Structural study of a highly O-acetylated core of Legionella pneumophila serogroup 1 lipopolysaccharide

A core oligosaccharide was obtained after mild acid degradation of Legionella pneumophila serogroup 1 lipopolysaccharide (LPS). On the basis of chemical, GLC-MS, 1H, and 13C NMR spectroscopic data, it was found that the oligosaccharide obtained is a highly O-acetylated heptasaccharide having the following structure: where Kdo is 3-deoxy-d-manno-octulosonic acid and QuiNAc is 2-acetamido-2,6-dideoxyglucose. In the LPS, the O-specific polysaccharide chain is linked to position 3 of the terminal rhamnosyl group and is cleaved during degradation of the LPS. The degradation also induced partial migration and partial removal of the O-acetyl group from the terminal rhamnosyl group which, together with the occurrence of the reducing Kdo residue in multiple forms, contributes to the heterogeneity of the isolated core oligosaccharide. No such highly O-acetylated core oligosaccharide has been reported so far for LPS of Gram-negative bacteria.