23] Synthesis of branched polysaccharide by chemical and enzymatic reactions and its hypoglycemic activity

Abstract

This chapter describes the synthesis of a branched (1→6)- α -D-glucopyranan by ring-opening polymerization of anhydro sugar derivative, chemical glycosylation, and enzymatic hydrolysis with cellulase. The hypoglycemic activity of the synthetic branched polysaccharide is also described. Enzymatic hydrolysis of the branched polysaccharide, which has α - and β -D-glucopyranosyl branching units, is carried out with cellulase to remove specifically β -D-glucopyranosyl branching units to complete the stereo-specific branching reaction. It must be confirmed that the cellulase has β -glucosidase activity, by using p -nitrophenyl β -D-glucopyranoside as a substrate. It must be tested by using using p -nitrophenyl α -D-glucopyranoside as a substrate, that the cellulase does not contain the α -glucosidase activity. The anomeric ratios of the branching units in the polysaccharides are affected by the glycosylation method and the glycosylation reaction conditions. However, treatment with cellulase affords branched polysaccharides having only α -D-glucopyranosyl branching units. Regardless of the content of β -D-glucopyranosyl residues, β -D-glucopyranosyl branches can be completely removed by enzymatic hydrolysis using cellulase as confirmed by 13 C nuclear magnetic resonance (NMR) spectroscopy.