Syntheses of model oligosaccharides of biological significance. XI. A short synthesis of fucosylated chitobiosides, also bound to asparagine in a synthon (as in N-linked glycoproteins)

Abstract

We describe a simple and efficient method for the preparation of the trisaccharide GlcNAc(β1-4)-[Fuc(α 1-6)-]GlcNAc(β 1-) (1) and of the protected form of GlcNAc(β 1-4)-[Fuc(α 1-6)-]GlcNAc(β1-Asn) (2). The key intermediate is benzyl 4,6-benzylidene chitobioside 5 giving the desired trisaccharide by insitu anomerization–glycosylation reaction with 2,3,4-tribenzylfucosyl bromide. The benzyl glycoside in the trisaccharide 6 has been replaced by acetate and then bromine; this glycosylating agent was used to prepare methyl and 8-methoxycarbonyloctyl glycosides as well as isothiocyanate 12, in a series of reactions. The latter compound gave, on reaction with 1-benzyl N-benzyloxycarbonyl-L-asparate, compound 13 (a protected derivative of 2), which should serve as a synthon for syntheses of glycopeptides. Keywords: glycopeptide, synthesis; oligosaccharide, synthesis; chitobiosides; fucosylated chitobiosides; N-linked oligosaccharides.