Complexation of steroid hormones:: prednisolone, ethinyloestradiol and estriol with β-cyclodextrin.: An aqueous 1H NMR study

The inclusion complexes of beta-cyclodextrin (beta-CD) with prednisolone 1, ethinyloestradiol 2 and estriol 3 in aqueous solution were investigated using H-1 NMR and molecular modelling. The NMR spectra of the steroids studied in the presence of beta-CD are fully assigned and interpreted by means of 2D GCOSY and NOESY spectra. The parallel interpretation of beta-CD chemical shift changes and dipolar contacts allows the mode of binding to be established. On the basis of ROESY data, the "low resolution" beta-cyclodextrin complexes of 1, 2 and 3 have been determined by multistep restrained molecular dynamics calculations. Calculated structures of beta-cyclodextrin complexes with 1, 2 and 3 fully agree with experimental data. Combined approaches allow the distinction of weak nonspecific binding for 1 as compared to stronger, "through cavity", inclusion established for 2 and 3.