Unformatted text preview: 723 CARBOHYDRATES To ﬁnd out which one of these is identical with the degradation product of compound A, carry compound A through the required transformations.
O O OH
O Ag2O HO OCH3
O CH3I CH3O OH OCH3 Compound A Tri-O-methyl ether of
compound A H3 O
(acetal hydrolysis) H CHO
OCH3 CH3O H HO H H H
O CH HO
CH3O OCH3 OCH3 OCH3
CH2OH 2,3,5-Tri-O-methylD-galactose 25.33 C21H24O10 The fact that phlorizin is hydrolyzed to D-glucose and compound A by emulsin indicates that it is a
-glucoside in which D-glucose is attached to one of the phenolic hydroxyls of compound B. H2O emulsin HO HOCH2 HO OH
CCH2CH2 HO OH OH d-Glucose (C6H12O6) Compound A (C15H14O5) The methylation experiment reveals to which hydroxyl glucose is attached. Excess methyl iodide reacts with all the available phenolic hydroxyl groups, but the glycosidic oxygen is not affected. Thus
when the methylated phlorizin undergoes acid-catalyzed hydrolysis of its glycosidic bond, the oxygen in that bond is exposed as a phenolic hydroxyl group.
CH3O O CH3O CCH2CH2 OCH3 OH
Compound B This compound must arise by hydrolysis of
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OCH3 -d-glucose Study Guide TOC Student OLC MHHE Website ...
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