Synthesis of 3- O-α- l-fucopyranosyl- l-fucose and methyl 3- O-β- l-fucopyranosyl-α- l-fucopyranoside

Abstract

A Koenigs-Knorr reaction of methyl 2,4-di- O-benzyl-α- l-fucopyranoside with 2- O-benzyl-3,4-di- O- p-nitrobenzoyl-α- l-fucopyranosyl bromide, followed by catalytic deacylation and hydrogenolysis, led to a stereospecific synthesis of methyl 3- O-α- l-fucopyranosyl-α- l-fucopyranoside. Use of 2,3,4-tri- O-acetyl-α- l-fucopyranosyl bromide as the halide in the same reaction afforded, in the ratio 2:3, a mixture of the α and β disaccharides from which the pure β-disaccharide could be isolated by crystallization of the intermediate methyl 2,4-di- O-benzyl-3- O-β- l-fucopyranosyl-α- l-fucopyranoside. The attribution of anomeric configuration and evaluation of optical purity of the products were based on optical rotation and g.l.c. of the per(trimethylsilyl) ethers. Acetolysis of methyl 3- O-α- l-fucopyranosyl-α- l-fucopyranoside, followed by catalytic deacetylation, gave 3- O-α- l-fucopyranosyl- l-fucose.