The enantiomer debate: current status and future directions

Psychopharmacology, and the treatment of depression in particular, is one area where there is currently an increasing awareness of chiral drug phenomena. It is now generally agreed that the pharmacological and pharmacokinetic properties of chiral drugs and their enantiomers should be assessed early on in the drug development process. However, issues surrounding the potential advantages and disadvantages of enantiomeric drugs, compared with racemates, continue to be debated. This article highlights some of the key issues raised during one such debate, the aim of which was to address the hypothesis that each enantiomeric drug should be considered on its own merit. The idea is considered both in general terms and specifically in the context of clinical psychiatry, with an emphasis on the treatment of depression. An update on recent developments in enantiomeric antidepressant therapy is also provided. Copyright 2001 John Wiley & Sons, Ltd.     

Liquid chromatographic chiral stationary phases in pharmaceutical analysis: determination of trace amounts of the (-)-enantiomer in (+)-amphetamine

A rapid and accurate method was developed for the determination of the enantiomeric composition of amphetamine preparations. Amide derivatives of the amphetamine enantiomers are first formed by using achiral 2-naphthoyl chloride. The resulting enantiomeric amides are then chromatographed on a commercially available chiral stationary phase. The capacity factors (k') of (-)- and (+)-2-naphthoylamphetamine are 20 and 22, respectively, and the separation factor (alpha) for the two enantiomers is 1.08. The method allows detection of as little as 0.5% of the (-)-enantiomer in (+)-amphetamine and is applicable to both bulk drug and single-tablet analyses.     

对映体选择性测定尿中N-甲基-1-(3,4-亚甲二氧苯基)-2-丙胺及其代谢物

建立了尿中Ｎ－甲基－（３，４－亚甲二氧苯基）－２－丙胺及其代谢物对映体浓度的分析方法。药物经手性衍生化后，于非手性ＧＣ固定相上分离。采用该法测定了大鼠屎中各对映体浓度，结果表明药物及其代谢物均呈立体选择性代谢．     

Direct HPLC enantioseparation of omeprazole and its chiral impurities: Application to the determination of enantiomeric purity of esomeprazole magnesium trihydrate

Analytical and semipreparative high-performance liquid chromatography (HPLC) enantioseparation of the proton-pump inhibitor omeprazole (OME) and its potential organic chiral impurities were accomplished on the immobilised-type Chiralpak IA chiral stationary phase (CSP) under both polar organic and normal-phase conditions. The (S)-enantiomers were isolated with a purity of >99% ee and their absolute configuration was empirically assigned by circular dichroism (CD) spectroscopy. A chemo- and enantioselective HPLC method was validated to control the enantiomeric purity of the (S)-enantiomer of OME (ESO), an active ingredient contained in drug products, in the presence of chiral and achiral related substances. The precision, linearity and accuracy of the determination of the (R)-impurity as well as the recovery of ESO from a pharmaceutical preparation were determined.     

Coupled column chromatography in chiral separation of salmeterol

A coupled achiral-chiral high-performance liquid chromatographic system has been developed for the determination of the enantiomers of salmeterol, S-(+)-salmeterol and R-(-)-salmeterol in urine. The salmeterol was separated from the interfering components in urine and quantified on the silica column, and the enantiomeric composition was determined on a Sumichiral OA-4700 chiral stationary phase. The two columns were connected by a switching valve equipped with a silica precolumn. The precolumn was used to concentrate the salmeterol in the eluent from the achiral column before backflushing onto the chiral phase. The coupled system was validated.     

Achiral liquid chromatography with circular dichroism detection for the determination of carnitine enantiomers in dietary supplements and pharmaceutical formulations

A simple and enantioselective method for the separation and determination of carnitine enantiomers in dietary supplements and pharmaceutical formulation samples is proposed. This method is based on achiral liquid chromatographic separation of carnitine enantiomers from interferences and direct circular dichroism (CD) detection. The calibration curve of the anisotropy factor (g) versus the enantiomeric excess was linear, with a correlation coefficient (R²) of 0.996. The precision evaluated by UV peak area and CD peak area was suitable (RSD <5% in all cases). The usefulness of the proposed method was demonstrated by analysing natural dietary supplements and pharmaceutical formulation samples. This method has the advantages of being rapid and precise, without using an expensive chiral column. The method was suitable for the simultaneous determination of both enantiomers and for assessing the chemical purity of carnitine.     

Gas-chromatographic resolution of enantiomeric secondary alcohols. Stereoselective reductive metabolism of ketones in rabbit-liver cytosol

Chiral secondary alcohols were treated with (S)-(-)-1-phenylethyl isocyanate. For each racemic alcohol, the resulting diastereomeric urethane derivatives were resolved on flexible fused-silica capillary GLC columns with retention times of 15 min or less. Derivatization of individual enantiomers showed that the urethane derivatives of (R)-(-)-2-octanol, (R)-(+)-1-phenylethyl alcohol, and (S)-(+)-2,2,2-trifluoro-1-phenylethanol are eluted before the corresponding diastereomers. The procedure is simple and rapid, and is suitable for the determination of the enantiomeric composition of chiral alcohols extracted from biological media. A series of aliphatic alcohols, aryl alkyl carbinols, and arylalkyl alkyl carbinols were resolved with the procedure, and the degree of resolution varied from good to excellent. Eight achiral ketones were incubated, individually, with rabbit-liver 90,000 g supernatant fractions, and the enantiomeric composition of the alcohol metabolites was determined with the GLC procedure. The reductions proceeded with high stereoselectivity to give alcohol products of 90% or greater enantiomeric purity. The reduction of 2-octanone and acetophenone gave predominant alcohols of (S)-configuration, in agreement with the Baumann-Prelog rule. The configuration of the predominant alcohols arising in the reduction of the remainder of the ketones could not be firmly established, but the evidence suggests that they are also of the (S)-configuration. Fluorine or methyl substitution in the ortho position of acetophenone produced an increase in the stereoselectivity, and the alcohol produced from ortho-methylacetophenone was enantiomerically greater than 99% pure.     

Resolution of Optical Isomers by Thin-Layer Chromatography: Enantiomeric Purity of Methyldopa. Dünnschichtchromatographische Enantiomerentrennung: Enantiomere Reinheit von Methyldopa

Just 20 % of chiral synthetic drugs are used as pure stereoisomers¹⁾, although it is known from numerous examples that optical isomers may have quite different biological effects²⁾. Therefore the enantiomeric purity is an important probe for monitoring the quality of drugs. The availability of reliable analytical techniques for the correct determination of enantiomeric compositions is therefore becoming increasingly important. Such a method should allow us to deal successfully with the determination of small enantiomeric impurities.     

羧甲基-β-环糊精为手性选择剂拆分托吡卡胺等4种手性药物对映体

目的以羧甲基-β-环糊精(CM-β-CD)为手性选择剂,建立毛细管区带电泳法分离托吡卡胺、文拉法辛、美托洛尔和瑞格列奈4种药物对映体。方法采用未涂壁熔融石英毛细管柱,磷酸盐缓冲液作为背景电解质溶液,分离电压为20 kV。考察了缓冲溶液的pH值、环糊精质量浓度、缓冲盐浓度对对映体分离的影响。结果在优化的分离条件下,4种手性药物均能达到完全分离。结论CM-β-CD适用于上述4种药物的对映体分离。     

Enantiomeric separations of illicit drugs and controlled substances using cyclofructan‐based (LARIHC) and cyclobond I 2000 RSP HPLC chiral stationary phases

Recently a novel class of chiral stationary phases (CSPs) based on cyclofructan (CF) has been developed. Cyclofructans are cyclic oligosaccharides that possess a crown ether core and pendent fructofuranose moieties. Herein, we evaluate the applicability of these novel CSPs for the enantiomeric separation of chiral illicit drugs and controlled substances directly without any derivatization. A set of 20 racemic compounds were used to evaluate these columns including 8 primary amines, 5 secondary amines, and 7 tertiary amines. Of the new cyclofructan‐based LARIHC columns, 14 enantiomeric separations were obtained including 7 baseline and 7 partial separations. The LARIHC CF6‐P column proved to be the most useful in separating illicit drugs and controlled substances accounting for 11 of the 14 optimized separations. The polar organic mode containing small amounts of methanol in acetonitrile was the most useful solvent system for the LARIHC CF6‐P CSP. Furthermore, the LARIHC CF7‐DMP CSP proved to be valuable for the separation of the tested chiral drugs resulting in four of the optimized enantiomeric separations, whereas the CF6‐RN did not yield any optimum separations. The broad selectivity of the LARIHC CF7‐DMP CSP is evident as it separated primary, secondary and tertiary amine containing chiral drugs. The compounds that were partially or un‐separated using the cyclofructan based columns were screened with a Cyclobond I 2000 RSP column. This CSP provided three baseline and six partial separations. Copyright © 2013 John Wiley & Sons, Ltd.     

手性药物高效毛细管电泳拆分方法的研究进展

高效毛细管电泳法（high performance capillary electrophoresis,HPCE）在手性药物拆分领域得到了广泛的应用。目前,手性离子液体用于毛细管电泳拆分手性药物时,常与环糊精（CD）类手性选择剂构成二元体系产生协同作用,增强了手性离子液体潜在的手性拆分能力。依据对映体拆分的手性选择剂的种类及浓度、缓冲液的浓度和pH、电泳工作电压和温度,选出手性拆分的最佳条件。综述手性药物的发展以及应用HPCE拆分手性药物的文献资料,并对其研究的新进展作了分析。     

The application of achiral/chiral coupled-column high-performance liquid chromatography to biomedical analysis

The use of achiral/chiral coupled-column HPLC in the direct analysis of the enantiomers of chiral drugs in biological samples is reviewed. The method has been applied to a study of the pharmacokinetics of (+)- and (-)-terbutaline, the resolution of the stereoisomers of leucovorin and the determination of warfarin enantiomers in serum.     

Chiral separation and quantitation of methylphenidate,ethylphenidate, and ritalinic acid in blood using supercritical fluid chromatography

Supercritical fluid chromatography (SFC) is a technique that analyzes compounds that are temperature-labile, have moderately low weight, or are chiral compounds. Methylphenidate (MPH) is a chiral compound with two chiral centers. MPH has two chiral metabolites, ethylphenidate (EPH) and ritalinic acid (RA). MPH is sold as a racemic mixture. The d-enantiomer of threo-MPH is responsible for medicinal effects. Due to the differing effects of the enantiomers, it is important to analyze the enantiomers individually to better understand their effects. This method utilizes SFCand solid-phase extraction (SPE) to separate and analyze the enantiomers of MPH, EPH, and RA in postmortem blood. The objective of this method was to assess a unique approach with SFC for enantiomeric separation of MPH, EPH, and RA. A SPE method was developed and optimized to isolate the analytes in blood and validated as fit-for-purpose following international guidelines. The linear range for MPH and EPH was 0.25–25 and 10–1000 ng/mL for RA in blood. Bias was −8.6% to 0.8%, and precision was within 15.4% for all analytes. Following method validation, this technique was applied to the analysis of 49 authentic samples previously analyzed with an achiral method. Quantitative results for RA were comparable to achiral technique, whereas there was loss of MPH and EPH over time. The l:d enantiomer ratio was calculated, and MPH demonstrated greater abundance of the d-enantiomer. This is the first known method to separate and quantify the enantiomers of all three analytes utilizing SFC and SPE.     

Supramolecular systems-based HPLC for chiral separation of beta-adrenergics and beta-adrenolytics in drug discovery schemes

Increasing amount of data considering polymorphism, splice variants and various affinity states of beta-adrenoceptors has resulted in a new range of opportunities for enantiopure beta-adrenergic and beta-adrenolytic drug discovery and continuous development of reliable high-throughput screening procedures enabling tissue specific pharmacological evaluation of these drugs. Design and fast pharmacological profiling of single enantiomeric molecules combining beta-adrenoceptor affinity with other pharmacophores is also still challenging ability. As the use of chiral stationary phases in HPLC has particularly benefited from results of supramolecular chemistry, this review summarises recent achievements provided by this technique in deciphering of enatiorecognition phenomena affecting pharmacological selectivity of beta-adrenergics and beta-adrenolytics and modifying the efficiency of currently proposed beta-adrenoceptor-targeted therapies. Detailed characteristic of chiral separation performance of these drugs in the range of available supramolecular HPLC systems has also been presented.     

(1)H NMR spectral simplification with achiral and chiral lanthanide shift reagents. Tranylcypromine, trans-2-phenylcyclopropanamine

The 60 MHz (1)H NMR spectra of racemic tranylcypromine, 1, have been studied with the achiral shift reagent, tris(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionato) europium(III), 2, and the chiral tris[3-(trifluoromethylhydroxymethylene)-d-camphorato] europium(III), 3. Appreciable values of the enantiomeric shift differences, DeltaDeltadelta, were observed for each cyclopropyl proton except for the proton beta and trans to the amino group (furthest from the expected europium complexation site). The proton alpha to the amino group showed DeltaDeltadelta as high as about 38 Hz for a 3:1 ratio of 0.71; the DeltaDeltadelta decreased at higher 3:1 ratios. Optical purity evaluations should be most practical using this alpha proton with 3:1 ratios near 1.07 to minimize interference due to peak overlap.     

Zur Bestimmung der Enantiomerenreinheit bei Phenyl-alkyl-carbinolen mittels chiraler Lanthaniden-Verschiebungsreagenzien

Determination of Enantiomeric Purity of Phenyl Alkyl Carbinols by Means of Chiral Lanthanide Shift Reagents The enantiomeric purities of 1-[1-methylphenyl]-1-propanol and 2-phenyl-2-butanol are determined by NMR spectroscopy using chiral shift reagents; Eu(t-bhmc)₃ and Eu(tfc)₃ have been investigated for this purpose. The latter reagent caused the best shift differences of enantiomeric protons. Addition of the achiral reagent Eu(fod)₃ was superior in the determination of the optical purity of the first mentioned carbinol.     

Chiral separation of verapamil and some of its metabolites by HPLC and CE

HPLC and CE assays were developed for chiral separations of verapamil and its metabolites in serum samples. Three chiral HPLC columns (Chiralcel OJ, Chiralpak AD and Chiralcel OD-R) were tested in normal and reverse-phase modes. All HPLC analyses were performed with fluorescence detection at 276 and 310 nm. CE was realized using CM-beta-CD as a chiral selector for the enantiomeric analysis. The results of HPLC and CE studies were compared and the possibilities for the applications in therapeutic drug monitoring were discussed.     

Stereoselective drug disposition: potential for misinterpretation of drug disposition data.

1. Although it is well recognised that the enantiomers of a chiral drug may possess different pharmacokinetic and pharmacodynamic properties, many studies dealing with chiral drugs which are administered as their racemates rely on non-stereoselective analytical techniques. 2. We present a theoretical analysis to illustrate the potential which exists for misinterpretation of drug disposition and plasma drug concentration-effect data generated for a racemic drug using a non-stereoselective assay. 3. It was shown that the use of such an analytical method can lead to the collection of data which may be both quantitatively and qualitatively inaccurate with respect to the individual enantiomers. For example, the clearance of the unresolved drug may indicate concentration- and time-dependence even though this pharmacokinetic process is concentration- and time-independent for each of the enantiomers. 4. The problems discussed emphasise the need to consider stereoselectivity in clinical pharmacological studies involving racemic drugs.