Synthesis of a Regiospecifically Fluorinated Polysaccharide 3-Deoxy-3-fluoro-(1→6)-α- d -glucopyranan via Ring-Opening Polymerization

3-Deoxy-3-fluoro-(1→6)-α- d -glucopyranan ( 4 ) was synthesized via deoxyfluorination of 1,6-anhydro-2,4-di- O -benzyl-β- d -glucopyranose ( 1 ) and ring-opening polymerization of 1,6-anhydro-2,4-di- O -benzyl-3-deoxy-3-fluoro-β- d -glucopyranose ( 2 ), followed by debenzylation of the resulting 2,4-di- O -benzyl-3-deoxy-3-fluoro-(1→6)-α- d -glucopyranan ( 3 ). Partially deoxyfluorinated (1→6)-α- d -glucopyranans were also prepared via copolymerization of 2 with 1,6-anhydro-2,3,4-tri- O -benzyl-β- d -glucopyranose ( 6 ). The assignments of steric arrangements of the C−F bond and stereoregularity of polymers were made from their 1 H- and 13 C-NMR spectral analysis. The deoxyfluorination at position 3 proceeded with retention of the configuration. The axial C−F orientation and β-anomeric configuration in the 1 C 4 conformer of monomer 2 was converted via polymerization to the equatorial C−F orientation and α-anomeric configuration of the 4 C 1 conformer in polymers 3 and 4 . Monomer 2 had only a little lower polymerization reactivity than that of 6 .