Chiral separation and molecular simulation study of six antihistamine agents on a coated cellulose tri-(3,5-dimethylphenycarbamate) column (Chiralcel OD-RH) and its recognition mechanisms.

Enantiomeric separation of six antihistamine agents was first systematically investigated on a cellulose-based chiral stationary phase (CSP), that is, cellulose tris-(3,5-dimethyl phenyl carbamate) (Chiralcel OD-RH), under the reversed-phase mode. Orphenadrine, meclizine, terfenadine, dioxopromethazine, and carbinoxamine enantiomers were completely separated under the optimized mobile phase conditions with resolutions of 5.02, 1.93, 1.68, 1.67, and 1.54, respectively. Mequitazine was partially separated with a resolution of 0.77. The influences of type and concentration of buffer salt, the pH of buffer solution, and the type and ratio of organic modifier on the chiral separation were evaluated and optimized. For a better insight into the enantiorecognition mechanisms, molecular docking was carried out via the Autodock software. The lowest binding energy and the optimal conformations of the analytes/CSP complexes were supplied, and the mechanisms of chiral recognition were determined. According to the results, the key interactions for the chiral recognition of these six analytes on CDMPC were π-π interactions, hydrophobic interactions, hydrogen bond interactions, and some special interactions.

Enantioseparation on a new synthetic ß-cyclodextrin chemically bonded chiral stationary phase and molecular docking study.

A novel ß-cyclodextrin derivative chemically bonded chiral stationary phase (EDACD) was synthesized by the reaction of mono-6-ethylenediamine-ß-cyclodextrin with the active alkyl isocyanate, anchoring to silica gel. After the successful analysis and characterization using scanning electron microscopy, Fourier transform infrared spectra, solid-state nuclear magnetic resonance spectra, elemental analysis, and thermogravimetric analysis techniques, the enantioselective performance of the as-prepared EDACD column was evaluated by non-steroidal antiinflammatory drugs and flavonoids under the reversed-phase HPLC condition. The factors that affected enantioseparation including mobile phase compositions and buffers were investigated in more detail. As a result, EDACD showed a satisfactory enantioselectivity for the tested drugs. With the mobile phase of acetonitrile and 20-mM ammonium formate adjusted to pH 4.0 using formic acid (85:15, v/v) at the flow rate of 0.6 mL min-1, the enantiomers of ibuprofen, carprofen, naproxen, indoprofen, ketoprofen, eriocitrin, naringin, and narirutin were separated with the best resolutions of 1.53, 1.64, 3.72, 2.40, 0.50, 0.61, 0.58, and 0.52. To adjust the proportion of acetonitrile to 80% (by volume), the enantiomers of pranoprofen and flurbiprofen were completely resolved with the best resolutions of 1.60 and 1.59. Additionally, by the study of the molecular docking, hydrogen bonding and inclusion complexation were believed to play an important role in chiral recognition. As a new material, EDACD will have a wider application in the analysis of chiral compounds.

Enantioseparation and molecular modeling study of eight psychoactive drugs on a coated polysaccharide-based chiral stationary phase.

The enantioseparation of eight psychoactive drugs has been firstly performed on a coated cellulose-based chiral stationary phase (Chiralcel OJ-H). To obtain optimum separation conditions, the influences of alcohol modifiers and basic/acidic additives have been studied. As a result, except for the partial separation of oxybutynin enantiomers, the other seven drug enantiomers including mirtazapine, sulpiride, promethazine, citalopram, oxazepam, donepezil, and cyamemazine have been completely separated. Additionally, for gaining a better insight into the chiral recognition mechanisms, molecular docking was carried out using the Autodock software. Herein, binding energy and conformations of the chiral stationary phase complexes were provided, and it was found that the distinction in enantiomeric conformation determined the number and strength of intermolecular interactions between analytes and chiral stationary phase which resulted in the difference in binding energies of two enantiomers, and ultimately led to the different migration. These modeling results were in accordance with the observed enantioseparation results in high performance liquid chromatography experiments. At last, chiral separation mechanisms have been discussed in detail, and it has been confirmed that hydrogen bond, π-π, hydrophobic interactions, and some special interactions synergistically contributed to the enantioseparation of psychoactive drugs. This article is protected by copyright. All rights reserved.

Evaluation of chiral separation based on bovine serum albumin-conjugated carbon nanotubes as stationary phase in capillary electrochromatography.

In this work, we utilized adsorbed BSA and multiwalled carbon nanoparticles (BSA/MWCNTs) as a stationary phase in open tubular (OT) capillary for separation of chiral drugs. (3-Aminopropyl)triethoxysilane was used to assist fabrication of BSA/MWCNTs-coated OT column by covalent bonding. Incorporation of MWCNTs nanomaterials into a polymer matrix could increase the phase ratio and take advantage of the easy preparation of an open tubular CEC column. SEM was carried out to characterize the BSA/MWCNTs OT columns. The electrochromatographic performance of the OT columns was evaluated by separation of ketoprofen, ibuprofen, uniconazole, and hesperidin. The effects of MWCNTs concentration, background solution pH and concentration, and applied voltage on separation were investigated. Chiral separations of ketoprofen, ibuprofen, uniconazole, and hesperidin were achieved using the BSA/MWCNTs-coated OT column with resolutions of 24.20, 12.81, 1.50, and 1.85, respectively. Their optimas were found in the 30 mM phosphate buffers at pH 5.0, 6.5, 7.0, and 6.5, respectively. In addition, the columns demonstrated good repeatability and stability with the run-to-run, day-to-day, and batch-to-batch RSDs of migration times less than 3.5%.

Enantioselective determination of econazole in rat plasma and its application to a pharmacokinetic study.

Econazole is a widely used chiral antifungal drug. In this paper, an enantioselective liquid chromatography-tandem mass spectrometry (LC-MS/MS) method has been developed and validated for determination of econazole enantiomers in rat plasma for the first time. After addition of the internal standard (IS) clotrimazole, plasma samples were extracted by liquid-liquid extraction with n-hexane:2-propanol (98.5:1.5, v/v). Baseline separation of the enantiomers was achieved on a Chiralpak® IC column (250 mm × 4.6 mm, 5 µm) using acetonitrile-ammonium acetate buffer (5 mM) (85:15, v/v) as mobile phase. The detection of the analytes was performed in multiple reaction monitoring (MRM) mode with positive electrospray ionization. Transitions of m/z 381.07 â†’ 124.92 and 276.78 â†’ 164.92 were monitored for econazole enantiomers and clotrimazole, respectively. The linear range was 0.20-50.00 ng/mL with the lower limit of quantification of 0.20 ng/mL for both econazole enantiomers in plasma. The intra-day and inter-day precisions were not exceeding 10.2% and the accuracies were within ±15.0%. The validated method was successfully applied to the stereoselective pharmacokinetic study of econazole enantiomers in rat plasma after transdermal administration of racemic econazole nitrate cream. Significant differences were observed in Cmax, AUC and CL/F of econazole enantiomers, indicating the enantioselective pharmacokinetic behavior of econazole in rats.

Enantioselective LC-MS/MS method for the determination of cloperastine enantiomers in rat plasma and its pharmacokinetic application.

Cloperastine is a central antitussive used to reduce the frequency and intensity of coughing on a short-term basis. In this study, a reliable chiral LC-MS/MS technology has been developed for the quantification of cloperastine enantiomers in the rat plasma. Carbinoxamine was selected as the internal standard. The enantioseparation of cloperastine was performed on a Chiralpak IA column with a mobile phase composed of acetonitrile-water-ammonium hydroxide (80:20:0.1, v/v/v) at a flow rate of 0.6 mL/min. Cloperastine enantiomers were detected by mass spectrometry in multiple reaction monitoring mode with a positive electrospray ionization source. The method was validated over the linear concentration range of 0.05 to 10.0 ng/mL (5.0 × 10-4 ng to 0.10 ng) for both enantiomers. The lower limit of quantification (LLOQ) for each analyte was determined as 0.05 ng/mL. The relative standard deviations (RSDs) of intraday and interday precision was less than 13.9%, and the relative error (RE) of accuracy ranged from -5.4% to 6.1%, which were within the acceptance criteria. Finally, an application to the stereoselective pharmacokinetics of cloperastine in rats was successfully realized in our assay. The developed method on a commercially available Chiralpak IA column under isocratic mobile phase is advantageous to analyze cloperastine enantiomers in plasma samples collected for enantioselective metabolism or drug interaction studies.

Hydroxypropyl ß-cyclodextrin nanohybrid monoliths for use in capillary electrochromatography with UV detection: application to the enantiomeric separation of adrenergic drugs, anticholinergic drugs, antidepressants, azoles, and antihistamine.

Two kinds of hydroxypropyl ß-cyclodextrin nanohybrid monoliths were synthesized and applied in capillary electrochromatography with UV detection. One column was fabricated by concurrently using glycidyl methacrylate-bonded hydroxypropyl ß-cyclodextrin (GMA-HP-ß-CD), sodium 3-mercaptopropanesulphonate, and alkoxysilanes in the "one-pot" process. The other was prepared by free radical polymerization of GMA-HP-ß-CD, vinylmethylcyclosiloxane, ethylene dimethacrylate, and 2-acrylamido-2-methyl propane sulfonic acid. Compared to the former hybrid monolith, the latter one displayed improved enantiomeric separation. For ten adrenergic drugs, six anticholinergic drugs, two antidepressants, six azoles, and one antihistamine enantiomeric separation was obtained on the monolith synthesized by free radical polymerization. Twelve out of twenty-five drugs were baseline-separated. Especially, anisodamine with two chiral centers was successfully separated with resolution values of 3.06, 2.11, and 2.17. The nanohybrid monoliths were characterized by optical microscopy, scanning electron microscopy, FT-IR, nitrogen adsorption analysis, and thermogravimetric analysis. Relative standard deviation values less than 5% were obtained through run-to-run, day-to-day, and column-to-column investigations (n = 3). Graphical abstract Schematic representation of two kinds of hydroxypropyl ß-cyclodextrin nanohybrid monoliths based on "one-pot" approach (route I) and free radical polymerization approach (route II), respectively.

Enantioseparation and Determination of Penconazole in Rat Plasma by Chiral LC-MS/MS: Application to a Stereoselective Toxicokinetic Study.

In this study, a specific and sensitive method of liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) was developed for the determination of penconazole enantiomers in rat plasma. The enantioseparation was achieved on a Chiralpak IC column by using acetonitrile/water (80:20, v/v) as the mobile phase. Penconazole enantiomers and internal standard l-lansoprazole (IS) were detected in multiple reaction monitoring (MRM) mode with positive electrospray ionization source. The method was validated over the concentration range of 2.5-250.0 ng mL-1 for penconazole enantiomers. Good linearity was obtained for both enantiomers with correlation coefficients (R) greater than 0.995. The relative error was well within the admissible range of -1.1-3.2%, and relative standard deviation was less than 6.0%. After validation, the established method was successfully applied to a stereoselective toxicokinetic study in female and male rats after oral administration of 50 mg kg-1 racemic penconazole. This is the first experiment regarding the stereospecific toxicokinetic study of penconazole and the bioanalytical approach for its quantitation in vivo.

Magnetic solid-phase extraction based on carbon nanosphere@Fe3 O4 for enantioselective determination of eight triazole fungicides in water samples.

In this work, a carbon nanosphere decorated by Fe3 O4 nanoparticles was prepared, characterized and used as the magnetic adsorbent. Eight commonly used chiral triazole fungicides, including penconazole, uniconazole, paclobutrazol, triazolone, tebuconazole, hexaconazole, triticonazole and epoxiconazole were extracted from two environmental water samples (river water and lake water) by magnetic solid-phase extraction, followed by the enantiomeric analysis on a Chiralpark IC column coupled with a triple quadrupole mass spectrometry to evaluate their possible stereoselective degradation occurring in the water samples. The possible factors affecting the extraction performance, such as amount of used adsorbents, pH and ionic strength of water solution, types and volumes of desorption solvents were systematically investigated. Under the optimum conditions, extraction yields of eight triazole fungicides were above 80% and the concentration factors were as high as 1000. Method detection and quantification limits for the enantiomers of eight triazole fungicides were in the range of 0.56-6.95 ng/L. Satisfactory accuracy (relative recovery 77.8-93.5%), good intraday precision (RSD 4.3-9.8%) and interday precision (RSD 3.1-7.9%) were also obtained. The developed method provided the simplicity of operation, rapidity and high enrichment factor, which can be used to monitor and evaluate the behavior of the individual enantiomer of chiral triazole fungicides.

Solid-phase extraction coupled with switchable hydrophilicity solvent-based homogeneous liquid-liquid microextraction for chloramphenicol enrichment in environmental water samples: a novel alternative to classical extraction techniques.

A simple and efficient method combining solid-phase extraction (SPE) with homogeneous liquid-liquid microextraction (HLLME) has been developed for fast pretreatment of chloramphenicol (CAP) from water samples prior to determination by high-performance liquid chromatography-ultraviolet detection. Oasis HLB sorbent was chosen for SPE. In HLLME, N,N-dimethylcyclohexylamine was used as a CO2-triggered switchable solvent that could switch reversibly between hydrophilic and hydrophobic forms. The parameters influencing both SPE and HLLME were investigated and optimized. Under the optimal conditions, the method exhibited low limit of detection (0.1 ng/mL), good linearity (0.5-50 ng/mL), acceptable precision (RSD <5.0%) and accuracy (RE <4.0%). An enrichment factor of 340 was obtained. The proposed method is simple, fast, cost-effective, and suitable for the determination of trace chloramphenicol in water matrices. Graphical abstract ᅟ.

Enantioseparation and determination of flumequine enantiomers in multiple food matrices with chiral liquid chromatography coupled with tandem mass spectrometry.

The present work firstly described the enantioseparation and determination of flumequine enantiomers in milk, yogurt, chicken, beef, egg, and honey samples by chiral liquid chromatography-tandem mass spectrometry. The enantioseparation was performed under reversed-phase conditions on a Chiralpak IC column at 20°C. The effects of chiral stationary phase, mobile phase components, and column temperature on the separation of flumequine enantiomers have been studied in detail. Target compounds were extracted from six different matrices with individual extraction procedure followed by cleanup using Cleanert C18 solid phase extraction cartridge. Good linearity (R2 >0.9913) was obtained over the concentration range of 0.125 to 12.5 ng g-1 for each enantiomer in matrix-matched standard calibration curves. The limits of detection and limits of quantification of two flumequine enantiomers were 0.015-0.024 and 0.045-0.063 ng g-1 , respectively. The average recoveries of the targeted compounds varied from 82.3 to 110.5%, with relative standard deviation less than 11.7%. The method was successfully applied to the determination of flumequine enantiomers in multiple food matrices, providing a reliable method for evaluating the potential risk in animal productions.

Separation of eight bedaquiline analogue diastereomers by HPLC on an immobilized polysaccharide-based chiral stationary phase.

The high-performance liquid chromatography (HPLC) is a powerful method in the area of stereoisomer separation. In this study, separation of eight bedaquiline analogue diastereomers (compounds 1-8) was first examined on a cellulose tris-(3,5-dichlorophenylcarbamate) chiral stationary phase, ie, Chiralpak IC in the normal phase mode. The influences of organic modifier types, alcohol content, and column temperature on diastereoseparation were evaluated. Under the optimum chromatographic conditions, all the analyte stereoisomers were successfully separated. The experimental results revealed the great influence of analytes' structures on the diastereoseparation with Chiralpak IC. In addition, thermodynamic parameters were calculated by Van't Hoff plots, and correlative chiral recognition mechanisms were discussed further.

Enantioseparation and molecular modeling study of five ß-adrenergic blockers on Chiralpak IC column.

A new high-performance liquid chromatography (HPLC) method was developed for the enantiomeric resolution of five ß-adrenergic blockers on a Chiralpak IC column (250 mm × 4.6 mm, 5.0 µm particle size) in normal phase mode. The mobile phase used was n-hexane-ethanol-diethylamine in different proportions at the flow rate of 1.0 mL/min with the column temperature of 25°C using a UV detector at 230 nm. The influences of base additives and alcohol modifiers were evaluated and optimized. The maximum resolution values for bevantolol, propranolol carteolol, esmolol, and metoprolol were 4.80, 2.77, 2.09, 2.30, and 1.11, respectively. To gain a better understanding of the interaction between chiral stationary phase and analyte enantiomers, the molecular docking of chiral stationary phase with five pairs of enantiomer was carried out using AutoDock molecular docking technique. By simulation studies, the mechanism of chiral recognition was determined. According to the results, hydrogen bond interactions and π-π interactions were the chief interactions for the chiral recognition.

Dissolvable layered double hydroxide as a sorbent in dispersive micro-solid phase extraction for the determination of acidic quinolones in honey by HPLC.

This study presents a simple and green dispersive micro-solid phase extraction method for preconcentration of acidic quinolones from honey prior to high performance liquid chromatography determination. A two-dimensional nanostructured zinc-aluminum layered double hydroxide was synthesized and used as the sorbent for dispersive micro-solid phase extraction. Its different characteristics from conventional sorbents is that it is dissolvable in acidic solution (pH < 4). After the extraction, the analyte elution step was omitted and thus the use of organic solvents was avoided. The key parameters influencing the extraction efficiency such as the amount of sorbent, pH of sample solution, vortex time, type and volume of acidic solution were investigated and optimized. The method exhibited low limits of detection (3.0-5.0 ng/g), good linearity (10-2000 ng/g) with coefficients of determinations higher than 0.9991, acceptable precision (RSD<9.1%) and accuracy (RE<5.8%). The proposed method is fast, efficient, eco-friendly, and suitable for the determination of acidic quinolones in honey samples.

Sol-gel technique for the preparation of ß-cyclodextrin gold nanoparticles as chiral stationary phase in open-tubular capillary electrochromatography.

A novel open-tubular capillary electrochromatography column coated with ß-cyclodextrin was prepared using the sol-gel technique. In the sol-gel approach, owing to the three-dimensional network of sol-gel and the strong chemical bond between the stationary phase and the surface of capillary columns, good chromatographic characteristics and unique selectivity in separating enantiomers were shown. The influences of capillary inner diameter, coating time, organic modifier, buffer pH, and buffer concentration on separation were investigated. The sol-gel-coated ß-cyclodextrin column has shown improved enantioseparation efficiency of chlorphenamine, brompheniramine, pheniramine, zopiclone in comparison with the sol-gel matrix capillary column. The migration time relative standard deviation of the separation of the enantiomers was less than 0.89% over five runs and 2.9% from column to column. This work confirmed that gold nanoparticles are promising electrochromatographic support to enhance the phase ratio of open-tubular capillary electrochromatography column in capillary electrochromatography.

Enantioselective degradation of chiral fungicides triticonazole and prothioconazole in soils and their enantioselective accumulation in earthworms Eisenia fetida.

Triticonazole and prothioconazole are widely used systemic agricultural triazole fungicides both with a chiral center. In this work, the enantioselective degradation of triticonazole and prothioconazole in three types of soils were investigated under native conditions using reversed phase liquid chromatography-tandem mass spectrometry with a Chiralcel OD-RH column. The results indicated that the enantioselective degradation was observed with S-triticonazole and R-prothioconazole preferentially degraded and the degradation rate was fast with a half-life within 6 days. It was also found that the presence of earthworms can accelerate the degradation and further enhance degradation enantioselectivity of triticonazole and prothioconazole in soils. Moreover, the enantioselective of triticonazole and prothioconazole in earthworms were studied. The results showed that the bioaccumulation was enantioselective with R-triticonazole and S-prothioconazole preferentially accumulated, which was similar to the soil. Our findings suggest that the enantioselective toxicity and potential effects of the metabolites should be considered for more accurate assessment of ecological risks of triticonazole and prothioconazole to target and non-target species.

Direct Enantiomeric Resolution of Seventeen Racemic 1,4-Dihydropyridine-Based Hexahydroquinoline Derivatives by HPLC.

1,4-Dihydropyridine (DHP) scaffold holds an outstanding position with its versatile pharmacological properties among all heterocyclic compounds. Although most of the commercially available DHPs are marketed as a racemic mixture, the chiral center at C-4 can lead to even opposite pharmacological activities between the enantiomers. In the present study, enantioseparation of seventeen DHP structural analogues, consisting of either pharmacologically active or newly synthesized derivatives, (M2-4, MD5, HM2, HM10, CE5, N11, N10, N7, M11, MC6-8, MC13, MD23, and 42IIP) by high-performance liquid chromatography was investigated using immobilized polysaccharide-based chiral stationary phase, Chiralpak IC column. Due to the solvent versatility of the covalently immobilized chiral stationary phase in enantiomer separation, multiple elution modes including standard normal phase, nonstandard mobile phase, and reversed phase were used to expand the possibility to find the optimum enantioselective conditions for the tested analytes. Under appropriate separation conditions, complete enantiomeric separation was obtained for nearly all compounds except MC6-8 and MC13 which contained two chiral centers. Additionally, the effects of the polar modifier, the additive, and column temperature on the chiral recognition were evaluated. The thermodynamic parameters calculated according to the linear van't Hoff equation indicated that the chiral separations in this study were enthalpy-driven or entropy-driven. Some parameters of method validation such as linearity, limit of quantitation, and repeatability were also measured for all studied compounds to prove the reliability of the method.

[Chemical constituents from rhizome of Menispermum dauricum and their anti-hypoxic activities].

To study the chemical constituents from the rhizome of Menispermum dauricum,fifteen compounds,N-methylcorydaldine( 1),thalifoline( 2),stepholidine( 3),acutumine( 4),daurisoline( 5),acutumidine( 6),dauricicoline( 7),bianfugecine( 8),6-O-demethylmenisporphine( 9),bianfugedine( 10),dauricoside( 11),eleutheroside D( 12),aristolactone( 13),aristoloterpenateⅠ( 14) and aristolochic acid( 15) were isolated from 75% ethanol extract of Menispermi Rhizoma by using thin layer chromatography and column chromatography methods. Their structures were identified based on their physicochemical properties and spectral data. Among them,compounds 12-15 were obtained from the genus Menispermum for the first time. Six alkaloids with higher contents were subjected to evaluate the anti-hypoxic activities by using MTT method. As a result,six alkaloids exhibited significant anti-hypoxia activities.

Preparation of ß-cyclodextrin-gold nanoparticles modified open tubular column for capillary electrochromatographic separation of chiral drugs.

In this paper, ß-cyclodextrin (ß-CD) modified gold nanoparticles (AuNPs) coated open tubular column (OT column) was prepared for capillary electrochromatography. The open tubular column was constructed through self-assembly of gold nanoparticles on 3-mercaptopropyl-trimethoxysilane (MPTMS) prederivatized capillary and subsequent modification of thiols ß-cyclodextrin (SH-ß-CD). Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and ultraviolet visible spectroscopy were carried out to characterize the prepared open tubular column and synthesized gold nanoparticles. By comparing different coating times of gold nanoparticles and thiols ß-cyclodextrin, we got the optimal conditions for preparing the open tubular column. Also, the separation parameters were optimized including buffer pH, buffer concentration and applied voltage. Separation effectiveness of open tubular column was verified by the separation of four pairs of drug enantiomers including bifonazole, fexofenadine, omeprazole and lansoprazole, and satisfactory separation results were achieved for these analytes studied. In addition, the column showed good stability and repeatability. The relative standard deviation values less than 5% were obtained through intra-day, inter-day, and column-to-column investigations.

Determination of brompheniramine enantiomers in rat plasma by cation-selective exhaustive injection and sweeping cyclodextrin modified electrokinetic chromatography method.

A method consisting of cation-selective exhaustive injection and sweeping (CSEI-sweeping) as online preconcentration followed by a cyclodextrin modified electrokinetic chromatography (CDEKC) enantioseparation has been developed for the simultaneous determination of two brompheniramine enantiomers in rat plasma. In this method, analytes were electrokinetically injected at a voltage of 8 kV for 80 s in a fused-silica capillary. Prior to the injection, the capillary was rinsed with 50 mM phosphate buffer of pH 3.5, followed by a plug of a higher conductivity buffer (150 mM phosphate pH 3.5, 20 psi, 6 min) and a plug of water (0.5 psi, 5 s). Separation was carried out applying -20 kV in 50 mM phosphate buffer, pH 3.5, containing 10% v/v ACN and 30 mg/mL sulfated-ß-cyclodextrin (S-ß-CD). Analytical signals were monitored at 210 nm. The detection sensitivity of brompheniramine enantiomers was enhanced by about 2400-fold compared to the normal injection mode (hydrodynamic injection for 3 s at 0.5 psi, with a BGE of 50 mM phosphate buffer containing 20 mg/mL S-ß-CD at pH 3.5), and LLOQ of two enantiomers were both 0.0100 µg/mL. In addition, this method had fairly good repeatability and showed promising capabilities in the application of stereoselective pharmacokinetic investigations for brompheniramine enantiomers in rat.