The structure of lipid A from the lipopolysaccharide of Rhodopseudomonas gelatinosa 29/1

The structure of the lipid A component of Rhodopseudomonas gelatinosa 29/1 lipopolysaccharide was established. It constitutes a β-1,6-glucosamine disaccharide substituted on either side by ester-and glycosidically-bound phosphate residues. Both phosphate groups are in turn nonstoichiometrically substituted by ethanolamine. The amino groups of the disaccharide are N-acylated by 3-acyloxyacyl residues: that at the reducing glucosamine by 3-O-(14:0) 10:0, and that at the non-reducing one by 3-O-(12:0)10:0. Hydroxyl groups at C-3 and C-3′ are esterified by hydroxycapric acid. Hydroxyl groups at C-4 and C-6′ in free hydroxycapric acid. Hydroxyl groups at C-4 and C-6′ in free lipid A were shown to be unoccupied by methylation with diazomethane. A similar methylation of the intact lipopolysaccharide revealed a free hydroxyl group only at C-4, indicating that C-6′ is the attachment site of 3-deoxy-d-anno-octulosonic acid.