Synthesis and n.m.r. analysis of branched trisaccharide and pentasaccharide haptens of the β-hemolytic streptococci group A and the preparation of synthetic antigens

The synthesis of branched trisaccharide and pentasaccharide portions of the cell-wall polysaccharide of the β-hemolytic Streptococci Group A is described. The key dissaccharide acceptors, allyl or 8-(methoxycarbonyl)octyl 3- O-(3,4,6-tri- O-benzyl-2-deoxy-2-phthalimido-β- d-glucopyranosyl)-4- O-benzyl-α- d-rhamnopyranoside, in conjunction with a selectively blocked α- l-rhamnopyranosyl chloride under Koenigs-Knorr conditions, afforded the branched trisaccharides in 81 and 62% yield, respectively. Analogously, glycosylation of the 8-(methoxycarbonyl)octyl disaccharide with a protected β- d-Glc pNAc-(1→3)-α- l-Rha p-(1→3)-α- l-Rha p chloride gave the pentasaccharide in 43% yield. The key disaccharide acceptors were obtained, in turn, from the allyl or 8-(methoxycarbonyl)octyl rhamnoside acceptors and 3,4,6-tri- O-benzyl-2-deoxy-2-phthalimido-β- d-glucopyranosyl chloride under Koenigs-Knorr conditions. The latter glycosyl donor has not been described previously. Removal of the protecting groups afforded the trisaccharide haptens as their 1-propyl and 8-(methoxycarbonyl)octyl glycosides and the pentasaccharide as its 8-(methoxycarbonyl)octyl glycoside. The compounds have been subjected to detailed analysis by two-dimensional n.m.r. methods. Preparation of the synthetic antigens followed coupling of the 8-(methoxycarbonyl)octyl glycosides to bovine serum albumin via the acyl azide intermediates.