The acidic specific capsular polysaccharide of Rhodococcusequi serotype 3. Structural elucidation and stereochemical analysis of the lactate ether and pyruvate acetal substituents

Abstract

The specific capsular polysaccharide produced by Rhodococcus equi serotype 3 was found to be a high-molecular-weight acidic polymer composed of D-glucose, D-galactose, D-glucuronic acid, 4-O-[(S)-l-carboxyethyl]-D-mannose, and pyruvic acid in equal molar proportions. Structural analysis, employing a combination of chemical and nuclear magnetic resonance techniques, established that the polysaccharide is composed of linear repeating tetrasaccharide units, [GRAPHICS] in which (R)-1-carboxyethylidene groups bridge the 0-2 and 0-3 positions of the beta-D-glucuronic acid residues. The H-1 and C-13 NMR resonances of the native and depyruvulated.serotype 3 polysaccharides were fully assigned by homo- and heteronuclear chemical shift correlation methods. The absolute configurations of the lactate-substituted mannopyranosyl residues and the pyruvate acetals were determined from H-1-H-1 NOE measurements on the intact polysaccharide. Unequivocal determination of the absolute chirality of the 4-O-[(S)-1-carboxyethyl]-beta-D-mannopyranose residues was achieved by H-1-H-1 NOE measurements on an acetylated lactone derivative of the glycose.