NMR investigation of the complexation and chiral discrimination of pyrazole sulfonamide derivatives with cyclodextrins

The complexes formed between six original chiral diaryl-pyrazole sulfonamide derivatives, displaying poor solubility, and various CDs (native α-, β- and γ-CDs, hydroxypropylated HP-β-CD, methylated Me-β-CD or amino NH2-β-CD) were studied by 1D and 2D 1H NMR at physiological pH in order to determine their apparent binding constant, stoichiometry and structure of the supramolecular assembly. For some complexes, the spectra obtained for free racemic compound and for racemic compound in presence of CD indicate a splitting of signal(s). Additional experiments with pure enantiomer and enriched enantiomer allow us to attribute this behavior to chiral discrimination. The complexing ability of the native β-CD towards our compounds appears the most promising since binding values around 7 × 102 M−1 are obtained. The two-dimensional ROESY (1H-1H) experiments prove the inclusion of the aliphatic part of the compound in the CD cavity. It is noteworthy that this inclusion occurs via the smaller opening of the cavity.