Structure of the O-polysaccharide of Providencia alcalifaciens O2 containing ascarylose and N-(l-alanyl)-d-glucosamine

•An O-polysaccharide was isolated from the bacterium Providencia alcalifaciens O2.•Structure of the polysaccharide was established by NMR and chemical approaches.•The polysaccharide contains a rarely occurring 3,6-dideoxyhexose, ascarylose.•One of the constituent amino sugars, GlcN, is acylated by l-alanine.

The O-polysaccharide was obtained by degradation of the lipopolysaccharide of Providencia alcalifaciens O2 under mild acidic conditions followed by GPC. The polysaccharide was found to contain two unusual components: 3,6-dideoxy-l-arabino-hexose (ascarylose, Asc) and 2-(l-alanyl)amino-2-deoxy-d-glucose (GlcNAla). Ascarylose was partially split off during lipopolysaccharide degradation and could be eliminated completely by selective acid hydrolysis, which also partially cleaved the β-GalNAc-(1→6) linkage. The following structure of the branched pentasaccharide repeating unit was established by 1H and 13C NMR spectroscopy of the O-polysaccharide and O-deacetylated polysaccharide, as well as products of partial acid hydrolysis:Figure optionsDownload full-size imageDownload as PowerPoint slide

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