The structure of the O‐specific polysaccharide of Citrobacter O16 containing glycerol phosphate

The O‐specific polysaccharide, obtained by mild acid degradation of Citrobacter O16 lipopolysaccharide, consists of D‐glucose, D‐galactose, 2‐acetamido‐2‐deoxy‐D‐galactose, glycerol and phosphate in the ratios 2:2:2:1:1. Selective cleavage of the polysaccharide was carried out by Smith degradation, N‐deacetylation‐deamination and dephosphorylation with 48% hydrofluoric acid, which was accompanied by unexpected splitting of one of the glycosidic linkages. The structures of the oligosaccharides thus obtained were established using 1H‐ and 13C‐NMR spectroscopy, including one‐dimensional NOE, two‐dimensional rotating‐frame NOE, homonuclear and heteronuclear 13C,1H correlation spectroscopy, and, for the Smith degradation product, positive‐ and negative‐ion‐mode fast‐atom‐bombardment MS and MS/MS with collision‐induced dissociation. On the basis of these data and the results of methylation analysis, it was concluded that the O‐specific polysaccharide has the following repeating unit structure: