Noriyasu Hada

Synthesis of a model compound related to an anti-ulcer pectic polysaccharide

A stereocontrolled synthesis of the model compound for an anti-ulcer active polysaccharide (Bupleuran 2IIc) is described. Glycosidation of the disaccharide acceptor, 2-O-acetyl-3-O-benzyl-4-O-(p-methoxybenzyl)-alpha-L-rhamnopyranosyl-(1-- >4)-2,3,6-tri-O-benzyl-alpha-D-galactopyranosyl trichloroacetimidate, with the disaccharide receptor, allyl 3,4-di-O-benzyl-alpha-L-rhamnopyranosyl-(1-->4)-2,3,6-tri-O-benzyl-beta- D-galactopyranoside, using silver triflate (AgOTf) as a promoter gave the desired tetrasaccharide derivative, which was transformed into the acidic tetrasaccharide, corresponding to a segment of the rhamnogalacturonan (Bupleuran 2IIc) polysaccharide, propyl alpha-L-Rha-(1-->4)-alpha-D-GalA-(1-->2)-alpha-L-Rha-(1-->4)-beta-D-GalA , via removal of the corresponding ether and ester protecting groups, followed by oxidation.

SYNTHETIC STUDIES ON GLYCOSPHINGOLIPIDS FROM THE PARASITE ECHINOCOCCUS MULTILOCULARIS

Novel neutral glycosphingolipids isolated from the metacestodes of Echinococcus multilocularis by Persat, may be expected to be involved in host-parasite interactions. We have synthesized these glycosphingolipid analogues containing 2-branched fatty alkyl residues in place of ceramide. The glycosylation of galactosyl donors 4 and 5 with each of the acceptors 2 and 11 in the presence of N-iodosuccinimide (NIS)/TfOH, and the glycosylation of fucosyl donor 13 with acceptors 12 and 20 in the presence of dimethyl(methylthio)sulfonium triflate (DMTST) gave the desired oligosaccharide derivatives at good yield. The fully per-O-acylated 2-(trimethylsilyl)ethyl glycosides 6, 15, 21, and 26 were converted to glycosylimidates 7, 16, 22, and 27, which were condensed with 2-(tetradecyl)hexadecanol and subsequently deacylated give four target glycosphingolipid analogues.

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 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 tetrasa...

Synthetic studies on an oligosaccharide of a glycolipid from the spermatozoa of bivalves IX. Syntheses 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.