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

The specific capsular polysaccharide produced by Rhodococcusequi serotype 3 was found to be a high-molecular-weight acidic polymer composed of D-glucose, D-galactose, D-glucuronic acid, 4-O-[(S)-1-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,[Formula: see text]in which (R)-1-carboxyethylidene groups bridge the O-2 and O-3 positions of the β-D-glucuronic acid residues. The 1H and 13C 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 1H–1H NOE measurements on the intact polysaccharide. Unequivocal determination of the absolute chirality of the 4-O-[(S)-1-carboxyethyl]-β-D-mannopyranose residues was achieved by 1H–1H NOE measurements on an acetylated lactone derivative of the glycose.