ring system 277. Interestingly, methylation 
conditions gave, in addition to the expected 278, a substantial quantity of 283. 
284 GORDON W. GRIBBLE 
Mn02 
CH2C12 
HoQ-$ CH3 98% rt 
260 CH3 259 
RCH2NH2 
DME rt 4h 
00 - 85% 
R 
261 R=mPr 
262 R = P h 
R 
RCH2NH2 ' N / / 
H DME EtOH H 
CH3 rt 4h CH3 
3 65 - 88% 263 R =mPr 
264 R=mBu 
266 R=IFCgH13 
265 R=mPen 
SCHEME 43. Oxidation and amine trapping reactions of 6-hydroxy- 1,4-dimethylcarbazole (259) 
and 9-hydroxyellipticine (3) (108). 
7. ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 285 
H DME EtOH H 
rt 7h 
55% 
158 268 
Similarly, hydroxypyridone 284 was converted to 285. As before, each of these 
2-chloropyridine compounds was heated neat at 160- 170°C with the appropriate 
amine to afford the target side-chain amine derivatives, the exact structures of 
which are presented and discussed in Section XI. 
Bisagni and co-workers (1 13,116) also explored several synthetic routes to the 
tricyclic y-carbolines (5H-pyrido[4,3-b]indole ring system). Unfortunately, the 
attractive one-step Nenitzescu reaction (114) proceeded in only 6% yield to 
afford 286 (113). The Fischer indolization sequence was far more efficient 
(Scheme 46) (113). Thus, condensation of phenylhydrazine with 279 in boiling 
diphenyl ether gave in one step the desired y-carboline 287 in excellent yield. 
Chlorination of the pyridone functionality gave chloropyridine 288, which was 
converted to the target amine-substituted y-carbolines 289-291 by heating with 
the appropriate amines. 
The same condensation-cyclization sequence with 4-methoxy- 
phenylhydrazine (292), however, proceeded in only 17% yield (113), so an 
alternative synthesis was devised for the important 8-oxygenated derivatives, 
such as 293 and 294, which employed a more conventional Fischer indole 
reaction (Scheme 47) (113). In the event, condensation of keto ketal 295 with 
hydrazine 280 gave hydrazone 296. Cyclization in hot diphenyl ether gave ke- 
tone 297, which, upon dehydrogenation, protection of the phenol as the benzo- 
ate, and chlorination gave 298. Deprotection and/or methylation afforded the 
target chloro-y-carbolines (299-301). 
To avoid the expense of keto ketal 295, Bisagni et al. (116) devised an 
alternative synthesis that began with 4-methoxycyclohexanone 302 (Scheme 48). 
The usual Fisher indolization, dehydrogenation, and chlorination gave methoxy 
derivative 303. A sequence of demethylation and/or methylation provided the 
target 8-methoxy- and 8-hydroxy-y-carbolines, which were transformed into the 
amine derivatives (e.g., 304, 305). By the same route (Scheme 48), Bisagni and 
team (1 16) converted hydrazine 306 to the 4-demethyl-y-carbolines (307-310). 
286 
&- 
Ph I 
269 
GORDON W. GRIBBLE 
1. t-BuLi 
Mn02 - 
2. CH3CHO Et20 -65”c N A T ~ ~ ~ ~ A CHC13 20h 
770/0 I OH 
*“c 
48% Ph 
270 
1. NaH DME 
( Et 0) 2 POC H2CQ Et 
ti 48h 
2. KOH aq EtOH 
Ph 98% Ph 
271 272 
1. EtOCOCl 
Et3N acet - 
Ph Ph 
P 
2. NaN3 
H2 10% Pd/C 
Et3N EtOH 
w 
latrn rt 2 h 
92% 
CI 
274 
CI 
1 
275 
SCHEME 44. Bisagni-Hung synthesis of diazacarbazoles 274-277 (I If). 
CI CI 
OH 
CH3 
I 
CH3 
188 
0 
N2H4 - 
A 4h 
76% 
HN+ NHNH, 
CH3 
0 DAc 
I 
278 
CH3 
0 
- 
EtOH 
A 1.5 h 
84% 
279 280 281 
~a-4 ’’ tfaHuFLi HMPT ~ ~a-4 
\ N / ‘ N / 
/ 4% 
CH3 CH3 CH3 CH3 
2. CH31 I 
\ N 
H 
277 278 (46%) 283 (39%) 
0 Cl 
284 
H 
285 
SCHEME 45. Hung-Bisagni improved synthesis of the diazacxbazole ring system (e.g., 278, 
285) (112). 
288 GORDON W . GRIBBLE 
0 
PhpO 
NHNH, 
88% 
CH3 
287 279 
NHR 
-Q)-+$=Q)--Q 16-96 h 160-1 4h 65°C 
CH3 CH3 
81% 
288 289 (57%) R = (CH2)3N(C2H& 
290 (50%) R = (CH&N(CH3)2 
291 (47%) R = (CH2)2NH(CH2)20H 
cH3073-NHNH2 - - cH3073--Q 
CH3 292 
293 R = (CH2)3N(CH$H3)2 
294 R = (CH2)3NHCHzCH3 
SCHEME 46. Nguyen-Bisagni synthesis of the SH-pyrido[4,3-b]indole ring system (e .g . , 289- 
291) (113). 
HOAc 
A 18h 
6% H 
CH3 
286 
CH3 
7. ELLIPTICINE ALKALOIDSAND RELATED COMPOUNDS 289 
295 280 296 
2. 1. Ph20 HCI 40 rnin A ~ ' W H loo/opd/c PhO A - "QT-H 
H 30 rnin 7 1 O/o H 
CH, 
81% 286 
CH3 
297 
0 CI 
(PhCOhO PhCo2 nT-~ I I - PhCo2 nT- I I 
CH3 
A 70h pyridine 
A 2 h 
74% 
75% 
298 
CH3 
NH3 
CH30H 
It 18h 
- 
80% 
2. NH3 
299 
300 
DMF CH31 
57% 
CH3 CH3 
301 
SCHEME 47. Nguyen-Bisagni synthesis of 8-oxygenated SH-pyrido[4,3-b]indoles 299-301 
(113). 
290 GORDON W. GRIBBLE 
EtOH 
A 4h 
- 
NHNH, 
86Yo 
CH3 
0 
CH3 
302 280 
CH3 CH3 
I 
301 
48%HBr 65yo 
l h A 1 
CH3 CH3 
300 
48% A 75% l h HBr *Hoqi$ 
H2NR2gg I I 
CH3 
200 - 210% 
4h 
NHR 
NHR 
H2NR 
200 - 21 0°C 
4h 
CH3 CH3 
305 
SCHEME 48. Bisagni er al. synthesis of 1-amino-substituted SH-pyrido[4,3-b]indoles 304 and 305 
(116). 
7. ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 29 1 
0 CI 
306 R2 
307 
308 R1 =R2=CH3 
309 R i = R 2 = H 
310 
R1= CH3, R2 = H 
R1 =H, R2 = CH3 
G . SYNTHESIS OF BISPYRIDOCARBAZOLES 
Although the potential importance of bis-intercalators of DNA was recognized 
long ago (17), the discovery of high antitumor activity for ditercalinium (212) 
has prompted renewed interest in the synthesis and study of potential polyinter- 
calators of DNA. illustrative of the general method for the synthesis of 
bispyridocarbazoles tethered through the pyridine nitrogens is the preparation of 
the ethyl ditercalinium analog 315 as reported by Roques and co-workers (1 18) 
(Scheme 49). The same general approach was used to prepare the ethylpyridocar- 
bazole 314, but lithiation methodology was employed to attach the pyridine 
grouping to the indole ring. This reaction (311 + 312 + 313) proceeded in poor 
yield because of competing enolization at the (very) acidic methylene group 
( pyridine nitrogen and carbonyl anion stabilization). Bisalkylation to yield 315 is 
typically performed in hot DMF. These conditions have been used to tether other 
pyridocarbazoles (102). 
The more flexible tether embodied in bispyridocarbazoles 321 and 322 was 
synthesized by Roques and colleagues (119) as shown in Scheme 50. The 
bischloro tether 319 was prepared from 4-bromopyridine (316) by halogen- 
metal exchange, condensation with 4-cyanopyridine, and Wolff-Kishner reduc- 
tion of the resulting ketone 317. Catalytic hydrogenation, chlorination, and then 
alkylation of 320 with 319 gave the desired bispyridocarbazoles (321, 322). An 
important discovery in this research is that the methosulfate salts impart excellent 
water solubility to the bispyridocarbazoles. 
Roques and co-workers (120) have described the preparation of asymmetric 
bispyridocarbazoles (325, 326) in which the linking chains are of different 
lengths (Scheme 51). By a sequence of alkylation and hydrogenation, they con- 
verted 4,4’-bipyridine (323) to 324. Coupling with pyridocarbazoles 320 gave 
the desired compounds 325 and 326. The same group (120) designed and con- 
structed novel potential bis-intercalators (327,328) in which the two intercalative 
rings are different, one being a pyrido[4,3-~]carbazole and one an acridine 
(Scheme 52). 
292 GORDON W. GRIBBLE 
1. 1-BuLi 
THF 5°C 20min 
TH F 
* KOH/DME 
PhS02CI 
80% 
I 
SOzPh 
cH3073-- 
H 20°C 40min 
139 31 1 
14% 312 
2HCI 
DMF 
85°C 15h 
* 
CHzCH, 
40% 
hv 12 
35h 
71 yo 
31 4 
CHZCH, I -!=+- H2CHzC I 
cH3oQ f) + 4CI - DOCHS 
/ \ N / 
H 
\ N 
Et Et 
31 5 
SCHEME 49. Synthesis of ditercalinium analog 315 by Roques and co-workers (118). 
7. ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 293 
H+N>E3r - 
316 
1. NaOH 0°C 
2. mBuLi 
t 
4. H30+ 
0 
317 
1. N2H4 
KOH A 
2. CICH2CH2OH 
3. H2 P I 0 2 
CH,O 
1. 
I 320 
R + t 
2. 4CH3S03AS 
319 
HO 
31 8 
I + 
. . 
I I 
R R 
321 R = H 
322 R=CH3 
SCHEME 50. Synthesis of bispyridocarbazoles 321 and 322 by Roques and co-workers (119). 
Sainsbury and co-workers (121) have synthesized several ellipticine dimers 
tethered through the C-5 methyl group (333) (Scheme 53) or the C-9 position 
(334). The 9-methoxy derivative of 333 was also prepared. The nitrile 329 was 
available from the Sainsbury ellipticine synthesis (122) and was transformed into 
the alkaloid 17-oxoellipticine (148). A clever maneuver was to add nitric acid to 
protonate the pyridine nitrogen of 330. This precluded N-oxide formation during 
dithiane hydrolysis. Reductive amination in two steps afforded the amine 332. 
Coupling with adipic acid gave the target bisellipticine 333. 
294 GORDON W. GRIBBLE 
H2 ROZ 
* HO(CH,),N\ / \ ,N - 
aq EtOH +3€ 90% 
BrCHzCH20H 
Et20 
rt 18h 
80Y0 
323 
Br(CH2)sOH H O ~ c H 2 ) 2 N 3 - - C N I C H 2 ) 3 0 H 
HO(CH,),N=NH EtOH Na2CO3 
A 4days 
83% 
320 (R = H, CH3) CH3S03Ag - CI(CH,),N * - 
3 3 - 3 ( c H 2 ) 3 c l aq DMF aq EtOH 
soc12 
CHC13 
95% A 2 h . 2 HCI 80% 24h 
72% 324 14 - 20% 
ct 
. . 
I 
R 
325 R = H 
326 R=CH3 
R 
SCHEME 5 I . Synthesis of unsymmetrical bispyridocarbazoles 325 and 326 by Roques and co- 
workers (120). 
H. SYNTHESIS OF ELLIPTICINE CONJUGATES 
In order to direct ellipticine and derivatives to specific biological targets, a 
number of ellipticine conjugates have been synthesized and evaluated for tissue 
specificity and antitumor activity. Roques and group (123) have synthesized 
several ellipticine conjugates that were designed to have strong affinity for breast 
tissue and also be DNA intercalators. The preparation of the ellipticine-estradiol 
derivative 337 is shown in Scheme 54. A Reformatsky reaction on estrone (335) 
gave hydroxy acid 336. Amide formation and coupling with ellipticine gave 337. 
This group of researchers (123) also synthesized several ellipticine-clomiphene 
7. ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 295 
N HCHZCHZOH 
OCH3 H~NCH~CHPOH 
PhoH 
120°C 1.5 h 
90% 
CI 
EtOH A 3days 
77% 
1. SOCI, to1 
A 6 h 320 CH3S03H 
e b + 
2. NH40H 
47% 
DMF 
80°C 20h 
17 - 27% 
CH30H 
99% 
CI 
/ 3 CH3SO3- N 
I 
R 327 R = H 
328 R=CH3 
SCHEME 52. Synthesis of acridine-pyridocarbazole bis-intercalators 327 and 328 by Roques and 
co-workers (120). 
296 GORDON W. GRIBBLE 
Q J - h N 
H NC 
329 
HNO3 
AgNO3 THF 
aq acetone 
40-50°C 20h 
63% 
n 
sys THF Li * - aqHOAc A 2h a--@ / / 
-78°C -+ rt 93% 
su 
330 o T - CH3NH2 PhH 
0 0 
CHO 
93% 
148 
NaBH4 
MeOH 0°C 3 h 
60% 
331 332 
CH3 
I 
* aJp 
333 0 L 2 
H02C(CH2)&02H 
Ph2P(O)N3 DMF 
Et3N -1O"C-trt 
37% 
H 
SCHEME 53. Synthesis of bisellipticines (e.g., 333) by Sainsbury and co-workers (121). 
7. ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 297 
0 OH & ” ?:fog:5, - &15H2c02H \ 
HO \ 2. aqNaOH 
EtOH rt 4 h 
HO 
336 76% 335 & Hz C ~ N H C H 2CH2Br 
H2NCH2CH2Br 
EbN M F ellipticine (1) * b 
EtN=C=N(CH,),NMe, HO \ DMF 90°C 7 h 
93% 42% 
@ H2coNHcH2cH~~p 
CH3 
\ 
HO 
337 
SCHEME 54. Synthesis of ellipticine-estrone derivative 337 by Roques and co-workers (123). 
conjugates, for example, 338 and 339. To probe the S-opioid receptor, Roques 
and co-workers (124,125) have synthesized several ellipticine-enkephalin conju- 
gates, one of which is shown in Scheme 55. Straightforward peptide chemistry 
afforded first the activated enkephalin 340 and then the ellipticine conjugate 341. 
The 9-hydroxyellipticine derivative was also prepared. 
Meunier and co-workers (126-128) have reported the construction of several 
ellipticine-porphyrin molecules, which are potentially capable of both intercala- 
tion and chelation (Scheme 56). The linking chain is first connected to the N-2 
position of‘9-methoxyellipticine (2) and the resulting ester 342 is attached to an 
amino porphyrin to give 343. The metal is introduced by letting 342 react with 
FeCl,, MnOAc, or ZnOAc in boiling 2,4,6-collidine to give 344-346, respec- 
tively, in 57-76% yield. 
Hoo;& / / ,cH,cONH(cH,),NH(cH,),O q? 
/ \ 
- 338 CH3 
339 
BOC-Tyr-D-Ala-Gly-Phe-D-Leu * BOC-T~~-D-A~~-G~~-P~E+D-L~U-NH(CH~)~B~ Qq 340 
CHC13 THF 
DCC 
OH 76% 
93% 
0% 45min 
+ 
H3N-Tyr-D-Ala-Gly-Phe-D-Leu-NH-(CH2)3 
0 
- II2 OCCF3 
341 
SCHEME 55. Rigaudy et al. synthesis of ellipticine-enkephalin conjugate 341 (124). 
7. ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 299 """w Br(CH2)&02Et cH3073,.@, (CHz)&O&t 
' N ' / Br- / / DMF 120°C 4 h 
87% H 
' N 
H 
CH3 CH3 
342 2 
1. 1MHCI 
2. EtOCOCl 47% 
3. amino porphyrin 
A 3 h (347) / 
343 A=H2 I 
344 A = Fe(lll)-OAc CH, 
345 A = Mn(lll)-OAc 
346 A=Zn(ll) 
SCHEME 56. Synthesis of metalloporphyrin-ellipticine hybrid molecules 344-346 by Meunier 
and co-workers (127). 
An obvious means by which to increase the affinity of a molecule for DNA is 
to link the molecule to a short segment of nucleic acid. Such a plan has been 
pursued by Paoletti and co-workers (129,130). To prepare the tetrathymidylate- 
ellipticine conjugate 348, these workers synthesized the appropriate ox- 
azolopyridocarbazole carboxylic acid, as described previously (i.e., 267), and 
coupled it to the appropriate tetradeoxynucleotide. A second method of linking 
ellipticine to a nucleic acid involves condensation of the aldehyde moiety of 3'- 
apurinic octathymidylate with 9-aminoellipticine, followed by reduction of the 
irnine with sodium cyanoborohydride (130). This reaction is depicted in a differ- 
ent context in Scheme 66 (see Section VIII). 
300 GORDON W. GRIBBLE 
0 
OYO 
348 
I. SYNTHESIS OF MISCELLANEOUS ANALOGS 
Although the exploration of novel ellipticine analogs continued in the late 
1980s, in general, the further one deviates from the fundamental ellipticine 
structure, the less will be the antitumor activity. This section delineates a pot- 
pourri of such analogs. 
7. ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 30 1 
Bergman and Pelcman (131) have discovered a one-step synthesis of the 
dimethylbenzo[b]carbazole ring system (Scheme 57) that is remarkable in its 
simplicity. An acid-promoted Michael reaction between 2-ethylindole (349) and 
enone 350, followed by cyclization of the methylene group onto the carbonyl 
leads to a tertiary alcohol. In situ dehydration and ring C (D) oxidation completes 
the sequence of events. It remains to be seen if this procedure can be applied to 
the synthesis of pyridocarbazoles. 
Hayler and Sainsbury (132) have synthesized the oxyphenylsulfonyl derivative 
360 of the indeno[2,l-g]isoquinoline ring system (Scheme 58). The key step in 
the preparation of the tricyclic precursor 355 was a Diels-Alder reaction between 
indenone 353 and hexadiene 354. Dehydrogenation and Wolff-Kishner reduc- 
tion gave fluorene 356, which underwent Vilsmeier-Haack formylation ortho to 
the methoxyl group at C-7 instead of at the desired C-2 position. This was 
circumvented by converting the methoxyl group to oxyphenylsulfonylfluorene 
357. Although 357 did not undergo formylation, it did react under chlo- 
romethylating conditions to yield 358. Subsequent conversion to amide 359 was 
followed by Bischler-Napieralski cyclization and dehydrogenation to give the 
target compound 360. 
Using Cranwell-Saxton (56) technology, Sengupta and Anand (133) have 
synthesized the known dibenzofuran analog 361 (134) of ellipticine [and of 
didemethylellipticine (362)l (Scheme 59). In the same paper (133, the interest- 
ing and apparently new pyrido[4,3-b]phenoxathiin (363) and pyrido- 
[4,3-b]phenothiazine (364) ring systems were reported. None of the compounds 
reported in this paper were cytotoxic. Anand and co-workers (135) have also 
described the preparation of several C-seco analogs of ellipticine (Scheme 60). 
10% P&C a2cH2cH: H 
HOAc 3A m01 A sieve 48h * 
349 350 
H 
CH3 
351 (38%) 352 (22%) 
SCHEME 57. Bergman-Pelcman synthesis of 6,l I-dimethyl-5H-benzo[b]carbazole (352) (131). 
302 GORDON W. GRIBBLE 
353 354 355 
1. demethylation = p h s 0 3 ~ chloromethylation 
2. phenylsulonylation 
CH3 
357 
’. NaCN PhSO, 
2. B2H6 
3. formylation 
- 
CHZCI 
CH3 
358 
-- PPE PdIC 
1 20°C diglyme 
A I 
27% from 359 CH3 
360 
CH3 
359 
SCHEME 58. Hayler-Sainsbury synthesis of 6-deazaellipticine analog 360 (132). 
7. ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 303 
0-6 CI~CHOBU a--cHo H2NCH2CH(OEt)2 ' 0 rt 45rnin A 30rnin / Sa14 CH2C12 \ / PhH 
CH3 58% CH3 99% 
' N 105% superphosphoric acid ~ 
140°C / / 
CH3 
oT/&oEt CH, OEt 43% 
36 1 
36 2 
SCHEME 59. Sengupta-Anand synthesis of the pyrido[4,3-b]dibenzofuran ring system (e.g., 361, 
362) (133). 
They utilized the reaction between indole Grignard reagents and either 3-acetyl- 
pyridine or nicotinoyl chloride to give the target structures 54 and 365, after the 
appropriate reduction. None of these compounds displayed antitumor activity 
anywhere comparable to that of ellipticine. 
Nantka-Namirski and co-workers (136) have described the synthesis and anti- 
tumor properties of a series of benzo-annulated iso-a-carbolines, some of which 
have significant antitumor activity. Coupling of 2-bromopyridine with naphtho- 
triazole 366 gave 367 (Scheme 61). Heating this material with polyphosphoric 
acid effected the Graebe-Ullmann carbazole synthesis to give 368, reminiscent 
of Miller's earlier strategy (47). Methylation afforded the iso-a-carboline 369. 
Similar reaction sequences led to the higher order linear iso-a-carbolines 370- 
372. A slightly different approach was used by these workers (136) to synthesize 
the nonlinear analogs shown in Scheme 62. The benzotriazole 375 was prepared 
by diazotization of amine 374, which was synthesized in a straightforward man- 
ner. Similarly, the 8H-benzo[g]-a-carboline (380) ring system was prepared. 
304 GORDON W. GRIBBLE 
1. EtMgl 
COCH3 
H 
2. Ng 100°C 5 3 H 50 
48h 8% 
10% - H2 Pd/C Q)--+J 
H 
latm 12h 
70% 54 
1. EtMgl 
H CH2CH3 2. N G c o c ' 
349 
11% 
OyJp B2H6 ___) THF 
A 3 h 
72% CH3 
365 
SCHEME 60. Synthesis of C-seco ellipticines (e.g., 54, 365) by Anand and co-workers (135). 
363 
I 
CH2CH3 
364 
7. ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 305 
H 
366 
160 - 170°C - 
15 rnin 
61% 
PPA 
1 10" --f 200°C 
50 min 
e 
28% 
367 
1. CH31 EtOH 
100°C 12h 
I H 55% 
368 CH3 369 
SCHEME 61. Synthesis of l-methyl-IH-benzo[5,6]indolo[2,3-b]pyridine (369) by Nantka- 
Namirski and co-workers (136). 
VI. Biological Detection 
The synthesis of N-2 trideuteriomethyl elliptinium (5) in 96% isotopic purity 
has been reported by Gouyette (237) for use in a study of the metabolism of 5 in 
rats. This compound was prepared in 90% yield by allowing 9-hydroxyellipticine 
(3) to react with CDJ in DMF at room temperature. A combination of liquid 
370 R = H 
371 R=CH3 
306 GORDON W. GRIBBLE 
R 
NaN02 * b N * N - PPA 
20% H2SO.4 320 - 350°C 
20 m'n 
41% (28%) 
H 
374 
375 
R hyQ :: rOyNaOH EtOH 100°C 12h * +yq 
CH3 \ 55% (59%) \ 
377 R = H 
378 R=CH3 
376 
SCHEME 62. Synthesis of the lOH-benzo[i]-a-carboline ring system (e.g., 377,378) by Nantka- 
Namirski and co-workers (136). 
chromatography (LC) and mass spectrometry was used to analyze the metabolites 
(Section X). These techniques [high-performance liquid chromatography 
(HPLC) and fast-atom bombardment (FAB) mass spectrometry] have also been 
employed by Gouyette et al. (138) to identify metabolites of 5 in human cancer 
patients. HPLC has been used by the same group (139) to measure the uptake of 
379 CH, 
380 
7. ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 307 
I 
CH, CH, 
381 
CH, 
382 
2,6-dimethylellipticinium (381) and 2-methyl-6-n-propylellipticinium (382) by 
NIH 3T3 cells. 
A fluorodensitometric assay was developed by Montague and co-workers 
(140) to analyze cultures from Ochrosiu ellipticu for ellipticine (l), 9-methoxy- 
ellipticine (2), and 9-hydroxyellipticine (3) by thin-layer chromatography (TLC) 
without the need for prior purification. Using silica gel impregnated with di- 
methyl sulfoxide and a mobile phase of EtOAc-water-1-octanol (17 : 2 : 2), 
these workers were able to achieve good separation of these alkaloids and to 
assay the resulting chromatograms by fluorodensitometry (40-300 fmol detec- 
tion limits ofalkaloid). 
VII. Antitumor Activity in Experimental Models 
Several significant developments have occurred during the late 1980s in the 
study of the antitumor activity of ellipticine and its derivatives, which are high- 
lighted in this section. Further discussion on the antitumor activity of these 
compounds is expounded upon in Section XI. 
In attempts to deliver ellipticine and derivatives to specific biological targets, a 
number of investigators have combined an ellipticine drug with the appropriate 
carrier molecule. Of the several ellipticine-estradiol receptor conjugates synthe- 
sized by Roques and co-workers (123), only 337 had good antitumor activity 
against the L1210 mouse leukemia system in vitro [IC,, 0.5 pkf; ellipticine, 
IC,, 0.85 pkf; elliptinium (9, IC,, 0.08 pkf], which is generally considered to 
provide a good indication of the efficacy of drugs against human cancer (141). 
The IC,, refers to the inhibitory concentration that reduces by 50% the growth 
rate of the cells after 24 (or 48) hr of drug exposure. The triarylethylene- 
ellipticine hybrid molecules (338, 339) were essentially devoid of cytotoxicity 
(123), even though they retain their affinity for DNA and estrogen receptor. 
Compound 337 also had activity against the human breast cancer cell line 
MCF-7. 
308 GORDON W. GRIBBLE 
The ellipticine-enkephalin conjugates (e.g., 341) exhibit in vitro binding 
properties both to DNA and to opioid receptors in NG108-15 mouse tumor cells 
that are similar to those of the parent molecules, although the conjugates did not 
exhibit the expected selectivity when tested on the opioid-receptor containing 
NG108-15 cells and Lfibroblasts as controls (125). The lack of specificity was 
explained in terms of an intracellular overconcentration of drug. 
A 9-methoxyellipticine (2)-low density lipoprotein (LDL) complex was for- 
mulated by Soula and co-workers (142) and found to be 10 times more active 
than 2 against L1210 and P388 leukemia in vitro. This activity seems to depend 
on the LDL high-affinity receptor since LDL reduces the antitumor activity. The 
complex was prepared by adding 2 to a dimyristoyl phosphatidylcholine, cho- 
lesteryl oleate-stabilized microemulsion and then fusing with human LDL. 
In a very significant study, Alberici et al. (143) synthesized several elliptinium 
(5)-monoclonal antibody conjugates, one of which (Fab AFO1-5) is at least 100 
times more cytotoxic in vitro against human hepatocarcinoma cell lines than is 5 
or doxorubicin. The conjugates were prepared by oxidizing 5 with HRP/H,O, 
(to give quinone imine 256) in the presence of the monoclonal antibody. 
Arteaga and co-workers (144) have utilized a human tumor cloning system to 
evaluate in vitro the effects of elliptinium (5) against 282 tumor lines, in order to 
determine which human tumors should be clinically treated with 5. The results 
indicated that phase I1 trials in patients with renal cell carcinoma, breast cancer, 
non small-cell lung cancer, and small-cell lung cancer should be pursued. 
Elliptinium (5) has been encapsulated within phospholipid vesicles by Sau- 
tereau et al. (14.9, although, as such, the drug is less cytotoxic against L1210 
cells in vitro and in vivo than when it is free. However, if the onset of leukemia is 
delayed in mice, then the entrapped drug has higher antitumor activity than the 
free form. An investigation by Ali-Osman et al. (146) has shown that 5 is able to 
cross the blood-brain barrier in rats and is cytotoxic in vitro against three human 
glioma cell lines (SF126, SF375, SF407). 
In a study on the effects of various agents, including ellipticine (l), on the 
initiation of skin tumors in mice by polycyclic aromatic hydrocarbons (PAH), 
Alworth and Slaga (147) have observed that, depending on the dose of 1 and the 
nature of the PAH, 1 can either stimulate or inhibit skin tumorigenesis. Thus, 
high doses of 1 inhibited the tumorigenesis by 7,12-dimethylbenz[a]anthracene 
but low doses of 1 stimulated it. In contrast, treatment of mouse skin with 1 at all 
doses tested stimulated dibenzo[a,h]anthracene tumorigenesis. Ditercalinium 
(212) and elliptinium (5) have been studied as agents against small cell lung 
cancer in bone marrow in vitro. Thus, Benard and co-workers (148) have found 
that 212 has high activity against NCI-H449 and NCI-N417 human cells (I& 
1.2 X l o p 3 and lo-, pM, respectively). By comparison, 5 is much less active 
(1 and 0.25 pM, respectively). 
In the late 1980s, several new ellipticine derivatives and modified ellipticines 
7. ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 309 
have been found to possess antitumor activity. One such class of compounds, 
developed by Honda et al. (68-70), are the ellipticine glycosides (e.g., Scheme 
18). Several of these compounds have excellent antitumor activity against L1210, 
P388, B16 melanoma, and colon 38 carcinoma in vivo. Two compounds, 104 
(SUN4599) and 383 (SUN5073), which have been selected for preclinical stud- 
ies, were curative against several of the above tumors as well as Ehrlich ascites 
carcinoma (EAC) and sarcoma 180. Additional details on the remarkable anti- 
tumor activity of these simple ellipticine sugars can be found in Section XI. 
Another extraordinarily simple ellipticine derivative that has excellent anti- 
tumor activity is carbamate 153 (“RPI-6”). As reported by Ruckdeschel and 
Archer (149), 153 has high activity (1000 times higher than doxorubicin) against 
two human small-cell lung cancer lines (NCI H69c, N417) and two human non- 
small cell lung cancer lines (H460, H358). This compound was previously re- 
ported by Archer and co-workers (84) to have better activity against P388 leuke- 
mia in vivo than does ellipticine. 
In addition to elliptinium (5) and ditercalinium (212), three new ellipticine 
derivatives have been entered into clinical trials. The first is a simple modifica- 
tion of the N-2 methyl group of 5 to give 2-[(2-diethylamino)ethyl]-9-hy- 
droxyellipticinium chloride hydrochloride (datelliptium) (384), which shows bet- 
ter in vivo activity than elliptinium (5) toward L1210, P388, B16, colon 38, and 
M5076 reticulosarcoma (150). The in vitro L1210 IC,, is 0.076 phf (5, 0.13 
phf). The increased antitumor potency is believed to be due to increased diffu- 
sion across cellular membranes and a more favorable biodistribution in vivo. An 
azaellipticine derivative, “pazellipticine” (PZE or BD-40) (385) { 10-[(3-di- 
ethylamino)propylamino] -6-methyl-5H-pyrido- [ 3 ’ ,4’ :4,5]pyrrolo[ 2,3-g] isoquin- 
oline}, is also in clinical trials (151). This derivative has excellent in vitro act- 
ivity against L1210 cells (&, 3.1 CLM). The third new clinical candidate is 
l-[(3-diethylamino)propylamino]-9-methoxyellipticinium chloride hydro- 
chloride (BD-84) (386) (152). This drug has high activity against P388, L1210, 
B16, M5076, and colon 38 in vivo. 
Although the oxazolopyridocarbazoles (i.e., 258) have good activity against 
383 
310 GORDON W. GRIBBLE 
2 CI - 
H 
CH3 
H 
CH3 
384 385 
("datelliptiurn") ("pazellipticine") 
("DHE) ("PZE") 
CH3 NH(CH,),NHEt, ("ED-40") 
c H 3 0 n y - H / / 2c1- + 
CH3 
386 
("BD-84) 
tumor cells in virro (e.g., L1210, IC,, 0.2-0.6 w), these compounds in general 
have no antitumor activity in vivo (153,154). One compound, 387, shows some 
antileukemic activity in vivo. Despite the fact that the 1 1H-pyridocarbazoles 
(Schemes 36, 37) have DNA binding affinities close to those of 6H- and 7H- 
pyridocarbazoles, these compounds have no measurable L1210 cytotoxicity 
(ZOO). 
As discussed in more detail in Section XI on structure-activity relationships, 
the tricyclic analogs of pyridocarbazole display some powerful antitumor activity 
(115,117,136). For example, compounds 388 and 389 have L1210 in virro ID,, 
values of 0.13 and 0.01 w, respectively. These compounds also exhibit in vivo 
activity against L1210, P388, B16, and colon 38 (116). Thus, 389 gives a T/C 
value of 236% and 40% survivorswith a 100 mg/kg dose. The TIC value refers 
to the median day of survival of treated animals at a given dose/median day of 
survival of control mice ( X 100%). Significant activity is present when the TIC 
value exceeds 125%. 
7. ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 31 1 
NH(CHZ),NEtz NH(CH,),NMe, 
N 3 - G ‘ O n - - / 
\ N 
I 
CH, CH, CH, CH, 
/ \ N 
I 
388 389 
The interesting benzo-annulated iso-a-carbolines (e.g., Scheme 62) display 
good in vitro cytotoxicity against human tumor KB cells (e.g., IC,, 1 pM for 
371 and 10 pM for ellipticine) and in vivo antitumor activity against P388, 
L1210, and B16 (e.g., TIC 224% at a dose of 100 mg/kg of 371) (136). Com- 
pound 371 can, of course, be viewed as an isoellipticine. Finally, of the several 
dimers prepared by Sainsbury and co-workers (121), only 334 and the 9-meth- 
oxyl derivative of 333 show significant activity against L1210 in vitro (IC50 -2 
and 2.6 pM, respectively). 
VIII. Mechanism of Action 
As Suffness and Cordell (10) discussed in their review, there is increasing 
evidence that the enzyme topoisomerase I1 may play an important role in the 
mode of action of ellipticine and its derivatives. The late 1980s bear witness to 
continued activity in this regard. Ross (155) has concisely summarized the im- 
portance of topoisomerase 11 as a potential target for anticancer drugs, and Riou 
and co-workers (156) have written an excellent minireview on the functions of 
this remarkable enzyme and the mechanistic details of its interaction with DNA. 
The rationale for pursuing topoisomerase I1 as a drug target is that the activity of 
this enzyme is thought to be higher in malignant cells than it is in normal cells, 
obviously leading to improved selectivity. 
In performing its role in the cleavage and rejoining of DNA strands (catena- 
tion, decatenation, relaxation, unknotting), topoisomerase I1 bonds to the 5‘ - 
phosphate on adjacent DNA strands four base pairs apart to form an enzyme- 
DNA complex. It is the interaction between this complex and certain drugs, such 
as ellipticine (l), that results in the stabilization of the complex and the formation 
of a “cleavable complex” which leads eventually to the cleavage of double- 
stranded DNA. Pommier et al. (157,158) have shown that low concentrations of 
elliptinium (5) (< lo pM) produce DNA double-strand breaks in mammalian 
cells, but higher concentrations (> lo I.M) produce no such breaks and, in fact, 
312 GORDON W. GRIBBLE 
inhibit those induced by ellipticine (1). It is believed that these DNA breaks occur 
from topoisomerase 11-DNA complexes. This group (159,160) also found that 
cells which are resistant to 9-hydroxyellipticine (3) have fewer DNA double- 
strand breaks than normal cells, suggesting that these breaks play a role in the 
antitumor activity of topoisomerase I1 inhibitors. Elliptinium (5) and other ellip- 
ticine-derived topoisomerase I1 inhibitors also lead to chromosomal abnor- 
malities in Chinese hamster ovary cells (161) and in mouse bone marrow cells 
(162). These abnormalities include chromosome clumping, micronuclei forma- 
tion, sister chromatid exchanges, and chromatid aberrations. There is observed a 
good correlation between antitumor activity and topoisomerase I1 inhibitory ac- 
tivity in vitro for 3, 5, 9-aminoellipticine, and 9-fluoroellipticine (142) (162). 
The interaction of ellipticine derivatives with topoisomerase I1 enzymes in 
Plasmodium berghei (163), a parasite of mouse red blood cells, mouse lympho- 
ma L5178Y cells (164), simian virus 40 CV-1 cells (165), Trypanosoma cruzi 
(166,167), and the human small-cell lung cancer cell line NCI N417 (168,169) 
has been studied. In the latter study, the highest in vitro activity in the topo- 
isomerase 11-DNA cleavage reaction and decatenation was observed for ellip- 
tinium (5) and datelliptium (384) (169). 
Another aspect of the mode of action of ellipticine and its derivatives that has 
been intensely scrutinized in recent years is the chemistry of ellipticine quinone 
imines 6 and 256. The oxidation product of 9-hydroxyellipticine (3), formed by 
horseradish peroxidase-hydrogen peroxide or chemical (e. g . , manganese diox- 
ide) oxidation of 3, undergoes a rich array of chemical reactions. Meunier et al. 
( 1 70) have discussed in detail the oxidation parameters, chemical properties, and 
biological activities of several oxygenated ellipticine derivatives. In particular, 
molecular obital calculations support the fact that the C-10 position of 256 (and 
6) is the preferred site of nucleophilic attack, as discussed earlier for the reaction 
of quinone imine 256 with amino acids (Scheme 42). It has been hypothesized 
(1 71) that this quinone imine is involved in the observed covalent binding in vivo 
to DNA in L1210 cells exposed to elliptinium (5). This DNA damage is not 
readily repaired, and 2-methylellipticinium (110) acetate is 20-30 times less 
active than 5 in terms of this binding. When elliptinium (5) was oxidized with 
HRP/H,O, to quinone imine 256 in the presence of DNA in v i m , a fluorescent 
compound irreversibly bound to the DNA was observed. The fluorescent proper- 
ties of this complex were consistent with binding between C-10 of the quinone 
imine 256 and a primary amine group (N-2 guanine, N-6 adenine, or N-4 
cytosine) of DNA (summarized in the hypothetical 390). With excess H,O,, the 
major product was the C-9,lO o-quinone (172,173). 
Quinone imine 256 also reacts very easily with the sugar groupings of nu- 
cleosides or nucleotides. Meunier and co-workers (1 74-1 76) have continued 
their studies of these reactions with simple nucleosides (Scheme 63 and 393) and 
diribonucleoside monophosphates (394). The 2'-deoxy diribonucleoside mono- 
7. ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 313 
* . 0 
390 
phosphate (dApdG) did not yield a detectable adduct (175), and purine sugars 
seemed to be more reactive than pyrimidine sugars (176). The cytotoxicity of 
these spiro derivatives of elliptinium (5) was less than that of 5 itself. However, 
C- 10 thioelliptinium adducts retained the high cytotoxicity of 5 (1 76). 
Potier and co-workers (and some members of the Meunier group) (177,178) 
have explored the chemistry of quinone imines 6 and 256 and oxygen nu- 
cleophiles including sugars. They found that 256 can be generated from ellip- 
tinium with Cu,Cl,/pyridine/air, as well as with HRP/H,O,. The structure of the 
product formed between 256 and methanol has been revised as 396 instead of 
3 14 GORDON W. GRIBBLE 
5 
cordycepin 
* 
60% 
256 
NHZ 
I 
CH3 
392 
SCHEME 63. Arylation of purine nucleosides by elliptinium (5) (174-176). 
7. ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 315 
393 394 
395. These ketals can also be synthesized from 9-hydroxyellipticine (3) and lead 
tetraacetate/methanol/pyridine [room temperature (rt), 3 hr] . In similar fashion, 
the ribonucleotide adduct 397 was synthesized and characterized by an ex- 
haustive NMR study including nuclear Overhauser effect (NOE) measurements 
to establish the precise stereochemistry (1 78). 
To rationalize the remarkable regioselectivity and stereoselectivity of these 
alkylation reactions, Potier and co-workers (I 77,178) proposed that a stacking 
interaction occurs between quinone imine 256 and the nucleic acid base prior to 
covalent bond formation. Moreover, the appropriate intermolecular NOE is ob- 
served to support this contention. The fact that these ribonucleotide adducts form 
so easily may suggest that ellipticine quinone imines could alkylate at the 3’ end 
of transfer RNA or at similar sites on other RNA molecules to inhibit protein 
synthesis. Thus, RNA would seem to be a reasonable target for elliptinium and 
related ellipticines (1 78). 
It has been found by Dugue and Meunier (179) that the combination of 
Fe(II1)-EDTA-H202 in the presence of elliptinium (5) is capable of degrading 
deoxyguanosine apparently by generating hydroxyl radical (Scheme64). The 
isolated products are guanine (398) and 8-hydroxydeoxyguanosine (399). Other 
nucleosides and nucleotides behave similarly, but Cu(II) is much less effective 
316 GORDON W. GRIBBLE 
OCH3 
CH3 
395 
than Fe(III), and 2-methylellipticinium (110) acetate does not participate in such 
chemistry. Auclair (110) has reported the generation of superoxide when ellip- 
tinium (5) is photolyzed in the presence of leucine to form the oxazolopyridocar- 
bazole 387, and Kovacic ef al. (180) have presented a detailed proposal that 
many anticancer drugs, including ellipticines, operate by charge transfer result- 
ing in the formation of oxygen radicals that can cleave DNA or other cellular 
constituents. 
Several studies have reported on ellipticine- or elliptinium-DNA interactions. 
The effects of elliptinium on chromatin in v i m or in the nuclei are an unfolding 
of the overall structure and a disorganization of the partial structure of the core, 
leading to an unwrapping of the DNA from the histone core (181). The kinetics 
and thermodynamics of ellipticine and ellipticinium (protonated ellipticine) 
binding to calf thymus DNA have been carefully investigated (182). It was 
7. ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 317 
Fe( Ill) Fe(ll) - 
1. 
EDTA 
2. Fe(ll)-EDTA + H2Q - 
OH 
H I 
CH3 
Fe(ll1)-EDTA + OH + OH- 
398 OH 399 
SCHEME 64. Proposed mechanism for the generation of hydroxyl radical and degradation of 
nucleosides (179). 
concluded that the main force behind the DNA binding of ellipticine is hydro- 
phobic and/or dipolar. At pH 9, the affinity constant of 1 ( 3 . 3 X lo5 M - I ) is 
only slightly less than that of the ellipticinium cation (8.3 X lo5 M - I ) . The base 
specificity of elliptinium (5) and 2-methylellipticinium (110) has been reinvesti- 
gated (183). In contrast to earlier work, it was demonstrated that the 9-hydroxyl- 
ated ellipticine derivatives, such as elliptinium (9, express a guanine-cytosine 
(G-C) base-pair preference, with the preferred binding site being a doublet 
sequence of two adjacent G-C base pairs flanked by either another G-C or an 
adenine-thymine (A-T) base pair. In contrast, 2-methylellipticinium (110) ace- 
tate expresses no preference. 
318 GORDON W. GRIBBLE 
The effect of ellipticine derivatives on membranes and model membranes 
continues to be of interest to Sautereau and co-workers (184-186), who included 
31P-NMR techniques in their study (185). The ellipticine derivatives, such as 5, 
are deeply embedded in the acyl chain region of cardiolipin-containing model 
membranes. Sautereau et al. (186) studied the effects of elliptinium (5) on 
Streptococcus pneumoniae and concluded that the toxicity of 5 is related to its 
intracellular concentration. 
The interaction of elliptinium with numerous other biological targets has been 
studied in recent years. Elliptinium (5) is a potent inhibitor of fetal thymidine 
kinase and other enzymes that are induced by estradiol(187). Thus, 5 could bind 
the acceptor sites for estradiol receptor and, therefore, inhibit the activity of 
estradiol-regulating genes. Ellipticine (1) is the most potent inhibitor, of several 
compounds tested, of microsomal cholesterol 5,6-oxide hydrolase (188), an en- 
zyme that converts cholesterol epoxide to the corresponding 3,5,6-triol. This 
work suggested that cholesterol epoxide could be a carcinogen involved in liver 
cancer. Elliptinium (5) and 9-hydroxyolivacinium are potent muscarinic antag- 
onists and demonstrate pronounced affinity for muscarinic receptors (189). These 
compounds are only one-hundredth as active as atropine in their antagonism, but 
they show no interaction with three other neurotransmitter receptors. 9-Hy- 
droxyellipticine (3) also binds to the 2,3,7,8-tetrachlorodibenzo-p-dioxin 
(TCDD) receptor in the rat lung (190). In another study of TCDD binding sites in 
rat liver cytosol, ellipticine had very weak binding affinity, but 5H-benzo[b]car- 
bazole (400) and, especially, 5H, 1 1H-indolo[3,2-b]carbazole (401) had binding 
that was comparable to that of TCDD (191). 
Ellipticine and several derivatives were able to displace 7,12-dimethyl- 
benz[a]anthracene from binding to bovine and human serum albumin using the 
fluorescence-quenching technique (192,193). The site of binding of ellipticines 
appears to be on the hydrophobic regions of the enzyme. A fast kinetic experi- 
mental technique, namely, temperature-jump spectroscopy, has been developed 
in order to study the interaction of elliptinium, and other molecules, with biolog- 
ical macromolecules (194). 
Several ellipticine derivatives were evaluated for their effects on Escherichia 
coli strains (195). There does not appear to be a correlation between the physio- 
logical effects of the ellipticines and their physiochemical behavior in vitro. 
H 
H H 
400 401 
7. ELLIF'TICINE ALKALOIDS AND RELATED COMPOUNDS 319 
Whereas the quaternarized ellipticines have no bactericidal activity, the noninter- 
calating 9-bromoellipticine is a strong bactericidal agent, which apparently 
causes the lysis of the bacteria. When malignant liver cell cultures are treated 
with elliptinium, the level of spermidine increases, apparently as a result of 
decreased nuclear-bound polyamines connected to RNA (196). Ellipticine inhib- 
its poly(ADP-ribose) glycohydrolase activity (297) and decreases DDT-induced 
tremors in rats (198). In the latter study, it was postulated that ellipticine acts 
directly on nerve or muscle tissue. 
A study of the Ir-stacking and edge-to-edge associations in several ellipticine 
derivatives using 'H-NMR techniques has appeared (199). As would be ex- 
pected, methyl substitution at the N-6 and C-1 positions of ellipticine (1) signifi- 
cantly reduces the association constant, but, interestingly, the authors attribute 
this to electronic effects at the nitrogen atoms rather than to steric effects of the 
methyl groups. A quantum mechanical study on the intermolecular interaction 
energies of ellipticine with G-C and A-T base pairs has attempted to correlate 
these energies with the site of drug binding (200). 
A substantial number of reports have appeared since 1984 describing the 
effects of ellipticines on the cytochromes P-448 and P-450. The structural re- 
quirements for the substrate binding sites of these cytochromes have been studied 
and discussed at length by Lewis, Ioannides, and Parke in several excellent 
papers (201-204). Ellipticine (1) has been shown to inhibit rat embryo tissue 
cytochrome P-450 that is involved in the detoxification of the teratogen di- 
phenylhydantoin (205). Thus, ellipticine enhances the in vitro toxicity of di- 
phenylhydantoin. Ellipticine (1) also protects cells against the cytotoxicity of 
mitomycin C by inhibiting NADPH-cytochrome P-450 reductase (206). Ellip- 
ticine (1) and 9-hydroxyellipticine (3) also inhibit cytochrome P-450 in its role in 
the metabolism (hydroxylation, epoxidation) of pentachlorophenol (207), 
aflatoxin B-1 (208), 2-amino-3,8-dimethylimidazo[4,5-flquinoxaline and other 
protein pyrolysates (209), ecdysone (210), halogenated biphenyls (221), and 
coumarin (212). Ellipticine (l), 9-hydroxyellipticine (3), and other derivatives 
have been studied with regard to their effects on the estrogen receptor (213), 
cytochrome-c oxidase in plant mitochondria ( 2 1 4 , and Ah receptor proteins and 
4-S proteins in rodents (215). In the latter study, it was found that ellipticines are 
powerful binders of the 4-S carcinogen-binding proteins (stronger than ben- 
zo[a]pyrene) (215). The technique of microspectrofluorimetry was used to probe 
the effects of ellipticine on the metabolism of benzo[a]pyrene in intact cells 
(216,217). 
The binding characteristics of oxazolopyridocarbazoles toward bacterial DNA 
have been studied (218). It was found that these ellipticine derivatives invariably 
exhibit DNA intercalation but with no sequence specificity. The new clinical 
candidate datelliptium (384) showsincreased lipophilicity but no difference in 
binding or intercalation to DNA compared to elliptinium (5) (250). This new 
320 GORDON W. GRIBBLE 
derivative also has the same effect on topoisomerase I1 as does 5 but shows a 
pronounced increase in antitumor activity. Although the DNA binding properties 
of a series of N-2 and N-6 side-chain amine ellipticines 105-109, 111 were 
increased over that of ellipticine (l), the in vivo antitumor activity was less than 
desired (71). 
The excellent antitumor activity of ellipticine carbamate 153 led Archer and 
co-workers (84) to propose a new mechanism for the antitumor effects of ellip- 
ticine in general (Scheme 65). It is suggested that the C-5 methyl group is 
enzymatically hydroxylated and then converted either to the sulfate (402) or 
phosphate ester. This can now react with a cellular nucleophile (e.g., DNA, 
topoisomerase 11), by an SN1 or SN2 mechanism, to give the covalent adduct 
403. This type of mechanism has been invoked to explain the antitumor activity 
of lucanthone (404) and hycanthone (405) (219,220). A study of the azaellip- 
ticines 204 and 406 showed that both compounds are active on topoisomerase I1 
and initiate the cleavage of DNA (151,221). However, unlike ellipticine, these 
azaellipticines did not cleave DNA in isolated nuclei. 
Several papers have described the physicochemistry and biological activity of 
the oxazolopyridocarbazoles (i. e., 258). These interesting compounds behave as 
metabolism 
1 * 3 - 
"Q7& - Nuc:- " Q y - I I / / 
CH,Nuc 
403 
SCHEME 65. Archer et al. proposal for the mechanism of action of ellipticine (84). 
7. ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 32 1 
reversible intercalators and are less cytotoxic than elliptinium ( 5 ) (153,154,222), 
and they are frameshift mutagens (223,224). With regard to their low antitumor 
activity, it is such that the oxazolopyridocarbazoles cannot undergo biological 
conversion to quinone imines and are unable to generate “cleavable complexes” 
in DNA by interacting with topoisomerase I1 (154). 
The most frequent spontaneous mutation in DNA is depurination, occurring in 
mammalian cells at a rate of 10,000 per cell per day (225). It has been proposed 
that these sites can be trapped by condensation with aldehyde condensing re- 
agents, such as primary amines, leading to DNA cleavage (226). Indeed, it has 
been found that 9-aminoellipticine (407) is remarkably effective at causing DNA 
cleavage at apurinic sites but not apyrimidinic sites (227-230). The concentra- 
tion of 407 required to cause such breaks is the lowest of any chemical known to 
be active in this reaction (227). Molecular models (CPK) show that an apurinic 
site is ideally arranged for an insertion of 407 into the minor groove of DNA but 
that this is not feasible for an apyrimidinic site (228). One can quantify the 
number of such apurinic sites by fluorescence (229). The mechanism for the 
reaction of 9-aminoellipticine with apurinic DNA is shown in Scheme 66 (230). 
The intermediate imine (Schiff base) 408 has been trapped with sodium 
cyanoborohydride to give 409. Interestingly, this reductive amination reaction of 
apurinic DNA with 9-aminoellipticine in the presence of sodium 
cyanoborohydride has been used to synthesize an ellipticine-octathymidylate 
conjugate (130). The azaellipticine 204 has been reported in preliminary form 
(231) to break DNA at apurinic sites. 
As we have seen, the 11H-pyridocarbazoles (Schemes 36 and 37) are not 
cytotoxic, yet some of these derivatives have high DNA binding affinities and are 
NH(CH,),NEtz CH3 
I I 
204 406 
322 GORDON W. GRIBBLE 
0 
A 
0 
A 
SCHEME 66. Hypothesis for the reaction of 9-aminoellipticine (407) with apurinic DNA (230). 
true intercalators (100). Even more intriguing is the observation that some 11H- 
pyridocarbazoles are not intercalators but, nevertheless, have high affinities for 
DNA. For example, 410 and 411 have high DNA affinities but are not inter- 
calators, but 412 and 413 are true intercalators. 
The 7H-pyridocarbazoles (Schemes 38 and 39) have been exhaustively studied 
by Roques and co-workers (102). It is seen that, for highly active antitumor 
compounds, it is necessary to have high DNA binding and intercalation. The 
structure-activity relationships of these nonlinear pyridocarbazoles are discussed 
in Section XI. Some very elegant theoretical (232) and 'H-NMR studies (233) 
have shown that the concave side of 7H-pyridocarbazoles, such as 414, protrudes 
into the major groove of a minihelical self-complementary tetranucleotide 
7. ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 323 
41 0 CI - 411 tH3 
41 2 41 3 
[d(CpGpCpG),] and hexanucleotide [d(CpGpApTpCpG),] . The quinoxaline an- 
alog 415 has also been studied by 'H-NMR techniques to evaluate its interaction 
with the self-complementary decanucleotide d(GpCpApTpTpApApTpGpC), 
(234). The binding sites appear to involve only the A-T base pairs. 
In a monumental piece of research, Roques and co-workers (235-239) have 
employed exceedingly sophisticated and difficult high-field 'H- and 31P-NMR 
experiments to examine the interaction of nonlinear bispyridocarbazoles, such as 
ditercalinium (212), with small polynucleotides. As in their earlier work on 
monomers (233), the self-complementary tetra- and hexanucleotides were used. 
It was found that ditercalinium is a bis-intercalator with a preference for alternat- 
ing sequences, pyrimidine-purine or purine-pyrimidine, and, in agreement with 
the classic pyrimidine-purine model (240,241), it was found that the linking 
chain lies in the major groove of the helix. 
Although ditercalinium (212) has since been withdrawn from clinical trials 
414 
I 
CH,CH,NMe, 
41 5 
324 GORDON W. GRIBBLE 
because of unacceptable liver toxicity (242), it exhibits very interesting biolog- 
ical properties. Ditercalinium (212) seems to act as a DNA condensing agent by 
altering chromatin structure in vivo (L1210), but it does not cause DNA strand 
breaks or DNA-DNA or DNA-protein cross-links (243). Thus, the cytotoxicity 
of 212 may be due to the condensation of DNA rather than to the initiation of 
topoisomerase 11-associated DNA strand breaks. It has been shown that diter- 
calinium (212) forms a high-affinity yet reversible and noncovalent DNA adduct 
in E. coli (243). Nevertheless, cell death results (although delayed for five or six 
generations) because a conformational change is induced in the DNA that is 
similar to the changes induced by covalent adducts, thus triggering the DNA 
repair system. Although similar bispyridocarbazoles, but with longer linking 
chains, form high-affinity reversible DNA adducts, they do not induce conforma- 
tional changes in the DNA, and, thus, the complex is not recognized by the 
repair system. Why this recognition of essentially normal DNA by the repair 
system leads to cell death in E. coli is unclear. A study of ditercalinium on 
leukemic cells indicates that it increases the sensitivity of DNA to denaturation 
induced by acid (244). Furthermore, 212 exhibits no cell cycle phase specificity, 
unlike most DNA intercalators which arrest cells in G, phase. A kinetic and 
thermodynamic investigation of ditercalinium and its interactions with anions 
and DNA has been reported (242). This study reveals the important fact that 
intermolecular and intramolecular stacking does not occur in 212. 
Although the unsymmetrical bispyridocarbazoles (Scheme 5 1) and the 
pyridocarbazole-acridine hybrids 327 and 328 have high DNA binding and seem 
to be bis-intercalators, they display little or no antitumor properties in vitro or in 
vivo (120). The position of the pyridine nitrogen in the D ring of ditercalinium 
(212) and the presence or absence of methyl groups play a very important role in 
the antitumor activity of the resulting derivatives (102). These are presented in 
Section XI. 
The tricyclic analogs of ellipticine and 9-azaellipticine (Schemes 46 and 45, 
respectively)are poorer DNA intercalators than their tetracyclic analogs but, 
nevertheless, have interesting and significant antitumor activity (Section XI) 
(115-117). Moreover, some derivatives have high DNA affinity but are essen- 
tially inactive in vitro or in vivo (L1210). Although there is no direct relationship 
between DNA affinity and cytotoxicity in vitro of the tricyclic analogs, high 
DNA affinity is necessary for antitumor activity. The observed close correlation 
between in vitro cytotoxicity and the induction of DNA cleavage in cells suggests 
that these breaks are responsible for cell death. These authors further conclude 
that the DNA breaks are probably induced by an interaction between drug and 
topoisomerase 11-DNA complex (11 7). 
In conclusion, although it is fair to say that the mechanism of the antitumor 
activity of ellipticines and related compounds remains unproved, metabolic ac- 
tivation of an ellipticine to a quinone imine or related species of high elec- 
7. ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 325 
trophilicity, DNA intercalation (not just binding), and topoisomerase I1 as a 
critical cellular target all seem to be important factors in this mechanism. 
IX. Mutagenicity 
Several reports have appeared recently that describe the mutagenicity of ellip- 
ticine and derivatives. Moore and co-workers (245) have shown that ellipticine 
(1) is both mutagenic and clastogenic at the tk locus of mouse lymphoma cells, 
and the major mechanism is chromosomal cleavage. Similar effects were seen 
when 1 was applied to rat bone marrow cells an? human peripheral blood lym- 
phocytes (246). Interestingly, the source of ellipticine for this latter research was 
natural, Aspidosperma williansii (Apocynaceae). Ellipticine was also mutagenic 
in bacteriophage T4, whereas 9-aminoellipticine (407) and 9-methoxyellipticine 
(2) were not (247). The reversible DNA intercalators oxazolopyridocarbazoles 
(258) induce frameshift mutations of the mismatch-repairable type in Salmonella 
typhimurium and E . coli (223,224,248,249). 
X. Metabolism and Microbial Transformation 
The metabolism of any drug is invariably of theoretical and practical impor- 
tance, and the metabolic behavior of the ellipticine family of antitumor alkaloids 
and synthetic derivatives is no exception. A number of new developments have 
been described since the Suffness and Cordell review (10). The pharmacokinetics 
of elliptinium (5) have been studied in a human brain tumor clonogenic cell assay 
(250) and in metastatic breast cancer patients (251). In the latter study, the drug 
was mainly excreted in the feces (I4C-labeled 5 ) 
The metabolism of elliptinium has been investigated in rat kidney cells and 
yields four metabolites: 10(S)-N-acetylcysteine 416 (major), lO(S)-glutathione 
417 (minor), lO(S)-cysteine 418 (minor), and 9(0)-glucuronide conjugate 419 
(minor) (252). From the bile of human cancer patients treated with elliptinium, 
there have been isolated, in addition to unchanged 5, the 0-glucuronide 419 and 
the 10(S)-cysteine 418 adducts (253). From the urine of such patients, the glu- 
tathione 417 conjugate can be isolated (138). In contrast, elliptinium ( 5 ) is 
metabolized in rats such that the glutathione 417 is found in bile, along with 
unchanged drug, whereas N-acetylcysteine 416 is found in bile and urine, along 
with unchanged drug (137). Red blood cells also provide a medium for the 
326 GORDON W. GRIBBLE 
metabolism of elliptinium, giving rise apparently to the glutathione adduct 417, 
after incubation of the cells in the presence of glutathione and hydrogen peroxide 
or tert-butyl peroxide (254). This study would suggest that red blood cells may 
be a significant site of bioactivation of ellipticines into their quinone imine 
intermediates. 
Rats metabolize 9-methoxyellipticine (2) into 9-hydroxyellipticine (3), the 
glucuronide 419, the 9(O)-sulfate, and the glutathione conjugate 417, all isolated 
from the bile (255). This unexpected demethylation had been previously ob- 
served when 2 was exposed to HRP/H,O, (256) or rodent liver microsomes 
(257). The latter study demonstrated the demethylation of BD-84 (386) as well. 
The mechanism of this HRP/H,O, demethylation has been studied (258,259), 
and it is clear from elegant 180-labeling experiments that the aryl-oxygen bond 
is cleaved (Scheme 67). When 2 was incubated in H2l80, there was observed 
100% inclusion of the l 8 0 label into the product quinone imine 6, which was 
isolated in 64% yield. Moreover, the methanol could be isolated by gas chro- 
matography, and it was found to be devoid of l80. A proposed mechanism is 
shown in Scheme 67. A similar demethylation of the 9-methoxyl derivative of 
elliptinium has also been observed in the presence of HRP/H,O, to yield the 
0 
II 
H02cy"HccH3 Hob ~ @ 0CH3 
\ / / 
CH3 
416 
H I 
41 7 
CH3 
HozcTNHz 
418 41 9 
7. ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 327 
H20 - ["I 
CH30 HoQ--d] -CH30H ~ on--+ 
64% 
C"3 
6 
SCHEME 67. Possible mechanism for the demethylation of 9-methoxyellipticine with HRP/H202 
C-10 N-acetylcysteine adduct 416 (40% yield) when the incubation is performed 
in the presence of N-acetylcysteine (259). 
The metabolism of 6-methylelliptinium (420) in rats (bile and urine) gives rise 
to the 0-sulfate and 0-glucuronide conjugates, but no demethylation of the N-6 
methyl group (260) (Scheme 68). Likewise, the HRP/H,O, system gives rise to 
the orrho-quinone 421 and the oxazolopyridocarbazole 422, when alanine is 
present, but not to N-6 demethylation (261). The metabolism of olivacine (4) in 
rats and microsomes is faster than that of ellipticine, and leads to hydroxylation 
at the C-7 and C-9 positions (as conjugates) (55). 
In very preliminary work, the metabolism in vitro and in vivo of the new 
clinical candidate datelliptium (384) has been reported to involve oxidative 
328 GORDON W. GRIBBLE 
- 
/ / 
alanine I 
' N 
I 
CH3 CH3 OAc- CH3 CH3 
420 
421 422 
SCHEME 68. Peroxidase oxidation of 6-methylelliptinium (420) and reaction with alanine (261). 
degradation of the amine side chain and glucuronide formation of the corre- 
sponding products, as well as ortho-quinone production (262). 
XI. Structure-Activity Relationships 
An extensive study by Meunier et al. (170) of the electrochemical, bio- 
chemical, theoretical, and antitumor properties of a series of ellipticines and their 
quinone imines strongly implicates the latter species in the mechanism of the 
antitumor action of ellipticines. As Table I reveals, there are strong correlations 
between the ease of formation of quinone imines, their reactivities with nu- 
cleophiles, and their antitumor potency. Although 7-hydroxy-2-methylellip- 
ticinium (425) undergoes oxidation to the corresponding quinone imine, the 
latter intermediate apparently is extremely susceptible to polymerization. It is 
interesting that the presence of a C-10 methyl group does not seem to block the 
formation of a covalent adduct (as yet unidentified) with the corresponding 
quinone imine. Indeed, 9-hydroxy-2,8,l0-trimethylolivacinium (428) has good 
antitumor activity. 
7. ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 329 
The kinetics of decomposition of benzoyl peroxide in the presence of various 
hydroxypyridocarbazoles have been studied by Auclair and co-workers (263). 
These data were then used to determine the bond dissociation energies of the 
0-H bond. A reasonable correlation is seen between the bond dissociation 
energy and the cytotoxicity of the compound (Table 11). 
The effects of amine-substituted ellipticine derivatives 88 and 105-111 on 
L1210 and the human colon tumor (HCT8) in vitro (Table 111) indicate that these 
compounds are not more cytotoxic than ellipticine (1) (71). Furthermore, only a 
low order of activity was revealed in vivo against P388 for 110 and 111. The N-6 
derivatives were inactive as antitumor agents. However, the DNA binding prop- 
erties of all of theseamine-substituted ellipticines were superior to 1, as deter- 
mined by the ethidium displacement assay. 
The antitumor activities and DNA affinities of several 1 -alkylamino deriva- 
tives 113-117 of 9-methoxyellipticine (2) have been measured (Table IV) (72). 
These compounds are cytotoxic and have some antitumor properties, but there 
does not appear to be a correlation between their cytotoxicity and DNA inter- 
calating ability. Moreover, these derivatives tend to accumulate in the cytoplasm 
rather than in the nuclei of the cells. Compound 118, with a longer alkyl chain, is 
not taken up by the cells, presumably owing to the hydrophobic nature of the 
decyl chain. From the DNA binding data, the authors conclude that only 113- 
115 behave as true intercalators. 
Table V lists a few of the 49 ellipticine glycosides that have been prepared and 
evaluated for anticancer activity by Honda and co-workers (69). From these data, 
it can be summarized that the 9-hydroxyl group is essential for high activity. 
Peracylated glycosides are less active than the hydroxylated counterparts, and the 
introduction of an amide group dramatically lowers the activity. The counterion 
X - (chloride, bromide, acetate) makes no difference. In a series of pyranosides, 
those having three hydroxyl groups are more active than those having four 
hydroxyl groups. Several 9-hydroxyellipticine 1 ’ ,2’-cis-glycosides also showed 
good activity, but a relationship with the 1’,2’-trans sugars could not be estab- 
lished. Also, no clear relationship between enantiomeric pairs, or between 
furanosides and pyranosides, could be identified. Nevertheless, these simple 
ellipticine derivatives show extraordinary antitumor activity against L12 10 in 
vivo (also against P388, B16, colon 38, EAC, and sarcoma 180 in vivo), and they 
seem to be much more active than ellipticine (l) , 9-hydroxyellipticine (3), and 
elliptinium (5) against these mouse tumors. 
Several ellipticines and 7Hypyrilo[4,3-c]carbazoles were examined for their 
effect on topoisomerase I and I1 from trypanosomes (Table VI) (163). The ac- 
tivity of 9-bromoellipticine on topoisomerase I1 is especially interesting since it 
is not a DNA intercalator. Several other bis-7H-pyrido[4,3-c]carbazoles were 
strongly active in this assay. As indicated in Table VII, a study of the cytotoxicity 
and uptake by TBL CL2 mouse sarcoma cells of several oxazolopyridocarbazoles 
330 GORDON W. GRIBBLE 
TABLE I 
REACTIVITY AND BIOLOGICAL ACTIVITY OF ELLIFTICINE DERIVATIVES (170) 
10 11 1 
SubstituentsO 
Compound C-1 N-2 N-6 C-7 C-8 C-9 C-10 C-11 
9-Methoxy-6-methylellipticine (423) CH3 OCH, CH3 
2-Methylellipticinium (110) CH3 CH3 
9-Methoxy-2-methylellipticinium (424) CH, OCH, CH, 
Ellipticine (1) CH, 
9-Methoxyellipticine (2) OCH, CH3 
6-Methylelliptinium (420) CH, CH, OH CH3 
7-Hydroxy-2-methylellipticinium (425) CH, OH CH3 
9-Hydroxy-2-(2-diethylamino)ethylellipticinium (384) DEAEf OH CH, 
Elliptinium (5) CH, OH CH, 
7-Methylelliptinium (427) CH, CH, OH CH3 
9-Hydroxyellipticine (3) OH CH3 
9-Hydroxy-6-methylellipticine (93) CH, OH 
9-Hydroxy-2-methylolivacinium (426) CH, CH3 OH 
9-Hydroxy-2,8,lO-trimethylolivacinium (428) CH, CH, CH, OH CH3 
8,1O-Dimethylelliptinium (429) CH, CH, OH CH, CH3 
Substituents not indicated are hydrogen (or unmethylated pyridine for N-2). 
Horseradish peroxidase turnover number (10-6 M HRP) as micromoles H,O, consumed per minute per micromole HRP. 
Dose which reduces by SO%, after 48 hr, the L1210 cell growth relative to controls. 
Antitumor activity symbols: -, no determination; 0, no activity (TIC < 125%); f, TIC > 125% and therapeutic index 5 2; 
c Anodic sweep in volts. 
++, TIC 125- 170% and therapeutic index 2 2; +++, T/C > 170%. 
I DEAE, (2-Diethylamino)amino group. 
(387, 434-438) and elliptinium (5) revealed that, although uptake was rapid, 
consistent with a diffusion mechanism, the cytotoxicity of these amino acid 
conjugates is less than that of elliptinium (5) (153,154). This lower cytotoxicity 
is believed to be due to the absence of the 9-hydroxyl group. However, the 
isoleucine adduct 387 is unusually cytotoxic for the series. 
An extensive study by Roques and co-workers (102) of the cytotoxicity, anti- 
tumor activity, and DNA binding affinities of a series of 7H-pyridocarbazole 
monomers and dimers is presented in Tables VIII and IX. These data reveal the 
importance of methyl substitution at positions C-6 or C-7 in the N-2 monomers 
7. ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 33 1 
Oxidation Adduct formation Biological activity 
HRP6 Electrochemicalc Alanine Nucleoside IC,,, phfd In vivo L121Oe In vivo P388e 
- - - 0 I .o No No 
- 18 0.820 No No 1.03 0 
25 0.625 Yes Yes 1.14 0 0 
30 0.600 No No 1.45 + + 
- 710 0.500 No Yes 1.80 + 
26,000 0.420 Yes Yes 0.089 ++ +++ 
- 0.295 No No 4.26 0 + 
38,500 0.260 Yes Yes 0.050 +++ +++ 
13,000 0.205 Yes Yes 0.29 ++ ++ 
28,000 0.180 Yes Yes 0.11 ++ ++ 
- 0.160 - - 1.19 + ++ 
12,000 0.130 No Yes? 0.86 ++ ++ 
33,500 0.100 No Yes 0.11 ++ - 
11,OOO 0.035 No Yes? 6.04 0 
- - 13,500 0.280 No Yes 0.076 
- 
for antitumor activity, although this is relatively weak. In the dimers, several 
highly active compounds belonging to the N-2 series were discovered, but none 
in the N-3 series. No clear and consistent correlation between antitumor potency 
and DNA affinity is found, although the inactive N-3 dimers are unable to bis- 
intercalate with DNA. 
The cytotoxicity of several benzo-annulated iso-a-carbolines (369-372, 377, 
378, 380) has been studied in vifro on human tumor IU3 cells (Table X) (136). 
The linear ellipticine analog 371 is 10 times more active than ellipticine (1) in 
this screen. As was mentioned earlier, this derivative also displays significant in 
vivo activity against P388, L1210, and B16 implanted mouse tumors (TIC values 
190, 175, and 224%, respectively). The resemblance of the imine grouping of 
these iso-a-carbolines to ellipticine quinone imine 6 is obvious. It will be of 
interest to see how the electrophilic behavior of these compounds compares to 
that of the quinone imines . 
332 GORDON W. GRIBBLE 
TABLE I1 
CORRELATION BETWEEN ( t H BOND DISSOCIATION ENERGIES A N D CYTOTOXICITY (263) 
11 1 
Bond 
energy, 
Substituentsa dissociation 
Compound C-1 N-6 C-7 C-9 C-11 kcal/rnol IC,,, pMb 
OH 79.4 - 9-Hydroxyolivacine (73) CH, 
6-Methyl-9-hydroxyellipticine (93) CH, OH CH, 81.5 0.022 
7-Hydroxyellipticine (431) OH CH, 86.3 5.44 
a-Tocopherol 78.2 - 
9-Hydroxyellipticine (3) OH CH, 79.6 0.015 
1 1 -Demethyl-9-hydroxyellipticine (430) OH 81.8 
Phenol 88.2 
- 
- 
a Substituents not indicated are hydrogen. 
b Dose that reduces by 50%. after 48 hr, the L1210 cell growth relative to controls 
TABLE I11 
ACTIVITY OF N-2 AND N-6 AMINE-SUBSTITUTED ELLIPTICINES (71) 
I 
CH, 
Substituents In vitro IC,,, pMa 
Compound N-2 N-6 L1210 HCT8 
88 
105 
106 
107 
108 
109 
110 
111 
Ellipticine (1) 
0.43 
0.11 
0.32 
0.17 
0.19 
Inactive 
0.6 
0.041 
0.1 
- 
0.39 
0. I 
0.082 
0.08 
Inactive 
0.5 
0.26 
- 
0 Dose that reduces by 50% the cell growth relative to controls, 2 days after drug exposure. 
TABLE IV 
ACTIVITY OF ~-(ALKYLAM1NO)-9-METHOXYELLIF'TlCINES (72) 
In virro IC,,, p,W In vivo ILS, %b DNA binding 
C-l Substituent L1210 NIH 3T3 (L 12 10) K,,,, M - l Unwinding angle, O Compound 
~ ~~~ ~ 
113 NH2 0.1 0.3 93 - 1 24 
114 NHCH,CH, 0.05 0.3 42 2.15 16 
115 NHCH,CH,CH, 0.1 0.3 2.00 15 - 
116 NHCH2CH(CH,), 0.09 0.3 - 2.35 12 
117 NHCH,CH,CH(CH,), 0.8 0.5 - 3.75 7 
9-Methoxyellipticine (2) H 0.1 0.3 20 0 .9 10 
* Dose that reduces by 50% the L1210 cell growth relative to controls, 48 hr after drug exposure 
Increase in mean life span. 
334 GORDON W. GRIBBLE 
TABLE V 
In vivo ACTIVITY OF ELLIPTICINE ~',~'-~?xI~S-GLYCOSIDES ON L1210 LEUKEMIA (69) 
Substituent 
Optimal dose, 
c-9 R m g m ILS, %a Curesb 
H P-D-Ribofuranoside 20 80 016 
OCH, P-D-Ribofuranoside 30 76 016 
OH P-D-Ribofuranoside 10 138 016 
OH P-L-Ribofuranoside10 >391 216 
OH P-L-Ribopyranoside 30 >944 616 
OH a-D- Arabinopyranoside 20 >606 316 
OH a-L- Arabinopyranoside (104) 30 >860 516 
OCH, a-L- Arabinopyranoside 30 56 016 
OH D-Lyxofuranoside (a-P 76 : 24) 30 >967 616 
OH a-L-Ly xopyranoside 30 >786 516 
OH P-D-Xylofuranoside (383) 30 >682 416 
OH L-Rhamnopyranoside (a-P 92 : 8) 30 >693 416 
Ellipticine (1) 120 128 - 
9-Hydroxyellipticine (3) 60 79 - 
- Elliptinium 5) 5 48 
Doxorubicin 2.5 90 - 
a Increase in mean life span. 
b Number of survivors/total at 80 days. 
TABLE VI 
ON TOFTIISOMERASE I AND I1 (163) 
ACTIVITY OF ELLIPTICINES AND 7ff-PYRIDo[4,3-C]CARBAZOLES 
Activity, IC, p M 
Compound 
Decatenation Relaxation 
(Topo 11) (Top0 I) 
Ellipticine (1) 
9-Hydroxyellipticine (3) 
Elliptinium (5) 
Ditercalinium (212) 
6-Methylelliptinium (420) 
2,7-Dimethyl- 10-methoxy-7H-pyrido- 
9-Aminoellipticine (407) 
9-Bromoellipticine (433) 
[4,3-~]carbolinium (432) 
26 
7 
7 
5 
8 
21 
38 
31 
I70 
170 
35 
150 
- 
7. ELLIPTICINE ALKALOIDS A N D RELATED COMPOUNDS 335 
TABLE VII 
ACTIVITY OF OXAZOLOPYIUDOCARBAZOLES (253,254) 
R 
Activity (L1210) 
Uptakea In vitro In vivo 
Compound R nmol/l06 nuclei IC,,, )WUb TIC, %c 
434 H 1.28 0.54 100 
435 CH, 1.40 0.20 123 
436 CH,CH, 1.35 0.36 I24 
437 C H ( C H 3 ) 2 0.88 0.31 131 
387 CH,CH(CH& 0.13 0.28 135 
438 CH(CH,)CH,CH, 0.15 0.58 118 
Elliptinium (5) 1.14 0.10 157 
a By isolated TBL CL2 mouse sarcoma nuclei. 
b Dose that reduces by 50% the cell growth relative to controls, 48 hr after drug exposure 
L. Treated mean survival time per untreated mean survival time; TIC % > 125:activity. 
The effect of the linker chain on the activity of bis-7H-pyridocarbazoles (Table 
XI) (119) reveals that the degree of flexibility inherent in the bipiperidine linker 
is crucial for activity. Thus, when n is 1, the dimer (321,322) can adopt a kinked 
structure, decreasing the tendency for intramolecular stacking and increasing the 
propensity for DNA bis-intercalation. However, when n is 0, 2 , or 3, the dimers 
are suggested to prefer a parallel arrangement of the pyridocarbazole rings in 
which intramolecular r stacking can occur, reducing DNA bis-intercalation. 
Although C-9 hydroxylation (73) of olivacine increases the in vitro activity 
against L1210 over that of olivacine (4), the in vivo antitumor activity is un- 
changed (Table XII) (55). This appears to be the result of a rapid elimination of 
drug. Hydroxylation at C-7 (71) leads to an inactive compound in vitro, remines- 
cent of the low degree of cytotoxicity of 7-hydroxyellipticine (IDso 5.44 pM) 
(55,170). 
The effect of several ellipticines and 9-azaellipticines on the cell cycle pro- 
gression and survival of NIH 3T3 mouse cells was studied (Table XIII) (264). 
The effects of both series of compounds are identical, leading to growth arrest 
and blockage in G , phase. The most interesting conclusion from this study is that 
BD-40 (385) may require metabolic activation prior to acting on the cells. 
TABLE VIII 
ACTIVITY OF 7ff-PYRIDOCARBAZOLES (102) 
DNA 
binding 
Substituent Activity (L1210) 
Compound N-R C-5 C-6 N-7 In v i m IC,,, p M In vivo TIC, %b ( X 105 M-1) 
439 2-NCH, H H H 0.95 NS 2.9 
233 2-NCH, CH3 H H >2.5 NT 0.6 
440 2-NCH, H CH, H 0.06 125 1.8 
441 2-NCH3 H H CH, 0.22 122 7.0 
443 4-NCH3 H CH, H >2.5 NT 0.61 
442 3-NCH3 H CH, H 0.30 NT 3 
444 2-NCH$H,N(CH2), H CH, H 0.11 123 9.3 
a Dose that reduces by 50% cell growth relative to controls, 24 hr after drug exposure. 
b Treated mean survival time per control mean survival time; NT, not tested; NS, not significant, 
7 . ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 337 
TABLE IX 
ACTIVITY OF 7ff-PYRIDOCARBAZOLE DIMERS (102) 
DNA 
binding 
Substituent Activity (L12 10) 
Compound N C-5 C-6 N-7 In virro IC,,, pM' In vivo T/C, % ( X lo7 M-I) 
212 2 H H H 0.19 182 1 
445 2 CH, H H > I 120 0.5 
446 2 H CH, H 0.37 172 50 
10 
1 
447 2 H H CH, 0.36 178 2 
448 2 H CH, CH, 3.27 - 
450 3 H CH, H > I 
449 3 H H H - 130 0.3 
451 3 H H CH, - <125 0.6 
- 
0 Dose that reduces by 50% cell growth relative to controls, 24 hr after drug exposure. 
From an enormous set of y-carbolines and diazacarbazoles, Bisagni and co- 
workers (115-11 7) have determined the structure-activity relationships for 
cytotoxicity, in vivo antitumor activity, and DNA affinity. For the y-carboline 
series, the requirements for cytotoxicity and DNA cleavage ability are the pres- 
ence of methyl substituents at N-5 and/or C-4, a hydroxyl group at C-8, and an 
TABLE X 
In vitro ACTIVITY OF BENZOISO-WCARBOLINES 
ON HUMAN TUMOR KB CELLS (136) 
Compound ICm w 
Ellipticine (1) 10 
369 10 
370 10 
37 1 1 
372 10 
377 10 
378 4 
380 2 
a Dose that reduces by 50% the KB tumor cell protein bio- 
synthesis relative to controls, 72 hr after drug exposure. 
338 GORDON W. GRIBBLE 
TABLE XI 
ACTIVITY OF 7H-PYRIDOCARBAZOLE DIMERS (119) 
\ N / 
I 
R 
.. 
I 
R 
DNA 
binding 
Activity (L1210) 
Compound R n In vitro IC,,, p,g/mlo In vivo TIC. %6 ( X lo7 M-') 
212 H O 0.2 182 1 
32 1 H I 1.2 175 10 
453 H 2 1.5 143 7 
455 H 3 0.5 NSc - 
452 CH, 0 0.32 178 2 
322 CH, 1 0.8 I90 20 
454 CH, 2 >1 170 3 
~~ 
a Dose that reduces by 50% the cell growth relative to controls, 24 hr after drug exposure. 
6 Treated mean survival time per control mean survival time. 
c NS, Not significant. 
TABLE XI1 
ACTIVITY OF OLIVACINE DERIVATIVES (55) 
Substituent Activity 
Compound C-7 C-9 ID,,, pW ILS, %b 
Olivacine (4) H H 2.03 35 
73 H OH 0.06 39 
71 OH H 12.8 NT 
a Dose that reduces by 50% the L1210 cell growth relative to 
6 Increase in life span over controls in L1210 system (single 
controls, 48 hr after drug exposure. 
injection). 
7. ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 339 
TABLE XI11 
ACTIVITY OF ELLIFTICINES AND 9-Azaellipticines 
on NIH 3T3 CELLS (264) 
Compound IC50, w 
Ellipticine (1) 2.95 
Elliptinium (5) 0 .9 
9-Hydroxyellipticine (3) 0.076 
BD-84 (386) 0.58 
BD-40 (385) 0.33 
9-Azaellipticine (456) 0.48 
Concentration that induces 50% inhibition of cell growth. 
amino alkyl group, preferably a dialkylaminopropyl side chain, at C- 1. For 
example, 389 is a very potent compound. For the diazacarbazole series (e.g., 
388), the presence of methyl groups at N-5 and/or C-4 and a dialkylaminopropyl 
side chain at C-1 is essential for activity. These tricyclic analogs of the azaellip- 
ticines have lower DNA affinity, cytotoxicity, and antitumor activity. It was 
NH(CH2),NMe, NH(CH2)3NEt2 
O ~ J - ~ J , cH30Q-f4, / 
/ ‘ N 
1 
CH3 CH3 
‘ N 
H 
457 458 
NH(CH,),NEtz NH(CH2)dNEtZ 
N a - - N a - 0 / 
/ ‘ N 
1 
CH3 CH3 
‘ N 
H 
CH3 
459 460 
Nq 
CH3 CH3 
461 462 
340 GORDON W. GRIBBLE 
suggested that the absolute requirement of a C-4 methyl group in both series may 
indicate that this position is involved in metabolic activation (115). As il- 
lustrative of the narrow range of activity, compounds 457-462 are inactive in 
vivo. 
XII. Toxicology Studies 
Although it is generally believed that the ellipticine group of anticancer drugs 
has lesser toxicity than do other anticancer drugs, certain specific toxic side 
effects are recognized for the ellipticines. Indeed, at least two deaths have been 
reported during clinical trials with elliptinium that were due to drug toxicity 
(265,266). 
The major problem in some patients [20% in one study (2631 treated with 
elliptinium is the development of antielliptinium antibodies (267-270). When 
these antibodies reach a certain concentration, the red blood cells rupture, caus- 
ing anemia. This hemolysis is more frequent in patients treated weekly with 5 
than in those who are treated every 2-4 weeks (271). Provided the antibody titer 
in patients is monitored, the onset of hemolysis can be prevented (268). In 
addition to elliptinium, several other ellipticine derivatives and analogs react 
with this specific antibody (420,463-465), whereas the oxazolopyridocarbazole 
466 (incorrect structure givenin Ref. 268), 9-methoxyellipticine (2), and 9- 
bromoellipticine do not (268). 
The toxicity of elliptinium in rat kidneys has been found to be dose dependent 
(272,273). Elliptinium induces cardiovascular effects (mainly systemic hypoten- 
sion) in dogs owing to the release of histamine (vasodilation) and catecholamines 
(tachycardia) (274). Similar effects were found in guinea pigs (275). Speculation 
was raised that the antitumor properties of elliptinium may be due to an increase 
of histamine, since this compound is known to slow tumor growth in animals 
(274). 
The biodistribution and mitochondria1 toxicity of ditercalinium (212) in rats 
has been studied (276). Indeed, the accumulation of this drug in mitochondria 
probably accounts for its dose-dependent irreversible liver toxicity in humans. 
XIII. Clinical Trials 
The clinical trials with elliptinium (5) have generally progressed to the phase I1 
stage. However, one phase I trial with 5 was reported in 1985 (277). Twenty-nine 
patients were treated with 5 (weekly intravenously, 40 mg/m2 increased to 150 
7. ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 34 1 &.’:” &MCH3 CH3 
0 / ‘ N / / 
I 
‘ N 
H CH3 CH, 
463 420 
CH3 
o\ &0cH3 6 i 0 c H 3 
0 / ‘ N / 
H 
‘ N 
H 
CH3 
464 465 
H 
CH3 
466 
mg/m2) and objective responses were observed in one patient each with 
Hodgkin’s disease, non-Hodgkin’s lymphoma, breast cancer, and nasopharyn- 
geal carcinoma. The dose-limited toxicity was emesis, xerostomia, and 
azotemia. The lack of myelosuppression was the most striking feature of the 
toxicity profile. The authors recommended a phase I1 protocol. 
Several phase I1 evaluations of elliptinium (5) have been camed out in recent 
years, with mixed results. Elliptinium is typically given to patients intravenously 
at a concentration of 100 mg/m2 in a 5% dextrose solution for 1-2 hr. A clinical 
study of 5 in the treatment of lymphoma was slightly encouraging in that, of 16 
evaluable patients, there were 1 partial response and 7 minor responses (278). 
However, in the treatment of metastatic soft tissue sarcoma, none of the 19 
patients had remission of their tumors (279). An extensive phase I1 trial of 
advanced breast cancer patients (74) was very encouraging: 19% had objective 
responses, and in those patients with soft tissue metastases the response rate was 
30% (280). These responses lasted from 3 to 12 months, and mild to moderate 
nausea and mouth dryness were the most frequently encountered side effects. 
342 GORDON W. GRIBBLE 
Hemolysis, as a result of the development of antielliptinium antibodies, was 
observed in 5 patients, and 1 patient had cumulative renal toxicity. Another study 
of advanced breast cancer in previously treated patients showed 1 complete 
remission, 4 partial remissions, and 6 minor responses of 33 evaluable patients 
(281). The authors concluded that elliptinium has modest but unmistakable ac- 
tivity and needs to be evaluated further in combination with other drugs. Indeed, 
one such study in which 5 was used in combination with mitomycin, vinblastine, 
and/or etoposide indicates that this mix of agents was active and well tolerated in 
patients with advanced breast cancer (282). 
Metastatic renal cell carcinoma is highly resistant to chemotherapy, and new 
anticancer drugs are crucial in the treatment of this disease. Several phase I1 
clinical trials with this cancer using elliptinium have been reported. For example, 
in a study of 38 patients, there were 5 (13%) objective responses with an average 
duration of 8 months (283). Of these 5 responses, 3 were partial and 2 were 
complete, including 1 patient whose subcutaneous metastases completely disap- 
peared. The major dose-limiting toxicity was the induction of antibodies and the 
attendant risk of hemolysis. Another study by the same team (284) of 14 evalua- 
ble patients with metastatic renal cell carcinoma resulted in no objective re- 
sponses, and all patients experienced rapidly progressing disease. However, 
toxic side effects were mild, and no hemolysis was seen. Another study of 
elliptinium in 14 patients with advanced renal cell carcinoma and 4 patients with 
breast cancer resulted in no response (285). In this trial, there was an unexpected- 
ly high incidence of xerostomia, hemolysis, and allergic reactions, causing the 
trial to be halted. 
A phase I1 study of elliptinium in 42 patients with non-small cell lung cancer 
was particularly disappointing: 1 partial response (286). In fact, the study was 
terminated because of unacceptable toxicity (mainly mouth dryness and nausea, 
but some phlebitis, neurological toxicity, hypotherma, and leukopenia). Ellip- 
tinium has also been used in the treatment of hepatocellular carcinoma 
(287,288). In the evaluation of 15 patients with this cancer, there were no 
objective responses, although the only major toxicity was mouth dryness (287). 
It was concluded that elliptinium is of no valuable therapeutic interest in the 
treatment of this tumor type. However, in combination with tamoxifen, ellip- 
tinium showed tumor stabilization in four patients (288). 
In an ongoing phase I evaluation of datelliptium (384), there have been ob- 
served no significant toxic effects (dry mouth, hemolysis, and hypotension) 
(289). The dose-limiting toxicity is local phlebitis (220 mg/m2). However, no 
antitumor response has been noticed thus far in the study. In another phase I trial 
of this new drug, similar low toxicity was observed (290). Hepatic toxicity was 
the only acute dose-limiting toxicity. Thus far, of 12 patients evaluated, there has 
been 1 minor response in a patient with metastatic cervical carcinoma and the 
stabilization of a patient with metastatic resistant rhabdomyosarcoma. 
7. ELLIPTICINE ALKALOIDS AND RELATED COMPOUNDS 343 
XIV. Conclusion 
Although it might be argued that the clinical success of elliptinium (5) in 
recent phase I1 trials has been less than anticipated, based on the promising phase 
I results, the discovery and development of several “second generation” ellip- 
ticine analogs, such as the azaellipticines, the tricyclic ellipticine mimics, the 
bispyridocarbazoles, and the ellipticine glycosides and carbamates, guarantee to 
keep the ellipticine family of antitumor agents in the spotlight of cancer chemo- 
therapy for the foreseeable future. Moreover, the diversity of structural variation 
and substitution pattern in these molecules will continue to fascinate and chal- 
lenge synthetic chemists, while the myriad of pharmacologic activities that have 
been revealed by the ellipticines will maintain their attraction to biochemists and 
pharmacologists. 
Acknowledgment 
This chapter is dedicated to the memory of Lance Corporal Wayne P. Gribble, United States 
Marine Corps, 1969-1990. 
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