Structural elucidation of the O-antigenic polysaccharide from Escherichia coli O175

The structure of the O-antigen polysaccharide (PS) from Escherichia coli O175 has been elucidated. Component analysis together with (1)H and (13)C NMR spectroscopy experiments were used to determine the structure. Inter-residue correlations were determined by (1)H, (1)H-NOESY, and (1)H, (13)C-heteronuclear multiple-bond correlation experiments. The PS is composed of pentasaccharide repeating units with the following structure: -> 2)-alpha-D-Glcp-(1 -> 4)-alpha-D-GlcpA-(1 -> 3)-alpha-D-Manp-(1 -> 2)-alpha-D-Manp-(1 -> 3)-beta-D-GalpNAc-(1 -> Cross-peaks of low intensity from an a-linked glucopyranosyl residue were present in the (1)H, (1)H-TOCSY NMR spectra. The alpha-D-Glcp residue is suggested to originate from the terminal part of the polysaccharide and consequently the biological repeating unit has a 3-substituted N-acetyl-D-galactosamine residue at its reducing end. The repeating unit of the E. coli O175 O-antigen is similar to those from E. coli O22 and O83, both of which carry an alpha-D-Glcp-(1 -> 4)-D-GlcpA structural element, thereby explaining the reported cross-reactivities between the strains. (C) 2010 Elsevier Ltd. All rights reserved.