NMR studies of the inclusion complex of cloprostenol sodium salt with β-cyclodextrin in aqueous solution

Purpose. Cloprostenol sodium salt (referred as cloprostenol) may be used for the synchronization of estrous cycles in farm animal species. Cyclodextrins (CDs) have potential as drug delivery systems through the formation of inclusion complexes between CDs and drugs. This is the first study of the inclusion complex of cloprostenol with beta-cyclodextrin (beta-CD) in aqueous solution using NMR and 3D molecular dynamics simulations. Methods. 1D proton NMR spectra of beta-CD, a complex of cloprostenol with beta-CD, and cloprostenol in D2O were assigned and confirmed. The cross relaxation interactions from ROESY were used as constraints for 3D molecular modeling studies. Results. In the 2D ROESY of the complex, cross-peaks were observed between the aromatic protons of cloprostenol and protons of the beta-CD as well as between aliphatic protons and protons of the beta-CD. The stoichiometry of the complex was found that beta-CD forms a 1:1 inclusion complex with cloprostenol. The association constant K was 968+/-120 M-1 at 298 K. Conclusions. Aromatic side and/or aliphatic side chains of the cloprostenol is included in the beta-CD while aliphatic side and/or aromatic side chains wraps around beta-CD, respectively. The molecular modeling also confirms that beta-CD forms a 1:1 inclusion complex with cloprostenol.