New mathematic model for predicting chiral separation using molecular docking: Mechanism of chiral recognition of triadimenol analogues

Enantioseparation and molecular modeling study of eight psychoactive drugs on a coated polysaccharide-based chiral stationary phase

The enantioseparation of eight psychoactive drugs has been firstly performed on a coated cellulose-based chiral stationary phase (Chiralcel OJ-H). To obtain optimum separation conditions, the influences of alcohol modifiers and basic/acidic additives have been studied. As a result, except for the partial separation of oxybutynin enantiomers, the other seven drug enantiomers, including mirtazapine, sulpiride, promethazine, citalopram, oxazepam, donepezil, and cyamemazine, have been completely separated. Additionally, for gaining a better insight into the chiral recognition mechanisms, molecular docking was carried out using the Autodock software. Herein, binding energy and conformations of the chiral stationary phase complexes were provided, and it was found that the distinction in enantiomeric conformation determined the number and strength of intermolecular interactions between analytes and chiral stationary phase which resulted in the difference in binding energies of two enantiomers, and ultimately led to the different migration. These modeling results were in accordance with the observed enantioseparation results in high performance liquid chromatography experiments. At last, chiral separation mechanisms have been discussed in detail, and it has been confirmed that hydrogen bond, π-π, hydrophobic interactions, and some special interactions synergistically contributed to the enantioseparation of psychoactive drugs.

Enantioresolution in electrokinetic chromatography-complete filling technique using sulfated gamma-cyclodextrin. Software-free topological anticipation

Few papers have tried to predict the resolution ability of chiral selectors in capillary electrophoresis for the separation of the enantiomers of chiral compounds. In a previous work, we have used molecular information available on-line to establish enantioresolution levels of basic compounds using highly sulfated β-CD (HS-β-CD) as chiral selector in electrokinetic chromatography-complete filling technique (EKC-CFT). The present study is a continuation of this previous work, introducing some novelties. In this work, the ability of sulfated γ-cyclodextrin (S-γ-CD) as chiral selector in EKC-CFT is modelled for the first time. Thirty-three structurally unrelated cationic and neutral compounds (drugs and pesticides) are studied. Categorical enantioresolution levels (RsC, 0 or 1) are assigned from experimental enantioresolution values obtained at different S-γ-CD concentrations. Novel topological parameters connected to the chiral carbon (C^*-parameters) are introduced. Four C^*-parameters and a topological parameter of the whole molecule (aromatic atom count) are the most important variables according to a discriminant partial least squares-variable selection process. It suggests the preponderance of the topology adjacent to the chiral carbon to anticipate the RsC levels. A software-free anticipation protocol for new molecules is proposed. Over the current set of molecules evaluated, 100% of correct anticipations (resolved and non-resolved compounds) are obtained, while anticipation of some compounds remains undetermined. A criterion is introduced to alert on compounds which should not be anticipated.

Computer-aided molecular modeling study of enantioseparation of iodiconazole and structurally related triadimenol analogues by capillary electrophoresis: chiral recognition mechanism and mathematical model for predicting chiral separation

Chiral separation of iodiconazole, a new antifungal drug, and 12 new structurally related triadimenol analogues had been developed by capillary electrophoresis (CE) using hydroxypropyl-γ-cyclodextrin (HP-γ-CD) as the chiral selector. The effect of structural features of analytes on Δt and R(s) was studied under the optimum separation conditions. Using molecular docking technique and binding energy calculations, the inclusion process between HP-γ-CD and enantiomers was investigated and chiral recognition mechanisms were discussed. The results suggest that hydrogen bonding between fluorine at position 4 of the phenyl group beside the chiral carbon and the hydroxyl group on the HP-γ-CD rim and face to face π-π interactions between two phenyl rings highly contributed to the enantiorecognition process between HP-γ-CD and iodiconazole. The N-methyl group beside chiral carbon also played an important role in enantiomeric separation. Additionally, the big difference in binding energy (ΔΔE) highly contributed to good separation in the presence of HP-γ-CD chiral selector, which may be a helpful initial guide for chiral selector selection and predicting the result of enantioseparation. Furthermore, the new mathematical equation established based on the results of molecular mechanics calculations exhibited good capability in predicting chiral separation of these triadimenol analogues using HP-γ-CD mediated CE.

Fundamental aspects of chiral electromigration techniques and application in pharmaceutical and biomedical analysis

Capillary electromigration techniques are often considered ideal methods for the analysis of chiral compounds due to the high resolution power and flexibility of the technique. Therefore, especially capillary electrophoresis using a chiral selector in the background electrolyte, also termed electrokinetic chromatography, has found widespread acceptance in analytical enantioseparations of drug compounds in pharmaceuticals and biological media. Moreover, mechanistic studies on analyte complexation by the chiral selectors have continuously been conducted in an effort to rationalize enantioseparation phenomena. These studies combined capillary electrophoresis with spectroscopic techniques such as nuclear magnetic resonance and/or molecular modeling. The present review focuses on recent examples of mechanistic aspects of capillary electromigration enantioseparations and summarizes recent applications of chiral pharmaceutical and biomedical analysis published between January 2009 and August 2010.