Structure of the O-polysaccharide from the lipopolysaccharide of Providencia alcalifaciens O28

An O-polysaccharide and oligosaccharides were isolated by GPC following mild acid degradation of the lipopolysaccharide of Providencia alcalifaciens O28. The O-polysaccharide was studied by sugar and methylation analyses, 1H and 13C NMR spectroscopy, including 2D ROESY and H-detected 1H,13C HSQC and HMBC experiments, and the following structure of the branched pentasaccharide repeating unit was established:This structure was confirmed by ESI MS of the isolated tridecasaccharide consisting of the lipopolysaccharide core and one O-polysaccharide repeat. The ESI mass spectrum also enabled inferring the composition of the core oligosaccharide.

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► We isolated a lipopolysaccharide from a strain of Providencia alcalifaciens O28.
► Carbohydrates were released by mild acid delipidation of the lipopolysaccharide.
► The O-polysaccharide was studied by chemical methods and 2D NMR spectroscopy.
► The core and O-unit-bearing core oligosaccharides were studied by ESI MS.
► A new structure of a pentasaccharide repeat of the O-polysaccharide was established.