Structural and immunochemical studies of O‐specific polysaccharide of Proteus vulgaris 5/43 belonging to OX19 group (O‐variants)

O‐specific polysaccharide was obtained on mild acid degradation of lipopolysaccharide of Proteus vulgaris 5/43 belonging to OX19 (O‐variants). It was found to contain d ‐glucose, 2‐acetamido‐2‐deoxy‐ d ‐glucose, and 2‐acetamido‐2,6‐dideoxy‐ l ‐glucose (QuiNAc, N ‐acetyl‐ l ‐quinovosamine) in the ratio of about 1:2:1, the last‐named sugar being rather uncommon for bacterial antigens. A computer‐assisted 13 C‐NMR‐based analysis, methylation analysis, and selective cleavage with anhydrous hydrogen fluoride and dilute hydrochloric acid were applied for structural elucidation of the polysaccharide and the following structure was established: → 2)‐β‐ d ‐Glc p ‐(1 → 6)‐α‐ d ‐Glc p NAc‐(1 → 3)‐α‐ l ‐Qui p NAc‐(1 → 3)‐β‐ d ‐Glc p NAc‐(1 →. Serological studies of the O‐antigen and oligosaccharides derived therefrom revealed the importance of the trisaccharide fragment β‐ d ‐Glc p ‐(1 → 6)‐α‐ d ‐Glc p NAc‐(1 → 3)‐α‐ l ‐Qui p NAc in manifesting the antigenic specificity. Serological cross‐reactions were demonstrated between lipopolysaccharides of P. vulgaris 5/43, 8/44, and OX19 strains.