Structure of the O-specific polysaccharide of the bacterium Proteus mirabilis O13 containing a novel component: an amide of D-galacturonic acid with N(epsilon)-(1-carboxyethyl)lysine.

An acidic O-specific polysaccharide was obtained by mild degradation of the lipopolysaccharide of the bacterium Proteus mirabilis O13 and found to contain D-galactose, 2-acetamido-2-deoxy-D-glucose, and N(epsilon)-(1-carboxyethyl)-N(alpha)-(D-galacturonoyl)lysine. On the basis of full acid hydrolysis and 1H- and 13C-NMR spectroscopy, including two-dimensional correlation spectroscopy (COSY), H-detected heteronuclear 1H, 13C multi-quantum coherence (HMQC), and rotating-frame nuclear Overhauser effect spectroscopy (ROESY), the following structure of the branched trisaccharide repeating unit of the polysaccharide was established [structure: see text]