Glycosides from 1,2-anhydro sugars

Scheme 5.69 Synthesis of N-glycosides from 1,2-anhydro sugars.

Holantosine-C (30), the a-L-glycoside of anhydro-holantogenin and of a new amino-sugar, L-holantosamine, 4-amino-4-deoxy-L-oleandrose, has been isolated from Indian H. antidysenterica ... 

However, the demonstration that 1,2-anhydro sugars are readily obtained from glycals by treatment with dimethyldioxirane led to a renaissance of their use in glycoside synthesis and, indeed, in solution-phase and solid-phase oligosaccharide synthesis.182... 

Thus activation by tributyltin leads to a fortuitous a-glycosidation, whereas activation by zinc chloride leads to the normal (3-glycosidation. Taking advantage of the 2-hydroxyl group produced from the 1,2-anhydro sugar opens up a route to (3-mannopyranosides. 

Polymers obtained from 1,2-anhydro sugars contain, however, varying proportions of a- and P-linkages whose content is determined by the specific rotation of the polymer (provided that the specific rotation of the corresponding glycosides, being models of a- and p-linkages, are known). 

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