Synthesis of streptococcal Groups A, C and variant-A antigenic determinants

Abstract

The antigenic determinants of the cell wall polysaccharides belonging to the β-haemolytic Streptococci Groups A, A-variant, and C have been synthesized as the glycosides of 8-methoxycarbonyloctanol. In this form they may be used to generate artificial antigens and immunoabsorbents. The terminal disaccharide, 3-O-(2-acetamido-2-deoxy-β-D-glucopyranosyl)-α-L-rhamnopyranoside, of the Group A polysaccharide was synthesized by a Königs–Knorr reaction between 8-methoxycarbonyloctyl 2,4-di-O-benzoyl-α-L-rhamnopyranoside (1) and 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-β-D-glucopyranosyl bromide (2) which gave the antigenic determinant (6) after removal of the blocking groups. Similarly, addition of 3,4,6-tri-O-acetyl-2-azido-2-deoxy-β-D-galactopyranosyl chloride (3) to (1) gave a disaccharide (7). The suitably blocked benzylidene acetal (11) was treated with the glactopyranosyl chloride (3) to yield the trisaccharide (12). The deblocked trisaccharide, O-(2-acetamido-2-deoxy-α-D-galactopyranosyl)-(1→3)-O-(2-acetamido-2-deoxy-α-D-galactopyranosyl)-(1→3)-α-L-rhamnopyranoside (14), is similar to the determinant of the Group C streptococcal cell wall and is also related to the Forssman antigen. The previously synthesized disaccharide glycoside, 8-methoxycarbonyloctyl 3,4-di-O-benzyl-2O-(2,4-di-O-benzoyl-α-L-rhamnopyranosyl)-α-L-rhamnopyranoside (15) was subjected to sequential chain-extension reactions with 2-O-acetyl-3,4-di-O-benzyl-α-L-rhamnopyranosyl chloride (4) to give the trisaccharide (16) and from this the slectively blocked precursor (17) from which the tetrasaccharide (18) was formed by reaction with (4). The tetrasaccharide glycoside O-(α-L-rhamnopyranosyl)-(1→2)-O-(α-L-rhamnopyranosyl)-(1→3)-O-(α-L-rhamnopyranosyl)-(1→2)-α-L-rhamnopyranoside (19) mimics the core structure of Groups A and C streptococcal polysaccharides and is identical to the sequence of the variant-A cell-wall polysaccharide.