Structural determination of the O-antigenic polysaccharide from Escherichia coli O74

Abstract

The structure of the O-antigen polysaccharide (PS) from Escherichia coli O74 has been determined. Component analysis, together with 1H and 13C NMR spectroscopy as well as 1H, 15N-HSQC experiments were employed to elucidate the structure. Inter-residue correlations were determined by 1H, 1H-NOESY and 1H, 13C-heteronuclear multiple-bond correlation experiments. The PS is composed of tetrasaccharide repeating units with the following structure: ▪ Cross-peaks of low intensity from an α-linked N-acetylglucosamine residue were present in the NMR spectra, and spectral analysis indicates that they originate from the penultimate residue in the polysaccharide. Consequently, the biological repeating unit has a 3-substituted N-acetyl- d-glucosamine residue at its reducing end. The 1H, 13C and 15N NMR chemical shifts of the α- and β-anomeric forms of d-Fuc p3NAc are also reported. The repeating unit of the E. coli O74 O-antigen is identical to that of the capsular polysaccharide from E. coli K45.