Synthesis of stereoregular heteropolysaccharides having amino-groups by ring-opening copolymerization of 1,6-anhydro-azido-sugar derivatives

The cationic, ring-opening copolymerization of 1,6-anhydro-2-azido-3,4-di-0-benzyl-2-deoxy-(2-ABG), -3-azido-2,4-di-0-benzyl-3-deoxy- (3-ABG), -4-azido-2,3-di-0-benzyl-4-deoxy-β-D -glucopyranose (4-ABG) with 1,6-anhydro-2,3,4-tri-0-benzyl-β-D -glucopyranose (LGTBE) was investigated with phosphorus pentafluoride as catalyst at low temperatures, giving highly stereoregular, (1→6)-α-linked copolymers with number-average molecular weights of 3.90 × 10⁴?9.27 × 10⁴. Structure and composition of the copolymers were determined by ¹H- and ¹³C-NMR spectroscopies and elemental analysis, which indicated that copolymerization occurred in a stereoregular manner to give azido groups containing (1→6)-α-linked glucopyranan derivatives. The differences in polymerizability among the three azido monomers are discussed. Regioselective reduction of three kinds of heteropolysacharide derivatives which had different quantities of azido groups at C-2, -3, or -4 position with lithium aluminum hydride and subsequent debenzylation of the copolymers with sodium in liquid ammonia produced amino-group-containing heteropolysaccharides.