SYNTHETIC STUDIES ON OLIGOSACCHARIDE OF A GLYCOLIPID FROM THE SPERMATOZOA OF BIVALVES .6. SYNTHESIS OF A PRECURSOR OF BETA-D-GLCPNAC(1-]2)-ALPHA-D-MANP-(1-]3)-[BETA-D-XYLP-(1-]2)]-BETA-D-MANP-(1-]4)-BETA-D-GLCP

The glycosphingolipids isolated from spermatozoa of a fresh-water bivalve, Hyriopsis 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-beta-D-xylopyranosyl)3-O-benzyl-alpha-D-mannopyranosyl bromide was treated with 2,3-di-O-acetyl-1, 6-anhydro-beta-D-glucopyranose in the presence of silver zeolite to afford the corresponding trisaccharide. The formation of the beta-glycoside took precedence as a major product in a ratio of 6.9:1. After debenzylation, the beta-mannosyl trisaccharide derivative was condensed with 3,4,6-tri-O-acetyl-2-g-chloroacetyl-alpha-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, 3-0-acetyl-6-0-benzyl-4-O-chloroacetyl-2-deoxy-2-phthalimido-beta-D-glucopyranosyl bromide as the donor and silver triflate as the promoter, respectively.