NOVEL REACTION ROUTE INCLUDING ENZYMATIC-REACTION FOR A SYNTHESIS OF A BRANCHED POLYSACCHARIDE

Stereoselective synthesis of alpha-D-glucosyl-branching polysaccharide by chemical and enzymic reactions was investigated. Ring-opening polymerization of 1,6-anhydro-3-O-benzoyl-2,4-di-O-benzyl-beta-D-glucopyranose (1) with PF5 as catalyst at low temperature gave a highly stereoregular polymer, which was converted to 2,4-di-O-benzyl-(1 --> 6)-alpha-D-glucopyranan by debenzoylation with sodium methoxide. The polymer was glucosylated according to the glycosyl imidate method. Deprotection of the branched polysaccharide was carried out with sodium in liquid ammonia at -78-degrees-C to give a (1 --> 6)-alpha-D-glucopyranan having alpha-D-glucopyranosyl and beta-D-glucopyranosyl branches. Only the beta-D-glucopyranosyl branch of the polymer was completely removed by enzymatic hydrolysis by the use of cellulase to provide stereoregular (1 --> 6)-alpha-D-glucopyranan having an alpha-D-glucopyranosyl branch at the C-3 position. Polymers were characterized by optical rotation, NMR spectroscopy, GPC, and X-ray diffractometry.