Synthesis of O-(2-O-sulfo-α-l-idopyranosyluronic acid)-(1 → 3)-2-acetamido-2-deoxy-4-O-sulfo-d-galactopyranose trisodium salt, a disaccharide fragment of dermatan sulfate

Benzyl 2-acetamido-2-deoxy-α, and β-d-glucopyranoside were converted in high yield into the corresponding d-galacto analogues through a three-step procedure. These later were transformed in a straightforward manner into benzyl 2-acetamido-4-O-acetyl-6-O-benzyl-2-deoxy-α, and β-d-galactopyranoside, respectively, which served as acceptors in glycosylation reactions with variously activated derivatives of methyl 2-O-benzoyl-3-O-benzyl-4-O-chloroacetyl-l-idopyranuronate. Condensation of the chloride derivative promoted by silver triflate led unexpectedly to the formation of the β-linked disaccharide, whereas the trichloroacetimidoyl derivative afforded the expected α-linked disaccharide in 63% yield. O-Dechloroacetylation of this later, followed by 4-methoxybenzylation at O-4 of the uronic acid moiety, saponification of the esters, O-sulfonation of the free hydroxyls, and catalytic hydrogenation provided the title disaccharide in high yield, as its sodium salt.