Betulonic acid-cyclodextrins inclusion complexes

Betulonic acid (BA) is a pentacyclic lupane-type triterpenoid possessing valuable pharmacological activities, exhibiting very low water solubility. Inclusion complexes between the substance and cyclodextrins (CDs) were obtained in order to improve its solubility and consequently its bioavailability. The aim of this study was to investigate the guest-host interaction of BA with gamma-cyclodextrin (gamma-CD) and its derivative, 2-hydroxypropyl-gamma-cyclodextrin (HP-gamma-CD), in solution and in solid state in order to prove the formation of inclusion complexes between the components. The kneading method was used for the inclusion complexes preparation, and different analytical techniques such as thermal analysis, powder X-ray diffractometry, universal attenuated total reflectance Fourier transform IR spectroscopy (UATR-FTIR) and UV spectroscopy were employed to investigate the interaction between substances. The stoichiometry of the inclusion complex BA/HP-gamma-CD was found to be 1:1 by employing continuous variation method, and the apparent stability constant was calculated as 1855.55 M-1 using Benesi-Hildebrand equation. Structural studies of the inclusion complexes were carried out using molecular modeling techniques in order to explain the complexation mechanism. The results of this study confirm the formation of inclusion complexes between BA and cyclodextrins both in solution and in solid state.