Enantioselective potential of chiral stationary phases based on immobilized polysaccharides in reversed phase mode

Effect of water and protic solvents on polysaccharide-based column efficiency

In the present study, polysaccharide-based columns were used to evaluate the efficiency of columns in response to the introduction of water and protic solvents (methanol and ethanol) into the mobile phase, replacing acetonitrile. While increasing water content frequently enhances enantiomer resolution, the inclusion of water, particularly when combined with methanol and ethanol in the mobile phase, has an adverse impact on mass transfer, thus influencing the column plate height. These effects are more pronounced with ethanol, and in many cases, van Deemter plots exhibit the absence of a minimum point optimal in the explored range. Consequently, acetonitrile and its water mixtures are the preferred choices to mitigate these effects for situations in which the chiral column is operated at a relatively high flow rate (> 1 mL/min in a 4.6 mm column).

An Evaluation of Immobilized Poly-(S)-N-(1-phenylethyl)acrylamide Chiral Stationary Phases

In this study, brush type and polymer type stationary phases were prepared based on (S)-N-(1-phenylethyl) acrylamide, and the polymeric stationary phase demonstrated superior chiral recognition ability. The two polymeric stationary phases were synthesized by two strategies, one was the “grafting from” method, which obtained polymer CSP by initiating monomer polymerization on the surface of 3-methacrylatepropyl silica gel, and the other was “grafting to”, which fixed the copolymer of (S)-N-(1-phenylethyl) acrylamide and trimethoxysilylpropyl methacrylate on silica gel. A comparison of these two bonding modes revealed that the stationary phase produced by “grafting to” had higher chiral recognition ability. Further improvement can be achieved by the end-capping of silanol groups with trimethylchlorosilane to reduce non-enantioselective retention caused by residual silanol groups and improve the peak shape of enantiomers. Chiral separation in subcritical fluid chromatography was also studied. Similar enantioselectivity results with higher resolution were observed due to the improvement of peak shape.

Preparation of chiral stationary phase based on a [3+3] chiral polyimine macrocycle by thiol-ene click chemistry for enantioseparation in normal-phase and reversed-phase high performance liquid chromatography

Polyimine macrocycles are a new class of organic macrocycles with cyclic structures, well-defined molecular cavities, and multiple cooperative binding sites, which have recently aroused considerable research interest in molecular recognition and separation. Herein, we report the bonding of a [3+3] chiral polyimine macrocycle (H₃L, C₇₈H₇₈N₆O₃) on thiol-functionalized silica gel using thiol-ene click chemistry to prepare a chiral stationary phase (CSP) for high performance liquid chromatography (HPLC). The fabricated column exhibited excellent chiral separation capability under both normal-phase and reversed-phase conditions. Fourteen and 10 racemates were well resolved on the column in normal-phase mode (using n-hexane/isopropanol as the mobile phase) and reversed-phase mode (using methanol/water as the mobile phase), respectively, including alcohols, esters, ethers, ketones, aldehydes, epoxides and organic acids. Moreover, the column also shows good selectivity toward positional isomers. Six positional isomers (dinitrobenzene, chloroaniline, bromoaniline, iodoaniline, nitrobrobenzene and nitrochlorobenzene) were well separated on the column. In addition, the effects of the injection mass and mobile phase composition on the separation were investigated. The column shows good reproducibility and stability after multiple injections with the relative standard deviation (RSD) (n = 5) of the retention time and resolution being < 0.96 % and 0.65 %, respectively. This study indicates that this type of chiral polyimine macrocycles is a promising chiral selector for HPLC enantioseparation and will push forward the applications of more novel chiral macrocycles for chiral chromatographic separation.

Development of a novel HPLC-ESI-MS/MS method to analyze the stereoselective pharmacokinetics and tissue distribution of isoconazole enantiomers in rats

Isoconazole with an asymmetrical carbon is a broad-spectrum antimicrobial imidazole, but there is still lack of relevant report about the potential enantioselectivity in biological samples. The object of this research was to develop and validate a sensitive and effective high performance liquid chromatography-electrospray ionization coupled with tandem mass spectrometry (HPLC-ESI-MS/MS) method for stereoselective separation and determination of isoconazole enantiomers in Sprague-Dawley (SD) rat plasma and tissues. The greater enantioseparation of isoconazole enantiomers was obtained on a Chiralpak IC column with a mobile phase consisted of acetonitrile-10 mM aqueous ammonium acetate (90:10, v/v) under the reversed-phase mode. Subsequently, the studied compounds and internal standard (IS) were detected on a multiple reaction monitoring (MRM) mode with positive electrospray ionization source. The experimental and theoretical Electronic Circular Dichroism (ECD) spectra were employed to confirm the absolute configuration of isoconazole enantiomers. Eventually, after full method validation, the newly developed method was successfully applied to the study of enantioselectivity in plasma and tissues in SD rats. Results illustrated that the enantioselective differences in plasma were observed for the evidence that the concentrations of S-(-)-isoconazole were always higher than R-(+)-isomer. In terms of tissue distribution, liver, kidney, lung, spleen, and small intestine were the mainly distributed tissues and then followed by heart and muscle. This is the first study to reveal the stereoselective behavior of isoconazole enantiomers in vivo, which also provides reliable and valuable reference for further elucidating the enantioselective metabolisms of isoconazole enantiomers.

'Ab Ovo' Chiral Phases and Chiral Reagents for Liquid Chromatographic Separation and Isolation of Enantiomers

The de-novo approach of mixing chirally pure reagents or Cu(II)-L-amino acid complexes in the slurry of silica gel for preparing TLC plates was reported from author's laboratory and was successful for separation and isolation of enantiomers. Using high molar absorptivity molecules, e. g., 1,5-difluoro-2,4-dinitrobenzene and cyanuric chloride, more than 38 new chiral derivatizing reagents were synthesized in our laboratory by straightforward nucleophilic substitution with simple chiral auxiliaries. Besides, (S)-naproxen, (S)-ketoprofen, and (S)-levofloxacin were used as chiral platforms. A conceptual approach using both achiral phases in chromatography for enantioseparation was also adopted. ¹ H NMR and DFT based software were used to explain structures of non-covalent and covalent diastereomeric pairs and determination of configuration and separation mechanism. The methods can be easily used to determine and control enantiomeric purity with advantages over a variety of commercial chiral phases.

The enantioseparation and determination of sulconazole enantiomers in rat plasma and tissues by a chiral HPLC–ESI–MS/MS method and its application to studies on stereoselective pharmacokinetics and tissue distribution

In our study, a chiral high performance liquid chromatography–electrospray ionization coupled with tandem mass spectrometry (HPLC–ESI–MS/MS) method for enantioselective analysis of sulconazole in rat plasma and tissues was developed and validated.

Stereoselective quantitative analysis of ranolazine in plasma and tissue samples: application in pharmacokinetics and tissue distribution studies

This study aimed to develop a rapid and sensitive reversed-phase mode high-performance liquid chromatography-electrospray ionization coupled with a tandem mass spectrometry method for the simultaneous determination of ranolazine enantiomers in rat plasma and tissues.

Chiral separation and molecular simulation study of six antihistamine agents on a coated cellulose tri-(3,5-dimethylphenycarbamate) column (Chiralcel OD-RH) and its recognition mechanisms

Enantiomeric separation of six antihistamine agents was first systematically investigated on a cellulose-based chiral stationary phase (CSP), that is, cellulose tris-(3,5-dimethyl phenyl carbamate) (Chiralcel OD-RH), under the reversed-phase mode. Orphenadrine, meclizine, terfenadine, dioxopromethazine, and carbinoxamine enantiomers were completely separated under the optimized mobile phase conditions with resolutions of 5.02, 1.93, 1.68, 1.67, and 1.54, respectively. Mequitazine was partially separated with a resolution of 0.77. The influences of type and concentration of buffer salt, the pH of buffer solution, and the type and ratio of organic modifier on the chiral separation were evaluated and optimized. For a better insight into the enantiorecognition mechanisms, molecular docking was carried out via the Autodock software. The lowest binding energy and the optimal conformations of the analytes/CSP complexes were supplied, and the mechanisms of chiral recognition were determined. According to the results, the key interactions for the chiral recognition of these six analytes on CDMPC were π-π interactions, hydrophobic interactions, hydrogen bond interactions, and some special interactions.

Evaluation of a polysaccharide-based chiral reversed-phase liquid chromatography screen strategy in pharmaceutical analysis

Chirality control plays a critical role in developing stereoisomeric drugs. Due to the complexity and lack of predictability in chiral separations, column screening remains the gold standard to initiate chiral method development for active pharmaceutical ingredients (APIs) and synthetic intermediates. Chiral reversed-phase (RP) liquid chromatography (LC) has gained favor over other modes due to its versatility and compatibility in analyzing a wide range of chiral compounds in various matrices. Herein, we established a tier-based chiral RPLC screen strategy by constructing and analyzing a database of 101 chiral screens with a total of 3,401 entries (unique LC runs) for proprietary APIs or intermediates at Bristol Myers Squibb. Up to 17 polysaccharide-based chiral stationary phases (CSPs) and four mobile phases (MPs) have been screened with gradient elution. A selection of ten CSPs with two MPs was found sufficient to achieve successful separation for 82% of the total screens. Two RPLC screen tiers (Tier 1: AZ, OD, ID, and IG) and (Tier 2: AY, OJ, OZ, IA, IC, and IH) were proposed along with two MPs (acidic and neutral) to target ~70% hit rate for Tier 1, and ~80% for the combined set. We also implemented a user-friendly workflow to enable walk-up chiral RPLC screening with automated reports and system suitability tests.

Immobilization of Chondroitin Sulfate A onto Monolithic Epoxy Silica Column as a New Chiral Stationary Phase for High-Performance Liquid Chromatographic Enantioseparation

Chondroitin sulfate A was covalently immobilized onto a monolithic silica epoxy column involving a Schiff base formation in the presence of ethylenediamine as a spacer and evaluated in terms of its selectivity in enantioseparation. The obtained column was utilized as a chiral stationary phase in enantioseparation of amlodipine and verapamil using a mobile phase consisting of 50 mM phosphate buffer pH 3.5 and UV detection. Sample dilution by organic solvents (preferably 25% v/v acetonitrile-aqueous solution) was applied to achieve baseline enantioresolution (Rs > 3.0) of the individual drug models within 7 min, an excellent linearity (R² = 0.999) and an interday repeatability of 1.1% to 1.8% RSD. The performance of the immobilized column for quantification of racemate in commercial tablets showed a recovery of 86–98% from tablet matrices. Computational modeling by molecular docking was employed to investigate the feasible complexes between enantiomers and the chiral selector.

Solid phase extraction procedure coupled with the chiral LC-ESI-MS/MS method for the enantioseparation and determination of butoconazole enantiomers in rat plasma and tissues: application to the enantioselective study on pharmacokinetics and tissue distribution

A significant enantioselective difference between (−)- and (+)-butoconazole existed in the stage of not only pharmacokinetics but also tissue distribution.

Enantioselective LC-MS/MS method for the determination of cloperastine enantiomers in rat plasma and its pharmacokinetic application

Cloperastine is a central antitussive used to reduce the frequency and intensity of coughing on a short-term basis. In this study, a reliable chiral LC-MS/MS technology has been developed for the quantification of cloperastine enantiomers in the rat plasma. Carbinoxamine was selected as the internal standard. The enantioseparation of cloperastine was performed on a Chiralpak IA column with a mobile phase composed of acetonitrile-water-ammonium hydroxide (80:20:0.1, v/v/v) at a flow rate of 0.6 mL/min. Cloperastine enantiomers were detected by mass spectrometry in multiple reaction monitoring mode with a positive electrospray ionization source. The method was validated over the linear concentration range of 0.05 to 10.0 ng/mL (5.0 × 10^-4 ng to 0.10 ng) for both enantiomers. The lower limit of quantification (LLOQ) for each analyte was determined as 0.05 ng/mL. The relative standard deviations (RSDs) of intraday and interday precision was less than 13.9%, and the relative error (RE) of accuracy ranged from -5.4% to 6.1%, which were within the acceptance criteria. Finally, an application to the stereoselective pharmacokinetics of cloperastine in rats was successfully realized in our assay. The developed method on a commercially available Chiralpak IA column under isocratic mobile phase is advantageous to analyze cloperastine enantiomers in plasma samples collected for enantioselective metabolism or drug interaction studies.

Preparation of a thiols β-cyclodextrin/gold nanoparticles-coated open tubular column for capillary electrochromatography enantioseparations

Inspired by the distinct chemical and physical properties of nanoparticles, here a novel open-tubular capillary electrochromatography column was prepared by electrostatic assembly of poly(diallydimethylammonium chloride) onto the inner surface of a fused-silica capillary, followed by self-adsorption of negatively charged SH-β-cyclodextrin/gold nanoparticles. The formation of the SH-β-cyclodextrin/gold nanoparticles coated capillary was confirmed and characterized by scanning electron microscopy and energy dispersive spectrometry. The results of scanning electron microscopy and energy dispersive spectrometry studies indicated that SH-β-cyclodextrin/gold nanoparticles were successfully coated on the inner wall of the capillary column. The performance of the SH-β-cyclodextrin/gold nanoparticles coated capillary was validated by the analysis of six pairs of chiral drugs, namely zopiclone, carvedilol, salbutamol, terbutaline sulfate, phenoxybenzamine hydrochloride, and ibuprofen. Satisfactory enantioseparation results were achieved, confirming the use of gold nanoparticles as the support could enhance the phase ratio of the open-tubular capillary column. Additionally, the stability and reproducibility of the SH-β-cyclodextrin/gold nanoparticles coated capillary column were also investigated. Then, this proposed method was well validated with good linearity (≥0.999), recovery (90.0-93.5%) and repeatability, and was successfully used for enantioseparation of ibuprofen in spiked plasma samples, which indicated the new column's potential usage in biological analysis.

Enantiomeric separation of six beta-adrenergic blockers on Chiralpak IB column and identification of chiral recognition mechanisms by molecular docking technique

Enantiomeric separation of six β-adrenergic blockers was systematically studied for the first time on a polysaccharide-based chiral stationary phase, i.e. Chiralpak IB, under the normal-phase mode. The effect of alcohol modifiers, alcohol content and basic additive on enantiomeric separation was evaluated and optimized. Under the optimal conditions, the enantiomers of atenolol, bevantolol, cartelol, esmolol, metoprolol and propranolol were all baseline resolved with resolutions of 1.50, 8.56, 2.05, 2.11, 3.56 and 4.02, respectively. Additionally, molecular docking was tested to explain chiral recognition mechanisms of this set of the drug enantiomers on Chiralpak IB. The details of the various interactions affecting enantiomeric separation were confirmed from the molecular level and the modeling data were in agreement with the chromatographic results concerning the enantioselectivity.

Enantioselective HPLC Analysis to Assist the Chemical Exploration of Chiral Imidazolines

In the present work, we illustrate the ability of high-performance liquid chromatography (HPLC) analysis to assist the synthesis of chiral imidazolines within our medicinal chemistry programs. In particular, a Chiralpak^® IB^® column containing cellulose tris(3,5-dimethylphenylcarbamate) immobilized onto a 5 μm silica gel was used for the enantioselective HPLC analysis of chiral imidazolines synthesized in the frame of hit-to-lead explorations and designed for exploring the effect of diverse amide substitutions. Very profitably, reversed-phase (RP) conditions succeeded in resolving the enantiomers in nine out of the 10 investigated enantiomeric pairs, with α values always higher than 1.10 and R_S values up to 2.31. All compounds were analysed with 50% (v) water while varying the content of the two organic modifiers acetonitrile and methanol. All the employed eluent systems were buffered with 40 mM ammonium acetate while the apparent pH was fixed at 7.5. Based on the experimental results, the prominent role of π-π stacking interactions between the substituted electron-rich phenyl groups outside of the polymeric selector and the complementary aromatic region in defining analyte retention and stereodiscrimination was identified. The importance of compound polarity in explaining the retention behaviour with the employed RP system was readily evident when a quantitative structure-property relationship study was performed on the retention factor values (k) of the 10 compounds, as computed with a 30% (v) methanol containing mobile phase. Indeed, good Pearson correlation coefficients of retention factors (r - log k_1st = −0.93; r - log k_2nd = −0.94) were obtained with a water solubility descriptor (Ali-logS). Interestingly, a n-hexane/chloroform/ethanol (88:10:2, v/v/v)-based non-standard mobile phase allowed the almost base-line enantioseparation (α = 1.06; R_S = 1.26) of the unique compound undiscriminated under RP conditions.

Enantiomeric separation and molecular docking study of seven imidazole antifungal drugs on a cellulose tris-(3,5-dimethylphenylcarbamate) chiral stationary phase

Chiral separation and molecular docking study of seven imidazole antifungal drugs were performed on a cellulose tris-(3,5-dimethylphenylcarbamate) chiral stationary phase (Chiralcel OD-RH).

Chiral separation of five antihistamine drug enantiomers and enantioselective pharmacokinetic study of carbinoxamine in rat plasma by HPLC-MS/MS

Chiral separation and pharmacokinetic study of antihistamine drugs.

Liquid chromatography separation of α- and γ-linolenic acid positional isomers with a stationary phase based on covalently immobilized cellulose tris(3,5-dichlorophenylcarbamate)

α-Linolenic acid (ALA) and its most important positional isomer γ-linolenic acid (GLA), are essential fatty acids (vitamin F). Therefore, ALA- and GLA-rich edible oils hold great potential in human and animal nutrition, as well as in nutraceutics and cosmetics. Quality control and nutritional validation of oil products is thus of increasing importance. In the present study, the cellulose tris(3,5-dichlorophenylcarbamate)-based chiral stationary phase was successfully used for separation of ALA and GLA, a major challenge in the liquid chromatography of these isomers. The chromatographic conditions were firstly optimized on a HPLC system with UV detection, and the use of a reversed-phase eluent system made up of aqueous 10 mM ammonium acetate/acetonitrile (40/60, v/v; _w^spH6.0) with a 25 °C column temperature resulted optimal for the simultaneous discrimination of the two isomers at a 0.5 mL/min flow rate (α = 1.10; R_S = 1.21). The method was then optimized for LC-MS/MS implementation. The proposed innovative separation method holds a great potential for the quantification of ALA and GLA in food and biological matrices, thus opening the way to further investigations involving the two positional isomers.

Fast enantioseparation of indole phytoalexins in additive free supercritical fluid chromatography

A series of chiral indole phytoalexins with potential anticancer and antimicrobial activity were enantioseparated in supercritical fluid chromatography. Two polysaccharide-based chiral stationary phases composed of tris-(3,5-dimethylphenylcarbamate) derivatives of amylose or cellulose coated on 2.5 μm silica particles were successfully used. The influences of the polysaccharide backbone, co-solvent type and co-solvent content in the mobile phase on retention, enantioselectivity and enantioresolution of indole phytoalexins were investigated. Fast baseline separations were achieved for 26 from 27 tested compounds. Amylose-based chiral stationary phase provided higher number of baseline resolutions of the indole phytoalexins than the cellulose-based one. However, certain complementary enantioresolution results towards the studied compounds were observed between the investigated columns. The relationship between structure of the indole phytoalexins and their chromatographic behavior in supercritical fluid chromatography was discussed.

Enantioselective analysis of pheniramine in rat using large volume sample stacking or cation-selective exhaustive injection and sweeping coupled with cyclodextrin modified electrokinetic chromatography

For the aim of simultaneously performing the enantioseparation and determination of the trace enantiomers in plasma samples, enantioseparation by HPLC using five kinds of chiral stationary phases were initially investigated. But unfortunately, enantioseparation could not be detected in reversed mobile phase mode with all the five columns. For this reason, two simple, economical and highly efficient online preconcentration methods, large volume sample stacking and sweeping (LVSS-sweeping) and cation-selective exhaustive injection and sweeping (CSEI-sweeping) both followed by the cyclodextrin modified electrokinetic chromatography (CDEKC) were examined in the present work. Parameters affecting the enantioseparation and enhancement efficiency of these two injection modes were monitored in detail, and migration order of the two enantiomers was identified by circular dichroism (CD) and HPLC. Upon optimization, two enantiomers were best separated with the improvement of sensitivity reaching 160-fold and 4000-fold respectively for LVSS-sweeping and CSEI-sweeping comparing with the normal CDEKC separation. Then the optimal condition of CSEI-sweeping-CDEKC was validated and showed high sensitivity (10 ng/mL for lower limit of quantification, LLOQ), satisfactory accuracy (96.8-111.6%) and precision (relative standard deviation, RSD within 9.4%). This demonstrated it to be a suitable strategy for the rapid enantioselective determination and quantitative analysis of pheniramine enantiomers in plasma samples. Therefore, the method was further applied in the enantiomeric analysis of pheniramine in rat pharmacokinetics and plasma protein binding investigations. Stereoselectivity in pharmacokinetics as well as plasma protein binding were observed, suggesting that the stereoselective protein binding might be responsible for the stereoselectivity in pharmacokinetics.

Thin Layer Chromatographic Resolution of Some β-adrenolytics and a β2-Agonist Using Bovine Serum Albumin as Chiral Additive in Stationary Phase

Direct enantiomeric resolution of commonly used five racemic β-adrenolytics, namely, bisoprolol, atenolol, propranolol, salbutamol and carvedilol has been achieved by thin layer chromatography using bovine serum albumin (BSA) as chiral additive in stationary phase. Successful resolution of the enantiomers of all racemic β-adrenolytics was achieved by use of different composition of simple organic solvents having no buffer or inorganic ions. The effect of variation in pH, temperature, amount of BSA as the additive, and composition of mobile phase on resolution was systematically studied. Spots were visualized in iodine vapors. Native enantiomers for each of the five analytes were isolated and identified and their elution order was determined. The limit of detection was found to be 0.7, 1.2, 0.84, 1.6 and 0.9 μg (per spot) for each enantiomer of bisoprolol, atenolol, propranolol, salbutamol and carvedilol, respectively.

Study on the HPLC-based separation of some ezetimibe stereoisomers and the underlying stereorecognition process

The enantioseparation of ezetimibe stereoisomers by high-performance liquid chromatography on different chiral stationary phases, ie, 3 polysaccharide-based chiral columns, was studied. It was observed that cellulose-based Chiralpak IC column exhibited the best resolving ability. After the optimization of mobile phase compositions in both normal and reversed phase modes, satisfactory separation could be obtained on Chiralpak IC column, especially in normal phase mode. The use of prohibited solvents as nonstandard mobile phase gave rise to better resolution than that of standard mobile phases (n-hexane/alcohol system). In addition, the presence of ethanol in nonstandard mobile phase has played an important role in enhancing chromatographic efficiency and resolution between ezetimibe stereoisomers. Various attempts were made to comprehensively compare the chiral recognition capabilities of immobilized versus coated polysaccharide-based chiral columns, amylose-based versus cellulose-based chiral stationary phases, reversed versus normal phase modes, and standard versus nonstandard mobile phases. Moreover, possible solute-mobile phase-stationary phase interactions were derived to explain how stationary and mobile phases affected the separation. Then the method validation with respect to selectivity, linearity, precision, accuracy, and robustness was carried out, which was demonstrated to be suitable and accurate for the quantitative determination of (RRS)-ezetimibe impurity in ezetimibe bulk drug.

Enantiomeric separation and simulation study of eight anticholinergic drugs on an immobilized polysaccharide-based chiral stationary phase by HPLC

Enantiomeric separation process of anticholinergic drugs and chiral recognition mechanisms on Chiralpak ID column.

Chiral separation and a molecular modeling study of eight azole antifungals on the cellulose tris(3,5-dichlorophenylcarbamate) chiral stationary phase

Four immobilized polysaccharide-based chiral stationary phases have been examined for their enantioselectivity on azole analytes using normal phase liquid chromatography.

Recent Liquid Chromatographic Approaches and Developments for the Separation and Purification of Carbohydrates

Carbohydate purification remains a bottleneck in securing analytical standards from natural sources or by chemical or enzymatic synthesis. This review highlights the scope and remaining limitations of recent approaches and methods development in liquid chromatography for robust and higher-throughput carbohydrate separation and isolation.

Structural dependence on the property of chiral stationary phases derived from chitosan bis(arylcarbamate)-(amide)s

The goal of present study was to investigate the structural dependence of chitosan derivatives on enantioseparation and mobile phase tolerance of the corresponding chiral packing materials for liquid chromatography. Hence, a series of chitosan bis(arylcarbamate)-(n-pentyl amide)s and the related chiral stationary phases (CSPs) were prepared from chitosans with different molecular weights. Because of the H-bond formed via CH₃-π interaction, the CSP bearing methyl substituent exhibited high tolerance than the ones bearing dichloro substituents. The CSP derived from the chitosan bis(3,5-dichlorophenylcarbamate)-(n-pentyl amide) with a higher molecular weight possessed high tolerance to mobile phases, whereas the enantioseparation capability of this CSP was not as good as that of the one prepared from the chitosan derivative with a lower molecular weight. Therefore, enantioseparation capability and mobile phase tolerance have to be counterbalanced in designing chiral selectors for the CSPs derived from chitosan bis(arylcarbamate)-(amide)s.

A novel chiral stationary phase HPLC-MS/MS method to discriminate between enzymatic oxidation and auto-oxidation of phosphatidylcholine

To elucidate the role of enzymatic lipid peroxidation in disease pathogenesis and in food deterioration, we recently achieved stereoselective analysis of phosphatidylcholine hydroperoxide (PCOOH) possessing 13S-hydroperoxy-9Z,11E-octadecadienoic acid (13(S)-9Z,11E-HPODE) using HPLC-MS/MS with a CHIRALPAK OP (+) column. Because enzymatic oxidation progresses concurrently with auto-oxidation, we need to distinguish them further. Here, we attempted such an analysis. First, we used lipoxygenase, linoleic acid, and lysophosphatidylcholine (LPC) to synthesize the enzymatic oxidation product 13(S)-9Z,11E-HPODE PC, and the auto-oxidation products 13(RS)-9Z,11E-HPODE PC and 13(RS)-9E,11E-HPODE PC, which were used as standards to test the ability of various columns to separate the enzymatic oxidation product from auto-oxidation products. Separation was achieved by connecting in series two columns with different properties: CHIRALPAK OP (+) and CHIRALPAK IB-3. The CHIRALPAK OP (+) column separated 13(R)-9Z,11E-HPODE PC and 13(S)-9Z,11E-HPODE PC, whereas CHIRALPAK IB-3 enabled separation of 13(S)-9Z,11E-HPODE PC and 13(RS)-9E,11E-HPODE PC. The results for the analysis of both enzymatically oxidized and auto-oxidized lecithin (an important phospholipid mixture in vivo and in food) indicate that our method would be useful for distinguishing enzymatic oxidation and auto-oxidation reactions. Such information will be invaluable for elucidating the involvement of PCOOH in disease pathogenesis and in food deterioration.

High performance chiral separation materials based on chitosan bis(3,5-dimethylphenylcarbamate)-(alkyl urea)s

Enantioseparation plays an important role for many fields and for pharmaceutical industry in particular. Chiral stationary phase (CSP) is the core of chiral liquid chromatography that effectively implements enantioseparation. In order to develop coated type CSPs with excellent enantioseparation capability and high tolerance against mobile phases, in this work, a series of chitosan bis(3,5-dimethylphenylcarbamate)-(alkyl urea)s were synthesized, which were coated on 3-aminopropyl silica gel to afford new CSPs. Owing to strong hydrogen bonds formed among the synthesized derivatives, the supra-structure of the derivatives should be highly ordered. Hence, these CSPs could provide excellent separation capability and could tolerate common organic solvents that are usually prohibited for coated type CSPs of cellulose and amylose derivatives. Therefore the newly prepared CSPs exhibited promising prospects for enantioseparation of chiral compounds.

Online post-column solvent assisted and direct solvent-assisted electrospray ionization for chiral analysis of propranolol enantiomers in plasma samples

An Online post-column solvent-assisted ionization (OPSAI) method was developed for enhancing the ionization of the beta-blocker propranolol utilizing normal phase LC-MS/MS. Solvent-assisted electrospray ionization (SAESI) was studied by the introduction of the assistant solvents A: 0.5% Formic acid in Isopropanolol, B: 0.5% Formic acid in Isopropanolol-Water (1:1), and C: 0.5% Formic acid in water into the electrospray ionization chamber using a spray needle. Analyte molecules can be directly ionized by the aid of the assistant solvent spray. Both methods were applied to the chiral separation of propranolol enantiomers using normal phase analysis on cellulose-based chiral column. Interestingly, both methods are easy to handle and offer a wide range of assistant solvents that can be used in order to gain the optimum ionization of the analyte molecules. The both methods considerably improved the analyte signal and the peak area greatly increased. The propranolol average signal-to-noise (S/N) ratio was enhanced from 26±1 and 42±1 to 2341±61 and 1725±29 for R-propranolol and S-propranolol, respectively, when the post-column solvent method (OPSAI) was used with isopropanol-assistant solvent (A). While in case of solvent-assisted electrospray ionization method (SAESI) signal was enhanced from 26±1 and 42±1 to 2223±72 and 2155±58 for R-propranolol and S-propranolol, respectively, with water as an assistant solvent. The limit of detection was 10ng/mL and the method was linear in the range 50-2000ng/mL. The NPLC-MS method was applied for the determination of propranolol enantiomers in human plasma after microextraction by packed C18 sorbent.