Structural determination of a 5-acetamido-3,5,7,9-tetradeoxy-7(3-hydroxybutyramido)-l-glycero-l-manno-nonulosonic acid-containing homopolysaccharide isolated from Sinorhizobium fredii HH103

The structure of a polysaccharide from Sinorhizobium fredii HH103 has been determined. This polysaccharide was isolated by following the protocol for lipopolysaccharide extraction. On the basis of monosaccharide analysis, methylation analysis, fast atom-bombardment MS, matrix-assisted laser desorption ionization MS, electron-impact high-resolution MS, one-dimensional H-1-NMR and C-13-NMR and two-dimensional NMR experiments. the structure was shown to consist of a homopolymer of a 3:1 mixture of 5-acetamido-3,5,7,9-tetradeoxy-7-[(R)- and (S)-3-hydroxybutyramido]-L-glycero-L-manno-nonulosonic acid. The sugar residues are attached via a glycosidic linkage to the OH group of the 3-hydroxybutyramido substituent and thus the monomers are linked via both glycosidic and amidic linkages. In contrast with the Sinorhizobium K-antigens previously reported, which are composed of a disaccharide repeating unit, the K-antigen polysacharide of S. fredii HH103 homopolysaccharide.