Carbohydrates gentiobiose

Enzyme-catalyzed hydrolysis of amygdalin gives the carbohydrate gentiobiose along with benzaldehyde cyanohydrin, which dissociates to benzaldehyde and hydrogen cyanide. 

Some of the original work in the carbohydrate area in particular reveals extensive protection of carbonyl and hydroxyl groups. For example, a cyclic diacetonide of glucose was selectively cleaved to the monoacetonide. A summary describes the selective protection of primary and secondary hydroxyl groups in a synthesis of gentiobiose, carried out in the 1870s, as triphenylmethyl ethers. 

Amygdalin has the same carbohydrate skeleton as gentiobiose. Draw the cyanohydrin of benzaldehyde, and form a bond between the hemiacetal oxygen and the carbonyl carbon of benzaldehyde, with elimination of water. 

When a solution of dextrose is allowed to stand for a month or more with emulsin, a glucoside splitting enzyme, gentiobiose, the carbohydrate mentioned above, is produced. It is probable that other disaccharides have been formed in this way, but their isolation from the large amount of the monosaccharides present prevented their satisfactory identification. 

Gentiobiose, a carbohydrate found in saffron, contains two glucose molecules linked by a /3-1,6-glycosidic bond. Draw the Haworth structure for a-gentiobiose. (18.1, 18.2)... 

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