| Research 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 4-0-methyl-D-glucopyranosyluronic acid groups. The trisaccharide depends on non-reducing end and the pentasaccharide derivative depends on reducing end, that constitute the partial structure of lipid IV were synthesized as follows. Condensation of 4,6-di-0-acetyl-2-azido-2-deoxy-3-0-methyl-alpha-D-galacto-pyranosyl bromide with 2-(trimethylsilyl)ethyl 4-0-acetyl-2-0-benzyl-beta-L-fuco-pyranoside, in the presence of mercuric cyanide, gave the corresponding disaccharide. Condensation of methy(2,3-di-0-acetyl-4-0-methyl-alpha-D-glucopyranosyl bromide)uronate with the appropriate OH-4-free disaccharide derivative afforded 2-(trimethylsilyl) ethyl 2-0-benzyl-3-0-(4,6-di-0-acetyl-2-azido-2-deoxy-3-0-methyl-alpha-D-galactopyranosyl)-4-0-[methyl(2,3-di-0-acetyl-4-0-methyl-beta-D-glucopyranosyl)uronate]-beta-L-fucopyranoside.
Meanwhile, in the case of the blockwise synthesis of pentasaccharide, 4,6-di-0-acetyl-2-0-(2,3,4-tri-0-acetyl-beta-D-xylopyranosyl)-3-0-benzyl-alpha-D-mannopyranosyl bromide was treated with 2,3-di-0-acetyl-1,6-anhydro-beta-D-glucopyranose in the presence of silver zeolite to afford the corresponding trisaccharide, 2,3-di-0-acetyl-4-0-[4,6-di-0-acetyl-3-0-benzyl-2-0-(2,3,4-tri-0-acetyl-beta-D-xylopyranosyl)-alpha- and -beta-D-mannopyranosyl]-1,6-anhydro-beta-D-glucopyranose. beta-Glycosidation took precedence. After debenzylation, trisaccharide derivative was condensed with mannose derivative, and the final pentasaccharide derivative was prepared by using a suitably protected tetrasaccharide and 3-0-acetyl-6-0-benzyl-4-0-chloroacetyl-2-phthalimido-2-deoxy-beta-D-glucopyranosyl bromide as the glycosyl donor, and silver triflate as the promoter.
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