Enantioseparations in nonaqueous capillary electrophoresis using charged cyclodextrins

Single isomer cyclodextrins as chiral selectors in capillary electrophoresis

Since decades, cyclodextrins are one of the most powerful selectors in chiral capillary electrophoresis for the enantioseparation of diverse organic compounds. This review concerns papers published over the last decade (from 2009 until nowadays), dealing with the capillary electrophoretic application of single isomer cyclodextrin derivatives in chiral separations. Following a brief overview of their synthetic approaches, the inventory of the neutral, negatively and positively charged (including both permanently ionic and pH-tunable ionizable substituents) and zwitterionic CD derivatives is presented, with insights to underlying structural aspects by NMR spectroscopy and molecular modeling. CE represents an ideal tool to study the weak, non-covalent supramolecular interactions. The published methods are reviewed in the light of enantioselectivity, enantiomer migration order and the fine-tuning of enantiodiscrimination by the substitution pattern of the single entity selector molecules, which is hardly possible for their randomly substituted counterparts. All the reviewed publications herein support that cyclodextrin-based chiral capillary electrophoresis seems to remain a popular choice in pharmaceutical and biomedical analysis.

Significance and challenges of stereoselectivity assessing methods in drug metabolism

Stereoselectivity in drug metabolism can not only influence the pharmacological activities, tolerability, safety, and bioavailability of drugs directly, but also cause different kinds of drug-drug interactions. Thus, assessing stereoselectivity in drug metabolism is of great significance for pharmaceutical research and development (R&D) and rational use in clinic. Although there are various methods available for assessing stereoselectivity in drug metabolism, many of them have shortcomings. The indirect method of chromatographic methods can only be applicable to specific samples with functional groups to be derivatized or form complex with a chiral selector, while the direct method achieved by chiral stationary phases (CSPs) is expensive. As a detector of chromatographic methods, mass spectrometry (MS) is highly sensitive and specific, whereas the matrix interference is still a challenge to overcome. In addition, the use of nuclear magnetic resonance (NMR) and immunoassay in chiral analysis are worth noting. This review presents several typical examples of drug stereoselective metabolism and provides a literature-based evaluation on current chiral analytical techniques to show the significance and challenges of stereoselectivity assessing methods in drug metabolism.

Clarithromycin as a chiral selector for enantioseparation of basic compounds in nonaqueous capillary electrophoresis

The first use of macrolide antibiotic clarithromycin (CLM) in nonaqueous media for enantioseparation (partial or baseline) of the following compounds: alprenolol, atenolol, metoprolol, clenbuterol, methoxyphenamine, pindolol, propranolol, sotalol, synephrine, labetalol, and fenoterol is reported. Each analysis took less than 15 min. To find optimal separation conditions, some properties of CLM (adsorption, solubility), as well as the effect of experimental parameters on the enantioseparation of analytes (background electrolyte composition, chiral selector concentration, temperature, and applied voltage) were studied. The best chiral resolution was achieved in methanolic solution of 100 mM citric acid, 10 mM NaOH, 240-300 mM H3 BO3 , and 60-75 mM CLM. Using the proposed procedure, adsorption of CLM on the capillary wall was negligible and the repeatability of the migration times (RSD) was as good as 1.6%. For the analysis of propranolol, the linearity was achieved in the concentration range 2.5 × 10(-2) - 3.0 × 10(-1) mg/mL with the LODs (3 × S/N) being equal 2.6 × 10(-3) mg/mL and 2.8 × 10(-3) mg/mL for the first and the second enantiomers, respectively. Linear range for metoprolol enantiomers was 1.0 × 10(-2) -1.6 × 10(-1) mg/mL. The LODs (3 × S/N) were determined as 2.8 × 10(-3) and 3.0 × 10(-3) mg/mL for the first and the second enantiomers, respectively.