Stereoselective HPLC analysis of tertatolol in rat plasma using macrocyclic antibiotic chiral stationary phase

Enantiomeric resolution of teratolol was achieved on a vancomycin macrocyclic antibiotic chiral stationary phase known as Chirobiotic V with UV detection set at 220 nm. The polar ionic mobile phase (PIM) consisted of methanol-glacial acetic acid-triethylamine (100:0.01:0.015, v/v/v) has been used at a flow rate of 0.8 ml min(-1) . The calibration curves in plasma were linear over the range of 5-500 ng ml(-1) for each enantiomer with detection limit of 2 ng ml(-1) . The proposed method was validated in compliance with the international conference on harmonization (ICH) guidelines. The developed method applied for the trace analyses of tertatolol enantiomers in plasma and for the pharmacokinetic study of tertatolol enantiomers in rat plasma. The assay proved to be suitable for therapeutic drug monitoring and chiral quality control for tertatolol formulations by HPLC.     

Enantiomeric separation of several cyclic imides on a macrocyclic antibiotic (vancomycin) chiral stationary phase under normal and reversed phase conditions

Several cyclic imidic compounds (barbiturates, piperidine-2,6-diones, and mephenytoin) are enantiomerically resolved via high-performance liquid chromatography (HPLC) on a macrocyclic antibiotic covalently bonded to a silica gel support. The Chirobiotic V chiral stationary phase (CSP) column contains the antibiotic vancomycin as the chiral selector. The results of the analysis show that the substituents at the chiral carbon position of the racemic drugs affect chiral resolution. In addition, ring size may also play a role when considering the formation of analyte-CSP inclusion complexes. Contrary to the piperidine-2,6-diones, the chromatographic parameters for the barbiturates are much the same under normal- or reversed-phase conditions. The details of these results are discussed. Chirality 10:358–361, 1998. © 1998 Wiley-Liss, Inc.     

Analysis of benidipine enantiomers in human plasma by liquid chromatography-mass spectrometry using a macrocyclic antibiotic (Vancomycin) chiral stationary phase column

We used a novel chromatographic method to rapidly and simply characterize the pharmacokinetics of benidipine enantiomers in human plasma. The stereoisomers of benidipine were extracted from plasma using diethylether under alkaline conditions. After evaporating the organic layer, the residue was reconstituted in the mobile phase (methanol:acetic acid:triethylamine, 100:0.01:0.0001, v/v/v). The enantiomers in the extract were separated on a macrocyclic antibiotic (Vancomycin) chiral stationary phase column. The mobile phase was eluted at 1 ml/min and was split by an interface. One-fifth of the eluent was used to quantify both isomers in a tandem mass spectrometer in multiple reaction-monitoring mode. The coefficient of variation of the precision of the assay was less than 8%, the assay accuracy was between 93.4 and 113.3%, and the limit of detection was 0.05 ng/ml for 1 ml of plasma. The method described above was used to measure the concentration of both benidipine enantiomers in plasma from healthy subjects who received a single oral dose of a racemate of 8 mg benidipine. The C(max) and AUC(inf) values of (+)-alpha benidipine were higher than those of (-)-alpha benidipine by 1.96- and 1.85-fold, respectively (p<0.001), whereas, the T(max) and t(1/2) for each of the benidipine stereoisomers were not significantly different.     

Analysis of carvedilol enantiomers in human plasma using chiral stationary phase column and liquid chromatography with tandem mass spectrometry

Carvedilol is an antihypertensive drug available as a racemic mixture. (?)‐(S)‐carvedilol is responsible for the nonselective β‐blocker activity but both enantiomers present similar activity on α₁‐adrenergic receptor. To our knowledge, this is the first study of carvedilol enantiomers in human plasma using a chiral stationary phase column and liquid chromatography with tandem mass spectrometry. The method involves plasma extraction with diisopropyl ether using metoprolol as internal standard and direct separation of the carvedilol enantiomers on a Chirobiotic T® (Teicoplanin) column. Protonated ions [M + H]⁺ and their respective ion products were monitored at transitions of 407 > 100 for the carvedilol enantiomers and 268 > 116 for the internal standard. The quantification limit was 0.2 ng ml^?1 for both enantiomers in plasma. The method was applied to study enantioselectivity in the pharmacokinetics of carvedilol administered as a single dose of 25 mg to a hypertensive patient. The results showed a higher plasma concentration of (+)‐(R)‐carvedilol (AUC^0–∞ 205.52 vs. 82.61 (ng h) ml^?1), with an enantiomer ratio of 2.48. Chirality, 2012. © 2012 Wiley Periodicals, Inc.     

Chiral separation of tryptophan enantiomers by liquid chromatography with BSA-silica stationary phase

The separation of tryptophan enantiomers was carried out with medium-pressure liquid chromatography using BSA (bovine serum albumin)-bonded silica as a chiral stationary phase. The influence of various experimental factors such as pH and ionic strength of mobile phase, separation temperature, and the presence of organic additives on the resolution was studied. In order to expand this system to preparative scale, the loadability of sample and the stability of stationary phase for repeated use were also examined. The separation of tryptophan enantiomers was successful with this system. The data indicated that a higher separation factor (α) was obtained at a higher pH and lower temperature and ionic strength in mobile phase. Addition of organic additives (acetonitrile and 2-propanol) in mobile phase contributed to reduce the retention time of L-tryptophan. About 30% of the separation factor was reduced after 80 days of repeated use.     

Immobilized vancomycin as chiral stationary phase in packed capillary liquid chromatography

Fused silica-packed capillary columns containing vancomycin immobilized by reductive amination on an aldehyde-silica were used to separate enantiomers of some non-steroidal anti-inflammatory drugs. Attempts have been made to qualitatively explain the influence of various mobile phase compositions on the enantioselective retention. The effects of mobile phase pH, buffer, and organic modifier concentrations were investigated as well as the influence of salts of hydrophobic ions added to the mobile phase to induce ion pair retention. Chirality 10:273–280, 1998. © 1998 Wiley-Liss, Inc.     

Structural features affecting chiral resolution of cannabimimetic enantiomers by amylose 3,5-dimethylphenylcarbamate chiral stationary phase

The effect of structural features of six pairs of enantiomers of cannabimimetic compounds on their chromatographic resolution on an amylose tris(3,5-dimethylphenylcarbamate) chiral stationary phase was studied using various compositions of n-hexane with 2-propanol and ethanol. Structural analysis by molecular mechanics was also performed to verify that the 3D conformation within this family of compounds was preserved with substitution. The homologous enantiomeric pairs showed better resolution when there was an additional OH group near the chiral centers (position 7 on the cannabinoid structure). Better resolution was observed also for the enantiomeric pair that had the smaller alkyl side chain. These differences indicated that the additional OH group contributed to a better discrimination of the enantiomers by the chiral sites of the stationary phase and that the bulkier alkyl side chain reduced it. The chromatographic resolution of two enantiomeric pairs of nonclassical cannabinoids HU-249 and HU-250, HU-255 and HU-256, was compared both in ethanol and 2-propanol. Both enantiomeric pairs showed relatively high resolution and selectivity, but the rigid benzofuran analogs (HU-249 and HU-250) exhibited better resolution using 2-propanol, in spite of the flexibility of the open chain analog (HU-255 and HU-256) and its additional OH group. The elution order of all the cannabinoids was (+)/(?) using both solvents. Unusual solvent effects were displayed by one enantiomeric pair, Δ⁶-THC, which was resolved easily using 2-propanol, but whose elution order reversed with 1% ethanol in the mobile phase. Partial separation was obtained at 5% ethanol [elution order (+)/(?)] and full separation was obtained at 0.5% ethanol [elution order (?)/(+)]. © 1995 Wiley-Liss, Inc.     

High‐performance liquid chromatography separation of enantiomers of mandelic acid and its analogs on a chiral stationary phase

The enantiomers of mandelic acid and its analogs have been chromatographically separated on a chiral stationary phase (CSP) derived from 4‐(3,5‐dinitrobenzamido) tetrahydrophenanthrene. The rationale of separations of these compounds is discussed with respect to the method development for determining enantiomeric purity and possibility of obtaining enantiomerically pure materials by high‐pressure liquid chromatography. The relationship of analyte structure to the extent of enantiomeric separation has been examined and separation factors (α) are presented for various groups of structurally related compounds. Chiral recognition models have been suggested to account for the observed separations. These models provide mechanistic insights into the chiral recognition process. Chirality 2010. © 2009 Wiley‐Liss, Inc.     

Separation of nicotine and nornicotine enantiomers via normal phase HPLC on derivatized cellulose chiral stationary phases

This paper describes the enantiorecognition of (±)nicotine and (±)nornicotine by high-performance liquid chromatography using two derivatized cellulose chiral stationary phases (CSPs) operated in the normal phase mode. It was found that different substituents linked to the cellulose backbone significantly influence the chiral selectivity of the derivatized CSP. The results showed that, in general, the tris(4-methylbenzoyl) cellulose CSP (Chiralcel OJ) surpasses tris(3,5-dimethylphenyl carbamoyl) cellulose CSP (Chiralcel OD). On the former column, the resolution (±)nicotine and (±)nornicotine enantiomers depended largely on mobile phase compositions. For the separation of the nicotine enantiomers, the addition of trifluoroacetic acid to a 95:5 hexane/alcohol mobile phase greatly improved the enantioresolution, probably due to enhanced hydrogen bonding interactions between the protonated analytes and the CSP. For (±)nornicotine separation, a reduction in the concentration of alcohol in the mobile phase was more effective than the addition of trifluoroacetic acid. Possible solute-mobile phase-stationary phase interactions are discussed to explain how different additives in the mobile phase and different substituents on the cellulose glucose units of the CSPs affect the separation of both pairs of enantiomers. Chirality 10:364–369, 1998. Published 1998 Wiley-Liss, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Resolution of terfenadine enantiomers by beta-cyclodextrin chiral stationary phase high-performance liquid chromatography.

Enantiomers of terfenadine were resolved by high-performance liquid chromatography (HPLC) using a chiral stationary phase (CSP) column packed with beta-cyclodextrin (beta-CD) covalently bound to silica. Separation was achieved in both the reverse phase and normal phase modes. Resolution of enantiomers was confirmed by ultraviolet-visible absorption, circular dichroism, and mass spectral analysis.     

Direct resolution of ergot alkaloid enantiomers on a novel chiral silica-based stationary phase

A new covalently-bonded, silica-based stationary phase, using as the chiral selector the 1-(3-aminopropyl) derivative of (+)-(5R,8S,10R)-terguride, has been developed to resolve optically active isomers by HPLC. Good resolution of structurally related racemic ergot alkaloids were obtained using water-methanol mixtures as the eluent. Analysis of the influence of the type and concentration of the organic modifier, and the pH of the buffer in the mobile phase allowed the enantioseparation of these compounds to be optimized. Determination of the optical purity of a lisuride-containig drug is reported. © 1994 Wiley-Liss, Inc.     

Direct enantiospecific HPLC bioanalysis of (R,S)-atenolol on a chiral stationary phase

The simultaneous determination of the enantiomers of the β₁-selective adrenergic antagonist atenolol in human plasma and urine is described. After an alkaline preextraction atenolol is extracted from biological material at pH 12.3 using dichloromethane/propan-2-ol. The separation of the underivatized enantiomers is achieved by high-performance liquid chromatography on a chiral stationary phase (Chiralcel OD, cellulose tris-3, 5-dimethylphenylcarbamate, coated on silica gel) with fluorimetric detection. (?)-(S)-Pindolol is used as an internal standard. The detection limits of 5 ng/ml enantiomer in plasma and 50 ng/ml enantiomer in urine are sufficient for pharmacokinetic studies after therapeutic doses. © 1993 Wiley-Liss, Inc.     

Diphenylethanediamine (DPEDA) as chiral selector: VII. Efficient HPLC resolution of a series of underivatized diarylcarbinols on a chiral stationary phase based on C5-amide-bonded N-3,5-dinitrobenzoyl-DPEDA

Fast and efficient baseline separation of asymmetrically substituted diarylmethanols and 1,1-diarylethanols was achieved on an endcapped, amide-linked N-3,5-dinitrobenzoylated, (R, R)-1,2-diphenyl-1,2-ethanediamine-derived chiral stationary phase (CSP). Optimal enantioselectivities on this CSP were obtained using 1% 2-propanol in n-heptane as the mobile phase. Enantiorecognition was found to be governed by π-basicity and the substitution pattern of the aromatic substituents. © 1996 Wiley-Liss, Inc.     

HPLC separation technique for analysis of bufuralol enantiomers in plasma and pharmaceutical formulations using a vancomycin chiral stationary phase and UV detection

A sensitive and selective high-performance liquid chromatographic (HPLC) method has been developed for the simultaneous determination of bufuralol enantiomers in plasma and pharmaceutical formulations. Enantiomeric resolution was achieved on a vancomycin macrocyclic antibiotic chiral stationary phase (CSP) known as Chirobiotic V with UV detection set at 254 nm. The polar ionic mobile phase (PIM) consisting of methanol-glacial acetic acid-triethylamine (100:0.015:0.010, v/v/v) has been used at a flow rate of 0.5 ml/min. The method is highly specific where other coformulated compounds did not interfere. The stability of bufuralol enantiomers under different degrees of temperature was also studied. The results showed that the drug is stable for at least 7 days at 70 degrees C. The method was validated for its linearity, accuracy, precision and robustness. An experimental design was used during validation to evaluate method robustness. The calibration curves in plasma were linear over the range of 5-500 ng/ml for each enantiomer with detection limit of 2 ng/ml. The mean relative standard deviation (RSD) of the results of within-day precision and accuracy of the drug were 0.05) between inter- and intra-day studies for each enantiomer which confirmed the reproducibility of the assay method. The mean extraction efficiency for S-(-)- and R-(+)-bufuralol from plasma was in the range 97-102% at 15-400 ng/ml level for each enantiomer. The overall recoveries of bufuralol enantiomers from pharmaceutical formulations was in the range 99.6-102.2% with %RSD ranging from 1.06 to 1.16%. The assay method proved to be suitable as chiral quality control for bufuralol formulations by HPLC and for therapeutic drug monitoring.     

Chiral HPLC analysis of milnacipran and its FMOC-derivative on cellulose-based stationary phases

The HPLC enantioseparation of the last generation antidepressive drug milnacipran (+/-)-1 was investigated on different cellulose-based chiral stationary phases (CSPs). On carbamate-type columns, Chiralcel OD and OD-H (+/-)-1 could be separated with alpha value about 1.20 but the resolution was quite low because of the tailing of the peaks. Direct determination of (+/-)-1 with high selectivity and resolution was obtained on Chiralcel OJ in normal phase mode elution. Precolumn derivatization of milnacipran with Fmoc-Cl gave compound (+/-)-2 which was enantioseparated on all the investigated CSPs and allowed enhanced UV or fluorimetric detection. The Chiralpak IB, that could be considered the immobilized version of Chiralcel OD-H, was found completely ineffective in the chiral recognition of (+/-)-1 and moderately efficient in the separation of (+/-)-2.     

Interactions of chiral molecules with an (r)-n-(3,5-dinitrobenzoyl) phenylglycine HPLC stationary phase

Forty different chiral molecules were studied by liquid chromatography with a Pirkle-type, (R)-N-(3,5-dinitrobenzoyl) phenylglycine (DNBPG), chiral stationary phase column. The dramatic effect of a small molecular change on chiral recognition was demonstrated using DL-amino acid derivatives. The inductive effect on chiral recognition was also studied using trifluoro-, trichloro-, dichloro-, monochloroacetyl, and acetyl derivatives of four different chiral amines. The study of the enantiomer separation of 11 different crown ethers of 2,2′-binaphthyldiyl showed that the rigidity of the chiral center can be an additional parameter in chiral recognition for the DNBPG phase but not for a β-cyclodextrin bonded chiral phase. It is apparent from this study that steric effects, inductive effects, and molecular rigidity play important roles in chiral recognition with DNBPG chiral stationary phases.     

The direct chiral separations of fungicide enantiomers on amylopectin based chiral stationary phase by HPLC

Amylopectin-tris(phenylcarbamate) was synthesized and coated to aminopropylsilica to prepare chiral stationary phase. The chiral separations of fungicide enantiomers were performed by the CSP using high-performance liquid chromatography. Mobile phase was n-hexane and isopropanol, and flow rate was 1.0 ml/min. Detection wavelength was 230 nm. The influence of the percentage of isopropanol in the mobile phase on the separations was studied. Twelve chiral fungicides were tested and seven of them were found to show stereoselectivity on the CSP. The enantiomers of metalaxyl and benalaxyl got near baseline separations and myclobutanil, hexconazole, tebuconazole, uniconazole, and paclobutrazol enantiomers were completely separated. The decreasing percentage of isopropanol in the mobile phase resulted in better separation and longer analysis time. The enantiomers were identified by a circular dichroism (CD) detector and the CD spectra of the individual enantiomers were also studied by online scanning.     

Enantioseparation of chiral pharmaceuticals by vancomycin‐bonded stationary phase and analysis of chiral recognition mechanism

The drug chirality is attracting increasing attention because of different biological activities, metabolic pathways, and toxicities of chiral enantiomers. The chiral separation has been a great challenge. Optimized high‐performance liquid chromatography (HPLC) methods based on vancomycin chiral stationary phase (CSP) were developed for the enantioseparation of propranolol, atenolol, metoprolol, venlafaxine, fluoxetine, and amlodipine. The retention and enantioseparation properties of these analytes were investigated in the variety of mobile phase additives, flow rate, and column temperature. As a result, the optimal chromatographic condition was achieved using methanol as a main mobile phase with triethylamine (TEA) and glacial acetic acid (HOAc) added as modifiers in a volume ratio of 0.01% at a flow rate of 0.3 mL/minute and at a column temperature of 5°C. The thermodynamic parameters (eg, ΔH, ΔΔH, and ΔΔS) from linear van 't Hoff plots revealed that the retention of investigated pharmaceuticals on vancomycin CSP was an exothermic process. The nonlinear behavior of lnk′ against 1/T for propranolol, atenolol, and metoprolol suggested the presence of multiple binding mechanisms for these analytes on CSP with variation of temperature. The simulated interaction processes between vancomycin and pharmaceutical enantiomers using molecular docking technique and binding energy calculations indicated that the calculated magnitudes of steady combination energy (ΔG) coincided with experimental elution order for most of these enantiomers.     

Use of a new pirkle-type chiral stationary phase in analytical and preparative subcritical fluid chromatography of pharmaceutical compounds

Good results have been obtained with use of the new bonded chiral stationary phase Whelk-O 1 in analytical and preparative subcritical fluid chromatography. A wide variety of enantiomeric pairs of compounds with different functional groups that are of pharmaceutical and biological interest have been resolved. This Pirkle-concept CSP appears to be more rugged than cellulosic phases (e.g., Chiralcel) with regards to solvents and pressure. In comparing the usefulness of the column for SFC versus HPLC chiral analysis, we have observed a clear superiority of SFC in terms of higher speed and efficiency of analysis, and faster method development. This is consistent with our experience with Chiralcel CSPs. With the Whelk-O 1 we have shown that the effects of temperature and modifier on SFC separations are similar to what has been reported for most other CSPs. We also observed a unique selectivity advantage of SFC for verapamil. We had good success with using a 1-in. diameter column packed with Whelk-O 1 to perform preparative SFC separations of a number of enantiomeric mixtures. The advantages of preparative SFC over preparative HPLC will be discussed. The feasibility of preparative SFC is dependent on how well we meet the practical challenges such as sample introduction issues, special hardware requirements due to the high pressure, and fraction collection issues. © 1994 Wiley-Liss, Inc.     

Direct high-performance liquid chromatography (HPLC) separation of etodolac enantiomers using chiral stationary phases

The enantiomers of the antiinflammatory drug Etodolac were separated without derivatization on Chiralcel OD and Pirkle (R)-DNBPG columns. Enantiomeric purity can be determined in less than 10 min. Optimization of separation was evaluated using various concentrations of 2-propanol (doped with TFA) in hexane as the mobile phase. © 1993 Wiley-Liss, Inc.