Chiral separations by non-aqueous capillary electrophoresis in DMSO-based background electrolytes.

Capillary electrophoresis (CE) is a powerful technique for enantioseparations due to its high separation efficiency, high versatility, speed of analysis and low consumption of samples and reagents. Non-aqueous capillary electrophoresis (NACE) appears as a promising technique to perform enantioseparations when the drugs, chiral selectors or samples are non-water soluble. Chiral separations have been performed by NACE mainly using alcoholic solvents as BGEs, with problems of current breakdowns and changes in the BGE composition, due to their high volatility. In this work, the suitability of DMSO as BGE in NACE has been evaluated. Different experimental variables affecting the enantioresolution of three drugs have been evaluated, finally achieving complete enantioresolution of two drugs (verapamil, Rs=1.5 and pindolol, Rs=2.0) and partial resolution of the third one (fenfluramine, Rs=1.2). DMSO has been demonstrated to be a good alternative to methanolic BGEs in NACE.

Modeling the chiral resolution ability of highly sulfated ß-cyclodextrin for basic compounds in electrokinetic chromatography.

Despite the fact that extensive research in the field of enantioseparations by capillary electrophoresis has been carried out, it is difficult to predict whether a concrete chiral selector would be useful for the separation of a racemic compound. Hence, several experimental effort is necessary to test the abilities of individual chiral selectors, usually by trial and error procedures. Thus, the enantioseparation of a new racemate becomes a time- and money-consuming task. In this work, the ability of highly sulfated ß-cyclodextrin (HS-ß-CD) as chiral selector in electrokinetic chromatography (EKC) is modeled for the first time, using exclusively directly-available structural data of forty compounds (structurally unrelated basic drugs and pesticides). A discriminant partial least squares (PLS)-based quantitative structure-property relationship (QSPR) approach is simplified, resulting in a consistent, predictive and descriptive model. It is converted into an explicit equation able to predict the enantioresolution level (Rs) of new compounds, from four structure properties available in an on-line open database: logarithm of octanol-water partition coefficient estimated at pH 7.4 (lgD), polar surface area (PSA), number of hydrogen bond donors (HBD) and acceptors (HBA). For the cases in which the model predicts good Rs only in concrete experimental conditions, a Box-Behnken experimental design is proposed for the fast PLS-based optimization of the most influential experimental variables: cyclodextrin concentration, temperature and pH.

In-line capillary electrophoretic evaluation of the enantioselective metabolism of verapamil by cytochrome P3A4.

In this paper a methodology for the in-line evaluation of enantioselective metabolism by capillary electrophoresis has been developed and applied to the study of verapamil metabolism by cytochrome P3A4. The developed methodology comprises an in-capillary reaction step carried out by electrophoretically mediated microanalysis and a separation step in which highly sulfated ß-cyclodextrin with partial filling technique has been employed as chiral selector for verapamil and norverapamil enantiomers resolution, joining the advantages of both methodologies in a unique assay. Kinetic parameters of the enzymatic reaction (Km and Vmax) have been evaluated for both verapamil enantiomers by non-linear fitting of experimental data obtained under intermediate precision conditions to Michaelis-Menten equation. Km and Vmax estimated values were 51±9 µM and 22±2 pmol min(-1) (pmol CYP)(-1) for S-VER and 47±9 µM and 21±2 pmol min(-1) (pmol CYP)(-1) for R-VER. Consequently, slight enantioselectivity was found for the CYP3A4 metabolism of verapamil. However, since confidence intervals of estimates overlap, we cannot assure a significant enantioselectivity. Intrinsic clearance values were also estimated from Km and Vmax for both enantiomers.

On the zopiclone enantioselective binding to human albumin and plasma proteins. An electrokinetic chromatography approach.

In this work, a methodology for the chiral separation of zopiclone (ZPC) by electrokinetic chromatography (EKC) using carboxymethylated-ß-cyclodextrin as chiral selector has been developed and applied to the evaluation of the enantioselective binding of ZPC enantiomers to HSA and total plasma proteins. Two mathematical approaches were used to estimate protein binding (PB), affinity constants (K(1)) and enantioselectivity (ES) for both enantiomers of ZPC. Contradictory results in the literature, mainly related to plasma protein binding reported data, suggest that this is an unresolved matter and that more information is needed. Discrepancies and coincidences with previous data are highlighted.