Experimental and theoretical study on chiral recognition mechanism of ketoconazole enantiomers using heptakis (2,3,6-tri-O-methyl)-β-cyclodextrin

Abstract

Capillary electrokinetic chromatography (EKC) has been established as a versatile and robust capillary electrophoresis (CE) method for the separation of enantiomers. One of the most attractive advantages of EKC for the separation of enantiomers is its ease of change of separation media in method development. The separation solution can easily be altered to find the optimum separation media and one can also use an expensive chiral selector because small amounts of it are required. This work aims to develop experimental and theoretical analysis of the chiral separation of ketoconazole using EKC and molecular modelling study, respectively. In the first part of the study, several cyclodextrins (CD) as the chiral selectors (CS) namely α-cyclodextrin, sulfated β-cyclodextrin, (2-hydroxylpropyl)-β-cyclodextrin, heptakis(2,6-di-O-methyl)-β-cyclodextrin, and heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin were screened. CDs were initially chosen as they are easily available and cheap. Heptakis (2,3,6-tri-O-methyl)-β-cyclodextrin (TMβCD) exhibited a higher enantioselectivity power compared with other tested CDs. The influence of TMβCD concentration, buffer pH, buffer concentration, separation temperature and applied voltage were investigated. The optimum conditions for chiral separation of ketoconazole was achieved using 10 mM phosphate buffer at pH 3.0 containing 20 mM TMβCD with an applied voltage of 30 kV at 35°C with 5 s injection time (hydrodynamic injection). The ketoconazole enantiomers were resolved in less than 10 min (Rs 1.79). In order to understand possible chiral recognition mechanisms of ketoconazole with TMβCD, host-guest binding procedures of TMβCD and ketoconazole were studied using the semi-empirical PM3 calculations.________________________________________GRAPHICAL ABSTRACT

Theoretical and Molecular Docking Study of Ketoconazole on Heptakis(2,3,6‐tri‐O‐methyl)‐β‐cyclodextrin as Chiral Selector

“…This study found that the inclusion mechanism of TMβCD and ketoconazole is favored by the inclusion of a dichlorophenyl moiety and imidazole group towards the wider rim / secondary hydroxyl group of the TMβCD, which is correlated with our previous study, where we manually modeled the inclusion of the complexes. In our previous study, Model A, which is insertion of the dichlorophenyl moiety towards the wider rim of TMβCD, was found as the most favorable inclusion as compared with Model B.…”

“…However, to the best of our knowledge, the chiral recognition mechanism of the four enantiomers of ketoconazole on heptakis(2,3,6‐tri‐ O ‐methyl)‐β‐cyclodextrin (TMβCD) has not yet been reported thus far using docking studies. Our previous study discussed the theoretical studies of chiral recognition mechanism of ketoconazole using a different approach by manually placing the ketoconazole inside the CD cavity. However, it does not take other spatial arrangements into account.…”

Enantioseparation of ketoconazole and miconazole by capillary electrophoresis and a study on their inclusion interactions with β‐cyclodextrin and derivatives

“…19 Enantioseparation by CE offers many advantages such as short analysis time, 3 little amount of chiral selector, analytes and buffer, and wide range of applications. 22 The selection of various chiral selectors that make CE an important and a versatile tool in enantioseparation have been previously reviewed, which include native and/or derivatized cyclodextrin (CD), protein, crown-ethers, chiral surfactants, metal-chiral amino acid complexes and macrocyclic antibiotics. 23 Among these, CD and their derivatives are the most popular chiral additives attributed to its characteristic such as high-resolution capability towards racemic compounds.…”

“…Figure 1 shows (R)-miconazole and (S)-miconazole, as well as (2R, 4S)-ketoconazole and (2S, 4R)-ketoconazole. 22,25 Details about the antifungal and biological properties, pharmaceutical and toxicity profiles of both compounds remain insufficient due to limited amounts of pure individual enantiomers available for study. 26 Hence, to the knowledge of the literature, the performances of ketoconazole and miconazole are stereoselective.…”

“…28 Nowadays, integration of molecular modelling and experimental technique in exploring the molecular recognition mechanisms has gained interest among the researchers. By combining the application of CE and the aid of computational technique, a deeper understanding of the enantioseparation process and formation of inclusion complex within the host and various guests 22 can be achieved and easily visualised.…”