CHEMICAL SYNTHESIS OF A COMB-SHAPED, BRANCHED STEREOREGULAR POLYSACCHARIDE, 4-O-ALPHA-D-MANNOPYRANOSYL-(1 -] 6)-ALPHA-D-MANNOPYRANAN

4-O-alpha-D-Mannopyranosyl-(1 --> 6)-alpha-D-mannopyranan (7) was prepared via ring-opening polymerization of 1,6-anhydro-2,3-di-O-benzyl-4-O-(2,3,4,6-tetra-O-benzyl-alpha-D-mannopyranosyl)-beta-D-mannopyranose (5) using phosphorus pentafluoride as initiator in dichloromethane at -60-degrees-C, followed by debenzylation. Compound 5 was obtained via glycosidation of 1,6-anhydro-2,3-O-isopropylidene-beta-D-mannopyranose (1) with 2,3,4,6-tetra-O-benzyl-1-O-trichloroacetimidoyl-alpha-D-mannopyranose (2) using p-toluenesulfonic acid as catalyst and subsequent transformation of the protecting groups of the resulting 1,6-anhydro-4-O-(2,3,4,6-tetra-O-benzyl-alpha-D-mannopyranosyl))2,3-O-isopropylidene-beta-D-mannopyranose (3).