Syntheses of chondroitin 4- and 6-sulfate pentasaccharide derivatives having a methyl beta-D-glucopyranosiduronic acid at the reducing end.

The syntheses are reported of beta-D-GlcpA-(1-->3)-beta-D-GalpNAc-(1-->4)-beta-D-GlcpA-(1- ->3)-beta-D-GalpNAc-(1-->4)-beta-D-GlcpA-(1-->OMe), O-sulfonated at C-4 or C-6 of the aminosugar moieties, which represent structural elements of chondroitin 4- and 6-sulfate proteoglycans. Starting from a synthetic disaccharide glycosyl acceptor, the stepwise or blockwise construction of the sugar backbone with appropriate synthons led to a pentasaccharide tetraol, which was used as a common intermediate. Selective 6-O-sulfonation of this tetraol, followed by saponification, gave the 6-sulfate derivative, whereas selective 6-O-benzoylation, followed by O-sulfonation and saponification, afforded the 4-sulfate derivative as their sodium salts.