The selective fragmentation of methylated leiocarpan A by β-D-glucosiduronic acid and β-D-glucosiduronamide cleavage

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Abstract
Selective cleavage of internal .beta.-D-glucopyranosiduronic acid linkages in permethylated leiocarpan A [from Anogeissus leiocarpus] was achieved by 2 procedures for structural modification involving decarboxylation-acetoxylation using lead tetraacetate or tert-butyl carbamate formation by a modified Curtius rearrangement, followed by controlled fragmentation of the modified polysaccharides to yield the same 2 main partially methylated pentitol-terminated oligosaccharides. Chemical and spectroscopic characterization of these oligosaccharides and their substitution products showed them to be derivatives of O-.beta.-D-xylopyranosyl-(1 .fwdarw. 6)-O-.alpha.-D-mannopyranosyl-(1 .fwdarw. 4)-D-xylitol and O-.beta.-L-arabinofuranosyl-(1 .fwdarw. 3)-[O-.beta.-D-xylopyranosyl-(1 .fwdarw. 6)]-O-.alpha.-D-mannopyranosyl-(1 .fwdarw. 4)-D-xylitol. These observations provide new information on the anomeric configuration and mode of attachment of side-chains in the polysaccharide.

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