Structure of the O-polysaccharide from the lipopolysaccharide of Providencia stuartii O43 containing an amide of d-galacturonic acid with l-serine

The O-polysaccharide was obtained by mild acid degradation of the lipopolysaccharide of Providencia stuartii O43:H28 and studied by sugar and methylation analyses, Smith degradation and 1H and 13C NMR spectroscopy, including 2D ROESY, and H-detected 1H, 13C HSQC and HMBC experiments, as well as a NOESY experiment in a 9:1 H2O/D2O mixture to reveal correlations for NH protons. It was found that the polysaccharide is built up of linear tetrasaccharide repeating units containing an amide of d-galacturonic acid with l-serine [d-GalA6(l-Ser)] and has the following structure: