3‐C‐Branched aldoses in lipopolysaccharide of phase I Coxiella buurnetii and their role as immunodominant factors

Mild acid hydrolysis with 1% acetic acid (100°C, 15–60 min) of lipopolysaccharide (LPS) isolated from Coxiella burnetii phase I cells leads to a drastic decrease in its serological reactivity as shown by the passive hemolysis test. This decrease in reactivity occurs parallel or even prior to the cleavage of LPS into free lipid A and the polysaccharide moiety. During this mild hydrolysis two unusual sugars (X and Y) are released from the LPS, which were obtained in pure state by thin‐layer chromatography. Analysis of their alditol acetate derivatives by gas chromatography/mass spectrometry revealed that sugar × is a 6‐deoxy‐3‐ C ‐methyl‐hexose and sugar Y a 3‐ C ‐(hydroxymethyl)‐pentose. Using a range of authentic standards and different thin‐layer and gas chromatographic conditions, × could be recognized as 6‐deoxy‐3‐ C ‐methyl‐gulose (virenose), very probably as the l form of this sugar ( l ‐virenose). Y has been identified as 3‐ C ‐(hydroxymethyl)‐lyxose (dihydro‐hydroxystreptose) by comparing it with newly synthesized 3‐ C ‐(hydroxymethyl)‐pentoses (Dahlman, O., Garegg, P. J., Mayer, H., Schramek, Š., unpublished results). Both branched sugars are (at least partially) in terminal positions since methylation analysis of LPS afforded (mainly) their permethylated derivatives. This analysis further showed virenose to be linked in C. burnetii phase I LPS as pyranose and dihydro‐hydroxystreptose as furanose. The terminal linkage and the chemical nature of × and Y are in accordance with the observed acid‐lability of the serological determinants.