The core oligosaccharide component from Mannheimia (Pasteurella) haemolytica serotype A1 lipopolysaccharide contains L-glycero-D-manno- and D-glycero-D-manno-heptoses:: Analysis of the structure and conformation by high-resolution NMR spectroscopy

Previous studies from our laboratory have indicated that the lipopolysaccharide (LPS) from Mannheimia haemolytica serotype A1 contains both L-glycero-D-manno-heptose and D-glycero-D-manno-heptose residues. NMR methods making use of ID H-1 selective excitation and 2D (H-1, C-13) and (H-1, P-31) heteronuclear experiments were used for the structural determination of the major core oligosaccharide components of the deacylated low-molecular-mass LPS obtained following sequential treatment with anhydrous hydrazine and aq KOH. The core oligosaccharide region was found to be composed of a branched octasaccharide linked to the deacylated lipid A moiety via a 3-deoxy-4-phospho-D-manno-oct-2-ulosonate residue having the structure, [GRAPHICS] Heterogeneity was found to be present at several linkages. NMR methods were devised to distinguish between the diastercomeric forms of the heptose residues. Synthesized monosaccharides Of L-D- and D-D-heptose were used as model compounds for analysis of the H-1 and C-13 NMR chemical shifts and proton coupling constants. Molecular modeling using a Monte Carlo method for conformational analysis of saccharides was used to determine the conformation of the inner core of the oligosaccharide and to establish the stereochemical relationships between the heptoses.