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 Cathinone and Amphetamine Derivatives by HPLC/UV Using Sulfated ß‐Cyclodextrin as Chiral Mobile Phase Additive

In the last years the identification of new legal and illegal highs has become a huge challenge for the police and prosecution authorities. In an analytical context, only a few analytical methods are available to identify these new substances. Moreover, many of these recreational drugs are chiral and it is supposed that the enantiomers differ in their pharmacological potency. Since nonenantioselective synthesis is easier and cheaper, they are mainly sold as racemic mixtures. The goal of this research work was to develop an inexpensive method for the chiral separation of cathinones and amphetamines. This should help to discover if the substances are sold as racemic mixtures and give further information about their quality as well as their origin. Chiral separation of a set of 6 amphetamine and 25 cathinone derivatives, mainly purchased from various Internet shops, is presented. A LiChrospher 100 RP‐18e, 250 x 4 mm, 5 µm served as the stationary phase. The chiral mobile phase consisted of methanol, water, and sulfated ß‐cyclodextrin. Measurements were performed under isocratic conditions in reversed phase mode using UV detection. Four model compounds of the two substance classes were used to optimize the mobile phase. Under final conditions (methanol:water 2.5:97.5 + 2% sulfated ß‐cyclodextrin) enantiomers of amphetamine and five derivatives were baseline separated within 23 min. In all, 17 cathinones were completely or partially chirally separated. However, as only 3 of 25 cathinones were baseline resolved, the application of this method is limited for cathinone analogs. Additionally, the results were compared with an RP‐8e column. Chirality 26:411–418, 2014. © 2014 Wiley Periodicals, Inc.     

Chiral separation of 2,3-allenoic acid by capillary zone electrophoresis using cyclodextrin derivatives

In this paper, five of six samples of 2,3-allenoic acid enantiomers were separated by capillary zone electrophoresis (CZE) using hydroxypropyl-beta-cyclodextrin (HP-beta-CD) and hydroxypropyl-gamma-cyclodextrin (HP-gamma-CD) as chiral selectors. Using HP-beta-CD for chiral separation, three of the six enantiomers were separated. Five experimental conditions including HP-beta-CD concentration, pH, buffer concentration, temperature, and running voltage were investigated for their influence on separation and migration using enantiomers of 2-methyl-4-phenyl-2,3-butadienoic acid (A) and 2-(n-propyl)-4-phenyl-2,3-butadienoic acid (B) as samples. Good separation results were observed when [HP-beta-CD] = 3-12 mmol/L and pH = 7-9 for samples A and B. The temperature range of 15-25 degrees C can be selected for convenience. According to the chiral separation results, HP-beta-CD and HP-gamma-CD should be valuable selectors to separate 2,3-allenoic acids and HP-gamma-CD was suggested to separate the 2,3-allenoic acid samples with a group at 4-position bulkier than phenyl.     

Screening Approach for Chiral Separation of β‐Aminoketones by HPLC on Various Polysaccharide‐Based Chiral Stationary Phases

Nine β‐aminoketones were synthesized via Mannich reaction when benzaldehyde was condensed with some primary amines and acetophenone. The purified compounds were identified by using spectroscopic methods. The enantiomeric separation of these derivatives was carried out by high‐performance liquid chromatography (HPLC) using several coated and immobilized polysaccharide stationary phases, namely, Chiralcel^® OD‐H, Chiralcel^® OD, Chiralcel^® OJ, Chiralpak^® AD, Chiralpak^® IA, and Chiralpak^® IB using different mobile phases composed of n‐hexane and alcohol mixed in various ratios or pure ethanol or isopropanol. The retention behavior and selectivity of these chiral stationary phases were examined in isocratic normal phase mode. The results indicate that cellulose derivatives have higher enantioselectivity than amylose derivatives for the separation of racemic β‐amino ketones. Chirality 27:332–338, 2015. © 2015 Wiley Periodicals, Inc.     

Combined Use of Ionic Liquid and Hydroxypropyl‐β‐Cyclodextrin for the Enantioseparation of Ten Drugs by Capillary Electrophoresis

In the present study, hydroxypropyl‐β‐cyclodextrin and an ionic liquid (1‐ethyl‐3‐methylimidazolium‐l ‐lactate) were used as additives in capillary electrophoresis for the enantioseparation of 10 analytes, including ofloxacin, propranolol hydrochloride, dioxopromethazine hydrochloride, isoprenaline hydrochloride, chlorpheniramine maleate, liarozole, tropicamide, amlodipine benzenesulfonate, brompheniramine maleate, and homatropine methylbromide. The effects of ionic liquid concentrations, salt effect, cations, and anions of ionic liquids on enantioseparation were investigated and the results proved that there was a synergistic effect between hydroxypropyl‐β‐cyclodextrin and the ionic liquid, and the cationic part of the ionic liquid played an important role in the increased resolution. With the developed dual system, all the enantiomers of 10 analytes were well separated in resolutions of 5.35, 1.76, 1.85, 2.48, 2.88, 1.43, 5.45, 4.35, 2.76, and 2.98, respectively. In addition, the proposed method was applied to the determination of the enantiomeric purity of S‐ofloxacin after validation of the method in terms of selectivity, repeatability, linearity range, accuracy, precision, limit of detection (LOD), and limit of quality (LOQ). Chirality 25:409–414, 2013. © 2013 Wiley Periodicals, Inc.     

Chiral separations of some β‐adrenergic agonists and antagonists on AmyCoat column by HPLC

Sixteen β‐adrenergic antagonists namely acebutalol, alprenolol, atenolol, bisoprolol, bopindolol, bufurolol, carazolol, celiprolol, indenolol, metaprolol, nebivolol, oxprenolol, practolol, propranolol, tertalol, and timolol, and two β‐adrenergic agonists namely cimeterol and clenbuterol were resolved on AmyCoat (150 × 46 mm, 3 μm size of silica particle) by using (85:15:0.1, v/v/v), (90:10:0.1, v/v/v), and (95:05:0.1, v/v/v) combinations of n‐heptane, ethanol, and diethylamine solvents, respectively. The flow rates used were 0.5, 1.0, 2.0, and 3.0 ml/min with detection at 225 nm. The values of capacity, separation, and resolution factors ranged from 0.38 to 19.70, 1.08–2.33, and 1.0 and 4.50, respectively. The maximum and minimum resolutions were achieved for celiprolol and bufurolol, respectively. The chiral recognition mechanisms were also discussed. The values of validation parameters were calculated. Chirality 2010. © 2009 Wiley‐Liss, Inc.     

Chiral discrimination by NMR spectroscopy of ephedrine and N-methylephedrine induced by β-cyclodextrin,heptakis(2,3-di-O-acetyl)β-cyclodextrin,and heptakis (6-O-acetyl)β-cyclodextrin

NMR spectroxcopy has been used to compare the interaction of ephedrine and N-methylephedrine with β-cyclodextrin, heptakis(2,3-di-O-acetyl)β-cyclodextrin, heptakis(6-O-acetyl)β-cyclodextrin. The stoichiometry of the complexes formed between all three cyclodextrins and N-methylephedrine was found to be 1:1 by UV spectroscopy by means of the Job technique. NMR spectra of the single enantiomers of ephedrine and N-methylephedrine in the presence of all three cyclodextrins gave information about the parts of the ligands which interact differently with the host molecules and may be responsible for the chiral discrimination. To quantify the complex stabilities, binding constants were calculated from the changes in the chemical shifts of the ligand signals upon complexation. Analyses of the coupling constants of both species showed that no significant conformational change occurs upon complexation. ROESY spectra of these optical isomers with all three cyclodextrins provided detailed information about the geometry of the complexes. Different intermolecular cross-peaks between the individual isomers of ephedrine and N-Methylephedrine were found for native β-cyclodextrin and its 2,3-diacetylated derivative but not for 6-acetyl cyclodextrin. Analyses of the intramolecular cross-signals of the ligands confirmed that no significant conformational change occurs upon complexation. Chirality 9:211–219, 1997. © 1997 Wiley-Liss, Inc.     

Resolution of the enantiomers of drugs containing amino alcohol structure after derivatization with bromoacetic acid

The separation of the enantiomers of drugs containing an amino alcohol structure like adrenergic drugs or β-blockers is described. The compounds are resolved on chiral ligand-exchange chromatography phases after derivatization with bromoacetic acid. © 1992 Wiley-Liss, Inc.     

HPLC‐method for determination of permethrin enantiomers using chiral β‐cyclodextrin‐based stationary phase

The liquid chromatographic separation of permethrin enantiomers on chiral β‐cyclodextrin‐based stationary phase has been investigated. All four enantiomers are obtained by using simple methanol and water mobile phase, under gradient mode. The method was optimized and validated. The relationship between temperature and chromatographic parameters: k′ (capacity factor), α (separation factor) and Rs (resolution factor) was studied. Van't Hoff's curves for each enantiomer were plotted for temperature range 288–318 K. It was noticed that the response factor ratio of permethrin isomers differ and calculated value is found to be 1.66 (cis/trans, for n = 5). This method has been used for determining permethrin enantiomer ratio for a few samples of working standards and one formulation. Chirality 2010. © 2009 Wiley‐Liss, Inc.     

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.     

Separation of enantiomers of drugs by capillary electrophoresis,part 7: Gamma-cyclodextrin as chiral solvating agent

Following an extended chiral drug screening program by capillary zone electrophoresis (CZE), the enantioseparation of 86 racemic drugs was tested with γ-cyclodextrin as a chiral solvating agent. Unified conditions were applied to all experiments. In total, 18 drug racemates were separated, 13 entries thereof that had not been separated at the lower CSA concentration applied in an earlier stage of the project. A comparison of the data with the results obtained for α- and β-cyclodextrin points to the significance of partial penetration (“side-on binding”) of aryl groups into the cyclodextrin cavity. Chirality 10:548–554, 1998. © 1998 Wiley-Liss, Inc.     

Enantiomeric Separation of Bicyclo[2.2.2]octane‐Based 2‐Amino‐3‐Carboxylic Acids on Macrocyclic Glycopeptide Chiral Stationary Phases

Direct high‐performance liquid chromatographic (HPLC) separation of four bicyclo[2.2.2]octane based 2‐amino‐3‐carboxylic acid enantiomers were developed on chiral stationary phases (CSPs) containing different macrocyclic glycopeptide antibiotic selectors. The analyses were performed under reversed‐phase, polar organic and polar ionic mode on macrocyclic‐glycopeptide‐based Chirobiotic T, T2, TAG, and R columns. The effects of the mobile phase composition including the acid and base modifier, the structure of the analytes, and the temperature on the separations were investigated. Experiments were achieved at constant mobile phase compositions on different stationary phases in the temperature range 5–40°C. Thermodynamic parameters were calculated from plots of ln k or ln α versus 1/T. It was recognized that the enantioseparations in reversed‐phase and polar organic mode were enthalpically driven, but under polar‐ionic conditions entropically driven enantioseparation was observed as well. Baseline separation and determination of elution sequence were achieved in all cases. Chirality 26:200–208, 2014. © 2014 Wiley Periodicals, Inc.     

Optical resolution and mechanism using enantioselective cellulose,sodium alginate and hydroxypropyl‐β‐cyclodextrin membranes

Chiral solid membranes of cellulose, sodium alginate, and hydroxypropyl‐β‐cyclodextrin were prepared for chiral dialysis separations. After optimizing the membrane material concentrations, the membrane preparation conditions and the feed concentrations, enantiomeric excesses of 89.1%, 42.6%, and 59.1% were obtained for mandelic acid on the cellulose membrane, p ‐hydroxy phenylglycine on the sodium alginate membrane, and p ‐hydroxy phenylglycine on the hydroxypropyl‐β‐cyclodextrin membrane, respectively. To study the optical resolution mechanism, chiral discrimination by membrane adsorption, solid phase extraction, membrane chromatography, high‐pressure liquid chromatography ultrafiltration were performed. All of the experimental results showed that the first adsorbed enantiomer was not the enantiomer that first permeated the membrane. The crystal structures of mandelic acid and p ‐hydroxy phenylglycine are the racematic compounds. We suggest that the chiral separation mechanism of the solid membrane is “adsorption – association – diffusion,” which is able to explain the optical resolution of the enantioselective membrane. This is also the first report in which solid membranes of sodium alginate and hydroxypropyl‐β‐cyclodextrin were used in the chiral separation of p ‐hydroxy phenylglycine.     

Chiral derivatization for separation of racemic amino and thiol drugs by liquid chromatography and capillary electrophoresis

Separation of racemic amino drugs (α-methylbenzeneethanamine, 6-amino-2-methyl-2-heptanol and 1-aminoethyl-benzenemethanol) and thiol drugs [N-(2-mercapto-1-oxopropyl) glycine, 2-mercaptopropanoic acid, and N-acetyl-3-mercaptovaline] has been evaluated after derivatization. ortho-Phthalaldehyde (OPA) and naphthalene-2,3-dicarboxaldehyde (NDA) were used with either homochiral thiols (N-acetyl-L-cysteine and N-acetyl-D-penicillamine) or amines [(-)-(1R,2S)-norephedrine, L-phenylalanine, L-tyrosine, and 3-hydroxy-L-tyrosine] as chiral selectors according to the analyte reactive group. The resulting 36 diastereoisomeric derivatives were studied using reversed-phase high-performance liquid chromatography (RP-HPLC) and capillary electrophoresis (CE). Of the CE modes, micellar electrokinetic chromatography (MEKC) using sodium dodecyl sulfate (SDS) as surfactant, β-cyclodextrin (β-CD)-modified capillary zone electrophoresis (β-CD-CZE), and β-CD-MEKC were applied. Results highlight respective performance of the reagents and separative techniques. All OPA derivatives of racemic amino drugs were resolved either by MEKC or β-CD-MEKC. In the case of racemic thiol drugs, 10 of the 12 OPA derivatives were resolved in β-CD-CZE. © 1995 Wiley-Liss, Inc.     

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.     

Simultaneous chiral analysis of amphetamine‐type stimulants and ephedrine by capillary electrophoresis coupled to time‐of‐flight mass spectrometry

This study focused on the chiral characteristics of methamphetamine seizures in Shanghai for inferring the synthetic pathways of drugs. Capillary electrophoresis coupled to time‐of‐flight mass spectrometry was used for simultaneous chiral separation of amphetamine‐type stimulants and ephedrine, including S(+)‐amphetamine/R(?)‐amphetamine, S(+)‐methamphetamine/R(?)‐methamphetamine, (±)‐MDA (3,4‐methylenedioxyamphetamine), (±)‐MDMA (3,4‐methylenedioxymethamphetamine), (±)‐MDEA (3,4‐methylenedioxy‐N‐ethylamphetamine), d,l‐N‐ethylamphetamine, methylephedrine/methylpseudoephedrine, and 1S,2R(+)‐ephedrine/(?)‐ephedrine. The running buffer was 50‐mM ammonium formate (pH 2.2 was adjusted by 1‐M formic acid) containing 0.26% highly sulfated γ‐cyclodextrin as the chiral selector. All enantiomers were well resolved within 40 minutes by capillary electrophoresis at 20 kV in an uncoated fused‐silica capillary (50‐μm I.D. × 375‐μm O.D. × 90‐cm length) and detected by micro time‐of‐flight mass spectrometry. Twenty seized methamphetamine samples were determined by the established method. They were classified into two groups through their chiral characteristics.     

Self‐assembly and chiral recognition of quartz crystal microbalance chiral sensor

A novel chiral sensor based on the self‐assembled monolayer of (6^A‐ω‐mercaptoethylureado‐6^A‐deoxy)heptakis(2,3‐di‐o‐phenylcarbamoyl)‐6^B, 6^C, 6^D, 6^E, 6^F, 6^G‐ hexa‐o‐phenylcarbamoyl‐β‐cyclodextrin (Ph‐β‐CD‐SH) on a quartz crystal transducer for chiral recognition was set up. (R,S)‐(±)‐(3‐Methoxyphenyl)ethylamine were recognized by this QCM chiral sensor with a QCM chiral discrimination factor of 1.33. Furthermore, UV spectroscopy was used to investigate the mechanism of host‐guest interactions between (6^A‐azido‐6^A‐deoxy)heptakis(2,3‐di‐o‐phenylcarbamoyl)‐6^B, 6^C, 6^D, 6^E, 6^F, 6^G‐hexa‐o‐phenylcarbamoyl‐β‐cyclodextrin (Ph‐β‐CD) and (R,S)‐(±)‐(3‐methoxyphenyl) ethylamine. The UV discrimination factor was determined to be 0.066. Chirality, 2010. © 2009 Wiley‐Liss, Inc.     

GC Separation of Enantiomers of Alkyl Esters of 2‐Bromo Substituted Carboxylic Acids Enantiomers on 6‐TBDMS‐2,3‐di‐alkyl‐ β‐ and γ‐Cyclodextrin Stationary Phases

The gas chromatographic separation of enantiomers of 2‐Br carboxylic acid derivatives was studied on four different 6‐TBDMS‐2,3‐di‐O‐alkyl‐ β‐ and ‐γ‐CD stationary phases. The differences in thermodynamic data {ΔH and –ΔS} for the 15 structurally related racemates were evaluated. The influence of structure differences in the alkyl substituents covalently attached to the stereogenic carbon atom, as well as in the ester group of the homologous analytes, and the selectivity of modified β‐ and γ‐ cyclodextrin derivatives was studied in detail. The cyclodextrin cavity size, as well as elongation of alkyl substituents in positions 2 and 3 of 6‐TBDMS‐β‐CD, also affected their selectivity. The quality of enantiomeric separations is influenced mainly by alkyl chains of the ester group of the molecule and this appears to be independent of the CD stationary phase used. In some cases the separations occur as the result of external adsorption rather than inclusion complexations with the chiral selector. It was found that the temperature dependencies of the selectivity factor were nonlinear. Chirality 26:279–285, 2014. © 2014 Wiley Periodicals, Inc.     

High‐Performance Liquid Chromatographic Enantioseparation of Cyclic β‐Amino Acids on Zwitterionic Chiral Stationary Phases Based on Cinchona Alkaloids

Stereoselective high‐performance liquid chromatographic separations of eight sterically constrained cyclic β‐amino acid enantiomer pairs were carried out using the newly developed Cinchona alkaloid‐based zwitterionic chiral stationary phases Chiralpak ZWIX(+) and ZWIX(?). The effects of the mobile phase composition, the nature and concentrations of the acid and base additives, the counterions and temperature on the separations were investigated. The changes in standard enthalpy, Δ(ΔH°), entropy, Δ(ΔS°), and free energy, Δ(ΔG°), were calculated from the linear van't Hoff plots derived from the ln α vs. 1/T curves in the studied temperature range (10–50°C). The values of the thermodynamic parameters depended on the nature of the selectors and the structures of the analytes. Unusual temperature behavior was observed on the ZWIX(?) column: decreased retention times were accompanied by increased separation factors with increasing temperature. On the ZWIX(+) column only enthalpically, whereas on the ZWIX(?) column both enthalpically and entropically driven separations were observed. The elution sequence was determined in all cases and was observed to be the opposite on ZWIX(+) and on ZWIX(?). Chirality 27:563–570, 2015. © 2015 Wiley Periodicals, Inc.