Separation of drug enantiomers by HPLC using chiral stationary phases — A selective review

Enantioseparation of ketoconazole and miconazole by capillary electrophoresis and a study on their inclusion interactions with β-cyclodextrin and derivatives

A chiral separation method coupled with capillary electrophoresis (CE) analysis for ketoconazole and miconazole enantiomers using chiral selectors such as β-cyclodextrin (β-CD) and hydroxypropyl-β-CD (HP-β-CD) was developed in this study, which included the optimisation, validation and application of the method on the antifungal cream samples. The formation of inclusion complex between the hosts (β-CD and HP-β-CD) and guests (ketoconazole and miconazole) were compared and analysed using ultraviolet-visible spectrophotometry, nuclear magnetic resonance (NMR) spectroscopy and molecular docking methods. Results from the study showed that in a concentration that ranged between 0.25 and 50 mg L^-1 , the linear calibration curves of each enantiomer had a high coefficient of regression (R² > 0.999), low limit of detection (0.075 mg L^-1 ) and low limit of quantification (0.25 mg L^-1 ). The relative standard deviation (RSD) of the intraday and interday analyses ranged from 0.79% to 8.01% and 3.30% to 11.43%, respectively, while the recoveries ranged from 82.0% to 105.7% (RSD < 7%, n = 3). The most probable structure of the inclusion complexes was proposed based on the findings from the molecular docking studies conducted using the PatchDock server.

Strong Enantiomeric Preference on the Macroion-Counterion Interaction Induced by Weakly Associated Chiral Counterions

The role of chiral counterions on the attraction and self-assembly of chiral Pd₁₂L₂₄ metal organic cages (MOCs) with NO₃^- being the original counterion is studied by laser light scattering and isothermal titration calorimetry. Nitrates can trigger the self-assembly of macrocationic Pd₁₂L₂₄ into hollow spherical blackberry-type supramolecular structures via counterion-mediated attraction. Although chiral counteranions, such as N-(tert-butoxycarbonyl)-alanine (Boc-Ala), have weaker interaction with the MOCs compared to NO₃^-, they can induce different assembly behaviors between two enantiomeric MOCs by inhibiting the MOC-nitrate binding and weakening the interaction between them. The d-counterions are capable of selectively suppressing and slowing down the assembly of l-MOCs and also considerably decreasing their assembly size due to the much weaker MOC-nitrate interaction. The same scenario is observed for l-counterions when interacting with the d-MOCs. This study unveils the role of weakly associated chiral counterions on the central chiral macroions, especially their supramolecular structure formation, and provides additional evidence on the mechanism of the homochirality phenomenon.

Directing the Handedness of Helical Nanofilaments Confined in Nanochannels Using Axially Chiral Binaphthyl Dopants

In this work, we demonstrate control of the handedness of semicrystalline modulated helical nanofilaments (HNF_mods) formed by achiral bent-core liquid crystal molecules by axially chiral binaphthyl-based additives as guest molecules solely under spatial nanoconfinement in anodic aluminum oxide nanochannels. The molecules of the same chiral additives are expelled from the HNF_mods in the bulk, and as a result thereof do not affect the handedness or helical pitch of bulk HNF_mods, resulting in an HNF_mod conglomerate with chirality-preserving growth within each domain. However, under confinement these axially chiral guest molecules, likely embedded in the HNF_mod host, do affect the helicity of the HNF_mods. The configuration of the axially chiral molecules decides the HNF_mod helix handedness and their concentration, and the helix angle is related to the helical pitch of the HNF_mods. In addition to local imaging data obtained by scanning electron microscopy, global studies by thin-film circular dichroism spectropolarimetry support the imaging results.

From Substituent Effects to Applications: Enhancing the Optical Response of a Four-Component Assembly for Reporting EE Values

High-throughput screening for asymmetric catalysts has stimulated an interest in optically-based enantiomeric-excess (ee) sensors, primarily for their improved time and cost efficiency when compared to the standard HPLC analysis. We present herein substituent-effect studies on a recently reported Zn(II) multicomponent assembly that is used for chiral, secondary alcohol ee detemination. The systematic altering of assemblies formed from select substituted pyridyl ligands pointed to the conclusion that steric effects dominate the mode of interaction at the pyridyl 3- and 6- positions. From these results we identified a new Zn(II)-centered multicomponent assembly with a higher dynamic range than previously reported. Calibration curves of the CD signals resulting from the new assembly led to an ee assay with a 1.7% error. To further the utility of the new assembly, a correlation was developed between alcohol substituent size to the respective enantiopure CD value.

Diastereomeric liquid crystal domains at the mesoscale

In many technologies used to achieve separation of enantiomers, chiral selectors are designed to display differential affinity for the two enantiomers of a chiral compound. Such complexes are diastereomeric, differing in structure and free energy for the two enantiomers and enabling chiral discrimination. Here we present evidence for strong diastereomeric interaction effects at the mesoscale, manifested in chiral liquid crystal guest materials confined in a chiral, nanoporous network of semi-crystalline helical nanofilaments. The nanoporous host is itself an assembly of achiral, bent-core liquid crystal molecules that phase-separate into a conglomerate of 100 micron-scale, helical nanofilament domains that differ in structure only in the handedness of their homogeneous chirality. With the inclusion of a homochiral guest liquid crystal, these enantiomeric domains become diastereomeric, exhibiting unexpected and markedly different mesoscale structures and orientation transitions producing optical effects in which chirality has a dominant role.

Enantiomeric separation of biaryl atropisomers using cyclofructan based chiral stationary phases

Normal phase chiral HPLC methods are presented for the enantiomeric separation of 30 biaryl atropisomers including 18 new compounds recently produced via a novel synthetic approach. Three new cyclofructan based chiral stationary phases were evaluated. Separations were achieved for all but six analytes and the LARIHC™ CF6-P alone provided 15 baseline separations. Effects of polar modifiers and temperature effects also were studied. Apparent thermodynamic parameters were determined by van't Hoff plots. Preparative scale methods were developed and employed resulting in the first ever isolation of these novel atropisomers in their pure enantiomeric form. Insights into the mechanism of retention and chiral discrimination are presented.

Enantioselectivity of mass spectrometry: challenges and promises

With the fast growing market of pure enantiomer drugs and bioactive molecules, new chiral-selective analytical tools have been instigated including the use of mass spectrometry (MS). Even though MS is one of the best analytical tools that has efficiently been used in several pharmaceutical and biological applications, traditionally MS is considered as a "chiral-blind" technique. This limitation is due to the MS inability to differentiate between two enantiomers of a chiral molecule based merely on their masses. Several approaches have been explored to assess the potential role of MS in chiral analysis. The first approach depends on the use of MS-hyphenated techniques utilizing fast and sensitive chiral separation tools such as liquid chromatography (LC), gas chromatography (GC), and capillary electrophoresis (CE) coupled to MS detector. More recently, several alternative separation techniques have been evaluated such as supercritical fluid chromatography (SFC) and capillary electrochromatography (CEC); the latter being a hybrid technique that combines the efficiency of CE with the selectivity of LC. The second approach is based on using the MS instrument solely for the chiral recognition. This method depends on the behavioral differences between enantiomers towards a foreign molecule and the ability of MS to monitor such differences. These behavioral differences can be divided into three types: (i) differences in the enantiomeric affinity for association with the chiral selector, (ii) differences of the enantiomeric exchange rate with a foreign reagent, and (iii) differences in the complex MS dissociation behaviors of the enantiomers. Most recently, ion mobility spectrometry was introduced to qualitatively and quantitatively evaluate chiral compounds. This article provides an overview of MS role in chiral analysis by discussing MS based methodologies and presenting the challenges and promises associated with each approach.

Application of click chemistry on preparation of separation materials for liquid chromatography

With the increasing requirement for analysis and separation of samples related to genomics, proteomics, metabolomics, pharmacology and agrochemistry, diverse stationary phases for liquid chromatography have been prepared by Cu(i)-catalyzed 1, 3-dipolar azide-alkyne cycloaddition reaction (CuAAC). It has been proved that CuAAC is a powerful tool for preparing covalently bonded stationary phases. In this tutorial review, we highlighted the preparation of separation materials by immobilization of functional groups on silica beads, polymer beads and agarose via CuAAC and their applications in liquid chromatography and related purposes, such as separation of polar compounds, enrichment of valuable bio-samples, orthogonal two-dimensional HPLC and chiral separation. Meanwhile, agarose-based separation materials for affinity chromatography are reviewed.

Comparison of high-performance liquid chromatography of cyclotriphosphazene derivatives with one or two equivalent stereogenic centres

High-performance liquid chromatographic (HPLC) methods have been developed for investigating the stereogenic properties of two analogous series of dibenzylamino derivatives of cyclotriphosphazene containing either one or two equivalent stereogenic centres. Separation of the enantiomers of all the racemic compounds has been investigated by chiral HPLC using Whelk-01 and Chiralcel OD columns. In all cases, conditions for separation of enantiomers have been found using a Whelk-01 column with different ratios of tetrahydrofuran in n-hexane as the mobile phase. It is found that both the separation factor (alpha) and resolution factor (R(S)) of molecules with two equivalent stereogenic centres are greater than those for analogues with only one centre.

Use of β-cyclodextrin bonded phase with s-triazine moiety in the spacer for separation of aromatic carboxylic acid isomers by high-performance liquid chromatography

The separation and retention behavior of five aromatic carboxylic acid isomers was investigated by means of high-performance liquid chromatography (HPLC) using a beta-cyclodextrin bonded phase with s-triazine ring in the spacer. The influence of mobile phase pH on the retention was examined. The presence of s-triazine moiety in the spacer enhances greatly the selectivity of the isomers of aromatic carboxylic acids. Baseline separations of the five aromatic carboxylic acid isomers were achieved. In particular, the isomers of toluic, aminobenzoic, nitrobenzoic and hydroxybenzoic acid were successfully and effectively separated. The chromatographic results indicate that, in addition to inclusion complexation, pi-pi interaction and hydrogen bonding interaction between the bonded phase and analytes play significant roles in the retention of these acid isomers. Different elution orders were observed for these acidic solutes with different substituents. Possible retention mechanisms are discussed.

On the separation of nonadditive symmetric mixtures in nanoscopic slitlike pores: A simple model for racemic fluids

A grand canonical ensemble Monte Carlo simulation method is used to study the adsorption of nonadditive symmetric mixtures of Lennard-Jones spherical particles in nanoscopic slitlike pores. The walls of the pore are assumed to be formed by the parallel (100) planes of the model face centered cubic crystal of adjustable corrugation potential. It is demonstrated that depending on the nonadditivity effects in the mixture and the pore width the condensed phases formed inside the pore may have different structures. In particular, it is shown that the mixture may separate into layers containing only one component each and the stacking may depend on the pore width and properties of the mixture.

Chiral recognition by mass-resolved laser spectroscopy

Chiral recognition is a fundamental phenomenon in life sciences, based on the enantioselective complexation of a chiral molecule with a chiral selector. The diastereomeric aggregates, formed by complexation, are held together by a different combination of intermolecular forces and are therefore endowed with different stability and reactivity. Determination of these forces, which are normally affected in the condensed phase by solvent and supramolecular interactions, requires the generation of the diastereomeric complexes in the isolated state and their spectroscopic investigation. This review deals with chiral recognition in the gas phase through the application of laser-resolved mass spectrometric techniques (R2PI-TOF and RET-MS). The measurement of the fragmentation thresholds of diastereomeric clusters by these techniques allows the determination of the nature of the intrinsic interactions, which control their formation and affect their stability and reactivity.

In vivo metabolism for the hydroxylation of FK778 to the metabolite M3 in humans studied by enantioselective liquid chromatography/tandem mass spectrometry

A major active metabolite of malononitrilamide FK778 (an immunosuppressant under development) is labeled M3. Due to a chiral center created during in vivo metabolism, the exploration of enantiomer profiles in clinical samples is critical to the characterization of the immunosuppressive activity of M3. An enantioselective liquid chromatography method with detection by tandem mass spectrometry (LC/MS/MS) was developed for the resolution of M3 enantiomers. It was experimentally confirmed that no interconversion between the two enantiomers occurred during sample preparation. This new approach was applied to measure the enantioselectivity of the M3 metabolite in human plasma samples from kidney transplanted patients. The assay results of 91 in vivo human samples from three subjects showed a ratio of 57:43 for the (-)-enantiomer (the 2nd eluter) vs. the (+)-enantiomer (1st eluter), indicating that the enantiometabolism of FK778 through human enzymes is essentially non-specific.

Chiral separation and CD characterisation of enantiomeric cyclotriphosphazene derivatives

The gem-disubstituted cyclotriphosphazene 1 reacted with piperazine (pip) to give the piperazine-bridged derivative 2, which is expected to exist in meso and racemic forms because the two PCl (pip) groups are stereogenic. The proton-decoupled (31)P NMR spectrum of 2 gave rise to two similar sets of ABX signals in a 1:1 ratio, consistent with formation of diastereoisomers. The meso and racemic forms of compound 2 were separated by column chromatography on silica gel and characterised by elemental analysis, mass spectrometry, (31)P NMR spectroscopy, and X-ray crystallography. Using HPLC with a chiral stationary phase, the racemic form of compound 2 was further separated into enantiomers, which were characterised by circular dichroism (CD) spectroscopy. This is the first report of the separation of enantiomers in the field of cyclophosphazene chemistry and hence the first CD spectra of derivatives in which the cyclophosphazene ring is at the chiral centre.

Analysis of chiral pharmaceuticals using HPLC with CD detection

Recent American Food and Drug Administration guidelines have effectively determined that mixtures of chiral compounds can no longer be brought to the pharmaceuticals marketplace. These guidelines require a means for chiral detection and compound separation. This article describes separation and detection of chiral pharmaceuticals using HPLC with circular dichroism detection. Two over-the-counter (OTC) medications, Prilosec and naproxen sodium, along with the prescription drugs Naproxen, Nexium, and Coumadin were analyzed using HPLC with CD, UV, and optical rotation (OR) detection. In all cases the CD and UV detectors displayed a much greater sensitivity than the OR detector. Although in many cases the UV detector did have a slightly better sensitivity than the CD detector, the CD detector had the advantage of only responding to the chiral compounds, eliminating the possibility of interference with the peaks of interest.

Preparation and enantioseparation characteristics of two chiral stationary phases based on mono(6A-azido-6A-deoxy)-perphenylcarbamoylated ?- and ?-cyclodextrin

Two chiral stationary phases, ph-alpha-CD and ph-gamma-CD, were prepared from mono(6(A)-azido-6(A)-deoxy)perphenylcarbamoylated alpha- and gamma-cyclodextrin immobilized onto silica gel via the Staudinger reaction. The chromatographic characteristics of these two chiral stationary phases were evaluated. The influence of different cyclodextrins (CDs) on the enantioselectivities was also investigated in this study. Compared to ph-gamma-CD, ph-alpha-CD exhibited quite good enantioselectivity toward the analytes with bulky molecular structures. It was found that the formation of inclusion complex might play a quite important role in the chiral recognition not only under reverse phases but also under normal phases.

Enantioselective liquid chromatography of C3-chiral 2,3-dihydro-1,2,5-benzothiadiazepin-4(5H)-one and thione 1,1-dioxides on polyacrylamide- and polysaccharide-based chiral stationary phases

Optically active synthetic and semisynthetic polymers were utilized as chiral stationary phases (CSPs) for the direct chromatographic enantioseparation of a series of 8-chloro-2,3-dihydro-3-methyl-1,2,5-benzothiadiazepin-4(5H)-one and thione 1,1-dioxide. Evaluation of stereochemical integrity of chiral analytes was assessed by enantioselective temperature and flow-dependent HPLC. A stopped-flow high-performance liquid chromatography (sfHPLC) procedure was developed for the determination of the rate constants and free energy barriers of enantiomerization of enantiomers of 8-chloro-2-(3-methylbut-2-enyl)-2,3-dihydro-3-methyl-1,2,5-benzothiadiazepin-4(5H)-thione 1,1-dioxide (compound 2) in the presence of Chiraspher and Chiralcel OD CSPs. In order to study the chiroptical properties of the individual enantiomers of analytes investigated, semipreparative chromatographic resolutions were performed. The assignment of the absolute configuration was empirically established by comparing the CD spectra of the separated enantiomers with those obtained from structural analogues.

Pharmacokinetics of the active antifungal enantiomer, SCH 42427 (RR), and evaluation of its chiral inversion in animals following its oral administration and the oral administration of its racemate genaconazole (RR/SS)

Genaconazole (SCH 39304) is a potent triazole antifungal agent that is active both orally and topically. Genaconazole is a racemic mixture which contains 50% of the RR (SCH 42427) and 50% of the SS (SCH 42426) enantiomers. The RR isomer accounts for most of the antifungal activity of genaconazole. Serum concentrations of the RR and SS enantiomers were analyzed by a chiral HPLC method which involved extraction of serum with organic solvent followed by separation on a Cyclobond I column and quantification by UV absorbance at 205 nm. The bioavailability and pharmacokinetic profiles of the two enantiomers after oral administration of the racemate (genaconazole) were very similar in cynomolgus monkeys. In rats following dosing with genaconazole, the RR enantiomer had a lower C(max) and a longer t(1/2) than the SS enantiomer, while the AUC(I) values of the two enantiomers were similar. Based on chiral HPLC analysis, there was no evidence for the inversion of the RR to the SR isomer, or of the SS to the SR isomer, indicating that there was no chiral inversion of the RR or SS enantiomers in either species. Genaconazole at 20 mg/kg and the RR (SCH 42427) enantiomer at 10 mg/kg had very similar serum concentration-time profiles and C(max), AUC(I), and t(1/2) values for the RR enantiomer in both rats and monkeys, indicating that the two treatments were equivalent with respect to the bioavailability of the RR enantiomer.

Micellar electrokinetic chromatography-mass spectrometry using a polymerized chiral surfactant

The coupling of chiral micellar electrokinetic chromatography (CMEKC) to mass spectrometry (MS) using conventional surfactant [above the critical micelle concentration (cmc)] is very challenging. Preliminary investigation in this laboratory indicates that the use of a chiral polymeric surfactant provides one possible solution to this difficult coupling. This is because of many positive attributes of micelle polymers which include zero cmc, lower surface activity, low volatility, high electrophoretic mobility, and function as a suitable separation medium even at lower concentrations of pseudophases. In this work, the feasibility of using poly(sodium N-undecanoyl-L-valinate (poly-L-SUV) in CMEKC-MS is demonstrated. After CMEKC separation, enantiomers of 1,1'-binaphthol (BOH) were detected using electrospray ionization mass spectrometry (ESI-MS) by selected ion monitoring (SIM) in the negative ion mode. Although in the SIM mode ESI-MS parameters (nebulizer pressure, drying gas flow rate, drying gas temperature, and sheath liquid flow rate) affected only the signal-to-noise ratio of (+/-)BOH, two of the ESI-MS parameters (nebulizer pressure, sheath flow rate) were found to have a significant impact on chiral resolution of (+/-)BOH. At the optimum ESI-MS conditions, the enantioseparation of (+/-)BOH was successfully accomplished by varying the buffer pH, concentration of the volatile background electrolyte, and poly-L-SUV.

Chiral separation by chromatographic and electromigration techniques. A review

This review gives a survey of different chiral separation principles and their use in high-performance liquid chromatography (HPLC), gas chromatography (GC), supercritical fluid chromatography (SFC), thin-layer chromatography (TLC), capillary electrophoresis (CE) and capillary electrochromatography (CEC) highlighting new developments and innovative techniques. The mechanisms of the different separation principles are briefly discussed and some selected applications are shown.

Enantiomeric analysis of pharmaceutical compounds by ion/molecule reactions

Protonated complexes involving cyclodextrin hosts and guest compounds that are pharmacologically important are produced in the gas phase and reacted with a gaseous amine. The guest is exchanged to produce a new protonated complex with the amine. The reaction is enantioselective and is used to develop a method for determining enantiomeric excess using only mass spectrometry. The pharmaceutical compounds include DOPA, amphetamine, ephedrine, and penicillamine. The presence of more than one reacting species is observed with DOPA and penicillamine. Molecular dynamics calculations are used to understand the nature of the interactions and the possible source of the variations in the reactivities.

Synthesis and characteristics of the human serum albumin-triazine chiral stationary phase

Human serum albumin (HSA) was successfully bonded to silica with s-triazine as activator. The coupling reaction by this method was rapid and effective. The triazine-activated silica is relatively stable and can be installed for at least 1 month without obvious loss of reactivity when stored below 30 degrees C, pH below 7. It was observed that the amount of bound HSA reached 120 mg/g silica calculated from the UV absorbance difference of the HSA solution. d, l-tryptophan was selected as the probe solute to characterize the properties of HSA bonded s-triazine chiral stationary phase, and separation factor of 9.4 was obtained for d,l-tryptophan. Furthermore, the amount of effective HSA on silica was measured by high-performance frontal analysis, and only 16.8 mg/g silica was responsible for the resolution of d,l-tryptophan. These results indicate that the amount of both the bound and effective HSA on silica with triazine as activator was much higher than those by the Schiff base coupling method. Different kinds of enantiomers were resolved successfully on the aminopropylsilica-bonded HSA s-triazine chiral stationary phase.

Chiral high-performance liquid chromatographic analysis of antifungal SCH 56592 and evaluation of its chiral inversion in animals and humans

SCH 56592 is a novel triazole antifungal agent that is active both orally and intravenously in animal models of infection. This compound is in Phase II-III clinical trials for the treatment of systemic fungal infections. SCH 56592 is a single enantiomer with four stereogenic centers; therefore, it was necessary to evaluate the possible chiral inversion of this drug candidate in animals and humans. Thus, chiral high-performance liquid chromatographic (HPLC) methods have been developed to separate SCH 56592 from its diastereomers and to evaluate its chiral inversion in rats, dogs, cynomolgus monkeys, and humans. Chiral HPLC analysis involved the use of a Chiralcel OD column set at 39 degrees C with a mobile phase of hexane-ethanol-diethylamine and a fluorescence detector set at an excitation wavelength of 270 nm and an emission wavelength of 390 nm. Plasma or serum samples were subjected to solid phase extraction on a C(2) cartridge followed by HPLC analysis. The method was sensitive with a limit of quantitation of 0.1 microg/ml in dog serum. The linearity was satisfactory, as shown by correlations of >0.997 and by visual examination of the calibration curves. The precision and accuracy were satisfactory, as indicated by coefficients of variation (CV) ranging from 1.1 to 12.1% and bias values ranging from -11.0 to 9.0%. Chiral HPLC analysis indicated that SCH 56592 was not subjected to chiral inversion in rats, dogs, cynomolgus monkeys, and humans.

Synthesis of a silica-bonded bovine serum albumin s-triazine chiral stationary phase for high-performance liquid chromatographic resolution of enantiomers

A novel method of synthesizing protein chiral stationary phase (protein-CSP) is proposed with 2,4,6-trichloro-1,3,5-triazine as the activator. The bovine serum albumin (BSA) based chiral columns (150 x 4.6 mm I.D.) were prepared successfully within 8 h. With tryptophan as the probe solute, it was observed that the BSA immobilized by this method had a better ability to distinguish enantiomers than that activated by glutaric dialdehyde. This may be due to the well-maintained BSA conformation and the larger amount of BSA immobilized on the silica gel. The BSA-CSP prepared by this method was relatively stable under experimental conditions, and the resolution of 13 chiral compounds was achieved. The coupling reaction in this method is mild, reliable and reproducible; it is also suitable for the immobilization of various biopolymers in the preparation of bioreactor, biosensor and affinity chromatography columns.

The influence of beta-cyclodextrin on the solubility of chlorthalidone and its enantiomers

The solubility of chlorthalidone in 16 solvent systems was determined in the absence and presence of different amounts of beta-cyclodextrin (beta-CD). Chlorthalidone (CT) was shown to be more soluble in hydrophilic organic solvents, with the highest solubility in ethylacetate (EtOAc) saturated with water. The solubility of CT in water, butanol, octanol, and dichloromethane (DCM) was enhanced by the addition of beta-cyclodextrin. The enantioselective partitioning of CT between water and EtOAc, DCM, butan-1-ol, butan-2-ol, and octan-1-ol was determined in the presence of beta-CD at pH 5, 7, and 9. According to the results, both the solubility and partitioning properties of CT are affected by beta-CD in aqueous solution. It was also shown that the solubility of the individual enantiomers differs in the presence of beta-CD.

High-performance liquid chromatographic analysis of the anti-tumor agent SCH 66336 in cynomolgus monkey plasma and evaluation of its chiral inversion in animals

SCH 66336 is a novel non-cytotoxic anti-tumor agent that is in phase I/II clinical trials for the treatment of solid tumors. This compound is a single enantiomer with one chiral center. Prior to evaluation of this drug candidate in man, it was necessary to evaluate its pharmacokinetics and possible chiral inversion in animals. Thus, high-performance liquid chromatographic (HPLC) methods have been developed for its determination in cynomolgus monkey plasma and for the evaluation of its chiral inversion in rats and cynomolgus monkeys. The achiral HPLC analysis involved extraction with 30% methylene chloride in hexane followed by separation on a CN column and quantitation by UV absorbance at 280 nm. The method was linear over a concentration range of 0.1 to 20 microg/ml in monkey plasma. The chiral HPLC analysis involved the use of a Chiralpak AD column set at 39 degrees C with a mobile phase of hexane-ethanol-diethylamine mixture and a UV detector set at 280 nm. Plasma samples were subjected to solid-phase extraction on a C2 cartridge prior to HPLC analysis. The method was linear over a concentration range of 0.25 to 10 microg/ml in rat and cynomolgus monkey plasma for both enantiomers. Both methods showed good linearity (r2>0.99), accuracy (bias< 13%) and precision (CV<12%). Chiral HPLC analysis indicated that SCH 66336 was not subjected to chiral inversion in rats and cynomolgus monkeys.

Direct resolution of optically active isomers on chiral packings containing ergoline skeleton. 6. Enantioseparation of profens

The enantioselective behaviour of some underivatized 2-arylpropionic acids (profens) and flobufen by HPLC using a terguride-based chiral stationary phase was tested. X-ray analysis of crystals of the chiral selector and its complexes with naproxen allowed a deeper insight into the enantiodiscriminative process. The column stability and reproducibility, and the potential of the packing for semipreparative scale separations were also determined. A method for determining flobufen enantiomers and metabolites in plasma samples is described.

Pharmaceutical development and specification of stereoisomers

The pharmaceutical development of chiral drugs requires the activities of many different research and development groups. Guidelines which help to coordinate the activities of these groups and assist in the successful development of compounds with either single or multiple chiral centers are outlined and discussed.