SYNTHETIC STUDIES ON SIALOGLYCOCONJUGATES .14. SYNTHESIS OF GANGLIOSIDE-GM3 ANALOGS CONTAINING THE CARBON-7 AND CARBON-8 SIALIC ACIDS

Ganglioside GM3 analogs, containing 5-acetamido-3,5-dideoxy-L -arabino- heptulosonic acid and 5-acetamido-3,5-dideoxy-D -galacto- octulosonic acid have been synthesiyed. Glycosylation of 2-(trimethylsilyl)ethyl (0-(6-0-benzoyl-β-D-galactopyranosyl)-(l→4)-2,6-di-0-benzoyl-β-D-glucopyranoside (5), with methyl (methyl 5-acetamido-4,7-di-0-acetyl-3,5-dideoxy-2-thio-β-L-arabino-2-heptulo- pyranosid)onate (2) or with methyl (methyl 5-acetamido-4,7,8-tri-O-acetyl-3,5-dideoxy-2-thio-0t-D-£alacto-2-octulopyranosid)onate (4) which were respectively prepared from the corresponding 2-S-acetyl derivatives (1 and 3) by selective 2-S-deacetylation and subsequent S-methylation, using dimethyl(methylthio)sulfonium triflate as a glycosyl promoter, gave 2-(trimethylsilyl)ethyl 0-(methyl 5-acet-amido-4,7-di-O-acetyl-3,5-dideoxy-β-L -arabino- 2-heptulopyranosvl- onate)-(2→3)-O-(6-O-benzoyl-β-D-galactopyranosyl)-(1→4)-2,6-di-O-benzoyl-β-D-glucopyranoside (6) and 2-(trimethylsilyl)ethyl 0-(methyl 5-acetamido-4,7,8-tri-O-acetyl-3,5-dideoxy-α-D -galacto- 2-octulopyranosylonate)-(2→3)-O-(6-O-benzoyl-β-D-galactopyranosyl)- (1-4)-2,6-di-O-benzoyl-β-D-glucopyranoside (10), respectively. Compounds 6 and 10 were converted, via O-acetylation, selective removal of the 2-(trimethylsilyl)ethyl group, and subsequent imidate formation, into the corresponding trichloroacetimidates 9 and 13 respectively. Glycosylation of (2S,3R,4E)-2-azido-3-O-benzoyl-4-octadecen-1,3-diol (14) with 9 or 13 afforded the 8-glycosides (15 and 18) which were converted, via selective reduction of the azide group, coupling with octadecanoic acid, 0-deacylation and deesterifica-tion, into the title compounds, respectively. © 1990, Taylor & Francis Group, LLC. All rights reserved.