Direct enantiomeric resolution of (+/-)-atenolol, (+/-)-metoprolol,and (+/-)-propranolol by impregnated TLC using L-aspartic acid as chiral selector

Resolution of three commonly used beta-blockers, (+/-)-atenolol, (+/-)-metoprolol and (+/-)-propranolol, into their enantiomers has been achieved using normal-phase TLC on silica gel plates impregnated with L-aspartic acid as the chiral selector. Different combinations of acetonitrile-methanol-water as mobile phase were found to be successful in resolving the enantiomers. The spots were detected with iodine and the detection limits were found to be 0.26 microg for atenolol and 0.23 microg for each of metoprolol and propranolol as racemate.     

Direct TLC resolution of atenolol and propranolol into their enantiomers using three different chiral selectors as impregnating reagents

Direct resolution of racemic atenolol and propranolol into their enantiomers was achieved by normal phase TLC on silica gel plates impregnated with optically pure L-tartaric acid, (R)-mandelic acid and (-)-erythromycin as chiral selectors. Different solvent systems were worked out to resolve the enantiomers. Spots were detected using iodine vapour. The TLC method was validated for linearity, limit of detection and limit of quantification. The influence of pH, temperature and concentration of chiral selector was studied.     

Thin-layer chromatography separation of enantiomers of verapamil using macrocyclic antibiotic as a chiral selector

Silica gel thin-layer chromatography plates impregnated with macrocyclic antibiotic, vancomycin, as chiral selector were prepared and used for the resolution of (+/-)-verapamil. A mobile phase system of acetonitrile-methanol-water (15:2.5:2.5, v/v) was worked out systematically. The effects of chiral selector, temperature and pH on resolution were also studied. The spots were detected with iodine vapors and the detection limit was found to be 0.074 microg of each enantiomers.     

Thin layer chromatographic resolution of some 2-arylpropionic acid enantiomers using L-(-)-serine,L-(-)-threonine and a mixture of L-(-)-serine and L-(-)-threonine-impregnated silica gel as stationary phases

Impregnated silica TLC plates with L-(-)-serine and L-(-)-threonine and a mixture of L-(-)-serine and L-(-)-threonine (1:1) as chiral selectors were prepared to use as chiral stationary phases (CSPs) in thin layer chromatography. The resolution of the enantiomers of 2-arylpropionic drugs, including ibuprofen, ibuproxam, ketoprofen, pranoprofen, benoxaprofen, flurbiprofen and tiaprofenic acid was investigated on these CSPs. A mobile phase system of acetonitrile-methanol-water (16:4:0.5, v/v/v) was used. The spots were detected with iodine vapours and the detection limits were found to range between 0.25 and 0.5 micro g/mL for all racemic compounds investigated. The effect of temperature, pH and concentration of the impregnating chiral selectors on resolution has been studied.     

Synthesis and application of clindamycin succinate as a novel chiral selector for capillary electrophoresis

A novel chiral selector, clindamycin succinate, was synthesized and first used as a chiral selector in capillary electrophoresis (CE). The chiral resolution ability of this kind of clindamycin derivation was studied by CE using some racemic drugs as model analytes. From the experimental results, it was found that both resolution and selectivity of the selector were dependent on the following parameters: concentration of chiral selectors, pH of the running buffer, temperature of the capillary column, applied voltage and organic modifier used. The results show that the chiral selector possesses high resolution toward some racemic drugs, including ofloxacin, chlorphenamine, tryptophan, propranolol, sotalol and metoprolol. Excellent chiral resolution of these tested drugs was achieved under the optimal conditions of 50 mM clindamycin succinate, 10% MeOH v/v, 50 mM Tris buffer, pH 4.0, at 22 kV and 20 °C within 25 min.     

Chiral separation of dansyl amino acids in capillary electrophoresis using mono-(3-methyl-imidazolium)-beta-cyclodextrin chloride as selector

Enantioseparations of fourteen dansyl amino acids were achieved by using a positively-charged single-isomer beta-cyclodextrin, mono-(3-methyl-imidazolium)-beta-cyclodextrin chloride, as a chiral selector. Separation parameters such as buffer pH, selector concentration, separation temperature, and organic modifier were investigated for the enantioseparation in order to achieve the maximum possible resolution. Chiral separation of dansyl amino acids was found to be highly dependent on pH since the degree of protonation of these amino acids can alter the strength of electrostatic interaction and/or inclusion complexation between each enantiomer and chiral selector. In general, the chiral resolution of dansyl amino acids was enhanced at higher pH, which indicates that the carboxylate group on the analytes may interact with the imidazolium group of cationic cyclodextrin. For most analytes, a distinct maximum in enantioresolution was obtained at pH 8.0. Moreover, the chiral separation can be further improved by careful tuning of the separation parameters such as higher selector concentration (e.g. 10 mM), lower temperature, and addition of methanol. Enantioseparation of a standard mixture of these dansyl amino acids was further achieved in a single run within 30 min.     

(S)-(-)-alpha,alpha-Di(2-naphthyl)-2-pyrrolidinemethanol, a useful tool to study the recognition mechanism in chiral ligand-exchange chromatography

A dynamic coating of the RP-18 carbon chain layers with the new chiral selector (S)-(-)-alpha,alpha-di(2-naphthyl)-2-pyrrolidinemethanol allowed the formation of a mixed chiral stationary phase that has been used in the separation of a selected set of amino acid racemates. Both a representative model and classification structure-property relationship studies have been performed in order to study the contribution of hydrophobic, bulky and electron-donating groups in the side chain of the chiral selector to the mechanism of chiral recognition.     

Chiral discrimination studies of (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid by high-performance liquid chromatography and NMR spectroscopy

Chiral discrimination studies using (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid (18-C-6-TA) as a chiral selector were performed by high-performance liquid chromatography (HPLC) and NMR spectroscopy. The enantiomers of alanine (Ala) or alanine methyl ester (Ala-ME) were well separated on the chiral stationary phases (CSPs) derived from (+)-18-C-6-TA by HPLC. The chiral selector, (+)-18-C-6-TA, used in the CSP was also applied for the chiral discrimination of the Ala and Ala-ME enantiomers, and it discriminated these enantiomers successfully by NMR spectroscopy. The chemical shift differences (Delta Delta delta) of the alpha-proton of these enantiomers in the presence of an equimolecular solution of 18-C-6-TA were observed to be 0.10 ppm for Ala in methanol-d4 containing 10 mM H2SO4 and 0.11 ppm for Ala-ME in methanol-d4. The observed NMR results agreed with the chromatographic data on the (+)-18-C-6-TA-derived CSP by HPLC in terms of both the elution order and solvents effects.     

Chiral separation of amino acids by capillary electrophoresis with 3-[(3-cholamidopropyl)-dimethylammonio]-1-propane sulfonate as chiral selector

Summary 3-[(3-cholamidopropyl)-dimethylammoniol-1-propane sulfonate (CHAPS) can be used as an effective chiral selector for the separation of dansyl-amino acids by capillary electrophoresis (CE). While CHAPS can serve as an chiral selector, better enantiomeric separation can be performed by using CHAPS not as the sole chiral selector but as one of a [CHAPS-SDS-cyclodextrin] three-component system. In this CHAPS-SDS-CD system, enantiomeric separations of the amino acids can be readily accomplished by judiciously adjusting the pH of the solution, concentrations of CHAPS and SDS, and the concentration and type of CD. All amino acids can be baseline resolved in less than 15 minutes with resolution as high as 2.01 at pH 6.5 with 50 mM of CHAPS and 75 mM of SDS. The resolution is also dependent on the size of the CD. Substantial increase in the resolution can be readily achieved by replacing β-CD with γ-CD. For example, theR _s for Leu was increased by four-folds (from 1.65 to 6.29) while the elution time still remains as short as 20 min when β-CD was replaced by γ-CD.     

Direct enantiomeric TLC resolution of dl-penicillamine using (R)-mandelic acid and l-tartaric acid as chiral impregnating reagents and as chiral mobile phase additive

DL-Penicillamine has been resolved into its enantiomers by normal-phase TLC using L-tartaric acid as chiral impregnating reagent as well as chiral mobile phase additive, while (R)-mandelic acid has been found to be successful as a chiral impregnating reagent. The solvent system acetonitrile-methanol-water (5:1:1, v/v) was found to be successful when L-tartaric acid was used as impregnating agent while the solvent combination acetonitrile-methanol-(0.5% l-tartaric acid in water, pH 5)-glacial acetic acid (7:1:1.1:0.7, v/v) was successful as mobile phase as it contained L-tartaric acid as the chiral additive. (R)-mandelic acid was successful as chiral impregnating reagent with ethyl acetate-methanol-water (3:1:1, v/v), as the mobile phase. The effects of concentration of chiral selectors, temperature and pH were examined on enantiomeric resolution. The spots were detected with iodine vapors and the detection limits were found to be 0.12 microg for each enantiomer of penicillamine with L-tartaric acid, under both the conditions, and 0.11 microg with (R)-mandelic acid.     

Simultaneous chiral resolution of monosaccharides as 8-aminonaphthalene-1,3,6-trisulfonate derivatives by ligand-exchange CE using borate as a central ion of the chiral selector

Six reducing monosaccharides (mannose, galactose, fucose, glucose, xylose, and arabinose) were derivatized with 8-aminonaphthalene-1,3,6-trisulfonate (ANTS). Based on the chiral ligand-exchange principle using borate as a central ion of the chiral selector and (S)-3-amino-1,2-propanediol (SAP) as a chiral selector ligand, all of the six ANTS-monosaccharides were simultaneously enantioseparated using absorbance at 245 nm for detection. The optimum conditions for both high resolution and moderately short migration time consisted of 200 mM SAP-200 mM borate buffer (pH 9.2) containing 10% ACN as a BGE at 30 degrees C with an applied voltage of +30 kV. It was revealed that the proposed chiral ligand-exchange CE using the SAP-borate system was applicable to enantioseparation of not only diols but also polyols.     

Liquid chromatographic resolution of 1-aryl-1,2,3,4-tetrahydroisoquinolines on a chiral stationary phase based on (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid

A liquid chromatographic chiral stationary phase (CSP) based on (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid was applied for the first time to the resolution of biologically important 1-aryl-1,2,3,4-tetrahydroisoquinolines. The unusual resolution of cyclic secondary amino compounds on a chiral crown ether-based CSP was quite successful with the use of a mixture of methanol-acetonitrile-triethylamine at a ratio of 30/70/0.5 (v/v/v) as a mobile phase. From the chromatographic behaviours for the resolution of seven 1-aryl-1,2,3,4-tetrahydroisoquinolines, the steric bulkiness of the 1-phenyl ring at the chiral center of analytes was concluded to play an important role in the chiral recognition.     

Enantioseparation of chiral aromatic acids by multiple dual mode counter‐current chromatography using hydroxypropyl‐β‐cyclodextrin as chiral selector

This work concentrates on extending the utilization of multiple dual mode (MDM) counter‐current chromatography in chiral separations. Two aromatic acids, 2‐(6‐methoxy‐2‐naphthyl)propionic acid (NAP) and 2‐phenylpropionic acid (2‐PPA), were enantioseparated by MDM counter‐current chromatography using hydroxypropyl‐β‐cyclodextrin (HP‐β‐CD) as chiral selector. The two‐phase solvent systems consisting of n‐hexane/ethyl acetate 0.1 mol/L phosphate buffer pH 2.67 containing 0.1 mol/L HP‐β‐CD (7.5:2.5:10 for NAP and 7:3:10 for 2‐PPA, v/v/v) were used. Conventional MDM and modified MDM were compared according to peak resolution under current separation mechanism. The influence of elution time after the first‐phase inversion and number of cycles for MDM were investigated. Peak resolution of NAP and 2‐PPA increased from 0.62 to 1.05 and 0.72 to 0.84, respectively, using optimized MDM conditions. Being an alternative elution method for counter‐current chromatography, MDM elution greatly improved peak resolution in chiral separations.     

Synthesis and application of a novel single-isomer mono-6-deoxy-6-(3R,4R-dihydroxypyrrolidine)-β-cyclodextrin chloride as a chiral selector in capillary electrophoresis

A novel positively charged single-isomer of β-cyclodextrin, mono-6-deoxy-6-(3R,4R-dihydroxypyrrolidine)-β-CD chloride (dhypy-CDCl), was synthesized and employed as a chiral selector for the first time in capillary electrophoresis (CE) for the enantioseparation of anionic and ampholytic acids. The effects of the running buffer pH, chiral selector concentration, analyte structure and organic modifier on the enantioseparation were studied in detail. The chiral selectivity and resolution for most of the studied analytes decreased as the buffer pH increased in the range of 6.0–9.0. Increasing selector concentration led to decreased effective mobility, increased chiral selectivity and resolution for most of the studied analytes. Moreover, the hydroxyl groups located on the dihydroxypyrrolidine substituent of the dhypy-CDCl could have influence on the chiral separation.     

Enantiomeric separation of gemfibrozil chiral analogues by capillary electrophoresis with heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin as chiral selector

The enantiomeric separation of gemfibrozil chiral analogues was performed by capillary zone electrophoresis (CZE). Resolution of the enantiomers was achieved using heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin (TM-beta-CD) as chiral selector dissolved into a buffer solution. In order to optimize the separation conditions, type, pH and concentration of running buffer and chiral selector concentration were varied. For each pH value, the optimum chiral selector concentration that produced the resolution of the isomers was found. The migration order of labile diastereoisomers formed was valued at the optimum experimental conditions by adding a pure optical isomer to the racemic mixture. Data from 1H NMR studies confirmed host-guest interaction between TM-beta-CD and 5-(2,5-dimethylphenoxy)-2-ethylpentanoic acid sodium salt. The hypothesized stoichiometry host:guest was 1:1. An apparent equilibrium constant (Ka) was estimated monitoring the chemical shift variation as a function of TM-beta-CD concentration. Salt effect on complexation equilibrium constant was also investigated.     

Comparison of enantiomer separation on two chiral stationary phases derived from (+)-18-crown-6-2,3,11,12-tetracarboxylic acid of the same chiral selector

Liquid chromatographic comparisons for enantiomer resolution of α-amino acids and chiral primary amino compounds were made using chiral stationary phases (CSPs) prepared by covalently bonding (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid (18-C-6-TA) of the same chiral selector. The resolution of all α-amino acids on CSP 1 developed in our group was found to be better than that on CSP 2 reported by Machida et al. All α-amino acids examined in this study were well enantioseparated on CSP 1 (α=1.22–2.47), while four analytes were not resolved or all the other analytes were poorly resolved on CSP 2 than on CSP 1. However, in resolving the primary amino compounds without a carbonyl group, CSP 1 was comparable with CSP 2. Although (+)-18-C-6-TA of the same chiral selector was used to prepare CSP 1 and CSP 2, this study showed that different connecting methods for the CSPs might influence their ability to resolve the analytes depending on their structures related to the chiral recognition mechanism.     

Enantioselective separation of the sunscreen agent 3-(4-methylbenzylidene)-camphor by electrokinetic chromatography: Quantitative analysis in cosmetic formulations

3-(4-Methylbenzylidene)-camphor (MBC) is a chiral sunscreen agent used in cosmetic products. In this work, the enantioseparation of MBC has been performed by EKC and applied to the analysis of the MBC enantiomers in cosmetic creams. Different experimental conditions (type and concentration of the chiral selector, temperature, and sample solvent) have been optimized. Due to the neutral nature of this compound, anionic CD derivatives were investigated as chiral selectors. Carboxymethylated-beta-CD (CM-beta-CD) showed the highest chiral separation power, observing that a 15 mM concentration of this CD at a working temperature of 15 degrees C enabled to obtain the highest enantioresolution. However, under these conditions, tailing of peaks obtained for the enantiomers was observed. The addition of increasing concentrations of the neutral alpha-CD to CM-beta-CD at a 15 mM concentration in a 100 mM borate buffer at pH 9.0 improved the enantiomeric separation and decreased peak tailing. The use of DMF for the total dissolution of the cosmetic creams, and methanol:water (1:1 v/v) for appropriate dilution enabled to observe good shape and size for the peaks of the MBC enantiomers. After optimizing a method for the preconditioning of the capillary, the analytical characteristics of the chiral separation method for the analysis of MBC were investigated. Linearity, LODs and LOQs, precision (instrumental repeatability, method repeatability, intermediate precision), accuracy, and selectivity were evaluated. The method was applied to analyze MBC enantiomers contained in two commercial cosmetic creams containing racemic MBC and to study the skin absorption of this compound with time.     

Efficient applications of capillary electrophoresis-tandem mass spectrometry to the analysis of adrenoreceptor antagonist enantiomers using a partial filling technique

Throughout the separation of chiral basic drugs by capillary electrophoresis (CE) with neutral hydroxypropyl-beta-cyclodextrin (HP-beta-CD) as chiral selector, the sensitivity of detection can be improved by using tandem mass spectrometric (MS-MS) detection with a partial filling technique rather than with UV spectrometric detection. Prior to sample injection. the capillary was partly filled with HP-beta-CD dissolved in volatile ammonium formate buffer (pH 4, ionic strength 50 mM). The effects of modifying the HP-beta-CD concentration in the selector zone and the length of the separation zone on the enantioresolution and the signal-to-noise ratio of the pseudo-molecular MH+ ion were investigated. For a given selector zone length, as the concentration of the neutral cyclodextrin increases, the resolution between enantiomers becomes higher (the opposite of the behavior of the signal-to-noise ratio) and then reaches an optimum value. The decrease of the selector zone length lowered the resolution between the enantiomers but increased peak efficiencies and signal-to-noise ratio values. Accordingly, partial capillary filling at 80% (v/v) and 10 mM concentration of HP-beta-CD was selected as a suitable compromise between resolution and sensitivity of MS detection. Limits of detection for each adrenoreceptor antagonist enantiomer were 5 ng/ml (0.02 microM) in CE-MS-MS instead of 150 ng/ml (0.60 microM) in CE-UV, which enhances sensitivity by a factor of 30.     

CEC enantioseparations on chiral monolithic columns: a study of the stereoselective degradation of (R/S)-dichlorprop [2-(2,4-dichlorophenoxy)propionic acid] in soil

For the study of the stereoselective degradation of the herbicide 2-aryloxipropionic acid dichlorprop (DCPP) in soil, a porous monolithic chiral column (100 microm id) was prepared by in situ copolymerization of glycidyl methacrylate, methyl methacrylate and ethylene glycol dimethacrylate in the presence of formamide and 1-propanol as the porogen solvents. Subsequently, the epoxide groups at the surface of the monolith were reacted with (+)-1-(4-aminobutyl)-(5R,8S,10R)-terguride as the chiral selector. Optimum conditions for the herbicide resolution by CEC were found using mobile phases consisting of acetic acid/triethylamine mixtures in ACN-methanol (9:1 v/v). Under these conditions fully separation of DCPP enantiomers in the presence of clofibric acid (internal standard) was achieved in about 5 min. Experiments on the incubation of rac-DCPP in soil at room temperature showed the herbicide undergone during 23 incubation days to a degradation to levels 相似文献   

Direct chiral resolution of tartaric acid by ion-pair capillary electrophoresis using an aqueous background electrolyte with (1R,2R)-(-)-1,2-diaminocyclohexane as a chiral counterion

Chiral resolution of native DL-tartaric acid was achieved by ion-pair capillary electrophoresis (CE) using an aqueous-ethanol background electrolyte with (1R,2R)-(-)-1,2-diaminocyclohexane (R-DACH) as a chiral counterion. Factors affecting chiral resolution and migration time of tartaric acid were studied. By increasing the viscosity of the background electrolyte and the ion-pair formation, using organic solvents with a lower relative dielectric constant, resulted in a longer migration time. The optimum conditions for both high resolution and short migration time of tartaric acid were found to be a mixture of 65% v/v ethanol and 35% v/v aqueous solution containing 30 mM R-DACH and 75 mM phosphoric acid (pH 5.1) with an applied voltage of -30 kV at 25 degrees C, using direct detection at 200 nm. By using this system, the resolution (Rs) of racemic tartaric acid was approximately 1. The electrophoretic patterns of tartaric and malic acids suggest that two carboxyl groups and two hydroxyl groups of tartaric acid are associated with the enantioseparation of tartaric acid by the proposed CE method.