SYNTHETIC STUDIES ON SIALOGLYCOCONJUGATES .16. ALPHA-PREDOMINANT GLYCOSIDE SYNTHESIS OF N-ACETYLNEURAMINIC ACID WITH THE PRIMARY HYDROXYL GROUP IN CARBOHYDRATES USING DIMETHYL(METHYLTHIO)SULFONIUM TRIFLATE AS A GLYCOSYL PROMOTER

Coupling of the primary hydroxyl group in the suitably protected 2-(trimethylsilyl)ethyl glycosides of O-glucopyranose (3), _N-acetyl-D-glucosamine (7), N-acetyl-D-galactosamine (9), 0-lactose (10), and N-acetylneuraminic acid (11), with methyl (methyl 5-acetamido-4,7,8,9-tetra-0-acetyl-3,5-dideoxy-2-thio-D-glycero-a-D-galacto-2-nonulopyranosid)onate (12) as the glycosyl donor in acetonitrile in the presence of dimethyl(methylthio)sulfonium triflate (DMTST) as a glycosyl promoter and molecular sieves 3A, gave predominantly the corresponding α-glycosides 13, 15, 17, 25, and 29_ of N-acetylneuraminic acid in 43-71% yields, respectively, together with the 8-glycosides (13-24%). © 1990, Taylor & Francis Group, LLC. All rights reserved.