Syntheses of Polysaccharides Having Various Contents of Carboxyl Groups by Ring-Opening Copolymerization

Polysaccharides having various contents of carboxyl group precursors were synthesized by ring-opening copolymerization of 1,6-anhydro-2,4-di-O-benzyl-3-O-1 -(methoxy-carbonyl)ethyl-β-D-glucopyranose (1) with tri-O-benzyl-levoglucosan (2) with phosphorus pentafluoride as catalyst in methylene chloride at -60°C. The monomer reactivity ratios calculated by Kelen-Tudos method were r 1 =0.77 and r 2 =0.71. Birch reduction with lithium metal was quite effective for the deprotection of both methyl ester and benzyl ether groups of the polymer.