Determination of enantiomeric excess for 2,3-dihydroxy-3-phenylpropionate compounds by capillary electrophoresis using hydroxypropyl-beta-cyclodextrin as chiral selector

A new capillary zone electrophoresis (CZE) method was developed to separate three chiral 2,3-dihydroxy-3-phenylpropionate enantiomers using neutral hydroxypropyl-beta-CD (HP-beta-CD) as chiral selector and borate as background electrolyte. The results showed that HP-beta-CD exhibited good enantioselectivity and high resolution was achieved under the optimum condition of pH 10.3, 200 mM borate buffer containing 6% methanol and 50 mM HP-beta-CD at 15 kV and 20 degrees C within 16 min. The precision of the method was <0.9% for migration time and 4.5% for corrected peak area. In addition, the developed method was successfully applied to the determination of enantiomeric excess (ee) of synthetic 2,3-dihydroxy-3-phenylpropionate samples. With this method, low as 0.2% impurity of the undesirable enantiomer in the presence of high amount of target enantiomer was determined. The results demonstrated that the proposed CZE method is a simple and useful technique and is applicable to ee assay of 2,3-dihydroxy-3-phenylpropionate enantiomers.     

Biphasic recognition chiral extraction: A novel method for separation of mandelic acid enantiomers

This article reports a new chiral separation method-biphasic recognition chiral extraction for the separation of mandelic acid enantiomers. Distribution behavior of mandelic acid enantiomers was studied in the extraction system with O,O'-di-benzoyl-(2S,3S)-4-toluoyl-tartaric acid (D-(+)-DTTA) in organic phase and beta-CD derivatives in aqueous phase, and the influence of the types and concentrations of extractants and pH on extraction efficiency was investigated. Hydroxypropyl-beta-cyclodextrin (HP-beta-CD), hydroxyethyl-beta-cyclodextrin (HE-beta-CD), and methyl-beta-cyclodextrin (Me-beta-CD) have stronger recognition abilities for S-mandelic acid than those for R-mandelic acid, among which HP-beta-CD has the strongest ability. D-(+)-DTTA preferentially recognizes R-mandelic acid. pH and the concentrations of extractants have great effects on chiral separation ability. A high enantioseparation efficiency with a maximum enantioselectivity of 1.527 is obtained at pH of 2.7 and the ratio of 2:1 of [D-(+)-DTTA] to [HP-beta-CD]. The obtained results indicate that the biphasic recognition chiral extraction is of stronger chiral separation ability than the monophasic recognition chiral extraction. It may be very helpful to optimize the extraction systems and realize the large-scale production of pure enantiomers.     

Chiral resolutions of (9-anthryl)methoxyacetic acid and (9-anthryl)hydroxyacetic acid by capillary electrophoresis

The resolutions of (9-anthryl)methoxyacetic acid (9AMAA) and (9-anthryl)hydroxyacetic acid (9AHAA) were performed by capillary electrophoresis using hydroxypropyl-beta-cyclodextrin (HP-beta-CD) as a chiral selector. Various factors affecting migration time and resolutions of these compounds were investigated with a run voltage of 20 kV, column temperature 20 degrees C and 20 mM Tris-H(3)PO(4) buffer (pH 6.5) containing 5 mM HP-beta-CD for 9AMAA, or 10 mM HP-beta-CD for 9AHAA, (+/-)-9AMAA and (+/-)-9AHAA were successfully separated at Rs 3.27 and 1.92, respectively.     

The role of pi-acidic and pi-basic chiral stationary phases in the high-performance liquid chromatographic enantioseparation of unusual beta-amino acids

The application of 3,5-dimethylphenyl-carbamoylated-beta-cyclodextrin (Cyclobond I 2000 DMP) and 2,6-dinitro-4-trifluoromethylphenyl-ether-beta-cyclodextrin-based (Cyclobond DNP) chiral stationary phases for the high-performance liquid chromatographic enantioseparation of unusual beta-amino acids is reported. The investigated amino acids were saturated or unsaturated alicyclic beta-3-homo-amino acids and bicyclic beta-amino acids. Prior to chromatographic analyses, all amino acids were transformed to N-3,5-dinitrobenzoyl- or N-3,5-dimethylbenzoyl form to ensure a pi-acidic or pi-basic function and to enhance the pi-acidic-pi-basic interactions between analytes and chiral selectors. Chromatographic results are given as retention, separation and resolution factors. The chromatographic conditions were varied to achieve optimal separation. The sequence of elution of the enantiomers was determined in some cases.     

Preparative Enantioseparation of β‐Substituted‐2‐Phenylpropionic Acids by Countercurrent Chromatography With Substituted β‐Cyclodextrin as Chiral Selectors

Preparative enantioseparation of four β‐substituted‐2‐phenylpropionic acids was performed by countercurrent chromatography with substituted β‐cyclodextrin as chiral selectors. The two‐phase solvent system was composed of n‐hexane‐ethyl acetate‐0.10 mol L‐1 of phosphate buffer solution at pH 2.67 containing 0.10 mol L^‐1 of hydroxypropyl‐β‐cyclodextrin (HP‐β‐CD) or sulfobutylether‐β‐cyclodextrin (SBE‐β‐CD). The influence factors, including the type of substituted β‐cyclodextrin, composition of organic phase, concentration of chiral selector, pH value of the aqueous phase, and equilibrium temperature were optimized by enantioselective liquid–liquid extraction. Under the optimum separation conditions, 100 mg of 2‐phenylbutyric acid, 100 mg of tropic acid, and 50 mg of 2,3‐diphenylpropionic acid were successfully enantioseparated by high‐speed countercurrent chromatography, and the recovery of the (±)‐enantiomers was in the range of 90–91% for (±)‐2‐phenylbutyric acid, 91–92% for (±)‐tropic acid, 85–87% for (±)‐2,3‐diphenylpropionic acid with purity of over 97%, 96%, and 98%, respectively. The formation of 1:1 stoichiometric inclusion complex of β‐substituted‐2‐phenylpropionic acids with HP‐β‐CD was determined by UV spectrophotometry and the inclusion constants were calculated by a modified Benesi‐Hildebrand equation. The results showed that different enantioselectivities among different racemates were mainly caused by different enantiorecognition between each enantiomer and HP‐β‐CD, while it might be partially caused by different inclusion capacity between racemic solutes and HP‐β‐CD. Chirality 27:795–801, 2015. © 2015 Wiley Periodicals, Inc.     

Chiral separation of pheniramine-like 3-phenyl-3-heteroarylpropylamines by CE and HPLC methods

Analytical CE and HPLC methods were developed for the chiral separation of halogen-substituted 3-phenyl-3-(2-pyridyl)propylamines 1-4 (1: 3-(4-fluorophenyl) approximately, 2: 3-(3,4-difluorophenyl) approximately, 3: 3-(4-chlorophenyl) approximately, 4: 3-(3,4-dichlorophenyl) approximately ), 3-(4-fluorophenyl)-3-(2-thiazolyl)propylamine (5), and 3-(4-fluorophenyl)-3-(1-benzylimidazol-2-yl)propylamine (6), which are building blocks for the preparation of very potent arpromidine-type histamine H(2) receptor agonists. All amines were enantioseparated by CE with resolutions of at least 1.8 using alpha-, beta-, or gamma-cyclodextrin (CD) as chiral selectors. With heparin as buffer additive for CE the optical antipodes of 1-4 and 6 were separated with resolutions > or = 1.8. On RP-18 columns the separation of the (+)-(S)-acetylmandelic acid amides of racemic 2 (R = 0.9, alpha = 1.07) and the thioureas prepared by addition of 6 to 2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosyl isothiocyanate (R = 2.0, alpha = 1.20) was successful, whereas the diastereomeric ureas prepared from 3 and (+)-(S)-1-(1-naphthyl)ethyl isocyanate could not be resolved. Separation of the diastereomeric isoindoles prepared from 1-5, o-phthaldialdehyde and 2,3,4,6-tetra-O-acetyl-1-thio-beta-D-glucopyranoside was achieved on a RP-18 phase (R > or = 0.4, a > or = 1.02). Direct separation of the enantiomers of 3 and 4 was achieved on a Cyclobond I column (R > or = 0.9, alpha > or = 1.07). alpha- and beta-CD were also useful as mobile phase additives for HPLC (3 and 4: RP-18 column, beta-CD, R > or = 0.4, alpha > or = 1.03; 3: RP-18 column, alpha-CD: R = 0.5, alpha = 1.04).     

Enantioselective chromatography of alkyl derivatives of 5-ethyl-5-phenyl-2-thiobarbituric acid studied by semiempirical AM1 method

Complexation of alkyl derivatives of 5-ethyl-5-phenyl-2-thiobarbituric acid (2-thiophenobarbital) enantiomers by beta-cyclodextrin was investigated by the AM1 method. The inclusion complexes of beta-cyclodextrin with neutral and anionic forms of these enantiomers have been modeled and energetically optimized. The chiral discrimination of enantiomers was analyzed in terms of differences in the interaction energies. The calculated interaction energies between each enantiomer of the investigated 2-thiobarbiturates and beta-cyclodextrin confirm the ability of beta-cyclodextrin to act as a mobile phase additive in reversed-phase HPLC to separate enantiomers by liquid chromatography and rationalize their order of elution.     

Analysis of optical purity and impurity of synthetic D-phenylalanine products using sulfated beta-cyclodextrin as chiral selector by reversed-polarity capillary electrophoresis

A new capillary electrophoresis (CE) method has been achieved for simultaneous separation and quantification of phenylalanine, N-acetylphenylalanine enantiomers, and prochiral N-acetylaminocinnamic acid, possibly co-existent in reaction systems or synthesized products of D-phenylalanine. The separation was carried out in an uncoated capillary under reversed-electrophoretic mode. Among the diverse charged cyclodextrins (CDs) examined, highly sulfated (HS)-beta-CD as the chiral selector exhibited the best enantioselectivity. The complete separation of the analytes was obtained under the optimum conditions of pH 2.5, 35 mM Tris buffer containing 4% HS-beta-CD, applied voltage -15 kV, and capillary temperature 25 degrees C. Furthermore, the proposed method was applied to the determination of optical purity and trace impurities in three batches of the asymmetric synthetic samples of D-phenylalanine, and satisfactory results were obtained. The determination recoveries of the samples were in the range of 97.8-103.8%, and precisions fell within 2.3-5.0% (RSD). The results demonstrate that this CE method is a useful, simple technique and is applicable to purity assays of D-phenylalanine.     

Evaluation of chiral discrimination of highly negatively charged enantiomers by quaternary ammonium beta-cyclodextrin using 1H NMR

The positively charged quaternary ammonium cyclodextrin, QA-beta-CD, was previously used as a chiral selector to achieve baseline resolution of two of the dianionic enantiomers of disodium 3-(p-isothiocyanatophenoxy)-3-(p-isothiocyanatophenyl)propane-1,2-disulfate by capillary electrophoresis. The basis of the chiral discrimination between QA-beta-CD and the enantiomers was investigated by (1)H NMR spectroscopy. COSY and NOESY spectra were used to infer the role that molecular interactions and the stereocenters have upon association of QA-beta-CD with the enantiomers. A parallel two-step complexation model is used to rationalize the NMR and the chiral discrimination observed during separation of the enantiomers.     

Enantiomeric Separation of 13 New Amphetamine‐Like Designer Drugs by Capillary Electrophoresis,Using Modified‐‐Cyclodextrins

An easy‐to‐prepare chiral CE method for the enantiomeric separation of 13 new amphetamine‐like designer drugs, using CDs as chiral selectors, was developed. Sulfated‐β‐CD was found to be the best chiral selector among the three used (sulfated‐β‐CD, caroboxymethyl‐β‐CD, dimethyl‐β‐CD). The separation of the analytes was achieved in a fused‐silica gel capillary at 20 °C using an applied voltage of +25 kV. The optimized background electrolyte consisted of 63.5 mM H₃PO₄ and 46.9 mM NaOH in water. Several electrophoretic parameters such as CD type, CD concentration (1 ? 40 mg/mL), buffer pH (2.6, 3.6, 5.0, 6.0), length of the capillary (70 ? 40 cm total length), amount of the organic solvent (methanol and acetonitrile) were investigated and optimized. Chirality 25:617–621, 2013. © 2013 Wiley Periodicals, Inc.     

Chiral separation of salbutamol and bupivacaine by capillary electrophoresis using dual neutral cyclodextrins as selectors and its application to pharmaceutical preparations and rat blood samples assay

An attempt for the simultaneous separation of salbutamol (Sal) and bupivacaine (Bup) enantiomers was performed by capillary elecytrophoresis with a dual mixture of neutral cyclodextrins as chiral selector. The influence on the separation of several parameters such as buffer composition, pH, the concentration ratio of 2-hydroxypropyl-beta-cyclodextrin (HP-beta-CD) to dimethyl-beta-cyclodextrin (DM-beta-CD) was investigated. A better separation was obtained for Sal and Bup with the CD mixtures compared to the use of HP-beta-CD or DM-beta-CD alone. The best simultaneous separation of Sal and Bup enantiomers was achieved with a 20 mM HP-beta-CD and 20 mM DM-beta-CD at pH 2.5 in a triethanolamine (TEA)/phosphate buffer. This method-utilized chlorphenamine (Chl) as an internal standard was found to be linear in the range 0.5-100 microg/mL and 0.5-150 microg/mL for Sal and Bup enantiomers, respectively. The limits of detection for both enantiomers of Sal and Bup were 0.18 and 0.24 microg/mL, respectively. The proposed method was applied to monitor Sal and Bup enantiomers concentration change in rat blood samples obtained from a male rat after celiac doses administration 0-30 min of Sal and Bup racemate. The method could also be used to determine Sal enantiomers in a pharmaceutical aerosol.     

High-performance liquid chromatographic enantioseparation of Betti base analogs on a newly developed isopropyl carbamate-cyclofructan6-based chiral stationary phase

The direct separation of the enantiomers of 1-(α-aminoarylmethyl)-2-naphthol, 1-(α-aminoalkyl)-2-naphthol, 2-(α-aminoarylmethyl)-1-naphthol analogs, and 2-(1-amino-2-methylpropyl)-1-naphthol) was performed on a newly developed chiral stationary phase containing isopropyl carbamate-cyclofructan6 as chiral selector, with n-heptane/alcohol/trifluoroacetic acid as mobile phase. The effects of the mobile-phase composition, the nature and concentration of the alcoholic and acidic modifiers, and the structures of the analytes on the retention and resolution were investigated. In some cases, separations were carried out at constant mobile-phase compositions in the temperature range 5-40°C. Thermodynamic parameters and T(iso) values were calculated from plots of ln k' or ln α versus 1/T. -Δ(ΔH°) ranged from 2.8 to 3.2 kJ mol(-1) , -Δ(ΔS°) from 7.7 to 10.1 J mol(-1) K(-1) , and -Δ(ΔG°) from 0.2 to 0.5 kJ mol(-1) . It was found that the enantioseparations were enthalpy driven. The sequence of elution of the stereoisomers determined in some cases was (R) < (S).     

Separation of cefoperazone enantiomers using beta-cyclodextrin as chiral additive by capillary zone electrophoresis

A capillary electrophoresis method was developed to separate the enantiomers of cefoperazone. Different cyclodextrins, including alpha-cyclodextrin (alpha-CD), beta-cyclodextrin (beta-CD), gamma-cyclodextrin (gamma-CD), 2-hydroxypropyl-beta-cyclodextrin (HP-beta-CD), and methyl-beta-cyclodextrin (Me-beta-CD), were tested as chiral additives in the running buffer. The effect of various parameters on enantioseparation such as concentration of NaH(2)PO(4), buffer pH, and CD concentration was also studied. The cefoperazone enantiomers were baseline separated under conditions of 0.04 mmol/L beta-CD, 75 mmol/L NaH(2)PO(4) buffer at pH 4.0. A fused silica capillary (40 cm effective length x 75 microm ID) was used. The applied voltage and capillary temperature were 20 kV and 25 degrees C, respectively. Under these conditions, linear calibration curves were obtained in the 5-500 microg/ml range using UV detection at 280 nm. The limit of detection for both isomers was 0.1 microg/ml. The method was used for the analysis of different pharmaceutical preparations (dose) and biological samples containing cefoperazone.     

Liquid chromatographic retention behavior and enantiomeric separation of three chiral center beta-blocker drug (nadolol) using heptakis (6-azido-6-deoxy-2, 3-di-O-phenylcarbamolyted) beta-cyclodextrin bonded chiral stationary phase

Nadolol, a beta-blocker used in the management of hypertension and angina pectoris, has three chiral centers and is currently marketed as an equal mixture of its four stereoisomers. Enantiomeric separation of nadolol by high-performance liquid chromatography was studied on a column packed with novel heptakis (6-azido-6-deoxy-2, 3-di-O-phenylcarbamolyted) beta-cyclodextrin bonded chiral stationary phase. The retention behavior and resolution of nadolol enantiomers were investigated and discussed with respect to the mobile phase composition and flow rate, pH, ionic strength, and temperature. The optimal separation condition was found; the mobile phase contained 80% buffer solution (1% triethylamine acetate, pH 5.5) and 20% methanol with 0.3 ml/min mobile phase flow rate at a temperature of 20 degrees C. At the optimal conditions, resolution of three stereoisomers of nadolol was obtained with a complete separation of the most active enantiomer, (RSR)-nadolol. Thermodynamic properties including enthalpy and entropy change of binding to the CSP for the enantiomeric separation were also determined.     

Role of capillary electrophoresis methods in the drug development process

In the past several years, capillary electrophoresis (CE) has generated considerable interest from pharmaceutical companies for control of both the chiral and achiral purity of bulk drugs and drug products. This paper evaluates the use of CE as: (1) a technique complementary to HPLC for the determination of peak homogeneity of a drug, (2) for determination of chiral purity, and (3) for determination of achiral purity. It would be greatly advantageous if CE could be used to determine both the chiral and achiral purity in a single assay. This investigation compares the results obtained for the separation of the enantiomers of duloxetine using several neutral cyclodextrins to those obtained using anionic cyclodextrins (sulfobutyl ether derivatives) as chiral selectors added to the separation buffer. In addition, it reports chiral separations obtained by using neutral cyclodextrins in a sulfonic acid-coated capillary column, which give a negatively charged capillary surface and electro-osmotic flow even in low pH buffers. The possible mechanism of separation is discussed. © 1996 Wiley-Liss, Inc.     

Chiral Separation of the Clinically Important Compounds Fucose and Pipecolic Acid Using CE: Determination of the Most Effective Chiral Selector

In this study, simple electrophoretic methods were developed for the chiral separation of the clinically important compounds fucose and pipecolic acid. In recent years, these analytes, and particularly their individual enantiomers, have attracted considerable attention due to their role in biological functions and disorders. The detectability and sensitivity of pipecolic acid and fucose were improved by reacting them with fluorenylmethyloxycarbonyl chloride (FMOC‐Cl) and 5‐amino‐2‐naphthalene‐sulfonic acid (ANSA), respectively. The enantioseparation conditions were optimized by initially investigating the type of the chiral selector. Different chiral selectors, such as polymeric surfactants and cyclodextrins, were used and the most effective ones were determined with regard to resolution and analysis time. A 10‐mM β‐cyclodextrin was able to separate the enantiomers of ANSA‐DL‐fucose and the polymeric surfactant poly(sodium N‐undecanoyl‐LL‐leucine‐valinate) was able to separate the enantiomers of FMOC‐DL‐pipecolic acid, with resolution values of 3.45 and 2.78, respectively. Additional parameters, such as the concentration and the pH of the background electrolyte (BGE), the concentration of the chiral selector, and the addition of modifiers were examined in order to optimize the separations. The addition of the chiral ionic liquid D‐alanine tert‐butyl ester lactate into the BGE was also investigated, for the first time, in order to improve resolution of the enantiomers. Chirality 25:556–560, 2013. © 2013 Wiley Periodicals, Inc.     

Enantioselective separation and online affinity chromatographic characterization of R,R- and S,S-fenoterol

BACKGROUND: rac-Fenoterol is a beta2-adrenoceptor agonist (beta2-AR) used in the treatment of asthma. It has two chiral centers and is marketed as a racemic mixture of R,R'- and S,S'-fenoterol (R-F and S-F). Here we report the separation of the R-F and S-F enantiomers and the evaluation of their binding to and activation of the beta2-AR. METHODS: R-F and S-F were separated from the enantiomeric mixture by chiral chromatography and absolute configuration determined by circular dichroism. Beta2-AR binding was evaluated using frontal affinity chromatography with a stationary phase containing immobilized membranes from HEK-293 cells that express human beta2-AR and standard membrane binding studies using the same membranes. The effect of R-F and S-F on cardiomyocyte contractility was also investigated using freshly isolated adult rat cardiomyocytes. RESULTS: Chiral chromatography of rac-fenoterol yielded separated peaks with an enantioselectivity factor of 1.21. The less retained peak was assigned the absolute configuration of S-F and the more retained peak R-F. Frontal chromatography using membrane-bound beta2-AR as the stationary phase and rac-3H-fenoterol as a marker ligand showed that addition of increasing concentrations of R-F to the mobile phase produced concentration-dependent decreases in rac-3H-fenoterol retention, while similar addition of S-F produced no change in rac-3H-fenoterol retention. The calculated dissociation constant of R-F was 472 nM and the number of available binding sites 176 pmol/column, which was consistent with the results from the membrane binding study 460 +/- 55 nM (R-F) and 109,000 +/- 10,400 nM (S-F). In the cardiomyocytes, R-F increased maximum contractile response from (265 +/- 11.6)% to (306 +/- 11.8)% of resting cell length (P < 0.05) and reduced EC50 from -7.0 +/- 0.270 to -7.1 +/- 0.2 log[M] (P < 0.05), while S-F had no significant effect. DISCUSSION: Previous studies have shown that rac-fenoterol acts as an apparent beta2-AR/G(s) selective agonist and fully restores diminished beta2-AR contractile response in cardiomyocytes from failing hearts of spontaneously hypertensive rats (SHR). Here we report the separation of the enantiomers of rac-fenoterol and that R-F is the active component of rac-fenoterol. Further evaluation of R-F will determine if it has enhanced selectivity and specificity for beta2-AR/G(s) activation and if it can be used in the treatment of congestive heart failure.     

Nonaqueous Capillary Electrophoretic Enantioseparation of Water Insoluble Tröger's Base Derivatives Using β‐Cyclodextrin as Chiral Selector

Racemic mixtures of six Tröger's base derivatives were separated by chiral nonaqueous capillary electrophoresis. The separation protocol was optimized first for suitable solvents. Then the applicability of various salts dissolved in organic solvents and their mixtures was evaluated. As chiral selectors β‐cyclodextrin and heptakis(2,6‐di‐O‐methyl)‐β‐cyclodextrin at various concentrations were used. The best enantioselectivity for the studied analytes was obtained utilizing formamide as organic nonaqueous solvent containing a mixture of sodium citrate and tris(hydroxymethyl)aminomethane acetate as electrolytes, and β‐cyclodextrin as chiral additive. The experimental results demonstrated the feasibility of nonaqueous capillary electrophoresis for enantioseparation of Tröger's base derivatives. This technique represents a suitable alternative to more commonly used capillary electrophoresis in aqueous environment. Chirality 25:810–813, 2013. © 2013 Wiley Periodicals, Inc.     

New chiral selectors: design and synthesis of 6-TBDMS-2,3-methyl beta-cyclodextrin 2-2' thioureido dimer and 6-TBDMS-2,3-methyl (or 2-methyl-3-acetyl) beta-cyclodextrin bearing an (R) Mosher acid moiety

Cyclodextrin (CD) derivatives are important selectors for analytical chiral recognition. Their enantioselectivities and chemical properties depend on ring size and on nature, number and location of substituents. This paper describes the synthesis of 6-O-TBDMS-2,3-O-methyl beta-cyclodextrins bearing in position 2 either a single (R)-Mosher acid moiety or a second CD unit, in view of their possible application as chiral selectors. Most synthetic steps were successfully carried out under high-intensity ultrasound using a new sonochemical reactor developed in the authors' laboratory. 6-O-TBDMS-2-O-methyl-3-[(S)-2-methylbutyl]-beta-CD was also synthesized and tested with gas chromatography; the enantiorecognition power of the other CD derivatives is also being tested. A computational study of model structures to design these CD derivatives.     

Separation of the enantiomers of some racemic nonsteroidal aromatase inhibitors and barbiturates by capillary electrophoresis

High-performance capillary electrophoresis (HPCE) and micellar electrokinetic capillary chromatography (MECC) were applied to the resolution of racemic nonsteroidal antiaromatase drugs and intermediates. Successful results were obtained in both modes using α-cyclodextrin (α-CD), β-cyclodextrin (β-CD), γ-cyclodextrin (γ-CD), or 2,6-di-O-methyl-β-cyclodextrin (DM-β-CD) as chiral selectors. Depending on the structure of the solute, one of the cyclodextrins was generally better suited for resolution of the racemate. The basic solutes were analyzed under HPCE conditions, whereas the nonionizable compounds such as glutethimide (Doriden®) were analyzed in MECC mode. For the azole-type antiaromatase Fadrozole, both HPCE and MECC modes could be used to achieve the separation of the enantiomers. The influence of experimental factors such as pH, the presence of organic modifier, temperature, the micelle concentration, and the concentration of the chiral selector is also discussed on the basis of the results obtained with some chiral barbiturates. The possibility of analyzing the enantiomers directly in plasma samples was also demonstrated. © 1993 Wiley-Liss, Inc.