Bezhan Chankvetadze

Enantioseparations in capillary electromigration techniques : recent developments and future trends

This review summarizes the current status of enantioseparations using capillary electromigration techniques and gives the authors insights on the selected fundamental aspects and future trends in this field. The most recent developments in the field of chiral separations using capillary electrophoresis (CE) and capillary electrochromatography (CEC) are summarized. The status of chiral electromigration techniques is evaluated tacking into account the most recent developments in related techniques such as chiral HPLC, GC and SFC.

Recent developments on polysaccharide-based chiral stationary phases for liquid-phase separation of enantiomers.

This paper summarizes recent developments in the synthesis, application and mechanistic studies on polysaccharide-based chiral stationary phases (CSPs) for liquid phase separation techniques. Together with applications in conventional high-performance liquid chromatography (HPLC) applications in nano-liquid chromatography (nano-LC), capillary electrochromatography (CEC), super/sub-critical fluid chromatography (SFC) and preparative and product scale separations are also summarized. In the final part of the overview mechanistic aspects and some unusual effects observed in HPLC with these materials are shortly discussed and the authors view regarding future trends in this field is provided.

Separation selectivity in chiral capillary electrophoresis with charged selectors

This review summarizes the separation selectivity in chiral capillary electrophoresis with charged selectors. Different parameters for a description of the separation selectivity, i.e., the absolute and the relative mobility difference between the enantiomers, the ratio of apparent mobilities and the ratio of effective mobilities as well as the intrinsic (recognition) selectivity, are compared. The electrophoretic mobility of the enantiomers and their migration with the electroosmotic flow are discussed from the viewpoint of separation selectivity. The affinity and mobility-related contributions in the separation selectivity with charged chiral selectors are separately considered. The selectivity of the separations using charged chiral selectors as carriers, in systems with a combination of chiral selectors as well as selectivity in chiral capillary electrochromatography are also briefly addressed.

Enantiomer separation of drugs by capillary electromigration techniques

The review summarizes the most recent developments in the field of enantioseparation of chiral drugs using capillary electromigration techniques. The basic principles of enantioseparations in CE are discussed. Recent developments in sample introduction, separation and detection in capillary electrophoresis and capillary electrochromatography are summarized. The applications are arbitrarily divided into the following three groups: (a) racemates and artificial mixtures of enantiomers, (b) drug forms and (c) chiral drugs and their metabolites in biological fluids. Among the various techniques involved the relatively new developments such as CEC in aqueous and nonaqueous buffers, on-line CE-MS coupling, etc. are emphasized.

Chloromethylphenylcarbamate derivatives of cellulose as chiral stationary phases for high-performance liquid chromatography

A new class of eight chloromethylphenylcarbamate derivatives of cellulose was prepared by introducing both an electron-donating methyl group and an electron-withdrawing chloro group on to the phenyl moieties and their chiral recognition abilities were evaluated as chiral stationary phases (CSPs) for high-performance liquid chromatography. The superiority of these derivatives over dichloro- and dimethylphenylcarbamates of cellulose as CSPs was demonstrated for some racemic compounds. The elution order and enantioselectivity were greatly dependent on the positions of the substituents. Meta- and para-disubstituted derivatives showed higher chiral recognition than ortho- and meta- or para- disubstituted derivatives. The correlation between the chemical shifts of the NH protons of the carbamate moieties and the enantiomer-resolving abilities of the derivatives is discussed. Some of the derivatives were effective CSPs in both normal- and reversed- phase conditions and could efficiently separate some chiral drug enantiomers.

Enantioseparations by capillary electrochromatography.

The review summarizes recent developments in enantioseparations by capillary electrochromatography (CEC). Selected fundamental aspects of CEC are discussed in order to stress those features which may allow the success of this technique in the competitive field of enantioseparations. In addition, the comparative characteristics of the different modes of chiral CEC and the stationary phases are presented. The effects of the characteristics of the stationary and liquid phases and operational conditions on the separation results are discussed. Finally, some future trends are briefly addressed.

Enantioseparations in normal- and reversed-phase nano-high-performance liquid chromatography and capillary electrochromatography using polyacrylamide and polysaccharide derivatives as chiral stationary phases

Enantioseparations of chiral compounds with different structures (β-blockers, benzodiazepines, diuretica, etc.) were performed in fused-silica capillaries packed with silica gel which was modified by covalent attachment of poly-N-acryloyl-l-phenylalanineethylester (Chiraspher®) or by coating with cellulose tris(3,5-dimethylphenylcarbamate). Three different separation modes, normal- and reversed-phase nano-HPLC and capillary electrochromatography (CEC) with and without pressure-assistance were performed in these capillaries using essentially the same experimental set-up. This allows a more reliable comparison of the different techniques. Nano-HPLC separations in the normal-phase mode gave relatively high peak efficiency compared to HPLC in regular size columns. However, under the experimental conditions of this study no significant gain in separation efficiency could be obtained by changing from pressure-driven to electrically-driven migration of the solutes.

Enantioseparation of selected chiral sulfoxides using polysaccharide-type chiral stationary phases and polar organic, polar aqueous-organic and normal-phase eluents.

HPLC enantioseparation of selected chiral sulfoxides was studied using cellulose and amylose phenylcarbamate derivatives as chiral stationary phases (CSPs). The contributions of various functional groups of a chiral analyte as well as the polysaccharide derivatives in the analyte retention and chiral recognition were evaluated. A very high enantioseparation factor exceeding 110 was observed in the enantioseparation of 2-(benzylsulfinyl)benzamide (BSBA) on cellulose tris(3,5-dichlorophenylcarbamate) (CDCPC) CSP by using 2-propanol as a mobile phase. The enantiomer elution order was opposite on cellulose and amylose phenylcarbamates. For the polysaccharide-type CSPs, pure alcohols such as methanol, ethanol and 2-propanol represent a valuable alternative to more common alcohol-hydrocarbon and reversed-phase eluents.

Dimethyl-, dichloro- and chloromethylphenylcarbamates of amylose as chiral stationary phases for high-performance liquid chromatography

Abstract Twelve dimethyl-, dichloro- and chloromethylphenylcarbamate derivatives of amylose were prepared and their chiral recognition abilities were evaluated as chiral stationary phases for high-performance liquid chromatography. ortho-Substituted phenylcarbamate derivatives of amylose showed high chiral recognition abilities, although cellulose phenylcarbamate derivatives with ortho substituents on the phenyl moiety showed low chiral recognition. The superiority of 5-chloro-2-methylphenylcarbamate over the corresponding dimethyl- and dichlorophenylcarbamate derivatives of amylose was demonstrated. The roles of the NH residue of the carbamate moieties and methyl and chloro groups in chiral recognition were elucidated using IR and 1H NMR spectroscopic data. The tris(5-chloro-2-methylphenylcarbamate) of amylose exhibited the highest chiral recognition ability among the amylose derivatives synthesized, and can be used for the separation of some chiral drug enantiomers.

Separation of enantiomers with charged chiral selectors in CE

In this short overview the major developments in separation of enantiomers with charged chiral selectors are summarized in CE. The advantages of charged chiral selectors in comparison with their uncharged analogues are emphasized from the viewpoints of higher flexibility, higher and alternative separation selectivity, as well as alternative chiral recognition mechanism.