First total synthesis of ganglioside GT1aα

A first total synthesis of ganglioside GT1aα (IV3III6II3Neu5AcGg4Cer) is described. The suitably protected sialyl α-(2 → 6) ganglioside was glycosylated with the phenylthioglycoside of sialic acid in the presence of N-iodosuccinimide (NIS)-trimethylsilyl trifluoromethanesulfonate (TMSOTf), followed by further glycosylation with the methyl thioglycoside promoted by dimethyl(methylthio)sulfonium triflate (DMTST), to give the heptasaccharide. The oligosaccharide obtained was converted into the title ganglioside by the introduction of ceramide and then complete deprotection.