Isolation and characterization of the unusual lipopolysaccharide component, 2-amino-2-deoxy-2-N-(27-hydroxyoctacosanoyl)-3-O-(3-hydroxy- tetradecanoyl)-gluco-hexuronic acid, and its de-O-acylation product from the free lipid A of Rhizobium trifolii ANU843.

Two new, unusual lipid A components have been isolated and characterized from the free lipid A of Rhizobium trifolii ANU843. 2-Amino-2-deoxy-2-N-(27-hydroxyoctacosanoyl)-3-O-(3-hydroxy- tetradecanoyl)-gluco-hexuronic acid and its de-O-acylation product were purified from the chloroform/methanol extract of a mild acid hydrolysate of the lipopolysaccharide by chromatography on C18 reverse-phase columns and layers. The compositions of the two compounds were determined by releasing the acyl components by exhaustive acid-catalyzed methanolysis and identifying them as their methyl esters by gas chromatography and gas chromatography/mass spectrometry. The sugar component was identified by converting it to the alditol acetate derivative of glucosamine in a two-step reduction and identifying it as such by gas chromatography/mass spectrometry. The linkages of the fatty acyl components to the sugar residue and the configuration of the sugar component was confirmed by 1H and 13C NMR spectroscopy. The complete structures of the two compounds were further confirmed by fast atom bombardment mass spectrometry. It is still unsure whether the de-O-acylated derivative was formed from the di-acyl compound by de-O-acylation during acid hydrolysis. These structures represent the first report of 2-amino-2-deoxy-gluco-hexuronic acid in the free lipid A of a Gram-negative bacterium and confirms our earlier contention (Hollingsworth, R.I., and Carlson, R. W. (1989) J. Biol. Chem. 264, 9000-9303) of the involvement of 27-hydroxyoctacosanoic acid in the structure of the lipopolysaccharide of Rhizobium trifolii ANU843.