Synthetic studies on an oligosaccharide of a glycolipid from the spermatozoa of bivalves. IX. Synthesis of lipids I, II, and IV.

Glycosphingolipids isolated from the spermatozoa of the freshwater bivalve, Hyriopsis schlegelii, have a unique structure containing one or two mannosyl residues and novel linkages, including an internal fucopyranosyl residue, as well as terminal xylosyl and 4-O-methyl-D-glucopyranosyluronic acid groups. The octasaccharide of lipid IV was synthesized as follows. Condensation of methyl (2-acetamido-4,6-di-O-acetyl-2-deoxy-3-O-methyl-alpha-D-galactopyranosyl )- (1-->3)-[methyl(2,3-di-O-acetyl-4-O-methyl-beta-D-glucopyranosyluronate) - (1-->4)]-2-O-benzyl-1-thio-alpha,beta-L-fucopyranoside (18) with (3-O-acetyl-6-O-benzyl-2-deoxy-2-phthalimido-beta-D-glucopyranosyl)-(1-- >2)- (3,4,6-tri-O-acetyl-alpha-D-mannopyranosyl)-(1-->3)-[(2,3,4-tri-O-acetyl -beta - D-xylopyranosyl)-(1-->2)]-(4,6-di-O-acetyl-beta-D-mannopyranosyl)-(1-->4 )- 2,3-di-O-acetyl-1,6-anhydro-beta-D-glucopyranose (14), in the presence of dimethyl (methylthio) sulfonium triflate (DMTST), gave the corresponding octasaccharide (19). Removal of the protecting groups gave 2-acetamido-2-deoxy-3-O-methyl-alpha-D-galactopyranosyl-(1-->3)-[4-O- methyl-beta-D-glucopyranosyl uronic acid-(1-->4)]-alpha-L-fucopyranosyl-(1-->4)-2-acetamido-2-deoxy-beta-D- glucopyranosyl-(1-->2)-alpha-D-mannopyranosyl-(1-->3)- beta-D-xylopyranosyl- (1-->2)]-beta-D-mannopyranosyl-(1-->4)-1,6-anhydro-beta-D-glucopyranose (22). The other two oligosaccharides that constitute the partial structure of lipid IV, called lipid I and II, were also synthesized.