Structure of the core part of the lipopolysaccharides from Proteus penneri strains 7, 8, 14, 15, and 21

The core-lipid A region of the lipopolysaccharides from Proteus penneri strains 7, 8, 14, 15, and 21 was studied using NMR spectroscopy, ESI MS, and chemical analysis after alkaline deacylation, deamination, and mild-acid hydrolysis of the lipopolysaccharides. The following general structure of the major core oligosaccharides is proposed: abstract: see text] where all sugars are in the pyranose form and have the D configuration unless otherwise stated, Hep and DDHep=L-glycero- and D-glycero-D-manno-heptose, respectively, K=H, and Q=H in strain 8 or alpha-Glc in strains 7, 14, 15, and 21. In addition, several minor structural variants are present, including those lacking Ara4N in strains 7 and 15 and having the alpha-GlcN residue N-acylated to a various degree with glycine in strains 7, 8, 14, and 21. In strain 14, there are also core oligosaccharides with K=amide of beta-D-GalpA with putrescine, spermidine, or 4-azaheptane-1,7-diamine; remarkably, these structural variants lack either the PEtN group or the alpha-Hep-(1-->2)-alpha-DDHep disaccharide fragment at alpha-D-GalpA. While structural features of the inner core part are shared by Proteus strains studied earlier, the outermost Q-(1-->4)-alpha-GalNAc-(1-->2)-alpha-DDHep-(1-->6)-alpha-GlcN oligosaccharide unit has not been hitherto reported.