Stereochemistry of Anhydro Sugar Polymerization

Synthetic polysaccharides are prepared mainly to obtain models which may be helpful in establishing the biological functions of natural polysaccharides. It is desirable to find systems in which the polymerization of anhydro sugars proceeds stereospecifi-cally, i.e. to prepare uniform and well defined structures. 

This type of lack of specificity is thus related to ring strain. 

The other source of inhomogenity, related to the mechanism of polymerization, is the possibility of inversion on C-l during monomer incorporation into the growing chain  

If this reaction proceeds exclusively with inversion the resulting polymer would contain a- or p- linkages. If, however, racemization occurs, the polymer would contain both a- and p-linkages.4 

NMR analysis and identification of hydrolysis products, have shown that the polymerization of 1,2-anhydro sugars proceeds exclusively by opening of the oxirane ring and that the polymer contains exclusively pyranose rings 6). 

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