STRUCTURAL ELUCIDATION OF 2 CAPSULAR POLYSACCHARIDES FROM ONE STRAIN OF BACTEROIDES-FRAGILIS USING HIGH-RESOLUTION NMR-SPECTROSCOPY

The capsule of Bacteroides fragilis is unusual in that it consists of two distinct capsular polysaccharides. Using a combination of high-resolution NMR spectroscopy, theoretical calculations, and as few chemical procedures as required, the structure of both polysaccharide antigens (polysaccharides A and B) was elucidated. Using the above procedures, it was possible to obtain the complete structures using minimal quantities of polysaccharides A and B (8 and 5 mg, respectively). Only small amounts of each subjected to chemical analysis were not recoverable. Polysaccharide A is composed of the following repeating unit: [--> 3)alpha-D-AATp(1 --> 4)[beta-D-Galf(1 --> 3)]alpha-D-GalpNAc(1 --> 3)beta-D-Galp(1 --> ], where AAT is 2-acetamido-4-amino-2,4,6-trideoxygalactose. A pyruvate substituent having the R configuration spans O-4 and O-6 of the beta-D-galactopyranosyl residue. Polysaccharide B is composed of the following repeating unit: [--> 4)alpha-L-QuipNAc(1 --> 3)beta-D-QuipNAc(1 --> 4)[alpha-L-Fucp(1 --> 2)beta-D-GalpA(1 --> 3)beta-D-GlcpNAc(1 --> 3)]alpha-D-Galp(1 --> ]. A 2-aminoethylphosphonate substituent is situated on O-4 of the N-acetyl-beta-D-glucopyranosyl residue.