Determination of optical purity by nonenantioselective LC using CD detection

The use of a circular dichroism (CD) based HPLC detection system was recently described by some authors and proposed for a nonenantioselective HPLC enantiomeric purity determination. Indeed the system, measuring both CD and UV signals simultaneously, allows the evaluation of the g anisotropy factor. In order to experimentally support such an analytical procedure as an alternative to the enantioselective chromatographic method currently found in some pharmacopoeial monographs, we have studied its application to the analysis of dexchlorpheniramine maleate, an active substance which exhibits a poor CD signal in the 250–270 nm spectral region with a g value of the order of 10⁻⁴. The results reported indicate that the suitability of the studied procedure for the enantiomeric purity determination is obtained only when the CD-detector reaches high stability; indeed a certain time lag is systematically necessary to obtain stable responses, i.e. adequate precision. The enantioselective HPLC procedure seems to be more precise for enantiomeric purity values ≤2% than the CD based detection system; such a disadvantage might be counterbalanced by the use of non chiral stationary phases.     

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.     

Determination of the enantiomeric purity of S-ropivacaine by capillary electrophoresis with methyl-beta-cyclodextrin as chiral selector using conventional and complete filling techniques.

Capillary electrophoresis (CE) methods based on the conventional and complete filling techniques for determination of the enantiomeric purity of S-ropivacaine are described. The complete filling technique is a separation method which can be used instead of the partial filling technique in order to reduce the total analysis time, when the chiral selector solution does not absorb UV light. In the complete filling technique the total length of the capillary is filled with the chiral selector solution, prior to application of the analyte. During the run both ends of the capillary are connected to the background electrolyte, i.e. without chiral agent. An interlaboratory study was performed to validate the method. The limit of detection and quantification for R-ropivacaine were found to be about 0.6 and 1.6 microg/ml, respectively, corresponding to 0. 1 and 0.25% enantiomeric purity of S-ropivacaine. Good performances were demonstrated for the repeatability and linearity. The consumption of the chiral selector was about 160 times lower with the complete filling technique compared with the conventional CE technique.     

Analysis of amino acid enantiomers derived from antitumor antibiotics using chiral capillary electrophoresis

The chiral separation of enantiomeric forms of derivatized amino acids have been achieved based on a metal–chelate chiral capillary electrophoretic method and a cyclodextrin mediated host–guest interaction approach in micellar electrokinetic chromatography (MEKC) mode with laser-induced fluorescence detection. This approach has been applied to the determination of enantiomeric forms of amino acids derived from novel depsipeptide antitumor antibiotics, BMY-45012 and its analogs. Amino acids were analyzed by complete hydrolysis and the hydrolysate was derivatized with either dansyl chloride for UV absorbance detection or fluorescein isothiocyanate for laser based fluorescence detection. The presence of several amino acids, serine and β-hydroxyl-N-methy-valine in the proposed structure have been confirmed as d-serine and l-β-hydroxyl-N-methy-valine enantiomeric forms by both chiral capillary electrophoresis (chiral CE) and MEKC approaches. A non-chiral amino acid, sarcosine, was also confirmed. These methodologies provide a quick and sensitive approach for the determination of amino acids racemization of pharmaceutical natural products and have proven to be useful for structural elucidation refinement.     

HPLC法拆分氟比洛芬对映体

建立氟比洛芬手性药物的高效液相色谱拆分方法。方法:手性流动相添加剂HPLC法:利用C18柱,以羟丙基-β-环糊精作为手性流动相添加剂,调节有机修饰剂甲醇的比例和添加不同量的三乙胺对氟比洛芬进行拆分;手性固定相HPLC法:利用Chiral-pakAD手性柱,以正己烷-乙腈为流动相基本成分,调整两者不同比例和添加不同量的三乙胺,对氟比洛芬进行拆分。结果:手性流动相添加剂法:使用C18柱对氟比洛芬对映异构体进行拆分,调节流动相中有机修饰剂甲醇浓度、手性流动相添加剂羟丙基环糊精浓度、峰型修饰剂三乙胺的浓度等都不能使氟比洛芬对映体达到基线分离,只能部分分离。手性固定相法:氟比洛芬对映体在Chiral-pakAD手性柱上能达到较好的分离。在正己烷-乙腈流动相系统中,正己烷体积含量为90%,三乙胺体积含量为0.05%的条件下,氟比洛芬对映体得到了较好的分离,分离度为10.0。结论:建立的手性固定相法能有效拆分氟比洛芬对映体而手性流动相添加剂法不能拆分氟比洛芬对映体。     

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.     

Enantioselective Analysis of Ritalinic Acids in Biological Samples by Using a Protein-Based Chiral Stationary Phase

PURPOSE: This study was to develop and validate a new chiral HPLC-UV method for the quantitative analysis of enantiomeric ritalinic acid (RA) in human plasma. METHODS: An alpha1-acid glycoprotein column was used with the mobile phase containing 0.4% acetic acid and 0.1% dimethyloctylamine, pH 3.4. The detection of enantiomeric RAs was at 220 nm. RESULTS: A baseline separation for d- and l-RA was achieved by a separation factor of 2.08. Methylphenidate, the precursor of RA, was eluted with the front solvent, and thus does not interfere in the analysis of RA in our method. The assay was successfully applied for the in vitro analysis of enantiomeric ritalinic acids produced by human and dog plasma and dog liver. CONCLUSIONS: Data demonstrated that the esterase(s) in human plasma metabolize d-methylphenidate faster than its l-isomer. The yielded intrinsic clearances (Clint) are 1.02 and 2.17 microl/min/mg protein, respectively, for d and l-methylphenidate.     

Inhibition by SRI 63-072 and SRI 63-119 of PAF-acether and immune complex effects in the guinea pig

We have examined two PAF-acether receptor antagonists, SRI 63-072 and SRI 63-119, for their ability to inhibit PAF-acether and immune complex effects in the guinea pig. Both compounds exhibited dose-dependent inhibition of bronchoconstriction and hemoconcentration induced by 0.1 micrograms kg-1 PAF-acether, where the ED50 values of SRI 63-072 were 0.3/0.4 mg kg-1 i.a. and 0.14/0.17 mg kg-1 i.a. for SRI 63-119 for each response, respectively. The d and 1 chiral forms of both antagonists were equipotent towards inhibition of hemoconcentration and bronchoconstriction, suggesting a lack of enantiomeric selectively. SRI 63-072 was further evaluated for its ability to inhibit dermal extravasation in the reverse passive Arthus reaction. Guinea pigs given 125I-BSA i.v as antigen and anti-BSA antibodies by intradermal injection exhibited plasma leakage that was dose- and time-dependent relative to the antibody amount. SRI 63-072 exhibited 46% maximal inhibition of dermal plasma leakage when injected in the skin (100 micrograms site-1 i.d.) with the antibody but less than 10% inhibition when administered intra-arterially (3.0 mg kg-1 i.a.) with the antigen. Therefore, these antagonists effectively inhibit systemic effects of PAF-acether and are partially effective towards inhibition of the dermal extravasation induced by immune complexes. Furthermore, unlike the enantiomeric differences between R and S PAF-acether, the chiral molecules of 63-119 and 63-072 effectively antagonized hemoconcentration and bronchoconstriction induced by PAF-acether.     

A short synthesis of d‐[1‐14C]‐serine of high enantiomeric purity

Herein, we report a short, three‐step synthesis of d ‐[1‐¹⁴C]‐serine (4) in high enantiomeric purity. Starting from [¹⁴C]‐KCN and 2‐(benzyloxy)acetaldehyde, Strecker reaction using (R)‐1‐phenylethylamine as the chiral auxiliary gave two diastereomeric aminonitriles 1 and 2 in the ratio of 4:3, which were conveniently separated and purified chromatographically. Following hydrolysis and subsequent hydrogenolysis, the purified major diastereomer 1, was smoothly converted to d ‐[1‐¹⁴C]‐serine (4) in an enantiomeric excess of >99%, thus circumventing time intensive chiral HPLC enantiomeric resolution.     

Enantiodiscrimination by NMR spectroscopy

The analysis of enantiorecognition processes involves the detection of enantiomeric species as well as the study of chiral discrimination mechanisms. In both fields Nuclear Magnetic Resonance (NMR) spectroscopy plays a fundamental role, providing several tools, based on the use of suitable chiral auxiliaries, for observing distinct signals of enantiomers and for investigating the complexation phenomena involved in enantiodiscrimination processes.     

Enantiomeric differences in the effects of 3,4-methylenedioxymethamphetamine on extracellular monoamines and metabolites in the striatum of freely-moving rats: an in vivo microdialysis study.

The effects of (+) and (-) 3,4-methylenedioxymethamphetamine (MDMA) and racemic p-chloroamphetamine (PCA) on extracellular dopamine and its metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), as well as the metabolite of 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), were determined in dialysates of the striatum conscious rats by using intracerebral dialysis and high performance liquid chromatography with electrochemical detection (HPLC-EC). The (+) and (-)MDMA isomers (5, 10 mg/kg, s.c.) and PCA (2.5, 5 mg/kg, s.c.) caused a rapid increase of extracellular levels of dopamine and decreased extracellular levels of DOPAC and HVA immediately after administration in dialysates of striatum. The order of potency for this effect was PCA greater than (+)MDMA greater than (-)MDMA. The levels of 5-HIAA also decreased after the administration of drugs, but the effect had a slower time course than DOPAC and HVA and did not exhibit an enantiomeric difference. The data indicate that, although these drugs are thought to affect the 5-HT neuronal system preferentially, they also affect dopamine systems and by a mechanism in which the (+) isomer was more potent than the (-).     

Advantages of achiral h.p.l.c. as a preparative step for chiral analysis in biological samples and its use in toxicokinetic studies.

1. Achiral reverse-phase h.p.l.c. with semi-automated post-column fraction collection and solid-phase sample reconcentration, has been applied as the purification procedure during the enantiomeric quantification of two widely differing experimental drugs; an HMG-CoA reductase inhibitor (I) and an alpha 2-adrenoceptor antagonist (II). 2. The robust and specific achiral methodologies were available prior to the need for chiral analyses and recovery of drug from the fractions provided clean samples from a variety of biological matrices, without the need to develop compatible achiral/chiral mobile phases. 3. Compared with direct chiral chromatography of plasma extracts, this approach decreased the potential for metabolites and endogenous components to interfere or impair the performance of the chiral stationary phase. 4. The availability of quantitative data from achiral analysis of samples negated the need for internal standardization of the chiral analyses, helped confirm assay specificity and provided potential to determine enantiomeric ratios where only one isomer could be accurately measured. 5. Routine enantiomeric analyses were successfully carried out on samples taken from animals dosed orally with the racemic drugs, providing important data on the possible levels of exposure to individual enantiomers during toxicity testing.     

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.     

Nonequivalence behavior studies for the direct determination of enantiomeric purity and absolute configuration of timolol by NMR

Direct determination of both the enantiomeric purity and absolute configuration of timolol was accomplished utilizing 1H NMR (400 MHz) spectroscopy with fast diamagnetic chiral solvating agent to dissimilarly perturb the spectra of enantiomeric solutes. Nonequivalence behavior was studied for all variables that affect populations and intrinsic spectra of the diastereomeric solvates. Optimization of the experimental conditions in terms of probe temperature, substrate concentration and solvating agent to substrate molar equivalents provided resolved enantiomeric signals suitable not only for chiral recognition but also for quantification. Enantiomeric impurity was determined on the basis of relative intensities of the tert-butyl methyl protons resonances; the assignment of enantiomeric configuration was based on the relative field positions of these resonances. The analysis of synthetic mixtures of the enantiomers by the proposed NMR method resulted in assay values which agreed closely with the known quantities of each enantiomer in mixtures tested. The mean +/-SD recovery values for the (R)-(+)-enantiomer was 100.0+/-1.6% of added antipode (n = 8). The optically pure enantiomers were used to establish the minimum detection limits of0.1%. The developed methodology represents a rapid and powerful tool for regulatory analysis.     

α_1酸性糖蛋白柱拆分西布曲明对映体

目的以α1酸性糖蛋白为固定相,建立了西布曲明的HPLC对映体拆分方法。方法考察了有机改性剂种类、比例、缓冲盐浓度、pH值、柱温以及流速等因素对西布曲明对映体拆分的影响,并对拆分机理进行了探讨。结果优化实验条件后,分离西布曲明的最佳色谱条件:流动相为异丙醇20 mmol.L-1NH4Ac(pH 5.0)(体积比为6∶94),柱温为20℃,流速为0.6 mL.min-1,在223 nm下检测。结论西布曲明对映体在α1酸性糖蛋白柱上能被完全分离。     

Enantiomeric determination of ephedrine derivatives in unregulated drugs using capillary electrophoresis

Capillary electrophoresis (CE) was applied to enantiomeric separation of chiral ephedrine derivatives (d/l-ephedrine, d/l-methylephedrine, d/l-pseudoephedrine, and d/l-norephedrine) in unregulated drug products. Unregulated drugs, referred to as dietary supplements in U.S.A., have been used legally as tonic agents, but illegal substances such as ephedrine were often detected. Baseline separation of all enantiomers of ephedrine derivatives was achieved using an electrophoretic solution containing heptakis (2,6-di-O-methyl)-beta-cyclodextrin (DM-CD) as a chiral selector. The optimal conditions were established to be: capillary column of fused silica (50 microm i.d. x 56 cm); running buffer of 20 mM DM-CD with 50 mM potassium dihydrogenphosphate background electrolyte, pH 2.6; capillary temperature of 20 degrees C; applied voltage of 30 kV; on-column detection at 195 nm; and injection pressure of 50 mbar x 3 s. Under these conditions, all four pairs of enantiomers were sufficiently resolved, and eight peaks were observed with resolution factors of greater than 1.5. The calibration curves of all enantiomers showed good linearity over the concentration range of 2.5-10 microg/ml (r =0.999). The present method was used in a survey of marketed products. The resultant chiral contents were reported and the analytical data were also compared with those from HPLC. This method is useful in the simple and rapid analysis of ephedrine derivatives in marketed products.     

Determination of enantiomeric drugs in physiological fluids using on-line solid phase derivatizations and reversed-phase liquid chromatography

A new analytical approach has been developed for the determination of d,l-amphetamine in urine using on-line solid phase derivatizations in HPLC-UV/FL. Several other enantiomeric drugs were also investigated using the same method. The method was validated by several experiments, including: (1) kinetic studies for the reaction of each enantiomeric drug with the solid phase chiral reagent; (2) "single blind spiking" experiments; and (3) polarimetry for confirmation of the enantiomeric composition determined by the solid phase diastereomer formation-HPLC-UV/FL method. The resulting diastereomers were well resolved (Rs = 1.05-1.40) under typical reversed-phase HPLC conditions. Enantiomeric contamination at the 1.1% level could be detected. The lowest amount of d,l-amphetamine that could be simultaneously derivatized and detected was about 50 ng ml-1. The linearity of the overall measurement was 3-4 orders of magnitude. d,l-Amphetamine spiked into urine at different concentration levels and different d,l-ratios, only followed by filtration, were directly injected into the on-line solid phase derivatization-HPLC-UV/FL system for quantitation with relative standard deviations 1.8-6.4% and relative errors 0.6-9.8%.     

Cellulose tris(3,5-dichlorophenylcarbamate) immobilised on silica: a novel chiral stationary phase for resolution of enantiomers

CHIRALPAK IC is a new chiral stationary phase (CSP) made by immobilising cellulose tris(3,5-dichlorophenylcarbamate) on silica gel. The chiral selector is distinct from any other commercially available polysaccharide-based CSPs. Apart from its compatibility with the whole series of solvents; this CSP is able to operate under various chromatographic conditions and bring about new characteristics in enantiomeric recognition. It can afford many large and specific enantiomeric separations. It exhibits complementary properties with regard to the existing immobilised chiral packing materials of the same category.     

A rational approach to the design of highly effective chiral stationary phases for the liquid chromatographic separation of enantiomers

The design and rationale of some novel chiral stationary phases (CSPs) are discussed with respect to methods for determining enantiomeric purity, absolute configuration and for obtaining enantiomerically pure materials by liquid chromatography. The commercially-available dinitrobenzoylamino CSP type 1 is discussed with respect to the chiral recognition mechanisms which may operate in the resolution of some polycyclic and heterocyclic aromatic molecules and some benzodiazepines. N-Acyl alpha-arylalkylamines are also employed as models to formulate mechanisms for the chiral properties of type 1 CSPs in terms of enantiomeric stacking of the most stable conformations in solution. The properties of new types of 'reciprocal' CSPs are discussed and illustrated by enantiomeric separation of some amino acid and amino phosphoric acid derivatives, and by the separation of the following enantiomeric drugs as their 3,5-dinitrobenzoyl derivatives: metoprolol, oxoprenolol, ephedrine and alprenolol.     

Determination of the optical purity of (R)-terbutaline by 1H-NMR and RP-LC using chiral derivatizing agent, (S)-(-)-alpha-methylbenzyl isocyanate

A simple, convenient and precise 1H-NMR and indirect HPLC methods were used for the determination of (S)-terbutaline in (R)-terbutaline. The enantiomers were converted to diastereomeric derivatives using (S)-(-)-alpha-methylbenzyl isocyanate and were successfully separated on an ODS column within 40 min with RS=1.41 and alpha=1.09. Interaction between chiral solutes by the formation of the diastereomeric complexes also led to differentiations of the 1H-NMR spectra of enantiomers and optical purities were determined on the basis of the peak area of the enantiomeric amine proton resonance. The effect of various experimental parameter, such as reaction time, reaction temperature and concentration of chiral derivatizing agent on the derivatization reaction and composition of mobile phase on the ODS column is discussed. Validation data such as recovery, linearity and detection limit are also presented. The results from 1H-NMR and RP-HPLC methods were compared with those from chiral HPLC method and no racemization was found during the experiments. NMR results had agreed with those obtained by indirect HPLC method and two methods could be used as a quality control method for the enantiomeric purity determination of (R)-terbutaline.