Synthesis of branched aminopolysaccharides by acid-catalyzed polymerization of sugar oxazoline monomer

Acid-catalyzed polymerization of a sugar oxazoline monomer 1b having two free hydroxy groups was carried out to produce a branched aminopolysaccharide 2b. The reaction proceeded via the stereoregular glycosylation through oxazoline ring-opening process, giving rise to 2b consisting of β-glycosidic linkages. The structure of 2b was determined by the 1H NMR, 13C NMR, and IR spectra. The molecular weights determined by GPC measurements were 4200–6100. The degrees of branching were estimated by the 1H NMR spectra of the products by the reaction of 2b with 3,5-dinitrobenzoyl chloride. Deprotection of 2b was carried out by the catalytic hydrogenation in the presence of 10% Pd–C to produce a free branched aminopolysaccharide.