An improved method for synthesizing antennary β-D-mannopyranosyl disaccharide units

The merits of an indirect protecting method for hydroxyl groups using allyl groups via allyloxycarbonyl groups in the synthesis of antennary beta-D-mannopyranosyl disaccharides from P-D-galactopyranosyl disaccharides were studied. Regioselective allyloxycarbonylation and conversion reactions involving simultaneous double S(N)2 nucleophilic substitution at C-2' and C-4' of benzyl O-[beta-D-galactopyranosyl]-(1-4)-3,6-di-O-benzyl-2-deoxy-2-N-phthatimido-beta-D-glucopyranoside were examined for comparison with the direct allylation method. The required P-D-mannopyranosyl disaccharide having proper protecting groups was obtained using this indirect method in 52% yield. In contrast, the reported direct allylation method using methyl O-(P-D-galactopyranosyl) disaccharide gave the corresponding beta-D-mannopyranosyl disaccharide in only 7.5% yield. (C) 2004 Elsevier Ltd. All rights reserved.