Aldoses and aldosides

Aldoses and aldosides, cyclic acetals of, 20, 219-302 Alkaline degradation, of polysaccharides, 13, 289-329 Altrose,... 

In this Section, hydrolysis, acetolysis, and isomerization of acetals are considered. Selective deprotection of acetals may also be achieved through halogenation, hydrogenolysis, ozonolysis, and photolysis, but these topics, are covered in an accompanying article in this Series, on the reactivity of cyclic acetals of aldoses and aldosides,3 and will not be discussed here. 

This article is limited to the reactions involving cyclic acetals of aldoses and aldosides. However, for comprehensiveness, or for their potential usefulness in carbohydrate chemistry, some properties of cyclic acetals not directly relevant to aldoses and aldosides are included. It may be recalled that the chemistry of dithioacetals had already been reviewed in this Series.7... 

Study of this reaction has not been limited to cyclic acetals of aldoses and aldosides, and synthetic applications in the ketose series have been developed,273,276,278,278 particularly for isopropylidene acetals of D-fructose. As an illustration of these reactions, two examples are given here. The action of butyllithium on 2,3 4,5-di-0-isopropyli-dene-l-0-methyl-/3-D-fructopyranose (280) gave273 a 30% yield of the 5-enopyranose 282. Abstraction by the base of the axial hydrogen atom from the 6-methylene group, giving the anion 281, was invoked... 

Several reviews have already been published on the subject, for example, the acetala-tion of alditols [4], of aldoses and aldosides [5,6], and of ketoses [7]. Some aspects of the stereochemistry of cyclic acetals have been discussed in a review dealing with cyclic derivatives of carbohydrates [8], also in a general article [9] and, more recently, in a chapter of a monograph devoted to the stereochemistry and the conformational analysis of sugars [10], Aspects on predicting reactions patterns of alditol-aldehyde reactions are reviewed within a general series of books on carbohydrates [11]. The formation and migration of cyclic acetals of carbohydrates have also been reviewed [12,13],... 

J. Gelas, The reactivity of cyclic acetals of aldoses and aldosides, Adv. Carbohydr. Chem. Biochem. 39 71 (1981). 

As previously reported (Ref. 1, pp. 1118, 1119) ketoses are essentially inert to the action of hypoiodites under the conditions used for the determination of aldoses, and aldosides are converted by hypoiodite or hypobromite into glycosiduronic acids in rather low yield. For example, methyl a-D-mannopyranoside (3) afforded methyl a-D-mannopyranosidu-ronic acid (4), although cleavage of carbon-carbon bonds also occurred to give 5 (Scheme 3). 

---