Structure of the O-polysaccharides of the lipopolysaccharides of Mesorhizobium loti HAMBI 1148 and Mesorhizobium amorphae ATCC 19655 containing two O-methylated monosaccharides.

The O-polysaccharide of Mesorhizobium loti HAMBI 1148 was obtained by mild acid degradation of the lipopolysaccharide and studied by sugar and methylation analyses, Smith degradation, and (1)H and (13)C NMR spectroscopies, including 2D (1)H/(1)H COSY, TOCSY, ROESY, and H-detected (1)H/(13)C HSQC experiments. The O-polysaccharide was found to have a branched hexasaccharide-repeating unit of the following structure: [Formula: see text] where 2-acetamido-2-deoxy-4-O-methyl-D-glucose (D-GlcNAc4Me) and methyl group on 2-substituted D-rhamnose (Me) shown in italics are present in approximately 80% and approximately 40% repeating units, respectively. Similar studies of the O-polysaccharide from Mesorhizobium amorphae ATCC 19655 by sugar analysis and NMR spectroscopy revealed essentially the same structure but a higher content of 3-O-methyl-D-rhamnose ( approximately 70%).