Complete NMR Structural Elucidation of the Capsular Polysaccharide Adjuvant from Klebsiella I‐714

The capsular polysaccharide (CPS) produced by the non‐pathogenic Klebsiella strain 1–714, 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. & Puzo, G. (1995)Anal. Biochem. 225, 321–3271, 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: 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.