Chemical structure of the lipid A of Escherichia coli J‐5

The lipopolysaccharide, and particularly its lipid A moiety, of the J-5 mutant of Escherichia coli O111 plays a central role in studies on potential induction of cross-reactive and cross-protective antibodies, however, its chemical and antigenic structure was hitherto unknown. Here, the chemical structure of the J-5 lipid A is reported. It is composed of the bisphosphorylated disaccharide beta-D-GlcpN-4-P-(1-6)-alpha-D-GlcpN-1-P which carries four residues of 3-hydroxytetradecanoic acid, one each at positions 2, 3, 2', and 3'. The hydroxyl groups of the acyl residues at 2' and 3' are esterified with dodecanoic and tetradecanoic acid, respectively. The hydroxyl group at C-6' functions in the lipopolysaccharide as the attachment site of the core oligosaccharide. Furthermore, a new method to isolate the hydrophilic backbone, i.e. the 1,4'-bisphosphorylated glucosamine disaccharide, and its structural analysis by 1H-, 13C-, and 31P-NMR spectroscopy, are described, leading to a new and easier strategy in structural analysis of lipid A from bacterial lipopolysaccharides.