SYNTHETIC STUDIES ON SIALOGLYCOCONJUGATES .30. SYNTHESIS OF A SERIES OF GANGLIOSIDE GM3 ANALOGS CONTAINING A DEOXY-N-ACETYLNEURAMINIC ACID RESIDUE

Ganglioside GM3 analogs containing 4-, 7-, 8-, and 9-deoxy-N-acetylneuraminic acids in the place of N-acetylneuraminic acid (Neu5Ac) have been synthesized. Glycosylation of 2-(trimethylsilyl)ethyl O-(6-O-benzoyl-beta-D-galactopyranosyl)-(1 --> 4)-2,O-di-O-benzoyl-beta-D-glucopyranoside with the methyl thioglycoside derivatives of the respective deoxy-N-acetylneuraminic acids, using dimethyl(methylthio) sulfonium triflate as a promoter, gave the four required 2-(trimethylsilyl)ethyl alpha-sialosyl-(2 --> 3b)-beta-lactosides. These were converted via 0-acetylation. selective removal of the 2-(trimethylsilyl)ethyl group, and subsequent imidate formation, into the corresponding alpha-sialosyl-(2 --> 3b)-alpha-lactose trichloroacetimidates 15, 17, 19, and 21. Glycosylation of (2S,3R,4E)-2-azido-3-O-benzoyl-4-octadecene-1,3-diol with 15, 17, 19, and 21 in the presence of boron trifluoride etherate afforded the expected beta-glycosides, which were transformed in good yields, via selective reduction of the azido group, coupling with octadecanoic acid, O-deacylation, and de-esterification, into the target compounds.