Structural analysis of deacylated lipopolysaccharide of Escherichia coli strains 2513 (R4 core-type) and F653 (R3 core-type)

Lipopolysaccharide (LPS) of Escherichia coli strain 2513 (R4 core-type) yielded after alkaline deacylation one major oligosaccharide by high-performance anion-exchange chromatography (HPAEC) which had a molecular mass of 2486.59 Da as determined by electrospray ionization mass spectrometry. This was in accordance with the calculated molecular mass of a tetraphosphorylated dodecasaccharide of the composition shown below. NMR-analyses identified the chemical structure as [GRAPHICS] where L-alpha-D-Hep is L-glycero-alpha-D-manno-heptopyranose and Kdo is 3-deoxy-alpha-D-manno-oct-2-ulopyranosylonic acid and all hexoses are present as D-pyranoses. We have also isolated the complete core-oligosaccharides of E. coli F653 LPS for which only preliminary data were available and investigated the deacylated LPS by [GRAPHICS] NMR and MS. The proposed structure determined previously by methylation analysis was confirmed and is shown below. [GRAPHICS] In addition we have quantified the side-chain heptose substitution of the inner core with GlcpN (approximate to30%) and confirmed that this sugar is only present when the phosphate at the second L, D-Hepp residue is absent.