STRUCTURAL ELUCIDATION OF THE NOVEL TYPE-VII GROUP-B STREPTOCOCCUS CAPSULAR POLYSACCHARIDE BY HIGH-RESOLUTION NMR-SPECTROSCOPY

The type VII capsular polysaccharide isolated from the newly discovered group B Streprococcus (GBS) strain contains D-glucose, D-galactose, N-acetyl-D-glucosamine and N-acetylneuraminic acid in the molar ratio 2:2:1:1. High-resolution one- and two-dimensional (1D and 2D) H-1 and C-13 NMR spectroscopy of the native and desialylated polysaccharides showed the type VII GBS capsular polysaccharide to contain the following branched hexasaccharide repeating unit: --> 4)-beta-D-Glc-(1 --> 4)-alpha-D-Glc-(1 --> 4)-beta-D-Gal-(1 --> 6 up arrow 1 alpha-Neu5Ac-(2 --> 3)-beta-D-Gal-(1 --> 4)-beta-D-GlcNAc Despite extensive structural similarity with the previously described GBS polysaccharides, the type VII polysaccharide showed no cross-reaction with the heterologous antisera.