Chiral recognition of abacavir enantiomers by (2-hydroxy)propyl-β-cyclodextrin: UHPLC, NMR and DFT studies

Abstract

The diastereomeric complexation of both abacavir (ABA) and its enantiomer (ABAE) with (2-hydroxy)propyl-β-cyclodextrin (2HPβCD) with a degree of substitution of seven was studied. The apparent binding constants of diasteromeric complexes, ABA-2HPβCD and ABAE-2HPβCD were determined by ultra high-pressure liquid chromatography (UHPLC) and found to be 517.0 and 684.4 M−1 respectively. The stoichiometry of the complexes was determined by UHPLC and by the continuous variation method using nuclear magnetic resonance spectroscopy giving 1:1 complexes. The apparent binding constants decrease as the temperatures increases. The observed enantio-differentiation was analyzed theoretically by density functional theory at the PBE/6-31 g** level using a polarizable continuous model (PCM) for solvent effects, the most stable complexes are the ones in which the chiral cyclopentenyl moiety is included in the cavity of CD and the protonated purine ring interact with the hydroxypropyl groups of 2HPβCD. The differences in stability of diasteromeric complexes, due to different intermolecular interactions are consistent with experimental data, providing further insights in the formation of inclusion complexes.