Synthesis of a Precursor of β-D-GlcpNAc(1→2)-α-D-Manp-(1→3)-[β-D-Xylp-(1→2)]-β-D-Manp-(1→4)-β-D-Glcp

Abstract

ABSTRACT The glycosphingolipids isolated from spermatozoa of a fresh-water bivalve, Hyriopsis schlegelii, have a unique structure containing one or two mannosyl residues, novel linkages including an internal fucopyranosyl residue, as well as terminal xylosyl and 4-O-methyl-D-glucopyranosyl uronic acid groups. The pentasaccharide derivatives that constitute the partial structure of lipid IV were synthesized as follows. 4,6-Di-O-acetyl-2-O-(2,3,4-tri-O-acetyl-β-D-xylopyranosyl)-3-O-benzyl-α-D-mannopyranosyl bromide was treated with 2,3-di-O-acetyl-1,6-anhydro-β-D-glucopyranose in the presence of silver zeolite to afford the corresponding trisaccharide. The formation of the β-glycoside took precedence as a major product in a ratio of 6.9:1. After debenzylation, the β-mannosyl trisaccharide derivative was condensed with 3,4,6-tri-O-acetyl-2-O-chloroacetyl- α -D-mannopyranosyl bromide in the presence of silver triflate, and the final pentasaccharide derivative was prepared by using a suitably protected tetrasaccharide as the glycosyl acceptor, 3-O-acetyl-6-O-benzyl-4-O-chloroacetyl-2-deoxy-2-phthalimido-β-D-glucopyranosyl bromide as the donor and silver triflate as the promoter, respectively.