Communication: Synthetic Studies on Sialoglycoconjugates 25: Reactivity of Glycosyl Promoters in α-Glycosylation of N-Acetyl-Neuraminic Acid with the Primary and Secondary Hydroxyl Groups in the Suitably Protected Galactose and Lactose Derivatives

Development of an efficient α-glycoside synthesis of sialic acids is critically significant for the syntheses of sialoglycoconjugates, especially gangliosides which carry important biological functions1 in biological systems. Previously, we demonstrated2 a new α-glycosylation of sialic acids by use of dimethyl(methylthio)sulfonium triflate (DMTST)3 as the glycosyl promoter, the suitably protected glycosyl acceptors and the methyl 2-thioglycoside 1 of N-acetylneuraminic acid (Neu5Ac) as the donor in acetonitrile under kinetically controlled conditions, and accomplished4 the syntheses of a variety of gangliosides and their analogs.