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590 CARBOHYDRATES
The reactions that take place are the following:
HO
OH
OH
H3O+ or
β-glucosidase
OH
O O
HO
OH
OH+ HO
X
Hydroquinone
D-Glucose
OH
O
CH3O
OCH3
OCH3
O O OCH3
CH3O
OCH3
OCH3 HO OCH3
O OH
Y
CH3O OCH3
Z
2,3,4,6-Tetra-O-methyl-D-glucose p-Methoxyphenol
p-Dimethoxybenzene
p-Methoxyphenol
(CH3)2SO4 (excess)
(CH3)2SO4
HO−
HO−
Arbutin
+
H3O+
OH
OH OH
OCH3
OCH3
22.40 Aldotetrose B must be d-threose because the alditol derived from it (d-threitol) is optically
active (the alditol from d-erythrose, the other possible d-aldotetrose, would be meso).
Due to rotational symmetry, however, the alditol from B (d-threitol) would produce only
two 13C NMR signals. Compounds A-F are thus in the family of aldoses stemming from
d-threose. Since reduction of aldopentose A produces an optically inactive alditol, A must
be d-xylose. The two diastereomeric aldohexoses C and D produced from A by a Kiliani-
Fischer synthesis must therefore be d-idose and d-gulose, respectively. E and F are the
alditols derived from C and D, respectively. Alditol E would produce only three 13C NMR
signals due to rotational symmetry while F would produce six signals.
22.41 There are four closely spaced upfield alkyl signals in the 13C NMR spectrum (δ 26.5, δ 25.6,
δ 24.9, δ 24.2), corresponding to the four methyls of the two acetonide protecting groups.
(The compound is, therefore, the 1,2,5,6-bis-acetonide of mannofuranose, below.)
O
O O
O
O
HO