Enantiomer Separations by Capillary Electrophoresis

Stereoselective enrichment and determination of citalopram enantiomers by cation-selective exhaustive injection and sweeping coupled with cyclodextrin modified electrokinetic chromatography

An highly sensitive, rapid and enantioselective method was developed for the enantioseparation and determination of citalopram enantiomers by cation selective exhaustive injection-sweeping-cyclodextrin modified electrokinetic chromatography (CSEI-sweeping-CDEKC). The optimized conditions were: 50 mM pH 3.0 phosphate solution with 25 mg·mL^-1 S-β-CD used as background buffer, 50 mbar 300 s hydrodynamical injection of 150 mM pH 3.0 NaH₂PO₄ buffer followed with 5 s water plug, 10 kV 600 s electrokinetic sample injection, -20 kV CDEKC run. Under the optimized conditions, the resolution was Rs=8.04, the enrichment factor as up to 2163 folds, the LOD values were: 3.6 ng·mL^-1 for R-citalopram, 4.1 ng·mL^-1 for S-citalopram, and 3 ng·mL^-1 for both enantiomers in plasma samples. This new method showed good precision, repeatability and stability, which had been successfully applied to the impurity inspection of escitalopram oxalate and the stereoselective pharmacokinetic study of citalopram enantiomers.

Enantioresolution and Binding Affinity Studies on Human Serum Albumin: Recent Applications and Trends

The interaction between proteins and drugs or other bioactive compounds has been widely explored over the past years. Several methods for analysis of this phenomenon have been developed and improved. Nowadays, increasing attention is paid to innovative methods, such as high performance affinity liquid chromatography (HPALC) and affinity capillary electrophoresis (ACE), taking into account various advantages. Moreover, the development of separation methods for the analysis and resolution of chiral drugs has been an area of ongoing interest in analytical and medicinal chemistry research. In addition to bioaffinity binding studies, both HPALC and ACE al-low one to perform other type of analyses, namely, displacement studies and enantioseparation of racemic or enantiomeric mixtures. Actually, proteins used as chiral selectors in chromatographic and electrophoretic methods have unique enantioselective properties demonstrating suitability for the enantioseparation of a large variety of chiral drugs or other bioactive compounds. This review is mainly focused in chromatographic and electrophoretic methods using human serum albumin (HSA), the most abundant plasma protein, as chiral selector for binding affinity analysis and enantioresolution of drugs. For both analytical purposes, updated examples are presented to highlight recent applications and current trends.

Analytical methodologies for the enantiodetermination of citalopram and its metabolites

Citalopram (CIT) is a highly selective serotonin reuptake inhibitor (SSRI) frequently used in the treatment of major depressive disorders. It has a chiral centre in its structure and is used in therapy both as a racemic mixture (R,S-CIT) and a pure enantiomer (S-CIT). The differences between the pharmacokinetic and pharmacological profiles of the two enantiomers are well established. Consequently, the development of new efficient chiral analysis methods for their enantiomeric separation is a topic of great actuality. CIT metabolism is stereoselective as it is metabolized in chiral active metabolites, which retain considerable SSRI activity and contribute to the pharmacological effect. Chiral analytical methods are employed for the determination of enantiomeric ratio in pharmaceutical preparations and for monitoring the enantiomer levels in biological samples for therapeutic and toxicologic purposes. The current study reviews the published literature for the chiral analysis of CIT and its metabolites based on chromatographic and electrophoretic methods coupled with UV, fluorescence and mass spectrometry detectors.

Distinguishing enantiomeric amino acids with chiral cyclodextrin adducts and structures for lossless ion manipulations

Enantiomeric molecular evaluations remain an enormous challenge for current analytical techniques. To date, derivatization strategies and long separation times are generally required in these studies, and the development and implementation of new approaches are needed to increase speed and distinguish currently unresolvable compounds. Herein, we describe a method using chiral cyclodextrin adducts and structures for lossless ion manipulations (SLIM) and serpentine ultralong path with extended routing (SUPER) ion mobility (IM) to achieve rapid, high resolution separations of d and l enantiomeric amino acids. In the analyses, a chiral cyclodextrin is added to each sample. Two cyclodextrins were found to complex each amino acid molecule (i.e. potentially sandwiching the amino acid in their cavities) and forming host-guest noncovalent complexes that were distinct for each d and l amino acid pair studied and thus separable with IM in SLIM devices. The SLIM was also used to accumulate much larger ion populations than previously feasible for evaluation and therefore allow enantiomeric measurements of higher sensitivity, with gains in resolution from our ultralong path separation capabilities, than previously reported by any other IM-based approach.