Complete NMR structural elucidation of the capsular polysaccharide adjuvant from klebsiella I-714

Abstract

The capsular polysaccharide (CPS) produced by the non-pathogenic- Klebsiella strain I-714, selected for its immunomodulating activity, has been purified and almost completely detoxified in a previous study [Adam, O., Vercellone, A., Paul, F, Monsan, P. F. and Puzo, G. (1995) Anal. Biochem. 225, 321-327]. The present report concerns the structural elucidation of this CPS by several one-dimensional and two-dimensional 1H-NMR and 13C-NMR experiments performed on the native molecule. It was found to be a high molecular-mass branched polymer constituted by a hexasaccharide repeating unit of following structure : 4)-α-L-Rhap-(1→3)-β-D-Galp-(1→2)-α-L-Rhap(1→4)-β-D-GlcpA-(1→3)-{α-L -Rhap-(1→2)-}-α-D-Galp-(1. The presence of two glycosidic substitutions on the Galp residue resulted in a strong overlapping of its proton signals, preventing direct assignment of both proton and carbon resonances. However, assignment could be achieved using the two-bond and three-bond 1H-13C heteronuclear coupling observed in the 1H-13C heteronuclear multiple-bond correlation (HMBC) spectrum.