title: Regio- and stereo-selective synthesis of ganglioside GM1b and some positional analogs.
abstract: Total syntheses of ganglioside GM1b (IV3NeuAcGgOse4Cer) and three of its positional analogs are described. Methyl O-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D- glycero-alpha-D-galacto-2-nonulopyranosylonate)- (2----3)-2,4,6-tri-O-benzoyl-1-thio-beta-D-galactopyranoside (7) and methyl O-(methyl 5- acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-alpha-D-galacto-2 -nonulopyranosylonate)-(2----6)-2,4-di-O-benzoyl-3-O-benzyl-1-thio - beta-D-galactopyranoside (8) were the key glycosyl donors, prepared according to our reported methods. Coupling of 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-alpha-D-galactopyranosyl bromide and 2-(trimethylsilyl)ethyl O-(2,3,6-tri-O-benzyl-beta-D- galactopyranosyl)-(1----4)-2,3,6-tri-O-benzyl-beta-D-glucopyranoside gave a trisaccharide, which after removal of O-acetyl and phthaloyl groups was converted separately, by benzylidenation and dibutyltin oxide-mediated selective benzylation, into two glycosyl acceptors. These were suitable respectively for C-3 and C-6 glycosylation reactions, promoted by dimethyl(methylthio)sulfonium triflate (DMTST), with the donors 7 and 8. The four possible coupling reactions gave the corresponding four pentasaccharide derivatives in high yields, and these were transformed into their respective alpha-trichloroacetimidates. Glycosylation of (2S,3R,4E)-2-azido-3-O-benzoyl-4-octadecene-1,3-diol with the alpha-trichloroacetimidates gave the corresponding beta-glycosides, which on channeling through selective reduction of the azido group, coupling of the thus formed amino group with octadecanoic acid, O-deacetylation, and saponification of the methyl ester group, gave the title compounds.
authors.affiliation: Department of Applied Bioorganic Chemistry, Gifu University, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Prabhanjan
authors.forename: A
authors.initials: A
authors.lastname: Kameyama
authors.forename: H
authors.initials: H
authors.lastname: Ishida
authors.forename: M
authors.initials: M
authors.lastname: Kiso
authors.forename: A
authors.initials: A
authors.lastname: Hasegawa
mesh_terms: D002240:Carbohydrate Sequence; D005677:G(M1) Ganglioside / Q000031:analogs & derivatives* / Q000737:chemistry; D005732:Gangliosides / Q000737:chemistry*; D007536:Isomerism; D008969:Molecular Sequence Data; D013237:Stereoisomerism
chemical_list: D005732:Gangliosides; D005677:G(M1) Ganglioside; C029624:ganglioside M1b