Structure of the O‐polysaccharide and serological cross‐reactivity of the Providencia stuartii O33 lipopolysaccharide containing 4‐( N ‐acetyl‐ d ‐aspart‐4‐yl)amino‐4,6‐dideoxy‐ d ‐glucose

The O‐polysaccharide of Providencia stuartii O33 was obtained by mild acid degradation of the lipopolysaccharide and the following structure of the tetrasaccharide repeating unit was established:→6)‐α‐ d ‐Glc p NAc‐(1→4)‐α‐ d ‐Gal p A‐(1→3)‐α‐ d ‐Glc p NAc‐(1→3)‐β‐ d ‐Qui p 4N(Ac‐ d ‐Asp)‐(1→, where d ‐Qui4N(Ac‐ d ‐Asp) is 4‐( N ‐acetyl‐ d ‐aspart‐4‐yl)amino‐4,6‐dideoxy‐ d ‐glucose. Structural studies were performed using sugar and methylation analyses and NMR spectroscopy, including conventional 2D 1 H, 1 H COSY, TOCSY, NOESY and 1 H, 13 C HSQC experiments as well as COSY and NOESY experiments in an H 2 O–D 2 O mixture to reveal correlations for NH protons. The O‐polysaccharide of P. stuartii O33 shares an α‐ d ‐Glc p NAc‐(1→3)‐β‐ d ‐Qui p 4N(Ac‐ d ‐Asp) epitope with that of Proteus mirabilis O38, which seems to be responsible for a marked serological cross‐reactivity of anti‐ P. stuartii O33 serum with the lipopolysaccharide of the latter bacterium. P. stuartii O33 is serologically related also to P. stuartii O4, whose O‐polysaccharide contains a lateral β‐ d ‐Qui4N(Ac‐ l ‐Asp) residue.