Enantioseparation and impurity determination of cinacalcet using solvent modified capillary zone electrophoresis and Quality by Design: study of the complexation with cyclodextrins by molecular modeling and NMR

The combination of capillary electrophoresis (CE), NMR and Molecular Modeling is presented to evaluate in depth the enantioselective complexation with cyclodextrins (CDs) of the new therapeutic agent Cinacalcet Hydrochloride (CINA), used for the treatment of chronic kidney disease. In our previous pharmaceutical quality control study, the enantioseparation and impurity determination of CINA was carried out using as operating mode solvent modified capillary zone electrophoresis with the addition of 2-hydroxypropyl-γ-cyclodextrin (HPγCD). The method was developed following Quality by Design (QbD) approach, leading to visualize the design space. The incorporation of QbD strategy into CE method development enabled dealing with optimization challenges in a rational and systematic way, providing the key for a better comprehension of the separation. In the scouting phase neutral and charged CDs were tested, showing different separation abilities. In electromigration techniques the separation depends on the affinity towards the chiral selector, but also on the different electrophoretic mobility of the formed enantiomer-chiral selector complexes. NMR spectroscopy provides a powerful tool to gain insight into the fine interactions between the analytes and the chiral selectors. Unlike other techniques, the main advantage of NMR spectroscopy is that it can gather information in conditions that mimic those of the CE runs, in particular pH, temperature and ionic strength. The molecular association of CINA with CDs, expressed by the binding constant of the inclusion complex, was calculated from the changes in the 1H NMR spectra of the drug in the presence of the cyclodextrin. The stoichiometry of the complex was calculated by use of the continuous variation method (Job Plot). Molecular Modeling studies complemented the obtained results in order to achieve a better understanding of the intermolecular affinities and recognition mechanism. The complexation behavior of CINA enantiomers and CDs was evaluated by dynamic simulations. Different geometries and conformations were designed and the stability of the inclusion complexes were calculated. The docking energies indicated that the most stable complexes were obtained with (2-carboxyethyl)-β-cyclodextrin. The obtained data showed a good agreement with the CE results.