Ring-opening polymerization of 1,6-anhydro-2,4-di- O-benzyl-3- O- tert-butyldimethylsilyl-β- d-glucopyranose and synthesis of α-(1→3)-branched dextrans

Abstract

Ring-opening polymerization of 1,6-anhydro-2,4-di- O-benzyl-3- O- tert-butyldimethylsilyl-β- dglucopyranose ( 1) with a Lewis acid catalyst and desilylation with tetrabutylammonium fluoride of the polymer obtained gave 2,4-di- O-benzyl-(1→6)-α- d-glycopyranan having a free hydroxyl group at C-3. Copolymerization of 3- O-acetyl-1,6-anhydro-2,4-di- O-benzyl-β- d-glucopyranose ( 2) with 1,6-anhydro-2,3,4-tri- O-benzyl-β- d-glucopyranose ( 3) and subsequent deacetylation of the copolymer with the use of N,N-dimethylformamide-methanol containing sodium methoxide also gave a partially benzylated (1→6)-α- d-glucopyranan. These polymer could be glycosylated to give branched polymers. Mannose, glucose, and galactose derivatives were used as glycosylation agents. Glycosylation by the orthoester method was used for mannose and the Eby and Schuerch method was used with glucose and galactose. Deprotection of the mannosylated polysaccharide was performed to give (1→6)-α- d-glucopyranan having 3- O-(α- d-mannopyranosyl) branches. Polymers were characterized by molecular weight, optical rotation, and by 1H- and 13C-n.m.r. spectroscopy.