A CONVENIENT ACCESS TO BETA-(1-]4)-LINKED 2-AMINO-2-DEOXY-D-GLUCOPYRANOSYL FLUORIDE OLIGOSACCHARIDES AND BETA-(1-]4)-LINKED 2-AMINO-2-DEOXY-D-GLUCOPYRANOSYL OLIGOSACCHARIDES BY FLUOROLYSIS AND FLUOROHYDROLYSIS OF CHITOSAN

beta-(1 --> 4)-Linked 2-amino-2-deoxy-D-glucopyranosyl oligosaccharides, in the form of their alpha-glucopyranosyl fluorides at the reducing end, were obtained by fluorolysis of chitosan in anhydrous hydrogen fluoride at room temperature. The average dp depended on the reaction time and was conveniently monitored by C-13 NMR spectroscopy, using the signal ratios for beta-(1 --> 4) bonded C-1 at similar to 98.5 ppm and the C-1 doublet for the terminal glycosyl fluoride moiety at similar to 104 ppm. Preparative fractionation of dp 2-11 glycosyl fluoride oligosaccharides, obtained after 18 h of fluorolysis, was achieved by gel-permeation chromatography on Bio-Gel P-4 with aqueous acetic acid-ammonium acetate as eluent. Hydrolysis of the anomeric fluoride, with either aqueous perchloric acid, or by a sequence involving formation of the C-2 N-trifluoroacetate and subsequent simultaneous hydrolysis of the glycosyl fluoride and the amide substituent with aqueous methanol, yielded the free beta-(1 --> 4)-linked 2-amino-2-deoxy-D-glucopyranosyl oligosaccharides which were separated, for dp 2-11, by the same gel-exclusion technique. Both oligosaccharide series, either free or in the form of their alpha-glycopyranosyl fluorides, were fully characterized.