Articial carbohydrate antigens: A block synthesis of a linear, tetrasaccharide repeating-unit of the Shigella flexneri varianty polysaccharide

Abstract

Glycosylation of methyl 2,4-di- O-benzoyl-α- l-rhamnopyranoside with 2,3,4-tri- O-acetyl-α- l-rhamnopyranosyl bromide gave methyl 2,4-di- O-benzoyl-3- O-(2,3,4-tri- O-acetyl-α- l-rhamnopyranosyl)-α- l-rhamnopyranoside ( 4) in 93% yield. Conversion of 4 into the corresponding glycosyl bromide was accomplished with dibromomethyl methyl ether. Under Koenings-Knorr conditions, this bromide reacted with 8-(methoxycarbonyl)octyl 2- O-(2-acetamido-4,6- O-benzylidene-2-deoxy-β- d-glycopyranosyl)-3,4-di- O-benzyl-α- l- rhamnopyranoside, to provide the protected tetrasaccharide in 91% yield. Removal of blocking groups gave 8-(methoxycarbonyl)octyl O-α- l-rhamnopyranosyl-(1→3)-α- l-rhamnopyranosyl-(1→3)- O-2-acetamido-2-deoxy-β- d-glucopyranosyl-(1→2)- α- l-rhamnopyranoside. Together with previously synthesized tetrasaccharides of the Shigella flexneri Y O-antigen, this oligosaccharide has been used to study the conformation of O-antigens and to assist in the selection of S. flexneri, variant Y, specific monoclonal antibodies.