Structural studies of the O‐antigenic polysaccharide of Fusobacterium necrophorum

The O-specific polysaccharide component of the lipopolysaccharide produced by Fusobacterium necrophorum is of the teichoic acid type, with repeating units connected by phosphoric diester linkages. Dephosphorylation of the polysaccharide by treatment with aqueous hydrogen fluoride yielded a carbohydrate composed of a trisaccharide linked to an acidic component. This product, and the polysaccharide, were investigated by chemical methods and 1H-, 13C-, 31P- and 15N-NMR spectroscopy and the former also by fast-atom-bombardment mass spectrometry. It is proposed that the polysaccharide is composed of repeating units having the following structure, in which Fuc represents fucose (6-deoxy-galactose), Am represents an acetamidino group and Sug 2,4-diamino-2,4,6-trideoxy-d-glucose (‘bacillosamine’) acetylated at the 2-position and acylated with a (S)-3-hydroxybutanoic acid at the 4-position. The acid was identified as a 2-amino-2-deoxy-2-C-methylpentonic acid (2-amino-2-methyl-3,4,5-trihydroxypentanoic acid). The configuration of this acid remains to be determined.