Mammals, birds, amphibians, and teleost fish all have similar brain gangliosides. These gangliosides are of the ganglio-series with predominantly, gangliotetraose, P-o-Gal-(1 + 3)-fl-D-GalNAc-(1 + +&o-Gal-( 1+ 4)-~-Gk, as the neutral oligosaccharide, though with a varying degree of sialylation. Since their discovery, the gangliosides have for several reasons elicited much interest. The concentration of complex gangliosides in membrane elements of the brain is suggestive of a functional role in the nervous system. Recently, the biological importance of gangliosides in the nervous system has been well documented*-'. As biologically derived gangliosides are polymolphous molecules and available in only limited quantity, the elucidation of their functions at the molecular level still remains to the carried out. We have reported8 the successful syntheses of several series of gangliosides and their analogues, which are based on a facile dimethyl(methylthio)sulfonium triflates" (DMTST) or N-iodosuccinimide (NIS)-trifluoromethanesulfonic acid'*". (TfOH) promoted, stereoselective cu-glycosylation of sialic acid with suitably protected sugar residues in an acetonitrile medium. We describe herein a facile, total synthesis of gangliosides GM, and GD,, in connection with development of the systematic synthesis of the ganglio-series of 'gangliosides. Ganglioside GM, was first synthesized by Ogawa and co-workers" after multiple steps in very low yield. For the synthesis of the both gangliosides, the core oligosaccharide 4 was selected as the glycosyl acceptor. Compound 4 has a sialyl a-(2 + 3) unit already linked and provides free hydroxyl groups at C-3 and C-4 of the GalNAc residue for further, regioselective glycosylation at C-3, with either methyl 2,4,6-tri-0-benzoyl-3-0-benzyl-1-thio-P_anoside
(5) or methyl 0-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-cY-o-gulucto-2nonulopyranosylonate)-( 2-+ 3)-2,4,6-tri-O-benzoyl-l-thio-B_D-galactopyranoside'*