PREPARATION OF DISACCHARIDES HAVING A BETA-D-MANNOPYRANOSYL GROUP FROM N-PHTHALOYLLACTOSAMINE DERIVATIVES BY DOUBLE OR TRIPLE SN2 SUBSTITUTION

Condensation of 1,2,3,4,6-penta-O-acetyl-β-d-galactopyranose with methyl 3,6-di-O-benzyl-2-deoxy-2-phthalimido-β-d-glucopyranoside, followed by alkaline methanolysis, gave a derivative of lactosamine that has an unsubstituted β-d-galactopyranosyl group. Tributyltin oxide-mediated allylation gave a good yield of the 3′-O-allyl (9) and a poor yield of the 3′,6′-di-O-allyl ether (8). Protection of 9 at O-6′ was achieved by reductive opening of the 4′,6′-O-anisylidene derivative, to give the 6′-O-(4-methoxybenzyl) ether 15. Conversion of 8 and 15 to their 2′,4′-bis(trifluoromethanesulfonates), followed by SN2 reaction with benzoate, gave the corresponding β-d-mannopyranosyl disaccharides. However, the model methyl 3-O-allyl-β-d-galactopyranoside and 9 were converted into β-d-mannopyranosyl derivatives in better yield (52-55%) by a one-pot, triple SN2 substitution of the tris(trifluoromethanesulfonates). © 1990.