Chemical characterization of the O-specific chain of Sphaerotilus natans ATCC 13338 lipopolysaccharide

The chemical structure of the O-specific chain of the Sphaerotilus natans lipopolysaccharide was established. The isolated polysaccharide moiety contained neutral sugars (rhamnose, glucose, and l-glycero-d-manno-heptose), 3-deoxy-d-manno-octulosonic acid (Kdo), phosphate and ethanolamine. Alditol acetate and methylation analyses showed that the O-specific chain contained linear pentasaccharide repeating units, composed of four units of rhamnose, substituted at 3-position, and one unit of glucose, substituted at 4-position. Oxidation by chromium trioxide showed that all sugars were α-linked. The structure proposed for the O-specific chain has been confirmed by periodate oxidation, and by ¹H-and ¹³C-NMR spectroscopic studies for the original and the Smith-degraded PS moiety. The O-specific unit of the S. natans LPS has the following structure: $$\begin{gathered} \to 4) - Glup - (1\xrightarrow{a}3) - Rhap - (1\xrightarrow{a}3) - Rhap - \hfill \\ - (1\xrightarrow{a}3) - Rhap - (1\xrightarrow{a}3) - Rhap - (1]_n \xrightarrow{a} \hfill \\ \end{gathered} $$