Equilibrium Studies on Liquid-Liquid Reactive Extraction of Phenylsuccinic Acid Enantiomers Using Hydrophilicβ-CD Derivatives Extractants

This paper deals with the enantioseparation of phenylsuccinic acid(H2A)enantiomers by liquid-liquid reactive extraction usingβ-CD derivatives as aqueous selectors.Cyclodextrin and its derivatives can interact with guest molecules selectively to form complexes with different stabilities.Cyclodextrin derivatives are not soluble in organic liquids,but highly soluble in water.In this work,hydroxypropyl-β-cyclodextrin(HP-β-CD),hydroxyethyl- β-cyclodextrin(HE-β-CD)and methyl-β-cyclodextrin(Me-β-CD)were selected as chiral selectors in aqueous phase for the reactive extraction of phenylsuccinic acid enantiomers from organic phase to aqueous phase.The results show that the efficiency of the extraction depends,often strongly,on a number of process variables,including the types of organic solvents andβ-CD derivatives,the concentrations of the extractants and H2A enantiomers,pH and temperature.HP-β-CD,HE-β-CD and Me-β-CD have stronger recognition abilities for R-phenylsuccinic acid than for S-phenylsuccinic acid.Among the three kinds ofβ-CD derivatives,HP-β-CD has the strongest separation ability. Excellent enantioseparation was achieved under the optimal conditions of pH of 2.5 and temperature of 5°C with a maximum enantioselectivity(a)of 2.38.Reactive extraction of enantiomers with hydrophilicβ-CD derivatives is of strong chiral separation ability and can be hopeful for separations of various enantiomers at a large-scale.

Study on Capillary Zone Electrophoretic Separation of Chlorpheniramine Enantiomers with β-Cyclodextrin

The chlorpheniramine enantiomers were separated with capillary zone electrophoresis using β-cyclodextrin as the chiral selector.The effects of the concentration of β-cyclodextrin, the electrolyte pH and organic modifier(urea) on the difference in apparent electrophoretic mobilities of the enantiomels were investigated.

Stereoselective HPLC Assay of TJ0711 Enantiomers by Precolumn Derivatization with GITC Using UV Detection and Its Application in Pharmacokinetics in Rats

This investigation describes a new precise, sensitive and accurate stereoselective RP-HPLC method for determination of the enantiomers of a novel α- and β-receptor blocking agent, 1-[4-（2-methoxyethyl） phenoxy]-3-[[2-（2- methoxyphenoxy） ethyl]amino]-2-propanol （T J0711）, in rat plasma. GITC was used for precolunm derivatization of T J0711 enantiomers. Enantiomeric resolution was achieved on a Eurospher-100 C18 column （250 mm×4.6 mm ID, 5-μm particle size）, with UV detection at 255 nm, and the mobile phase consisted of acetonitrile and water （58：42, v/v） containing 0.02% glacial acetic acid （v/v）. Using the chromatographic conditions described, T J0711 enantiomers were well resolved with mean retention time of 10.2 and 11.5 min, respectively. Linear response （r〉0.999） was observed over the range of 0.125-12.5 μg/mL of TJ0711 hydrochloride enantiomers. The mean relative standard deviation （RSD%） of the results of within-day precision was ≤ 10%. The proposed method was found to be suitable and accurate for the quantitative determination of T J0711 enantiomers in rat plasma, and it can be used in pharmacokinetic studies.

Analysis of species-dependent hydrolysis and protein binding of esmolol enantiomers

The stereoselective hydrolysis of esmolol in whole blood and in its separated components from rat,rabbit and human was investigated.Blood esterase activities were variable in different species in the order of rat>rabbit>human.Rat plasma showed the high esterase activity and had no stereoselectivity to enantiomers.Rabbit red blood cell（RBC） membrane,RBC cytosol and plasma all hydrolyzed esmolol but with different esterase activity,whereas the hydrolysis in RBC membrane and cytosol showed significant stereoselectivity towards R-（+）-esmolol.Esterase in RBC cytosol from human blood mainly contributed to the esmolol hydrolysis,which was demonstrated with no stereoselctivity.Esterase in human plasma showed a low activity,but a remarkable stereoselectivity with R-（+）-esmolol.In addition,the protein concentration affected the hydrolysis behavior of esmolol in RBC suspension.Protein binding of esmolol enantiomers in human plasma,human serum albumin（HSA） and α;-acid glycoprotein（AGP） revealed that there was a significant difference in bound fractions between two enantiomers,especially for AGP.Our results indicated that the stereoselective protein binding might play a role in the different hydrolysis rates of esmolol enantiomers in human plasma.

Chiral extraction of ketoprofen enantiomers with chiral selector tartaric esters

Distribution behavior of ketoprofen enantiomers was examined in methanol aqueous and organic solvent mixture containing tartaric esters. The influence of length of alkyl chain of tartaric esters, concentration of L-tartaric esters and methanol aqueous, kind of organic solvent on partition ratio and separation factors was investigated. The results show that L-tartaric and D-tartaric esters have different chiral recognition abilities. S-ketoprofen is easily extracted by L-tartaric esters, and R-ketoprofen is easily extracted by D-tartaric esters. L-tartaric esters form more stable diastereomeric complexes with S-enantiomer than that with R-enantiomer. This distribution behavior is consistent with chiral recognition mechanism. With the increase of the concentration of tartaric ester from 0 to 0.3 mol/L, partition coefficient K and separation factor a increase. Also, the kind of organic solvent and the concentration of the methanol aqueous have significant influence on K and a.

Chiral ionic liquids as chiral selectors for separation of tryptophan enantiomers by ligand exchange chromatography

Chiral ionic liquids (CILs) containing imidazolium cations and L-Proline (L-Pro) anions were applied as chiral selector to separate tryptophan (Trp) enantiomers on a C18 column by ligand exchange chromatography. Several factors influencing Trp enantiomers separation, such as alkyl chain length of CILs, concentrations of Cu2+ and CILs, pH of the mobile phase, flow rate, organic solvent and temperature, were studied. Under the optimal conditions, the Trp enantiomers could be successfully separated within 21 min with the resolution of 2.30. At the same time, some thermodynamical parameters were obtained. The experimental results show that the enthalpy values of the Trp enantiomers are negative, indicating that the separation process is exothermic. And the enthalpy values of D-Trp are larger than those of L-Trp, which indicates that L-Trp could form more stable ternary complexes with tryptophan enantiomers.

Separation of Enantiomers of Clopidogrel on Chiral Stationary Phases by Packed Column Supercritical Fluid Chromatography

A packed column supercritical fluid chromatography (SFC) method for the separation of clopidogrel enantiomers on a chiral stationary phase and CO2 with modifier as mobile phase has been developed at an analytical scale. Among 11 different 2 stationary phases the Chiral cel OD-H column showed by far the best separation properties. The influence of different modifiers, injection solvents, temperature, and pressure, and density of the fluid, respectively, on the separation behaviour has been studied. It was found that the separation behaviour strongly depends on the type of modifier and the modifier content. Temperature and pressure are of less influence.

Comparison of reversed-phase enantioselective HPLC methods for determining the enantiomeric purity of (S)-omeprazole in the presence of its related substances

A simple analytical high-performance liquid chromatography （HPLC） method was applied for the en- antiomeric excess determination of esomeprazole （（S）-OME）, the enantiopure active ingredient con- tained in drug products, in the presence of its potential organic impurities A-E. The enantioselective separation was accomplished on the immobilized-type Chiralpak ID-3 chiral stationary phase （CSP） under reversed-phase conditions. The results were evaluated and compared with those obtained by the official enantioselective method of European Pharmacopoeia used as the reference for checking the enantiomeric excess of （S）-OME. It has been established that the use of the Chiralpak ID-3 CSP allows the determination of the enantiomeric purity of （S）-OME without any interference coming from its chiral and achiral related substances. The analytical procedure of the drug regulatory agencies based on the AGP CSP suffered instead from poor specificity due to overlap of the peaks pertinent to the achiral impurity A and the chiral impurity （R）-OME （impurity F）.

Enantiomeric Separation of Meptazinol Hydrochloride by Capillary Electrophoresis

Aim To establish a capillary electrophoresis method for enantiomericseparation of meptazinol hydrochlo-ride. Methods The separation conditions such ascyclodextrin(CD)type, buffer pH, concentration of 2,3,6-O-trimethyl-β-cyclodextrin and organicadditives were optimized. An optimum concentration was 30 mmol· L^(-1) phosphate (pH 7.02) with 10%(W/V) TM-β-CD and 2% acetonitrile. Results Baseline resolution of the enantiomer was readilyachieved using 2, 3, 6-O-trimethyl-β-cyclodextrin. Conclusion This is a convenient method for fastenantiomeric resolution of meptazinol hydrochloride.

Separation and determination of acetyl-glutamine enantiomers by HPLC–MS and its application in pharmacokinetic study

A high-performance liquid chromatography coupled with mass spectrometry(HPLC–MS) method was established for the separation and determination of acetyl-glutamine enantiomers(acetylL-glutamine and acetylD-glutamine) simultaneously. Baseline separation was achieved on Chiralpak AD-H column(250 mm ×4.6 mm, 5 μm). n-Hexane(containing 0.1% acetic acid) and ethanol(75:25, v/v) were used as mobile phase at a flow rate of 0.6 m L/min. The detection was operated in the negative ion mode with an ESI source. [M-H]-m/z187.0540 for enantiomers and [M-H]-m/z 179.0240 for aspirin(IS) were selected as detecting ions. The linear range of the calibration curve for each enantiomer was 0.05–40 μg/m L. The precision of this method at concentrations of 0.5–20 μg/m L was within 7.23%, and the accuracy was 99.81%–107.81%. The precision at LOQ(0.05 μg/m L) was between 16.28% and 17.56%, which was poor than that at QC levels. The average extraction recovery was higher than 85% for both enantiomers at QC levels. The pharmacokinetics of enantiomers was found to be stereoselective. There was not chiral inversion in vivo or in vitro between enantiomers.

Enantiomeric Separation of Epinephrine and Salbutamol by Micellar Electrokinetic Chromatography Using β-Cyclodextrin as Chiral Additive

Enantiomeric separation of epinephrine and salbutamol was investigated by micellar electrokinetic chromatography employing β-cyclodextrin as chiral additive in ammonium chloride-ammonia solution. The analytes were detected by electrochemistry using gold microelectrode at +0.65 V versus SCE reference electrode. The effects of detection potential, concentration of β-cyclodextrin, concentration of sodium dodecyl sulfate, pH value of electrolyte and applied voltage were discussed.

Enantiomeric separation of phenylsuccinic acid by cyclodextrin-modified reversed phase high-performance liquid chromatography

The chiral separation of phenylsuccinic acid(PSA)was studied by reversed phase high-performance liquid chromatography(RP-HPLC)with cyclodextrins(CDs)as chiral mobile phase additives.The effects of types of CDs,concentration of hydroxypropyl-β-cyclodextrin(HP-β-CD),percentage of organic modifier,pH value and column temperature on enantioselective separation were investigated.The quantification property of the developed RP-HPLC method was examined.The chiral recognition mechanism of PSA was also discussed.The results show that a baseline separation of PSA enantiomers is achieved on a Lichrospher C18 column(4.6 mm(inner diameter)×250 mm,5μm)with HP-β-CD as chiral mobile phase additive.The capacity factors of R-PSA and S-PSA are 3.94 and 4.80,respectively.The separation factor and resolution are respectively 1.22 and 8.03.The mobile phase is a mixture of acetonitrile and deionized water(20-80,volume ratio)containing 10 mmol/L HP-β-CD and 0.05% trifluoroacetic acid(pH 2.5,adjusted with triethylamine)with a flow rate of 1.0 mL/min.The ultraviolet(UV)detector is set at 254 nm.The likely roles are inclusion interaction,induction and hydrogen bonding between HP-β-CD and PSA enantiomers.

A practical synthesis of (-)fosfomycin from its enantiomer

（＋）-cis-（1S, 2R）-Epoxypropylphosphonic acid, the enantiomer of fosfomycin, which is the industrial side-product in the preparation of the antibiotic fosfomycin, was converted into （-）fosfomycin by a seven-step procedure. The esterification of the dihydroxyphosphonic intermediate was the key step. The title compound was obtained in good yield and its optical purity was up to the medicine quality standard of Chinese Pharmacopoeia.

Direct Enantiomer Separation of 2-PhenylcyclopropanecarboxylateEsters on Cyclodextrin Derivatives Stationary Phases in GC

Direct enantiomeric separation of all four optical isomers of 2-phenylcyclopropane carboxylate ester was first achieved on each of the three different beta-cyciodextrin chiral stationary phases (CSPs) in GC. Using these CSPs, enantiomeric excess of the products of enantioselective cyclopropanation can be determined directly, conveniently and fast.

Kinetic study on reactive extraction of phenylalanine enantiomers with BINAP-copper complexes

Enantioselective liquid–liquid extraction has attracted considerable attention for its potential use in largescale production. Kinetic data are needed for the reliable scale-up of the process. This paper reports the kinetic study of reactive extraction of phenylalanine(Phe) enantiomers with BINAP–copper complex(BINAP–Cu) as a chiral selector. The theory of extraction accompanied by a chemical reaction was applied.The effects of agitation speed, interfacial area, p H value of aqueous phase, initial concentration of Phe enantiomers and initial concentration of BINAP–Cu on the specific rate of extraction were investigated. The forward rate constants of the reactions in the reactive extraction process are 7.93 × 10-5m5/2·mol-1/2·s-1for D-Phe and 1.29 × 10-4m5/2·mol-1/2·s-1for L-Phe.

Transport and uptake of clausenamide enantiomers in CYP3A4-transfected Caco-2 cells： an insight into the efflux-metabolism alliance

Aim The present study developed a CYP3A4-expressed Caco-2 monolayer model at which effects of the efflux-metabolism alliance on the transport and uptake of clausenamide（CLA） enantiomers as CYP3A4 substrates were investigated. The apparent permeability coefficients （Papp） of （ - ） and （ ＋ ）CLA were higher in the ab- sorptive direction than those in the secretory direction with efflux ratios（ER） of 0. 709 ± 0.411 and 0. 867± 0. 250 （ Х10^-6 -1 cm · s ）, respectively. Their bidirectional transports were significantly reduced by （75.6 ± 87.5）% af- ter treatment with verapamil （ a P-glycoprotein inhibitor） that increased the rate of metabolism by CYP3 A4, whereas the CYP3A4 inhibitor ketoconazole treatment markedly enhanced the basolateral to apical flux of （ - ） and （ ＋ ） CLA with ERs being 2. 934 ± 1. 432 and 1. 877 ± 0. 148 （ Х 10^-6 cm/s） respectively. These changes could be blocked by the duel CYP3A4/P-glycoprotein inhibitor cyclosporine A, consequently, Papp values for CLA enanti- omers in both directions were significantly greater than those obtained by using verapamil or ketoconazole, and their ERs were similar to those following （ - ） or （ ＋ ）-isomer treatment alone. Furthermore, the uptake of （ - ）CLA was more than that of （ ＋ ）CLA in the transfected cells. Incubation with ketoeonazole decreased the intracellular concentrations of the two enantiomers. This effect disappeared in the presence of a CYP3A4 inducer dexametha- sone. These results indicated that CYP3A4 could influence P-gp efflux, transport and uptake of CLA enantiomers as CYP3A4 substrates and that a duel inhibition to CYP3A4/ P-glycoprotein could enhance their absorption and bioavailability, which provides new insight into the efflux-metabolism alliance and will benefit the clinical pharma- cology of （？） CLA as a candidate drug for treatment of Alzheimer＇ s disease.

Single-run reversed-phase HPLC method for determining sertraline content,enantiomeric purity,and related substances in drug substance and finished product

A direct enantio-,diastereo-,and chemo-selective high-performance liquid chromatographic method was developed for determining the content,enantiomeric purity,and related substances of the chiral antidepressant drug sertraline HCl in a single chromatographic run.The separation was achieved on a chiral stationary phase based on amylose tris(3-chloro-5-methylphenylcarbamate)under reversed-phase conditions.The method was optimized by evaluating the influence of the temperature and mobile phase composition on the retention and selectivity.The application of the single-run approach allowed to baseline resolve all investigated species in less than 15 min,without using buffers or tandem-coupled columns.The chromatographic method was validated according to the guidelines of the Official Medicines Control Laboratory and applied to control the content of sertraline HCl and related chiral substances in a generic antidepressant formulation.

Separation of tryptophan enantiomers with molecularly imprinted polypyrrole electrode column

In this study,we have fabricated molecularly imprinted polypyrrole(PPy) packed electrode columns and investigated their effects on separation of tryptophan(Trp) enantiomers by using potential control.The results indicate that the imprinted PPy electrode columns could efficiently enhance the L-Trp uptake and separate Trp enantiomers effectively,implying the great potential for the enantioselective recognition of other amino acids enantiomers.

Preparation of insoluble β-CD polymer and its application to enantiomers and isomers separation

An insoluble β-cyclodextrin polymer cross-linked with epichlorohydrin was prepared, and its structure was identified with infrared spectrum. Colloid stationary phase was prepared by dissolving the polymer in the mixed solvent of diisopropyl ether, methylene dichloride and benzene and treated for 0.5 h by ultrasonication, and then was coated on a fused silica capillary column. The optimun reaction conditions are as follows: the mole ratio of epichlohydrin to β-cyclodextrin is 12.1:1, reacting at 65 °C for 24 h. The Chromatographic performance such as column efficiency, thermal stabilities and polarity were studied, two kinds of disubstituted benzene isomers and eight pairs of enantiomers were separated on the capillary column. The results show that the β-cyclodextrin polymer is suitable for use as a capillary gas chromatographic stationary phase, and possess excellent chromatographic properties in separating enantiomers and position isomers.

Syntheses, Crystal Structures, and Biological Activities of Two Enantiomeric 2-Trifluoromethylthieno[2,3-d]pyrimidin-4-amine Derivatives

Two enantiomeric 2-trifluoromethyl-6,7-dihydro-5H-cyclopenta[4,5]thieno[2,3-d] pyrimidin-4-amine derivatives were synthesized by nucleophilic substitution of two chiral amines with 4-chloro-2-trifiuoromethyl-6,7-dihydro-5H-cyclopenta[4~5]thieno[2-3-d]pyrimidine, which started from 2-amino-5,6-dihydro-4H-cyclopenta[b]thiophene-3-carbonitrile, trifluoroacetic acid （TFA） and phosphoryl trichloride via one-pot procedure. Their structures were determined by single-crystal X-ray diffraction. Enantiomer （R）-3,（R）-N-（1-phenylethyl）-2-trifluoromethyl-6,7- dihydro-5H-cyclopenta[4,5]thieno[2,3-d]pyrimidin-4-amine crystallizes in the tetragonal system, space group P43 with a = 8.6847（6）, b = 8.6847（6）, c = 22.419（2） A, V= 1690.9（3） A3, Z = 4, Dc = 1.428 g/cm^3, p = 0.228 mm-1, F（000） = 752, the final R = 0.0463 and wR = 0.1257 for 3442 observed reflections with 1〉 20（/）. Enantiomer （S）-3,（S）-N-（1-phenylethyl）-2-trifluoromethyl-6,7-dihydro- 5H-cycloperita[4,5]thieno[2,3-d]pyrimidin-4-amine crystallizes in the tetragonal system, space group P41 with a = 8.688, b = 8.688, c = 22.421 A, V = 1692.4 A3, Z = 4, Dc = 1.426 g/cm^3, μ= 0.227 mm^-1, F（000） = 752, the final R = 0.0682 and wR = 0.1806 for 3182 observed reflections with ≥20（I）. The preliminary bioassay indicated that the R-enantiomer exhibits higher antitumor activity against MCF-7 than gefitinib.