Structure of an acidic polysaccharide from a marine bacterium Pseudoalteromonas distincta KMM 638 containing 5-acetamido-3,5,7,9-tetradeoxy-7-formamido- l- glycero- l- manno-nonulosonic acid

An acidic polysaccharide was obtained from the lipopolysaccharide of Pseudoalteromonas distincta strain KMM 638, isolated from a marine sponge, and found to contain d-GlcA, d-GalNAc, 2-acetamido-2,6-dideoxy- d-glucose ( d-QuiNAc) and two unusual acidic amino sugars: 2-acetamido-2-deoxy- d-galacturonic acid ( d-GalNAcA) and 5-acetamido-3,5,7,9-tetradeoxy-7-formamido- l- glycero- l- manno-nonulosonic acid (Pse5Ac7Fo, a derivative of pseudaminic acid). Oligosaccharides were derived from the polysaccharide by partial acid hydrolysis and mild alkaline degradation and characterised by electrospray ionisation (ESI) MS and 1H and 13C NMR spectroscopy. Based on these data and NMR spectroscopic studies of the initial and O-deacetylated polysaccharides, including quaternary carbon detection, 2D COSY, TOCSY, ROESY, H-detected 1H, 13C HMQC and HMBC experiments, the following structure of the branched pentasaccharide repeating unit was established: where the degree of O-acetylation of d-Gal pNAcA at position 3 is ∼60%.