Multigram syntheses of the disaccharide repeating units of chondroitin 4- and 6-sulfates

The multigram syntheses of β-d-glucopyranosyluronic acid-(1→3)-2-acetamido-2-deoxy-4- and 6-O-sulfo-d-galactopyranose disodium salt, the disaccharide repeating units of chondroitin 4- and 6-sulfates, are described. The disaccharide benzyl methyl 2,3,4-tri-O-benzoyl-β-d-glucopyranosyluronate-(1→3)-2-acetamido-2-deoxy-α-d-galactopyranoside was used as a common intermediate. Selective benzoylation at O-6 followed by O-sulfonation at C-4 of the aminosugar moiety, saponification and catalytic hydrogenation afforded the 4-O-sulfo derivative, whereas selective O-sulfonation at C-6 followed by similar deprotection steps provided the 6-O-sulfo derivative in high yield.