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.