Structural studies of the O-antigenic polysaccharides from Shigella dysenteriae type 3 and Escherichia coli O124, a reinvestigation

The structures of the O-antigenic part of the lipopolysaccharides from Shigella dysenteriae type 3 and Escherichia coli O124 have been reinvestigated. (1)H and (13)C NMR spectroscopy in combination with selected 2D NMR techniques were used to determine the O-antigen pentasaccharide repeating units with the following structure: [see text]. From biosynthetic considerations this should also be the biological repeating unit. The structures of the repeating units also explain the previously observed cross-reactivity between the strains and to E. coli O164, which only differs in the terminal sugar residue that is lacking the (R)-1-carboxyethyl group.