Chiral Stationary Phase Column Research Articles

Optimization of Liquid Crystalline Mixtures Enantioseparation on Polysaccharide-Based Chiral Stationary Phases by Reversed-Phase Chiral Liquid Chromatography.

Enantioseparation of nineteen liquid crystalline racemic mixtures obtained based on (R,S)-2-octanol was studied in reversed-phase mode on an amylose tris(3-chloro-5-methylphenylcarbamate) (ReproSil Chiral-MIG) and a cellulose tris(3,5-dichlorophenylcarbamate) (ReproSil Chiral-MIC). These polysaccharide-based chiral stationary phase (CSP) columns for High-Performance Liquid Chromatography (HPLC) were highly effective in recognizing isomers of minor structural differences. The mobile phase (MP), which consists of acetonitrile (ACN)/water (H2O) at different volume ratios, was used. The mobile phases were pumped at a flow rate of 0.3, 0.5, or 1 mL·min-1 with a column temperature of 25 °C, using a UV detector at 254 nm. The order of the elution was also determined. The chromatographic parameters, such as resolution (Rs), selectivity (α), and the number of theoretical plates, i.e., column efficiency (N), were determined. The polysaccharide-based CSP columns have unique advantages in separation technology, and this study has shown the potential usefulness of the CSP columns in separating liquid crystalline racemic mixtures belonging to the same homologous series.

Stereoisomeric separation of the chiral herbicide profoxydim and residue method development in rice by QuEChERS and LC–MS/MS

A method for the simultaneous determination of the four stereoisomers of the chiral herbicide profoxydim in rice and husk was developed using the QuEChERS method and LC-tandem mass spectrometry. Four polysaccharide-based chiral stationary phase columns were evaluated. All four stereoisomers were successfully separated on a Chiracel OJ-3R column. The effects of mobile phase, modifiers, mobile phase flow rate and temperature on the separation were also investigated. Different QuEChERS methods were compared for the development of an optimized sample preparation procedure. The method, following SANTE guidelines, showed excellent linearity (R2 ≥ 0.99), the LODs were below 4.0 µg kg−1, and the LOQs did not exceed 12.5 µg kg−1. The overall average recoveries at three levels (12.5, 25.0 and 250 µg kg−1) ranged from 76.77 % to 106.53 %, with RSD values less than 7 %. The method is demonstrated to be convenient and reliable for the routine monitoring of profoxydim stereoisomers in rice and husk.

Enantioseparation and antioxidant activity of novel diarylpyrazoline derivatives

Three chiral pyrazoline derivatives were synthesized by a flavanone ring-opening reaction followed by cyclocondensation with hydrazine hydrate to give better yields. Their enantiomeric resolution was achieved using polysaccharide chiral stationary phase columns consisting of cellulose (Chiralcel®OD-RH, Chiralcel®OZ-3) and amylose (Chiralpak®IA) by high-performance liquid chromatography. The separation was affected by the nature and concentration of the alcohol modifiers in the mobile phase. Taking 5-methoxy-2-(3-phenyl-4,5-dihydro-1H-pyrazol-5-yl)phenol (3a) as an example, the best separation was obtained by using the Chiralpak®IA column, with a separation factor α = 1.24 and Rs = 5.66 within an analysis time of <30 min. The diarylpyrazolines showed good antioxidant activity, studied by the DPPH method.

Application of Polysaccharide-Based Chiral High-Performance Liquid Chromatography Columns for the Separation of Regio-, E/Z-, and Enantio-Isomeric Mixtures of Allylic Compounds.

Daicel Chiralpak IA, IB, and IC, which are the polysaccharide-based chiral stationary phase (CSP) columns for high-performance liquid chromatography (HPLC), were applied in the separation of the non-enantiomeric isomeric mixtures obtained by the various allylation reactions and were highly effective in separating the regio- and (E)/(Z)-isomers in the allylation products. Due to the close structural similarity of the isomeric allylic compounds in the reaction mixtures, separations of the isomers are laborious and could not be accomplished by the conventional methods such as silica gel column chromatography, silica gel HPLC, preparative GPC, distillation, and so forth. This study has shown potential advantages of using the polysaccharide-based CSP columns in the separation of not only enantiomeric but also non-enantiomeric isomeric mixtures.

Direct and simultaneous analysis of lipase-catalyzed hydrolysis of high-oleic oil model by chiral stationary phase HPLC-ELSD

A novel HPLC-based method for direct separation of trioleoylglycerol (TOG), a major component in high-oleic oils, and its seven hydrolysis products (i.e., oleic acid, monooleoylglycerol (MOG) and dioleoylglycerol (DOG) isomers) was established using a chiral stationary phase column, Chiralpak IA. Within 20 min, all species including enantiomeric MOG (1-sn-MOG and 3-sn-MOG) and DOG (1,2-sn-DOG and 2,3-sn-DOG) were baseline-resolved with resolution factors over 1.5 between adjacent peaks. The established method was used for investigating the integral stereoselectivity, which is the selectivity concerning all hydrolysis steps, of lipase from Pseudomonas fluorescens (PFL) with TOG as substrate. The time-course of DOGs and MOGs indicated that PFL had selectivity for TOG hydrolysis in the order of sn-1, sn-2, and sn-3 position, while it preferred to hydrolyze 2,3-sn-DOG over 1,2-sn-DOG. Being rapid and accurate to evaluate integral stereoselectivity, this method could promote the development and application of lipases with target stereochemistry in the food industry.

Solvent-induced enantioselectivity reversal in a chiral metal organic framework.

Solvent-induced enantioselectivity reversal is a rarely reported phenomenon in porous homochiral materials. Similar behavior has been studied in chiral high performance liquid chromatography, where minor modifications to the mobile phase can induce elution order reversal of two enantiomers on a chiral stationary phase column. We report the first instance of solvent-induced enantioselectivity reversal in a homochiral metal organic framework. Further, we highlight the complex enantioselectivity behavior of homochiral metal organic frameworks toward racemic mixtures in the presence of solvents through racemate-solvent enantioselectivity and loading experiments as well as enantiopure-solvent loading experiments. We hypothesize that this interesting selectivity reversal behavior is likely to be observed in other competitive adsorption, nonchiral selective processes involving a solvent.

A Simple Methodology for Preparing Synthetic Multiple-Interaction Chiral Stationary Phase Column for Chiral Drug Analysis

A simple methodology for preparing synthetic multiple-interaction (SMI) chiral stationary phase (CSP) column is described in this report, The column was synthesized by an in situ derivatizing procedure and can be easily prepared with a standard analytical HPLC set-up. The column is a no frills, low cost one, and can be tailored to various packing particle sizes and column lengths. The efficiency of the column is high; over 5,000 plates per 10 cm Applications on resolving some racemic drugs in plasma and formulation are illustrated.

Separation of bifenthrin enantiomers by chiral HPLC and determination of their toxicity to aquatic organism

In this study, we separate enantiomers of bifenthrin, a pyrethroid insecticide, by using high performance liquid chromatography with a chiral stationary phase (CPS) column. Toxicity tests of bifenthrin enantiomers were performed with Daphnia (water flea, Daphnia pulex), tilapia fish (Tilapia spp.) and carp fish (Cyprinus carpio). Two enantiomers of bifenthrin were separated successfully by injecting 20 μL of bifenthrin 1000 mg/L standard solution into a Sumichiral OA-2500-I column. The mobile phase solvent system was composed of n-hexane, isopropanol, and ethanol in a ratio of 99.8/0.06/0.14, and the flow rate was 1.0 mL/min. Both enantiomers were eluted within 20 min. Two separated enantiomers, (-)-bifenthrin and (+)-bifenthrin, were identified by gas chromatography with mass spectrometry detector (GC-MSD) and polarimeter. Each enantiomer of bifenthrin and the standard bifenthrin solution showed the same fragmentation pattern spectrum. The fragment ions were m/z 115, m/z 141, m/z 165, m/z 181, and m/z 422. The specific rotations [a]20365 of (-)-bifenthrin and (+)-bifenthrin were -66.41° and +69.63°, respectively. In the toxicity study, the LC50 (12 hr) of (-)-bifenthrin and (+)-bifenthrin for daphina were 2.1 μg/L and 28.9 μg/L, respectively. On the other hand, the result of fish toxicity indicated the LC50 (96 hr) of (-)-bifenthrin and (+)-bifenthrin for carp (C. carpio) were 0.99 and 2.08 μg/L, respectively, and for tilapia (Tilapia spp.) were 0. 19 and 0.80 μg/L, respectively. The study of biological activity showed that the toxicity of (-)-bifenthrin was 10-fold greater than (+)-bifenthrin for Daphnia, and 2-fold greater for fish. This study provided improved methods for separating enantiomers of bifenthrin and assessing hazard of individual enantiomers toward non-target aquatic fauna.

Female-Produced Sex Pheromone of Tetrastichus planipennisi, a Parasitoid Introduced for Biological Control of the Invasive Emerald Ash Borer, Agrilus planipennis.

The Asian eulophid wasp Tetrastichus planipennisi is being released in North America as a biocontrol agent for the emerald ash borer (Agrilus planipennis), a very destructive invasive buprestid beetle that is devastating ash trees (Fraxinus spp.). We identified, synthesized, and tested a female-produced sex pheromone for the wasp. The key component eliciting behavioral responses from male wasps in flight tunnel bioassays was identified as (6S,10S)-(2E,4E,8E)-4,6,8,10-tetramethyltrideca-2,4,8-triene. Female specificity was demonstrated by gas chromatographic (GC) comparison of male and female volatile emissions and whole body extracts. The identification was aided by coupled gas chromatography/mass spectrometry analysis, microchemical reactions, NMR, GC analyses with a chiral stationary phase column, and matching GC retention times and mass spectra with those of synthetic standards. The tetramethyl-triene hydrocarbon was synthesized as a mixture of two enantiomeric pairs of diastereomers, and as the pure insect-produced stereoisomer. In flight-tunnel bioassays, males responded to both the natural pheromone and the chiral synthetic material by upwind flight and landing on the source. In contrast, the mixture of four stereoisomers was not attractive, indicating that one or more of the "unnatural" stereoisomers antagonized attraction. Field trials, using yellow pan traps baited with natural pheromone, captured significantly more male wasps than control traps over a four week trial. The identified pheromone could increase the efficiency and specificity of the current detection methods for Tetrastichus planipennisi and aid in the determination of parasitoid establishment at release sites.

Supercritical fluid chromatography separation of chiral pesticides: Unique capabilities to study cyhalothrin and metalaxyl as examples

Evaluation of chiral pesticides remains a frequently neglected matter in routine food control laboratories. This fact is due to the existence of many residue definitions but also due to the lack of robust instrumental methods for the evaluation of these isomeric compounds. However, supercritical fluid chromatography coupled to mass spectrometry (SFC-ESI-MS/MS) has been demonstrated to perform fast and highly efficient separations without the need to change the mobile phase employed in multiresidue pesticide analyses. Regarding chiral stationary phase columns, the polysaccharide-based ones clearly demonstrate the best separation technology. Two polysaccharide-based columns were tested in this study, and the robustness of their combination with SFC was verified. The enantiomers of lambda-cyhalothrin and metalaxyl were studied precisely due to their markedly distinct toxicity and enantioselectivity. Furthermore, the acute reference dose for gamma-cyhalothrin is half in comparison with its enantiomer (0.0025 and 0.005 mg/kg respectively), which is present in the lambda-cyhalothin residue definition. These enantiomers were analyzed in terms of linearity, reproducibility, and matrix effects in four representative matrices (tomato, orange, leek, and cayenne). Additionally, field tests under greenhouse conditions for these compounds were performed. The results obtained after different sample collections revealed a similar degradation in lambda-cyhalothrin enantiomers (R, S, S, and S, R, R) but not in the case of metalaxyl-M (mefenoxam) where the degradation in tomato was 2 to 6 times less in comparison with its S-enantiomer.

Preparation of Poly-(GMA-EDA-β-CD-co-TMPTMA) Monolith as High Performance Liquid Chromatography Chiral Stationary Phase Column

An enantiomer molecule consisted of the chiral atom has different structure conformations, which exhibit different activities as well. Yet, its separation considerably difficult since ordinary separation could not separate both molecules. One of the popular enantioseparations which are often used was using organic polymer monolithic column modified by ethylenediamine-β-cyclodextrin (EDA-β-CD) as the enantioseparations site. The aim of this research was to produce chiral stationary phase column for enantioseparations of (±)-citronellal. It was conducted by preparing monolithic column using monomer glycidyl methacrylate (GMA), trimethylolpropane trimethacrylate (TMPTMA) as crosslinker, 1-propanol, 1,4-butanediol, and water as pore-forming agents (porogens) in the presence of α,α'-azoisobutyronitrile (AIBN) as radical initiator inside polyetheretherketone (PEEK) tubing. It was then modified with EDA-β-CD synthesized from β-CD. Finally, it was installed as a high-performance liquid chromatography column. The result shows the produced chiral stationary phase column could separate (±)-citronellal at a retention time of 44.76 and 45.71 min.

Application of tandem coupling of columns in supercritical fluid chromatography for stereoisomeric separation: Optimization and simulation

Chromatographic separation of compounds with more than one chiral center is challenging, requiring high resolution methods. Owing to the low viscosity of the mobile phase, Supercritical Fluid Chromatography (SFC) enables the tandem coupling of columns which increases resolution compared over a single column and can be effective in resolving stereoisomers. Enantioseparation of a dihydropyridone derivative with two chiral centers, synthetic API, was here studied using SFC. Six polysaccharide-based, chiral stationary phases with a mobile phase consisting of a carbon dioxide/methanol mixture (80:20 v:v) were investigated at 40 °C and a flow-rate of 3 mL/min, but only incomplete separation of the four expected stereoisomers was observed. We then examined different combinations of columns in tandem. It was found that, among the thirteen successful tandems, the OJ-H//AD-H system gave complete baseline resolution of the four stereoisomers with 4.98, 5.63, 6.06 and 6.89 as retention times and 2.97, 1.83 and 3.54 as resolution values. The conditions were further optimized to obtain the best resolution in the shortest elution time. The best conditions were transposed to semi-preparative scale to obtain the pure isomers, with yield increased by using stacked injections. The four fractions allowed the attribution of elution order on all tandem performed previously. The column order itself had no impact on the stereoisomeric elution order but the type of stationary phase and column order strongly influenced the resolution. In parallel, a previously reported mathematical model was used to predict the retention times of the four stereoisomers on each of the six polysaccharide-based, chiral stationary phase column tandems. This mathematical model was successfully applied to predict separation the dihydropyridone derivative’s isomers on two columns with chlorinated stationary phases.

Application of Polysaccharide-Based Chiral HPLC Columns for Separation of Nonenantiomeric Isomeric Mixtures of Organometallic Compounds

A series of polysaccharide-based chiral stationary phase (CSP) columns, Daicel Chiralpak IA, IB, and IC, were applied in the separation of the nonenantiomeric isomers of various organometallic compounds and were found to be highly effective in recognizing isomers of minor structural differences. The CSP columns have succeeded to separate the double-bond regioisomers in bridged (η5-formylcyclopentadienyl)manganese(I) dicarbonyl complexes 1a/1b, the structural isomers of methylbutenylferrocene derivatives in 2a/2b and 3a/3b, and the geometrical isomers of the (2-methyl-2-butenyl)ferrocenes in (Z)/(E)-3b. Due to the close similarity of the isomeric compounds in these mixtures, separations of the components are extremely difficult and could not be attained by conventional methods such as silica gel column chromatography, silica gel HPLC, recrystallization, distillation/sublimation, etc. Clearly, the polysaccharide-based CSP columns have unique advantages in separation/purification technology, and this study h...

Validation of LC method in determining enantiomeric purity of pramipexole using polysaccharide-derived chiral stationary phases under organic-aqueous mode

The separation of pramipexole enantiomers using polysaccharide-based chiral stationary phase (CSP) columns with organic-aqueous mobile phases was reported for the first time. The (R)-enantiomer was separated from pramipexole using a Lux® Cellulose-1 column with a mobile phase consisting of solvent A (acetonitrile):solvent B (0.1% diethylamine with 20 mM ammonium bicarbonate) (30:70, v/v). The elution time was about 7.0 min and the resolution between the enantiomers was greater than 8.0. The linear range of the method was 0.3–3.6 μg mL−1 with the limit of detection and limit of quantification for the (R)-enantiomer were 0.1 µg mL−1 and 0.3 µg mL−1, respectively. The percentage recovery of (R)-enantiomer ranged from 97.1 to 100.1 for tablet dosage forms of pramipexole dihydrochloride monohydrate. In this study, the enantiomeric separation of pramipexole was achieved. The results demonstrated good linearity, precision, and accuracy for quantifying (R)-enantiomer in tablet dosage forms, suggesting the applicability of a quantitative method that uses polysaccharide-based CSPs in combination with organic-aqueous mobile phases.

Analysis of bupivacaine enantiomers in plasma as total and unbound concentrations using LC-MS/MS: Application in a pharmacokinetic study of a parturient with placental transfer

Bupivacaine, a drug used in obstetric anesthesia and analgesia, is commercially available as a racemic mixture of the R-bupivacaine and S-bupivacaine enantiomers, which show differences in pharmacokinetics, efficacy and toxicity. Changes in bupivacaine plasma protein binding is of clinical relevance considering its high protein binding (approximately 95%) and its classification as an intermediate hepatic extraction ratio drug (E = 0.38). Furthermore, the plasma protein binding of bupivacaine is also of clinical relevance considering that pregnancy is a physiological condition associated with reduced plasma albumin concentration. Also, different pathological conditions, such as pre-eclampsia, can reduce the maternal plasma protein concentrations and consequently increase the bupivacaine placental transfer. This report describes the development and validation of analytical methods for the sequential analysis of the total and unbound concentrations of bupivacaine enantiomers in human plasma using liquid chromatography coupled to mass spectrometry (LC–MS/MS) with a sensitivity compatible with application in pharmacokinetic studies including placental transfer. Aliquots of 200 μL of plasma or plasma ultra-filtrate were extracted with n-hexane in alkaline medium after the deproteinization of the matrix with acetonitrile and water. The separation of bupivacaine enantiomers was obtained on a Chirex® 3020 chiral stationary phase column using as a mobile phase a mixture of 95% n-hexane:ethanol (80:20, v/v) at a flow rate of 0.8 mL/min. The lower limit of quantification was 0.25 ng of each enantiomer/mL of plasma as the total concentration and 0.125 ng of each enantiomer/mL of plasma as the unbound concentration. The methods were applied to study the pharmacokinetics of bupivacaine enantiomers after the administration of 2.5 mg of 0.5% racemic bupivacaine hydrochloride with 1:200,000 epinephrine via the epidural route to an HIV-positive parturient woman undergoing antiretroviral treatment. The parturient showed lower AUC0−∞ (25.42 vs. 30.57 ng.h/mL) and higher volume of distribution (841.96 vs 655.05 L) and total clearance (98.34 vs 81.79 L/h) for the R-bupivacaine enantiomer. The pharmacokinetics of bupivacaine were enantioselective displaying a lower plasma proportion of the enantiomer R-bupivacaine (AUC(R)/(S) ratio equal to 0.83). The placental transfer was approximately 60% for both bupivacaine enantiomers. The unbound fraction (Fu) for the R-bupivacaine enantiomer was higher (10.84%) than the eutomer S-bupivacaine (6.29%).

HPLC Separation of 2-Ethyl-5(6)-methylpyrazine and Its Electroantennogram and Alarm Activities on Fire Ants (Solenopsis invicta Buren).

2-Ethyl-3,6-dimethylpyrazine (EDMP) was an alarm pheromone component isolated from the mandibular gland of the red imported fire ant, Solenopsis invicta Buren. Several pyrazine analogues have been previously found to elicit significant alarm responses in S. invicta workers. This study aimed to separate the commercially available 2-ethyl-5(6)-methylpyrazine (EMP), i.e., a mixture of 2-ethyl-6-methylpyrazine (2E6MP) and 2-ethyl-5-methylpyrazine (2E5MP), and to examine both electroantennogram (EAG) and behavioral responses of S. invicta workers to EMP and the purified isomers. HPLC separations were achieved using a polysaccharide chiral stationary phase (Chiralpak AD-H) column with both mobile phases: Cyclohexane/isopropanol, and hexane/isopropanol. A ratio of 99:1 was selected for the separation of EMP at semipreparative level. The structures of the isomers obtained through the cyclohexane/isopropanol mobile phase were confirmed by detailed analyses of 2D-HSQC- and -HMBC-NMR data. The two isomers showed differential methine C–H correlations evidenced by 2D-HMBC-NMR spectra. The two concentrated fractions obtained through hexane/isopropanol mobile phase were subjected to EAG test and behavioral bioassay on S. invicta workers. The two HPLC−purified isomers, 2E6MP and 2E5MP, and their mixture (1:1) at same dose elicited similar EAG and alarm responses, indicating that these two isomers are equally active. The 2D-NMR−spectroscopic characterization, and electrophysiological and alarm activities of 2E6MP and 2E5MP were reported here for the first time.

(1S,3R)-cis-Chrysanthemyl Tiglate: Sex Pheromone of the Striped Mealybug, Ferrisia virgata.

Derivatives of 2,2-dimethyl-3-(2-methylprop-1-enyl)cyclopropanecarboxylic acid (chrysanthemic acid) are classic natural pyrethroids discovered in pyrethrum plants and show insecticidal activity. Chrysanthemic acid, with two asymmetric carbons, has four possible stereoisomers, and most natural pyrethroids have the (1R,3R)-trans configuration. Interestingly, chrysanthemic acid-related structures are also found in insect sex pheromones; carboxylic esters of (1R,3R)-trans-(2,2-dimethyl-3-(2-methylprop-1-enyl)cyclopropyl)methanol (chrysanthemyl alcohol) have been reported from two mealybug species. In the present study, another ester of chrysanthemyl alcohol was discovered from the striped mealybug, Ferrisia virgata (Cockerell), as its pheromone. By means of gas chromatography-mass spectrometry, nuclear magnetic resonance spectrometry, and high-performance liquid chromatography analyses using a chiral stationary phase column and authentic standards, the pheromone was identified as (1S,3R)-(-)-cis-chrysanthemyl tiglate. The (1S,3R)-enantiomer strongly attracted adult males in a greenhouse trapping bioassay, whereas the other enantiomers showed only weak activity. The cis configuration of the chrysanthemic acid-related structure appears to be relatively scarce in nature, and this is the first example reported from arthropods.

Preparation of chiral oxazolinyl-functionalized β-cyclodextrin-bonded stationary phases and their enantioseparation performance in high-performance liquid chromatography.

A simple procedure for the synthesis of three new oxazolinyl-substituted β-cyclodextrins (6-deoxy-6-R-(-)-4-phenyl-4,5-dihydrooxazolinyl-β-cyclodextrin, 6-deoxy-6-S-(-)-4-phenyl-4,5-dihydrooxazolinyl-β-cyclodextrin, and 6-deoxy-6-S-(-)-(4-pyridin-1-ium-4-methyl-benzenesulphonate)-4,5-dihy-drooxazolinyl-β-cyclodextrin) and their covalent bonding to silica are reported. The ability of these chiral stationary phase columns for separating compounds is also presented and discussed. Twenty-eight compounds were examined in the polar-organic mobile phase mode, and 11 β-nitroethanols were tested in the reversed-phase mode. Excellent enantioseparations were achieved for most of the analytes, even for several challenging compounds. The rigid and flexible structures of mono-substituted chiral groups and the fragments around the rim of the β-cyclodextrin cavity played an important role in the separation process. Factors such as π-π stacking, dipole-dipole interactions, ion-pairing, and steric hindrance effects were found to affect the chromatographic performance. Moreover, the buffer composition, and percentages of organic modifiers in the mobile phase, were investigated and compared. The mechanisms involved in the separation were postulated based on the chromatographic data.

First observable CD spectra from n-σ* excitation: TD-DFT calculation and determination of absolute configuration of 2,6-dithiaspiro[3.3]heptane 2,6-dioxide

Recently we reported that 2,6-dithiaspiro[3.3]hepta ne 2,6-dioxide 1a exists as enantiomers at ambient temperature and is able to be resolved. Th is is because the lone pair(s) on the sulfur atom(s) are rich in s-character, which results in h igh barrier for flipping the conformation of the four-membered ring, i.e., racemization of the spiro framework of 1a. During the HPLC analysis, we noticed considerably strong absorption of UV at 210 nm. We expected that the absorbance comes from n-σ* excitation. The acute bond angle of C-S-C leads to high p-character of the C-S bond(s), which lowers the σ* orbital energy. We performed the TD-DFT calculations of a model, constrained dimethylsulfoxide (DMSO) and 1a . The strong UV absorption of 1a is reproduced with the TD-DFT calculation. However, there are two sulfoxide groups arranged with chiral position in 1a , we could expect that the circular dichroism (CD) spectra are observable by coupling of two sulfoxide groups. Th e TD-DFT calculation showed that the Cotton effects should appear in the observable UV r ange. We separated the enantiomers of 1a by HPLC equipped with a chiral stationary phase col umn. The enantiomers are subjected to the CD analysis. We determined the absolute configurat ion of 1a , comparing the calculation and the obtained spectra. This is the first report of the CD spectra of n-σ* excitation.

Conventional Chiralpak ID vs. capillary Chiralpak ID-3 amylose tris-(3-chlorophenylcarbamate)-based chiral stationary phase columns for the enantioselective HPLC separation of pharmaceutical racemates.

A comparative enantioselective analysis using immobilized amylose tris-(3-chlorophenylcarbamate) as chiral stationary phase in conventional high-performance liquid chromatography (HPLC) with Chiralpak ID (4.6 mm ID × 250 mm, 5 µm silica gel) and micro-HPLC with Chiralpak ID-3 (0.30 mm ID × 150 mm, 3 µm silica gel) was conducted. Pharmaceutical racemates of 12 pharmacological classes, namely, α- and β-blockers, anti-inflammatory drugs, antifungal drugs, dopamine antagonists, norepinephrine-dopamine reuptake inhibitors, catecholamines, sedative hypnotics, diuretics, antihistaminics, anticancer drugs, and antiarrhythmic drugs were screened under normal phase conditions. The effect of an organic modifier on the analyte retentions and enantiomer recognition was investigated. Baseline separation was achieved for 1-acenaphthenol, carprofen, celiprolol, cizolirtine carbinol, miconazole, tebuconazole, 4-hydroxy-3-methoxymandelic acid, 1-indanol, 1-(2-chlorophenyl)ethanol, 1-phenyl-2-propanol, flavanone, 6-hydroxyflavanone, 4-bromogluthethimide, and pentobarbital on the 4.6 mm ID packed with a 5 µm silica column using conventional HPLC. Nonetheless, baseline separation was achieved for aminoglutethimide, naftopidil, and thalidomide on the 0.3 mm ID packed with a 3 µm silica capillary column.