Aldose Wohl degradation

Just as the Kiliani-Fischer synthesis lengthens an aldose chain by one carbon, the Wohl degradation shortens an aldose chain by one carbon. The Wohl degradation is almost the exact opposite of the Kiliani-Fischer sequence. That is, the aldose aldehyde carbonyl group is first converted into a nitrile, and the resulting cyanohydrin loses HCN under basic conditions—the reverse of a nucleophilic addition reaction. 

Conversion of the aldehyde into a nitrile is accomplished by treatment of an aldose with hydroxvlamine to give an oxime (Section 19.8), followed by dehydration of the oxJme with acetic anhydride. The Wohl degradation does not give particularly high yields of chain-shortened aldoses, but the reaction is general for all aldopentoses and aldohexoses. For example, D-galactose is converted by Wohl degradation into n-lyxose. 

Wohl degradation (Section 25.6) A method for shortening the chain of an aldose sugar. 

Problem 22.10 Outline the steps in the Wohl degradation, which employs a dehydration of an aldose oxime and is thus a reversal of the Kiliani-Fischer step-up method. 

WOHL DEGRADATION. Method for the conversion of an aldose into an aldose with one less carbon atom by the reversal of the cyanohydrin synthesis. In the Wohl method, the nitrile group is eliminated by treatment with ammoniacal silver oxide. 

Which two aldoses yield D-lyxose after Wohl degradation ... 

Reacts with aldoses to yield oximes as the first step in the Wohl degradation of aldoses (Section 25.6). 

Two common procedures in carbohydrate chemistry result in adding or removing one carbon atom from the skeleton of an aldose. The Wohl degradation shortens an aldose chain by one carbon, whereas the Kiliani-Fischer synthesis lengthens it by one. Both reactions involve cyanohydrins as intermediates. Recall from Section 21.9 that cyanohydrins are formed from aldehydes by addition of the elements of HCN. Cyanohydrins can also be re converted to carbonyl compounds by treatment with base. 

The Wohl degradation is a stepwise procedure that shortens the length of an aldose chain... 

The Wohl degradation converts a stereogenic center at C2 in the original aldose to an sp hybridized C=0. As a result, a pair of aldoses that are epimeric at C2, such as D-galactose and D-talose, yield the same aldose (D-lyxose, in this case) upon Wohl degradation. 

The Wohl degradation removes a carbon atom from the aldehyde end of an aldose. 

Wohl degradation (Section 27.10A) A reaction that shortens the carbon chain of an aldose by removing one carbon from the aldehyde end. 

USE Reagent for labeling a terminal amino acid group in modified Wohl degradations of aldoses. As hapten, Caution,- Vesicant. For proper handling see J. S, Thompson, O. P. Edmunds, Ann. Occup. Hyg, 23. 27 (1980). 

The Wohl deffvdation, an alternative to the Ruff d radation, is nearly the reverse of the Kiliani-Fischer synthesis. The aldose carbonyl group is converted to the oxime, which is dehydrated by acetic anhydride to the nitrile (a cyanohydrin). Cyanohydrin formation is reversible, and a basic hydrolysis allows the cyanohydrin to lose HCN. Using the following sequence of reagents, give equations for the individual reactions in the Wohl degradation of D-arabiiK>se to D-erythrose. Mechanisms are not required. 

D-Gluconic nitrile, which can be obtained in 55 % yield by the action of hydroxylamine acetate on n-glucose in acetic acid solution, is degraded quantitatively to n-arabinose simply by the action of hot water 196), However, the usual Wohl degradation via the acetylated nitriles 197), even in the most favorable instances, gives over-all (aldose aldose) yields of only 30 to 35%. 

The Wohl degradation is the reverse of the Kifiani-Fischer synthesis and involves the removal of a carbon atom from an aldose. The aldehyde group is first converted to a cyanohydrin, followed by loss of HCN in the presence of a base. 

The Wohl degradation can be used to shorten the chain of an aldose. 

The Wohl degradation is the opposite of the Kiliani-Fischer chain extension (Problem 21.59) in that it shortens an aldose chain by one carbon, converting C2 of the reactant into Cl of the product. Which two of the four D aldopentoses yield D-threose on Wohl degradation ... 

Aldoses are oxidized to aldonic acids or to aldaric acids. The Kiliani-Fischer synthesis increases the carbon chain of an aldose by one carbon it forms C-2 epimers. The Wohl degradation decreases the carbon chain by one carbon. 

Treatment with sodium borohydride converts aldose A into an optically inactive alditol. Wohl degradation of A forms B, whose alditol is optically inactive. Wohl degradation of B forms D-glyceraldehyde. Identify A and B. 

Wohl degradation a method used to shorten an aldose by one carbon. 

---