Polysaccharide-based Chiral Stationary Phases Research Articles

Supercritical fluid chromatographic chiral separation of potential P2RX7 antagonists containing one, two and three chiral centers

Eleven polysaccharide-based chiral stationary phases were screened to separate stereoisomers of six lactam derivatives by supercritical fluid chromatography (SFC). Those molecules are antagonists of the P2×7 receptor with potential anti-inflammatory activity. They present a mixture of either two enantiomers, or four or eight stereoisomers depending on the number of chiral centers in their structure. The effect of chiral stationary phase, either amylose- or cellulose-based, coated or immobilized, chlorinated or non-chlorinated, on retention and selectivity of those compounds was studied. The effect of the co-solvent nature (methanol, ethanol, propan-2-ol and acetonitrile) and percentage (15 to 40%), temperature (20 to 45°C) and backpressure (8 to 20 MPa) on the enantioseparation and retention of 1-(2-chlorobenzyl)-5-((4-methoxyphenyl)amino)pyrrolidin-2-one (compound 4) was thoroughly studied. Thus, optimal conditions were defined for each derivative in order to implement the preparative separation of the whole series, except of 1-((3,4-dimethoxyphenyl)(phenyl)methyl)-5-oxo-N-(1-phenylethyl)pyrrolidine-2-carboxamide) (compound 6) for which none of the eleven columns could resolve the eight stereoisomers. The small-scale preparative separation of the enantiomers of the most promising derivative, i.e 3-acetyl-1-(4-chlorophenyl)-N-(2,4-dichlorobenzyl)-5-oxopyrrolidine-2-carboxamide (compound 2), is presented.

Ion-pair chromatographic attribute in the retention of ammonium ion on a crown ether-based and a polysaccharide-based chiral stationary phases. Some mobile phase additives compatible with liquid chromatography-electrospray ionization-mass spectrometry

The design of the mobile phase additive useful in HPLC analysis on two types of chiral stationary phases, one based on chiral crown ether, and another based on polysaccharide derivative, was developed. CROWNPAK® CR-I, the chiral stationary phase bearing (R)- or (S)-(3,30-diphenyl-1,10-binaphtyl)-20-crown-6 (1) moiety is a useful CSP to separate primary amine enantiomers. While perchloric acid had been recommended as the mobile phase additive to attain a better separation, we have reexamined the effect of mobile phase additives and revealed that the retention of an ammonium ion is enhanced by a chaotropic or a hydrophobic anion in a water-based mobile phase like well-known ion pair chromatography in an RPLC. However, the retention was enhanced in reverse by a rather cosmotropic or a hydrophilic anion in an acetonitrile (ACN)-based mobile phase. These results looking contradictory to each other may be rationalized both in the basis of ion pair chromatography. A similar but smaller effect of pairing anion species was also observed on a polysaccharide-based CSP. Based on these findings, some types of mobile phase have been proposed and some of them were demonstrated to be compatible with liquid chromatography-electrospray ionization-mass spectrometry (ESI LC/MS).

Comprehensive Review on Chiral Stationary Phases in Single-Column Simultaneous Chiral-Achiral HPLC Separation Methods.

This comprehensive review explores the utilization of chiral stationary phases (CSPs) in the context of single-column simultaneous chiral-achiral high-performance liquid chromatography (HPLC) separation methods. While CSPs have traditionally been pivotal for enantioselective drug analysis, contemporary CSPs often exhibit notable chemoselective properties. Consequently, there is a discernible trend towards the development of methodologies that enable simultaneous enantio- and chemoselective separations utilizing a single CSP-based chromatographic column. This review provides an exhaustive overview of reported HPLC methods in this domain, with a focus on four major CSP types: cyclodextrin-, glycopeptide antibiotic-, protein-, and polysaccharide-based CSPs. This article delves into the diverse applications of CSPs, encompassing various chromatographic modes such as normal phase (NP), reverse phase (RP), and polar organic (PO). This review critically discusses method development, emphasizing the additional chemoselective separation mechanisms of CSPs. It also explores possibilities for method optimization and development, concluding with future perspectives on this evolving field. Despite the inherent challenges in understanding the retention mechanisms involved in chemoselective separations, this review highlights promising trends and anticipates a growing number of simultaneous enantio- and chemoselective methods in pharmaceutical analyses, pharmacokinetic studies, and environmental sample determinations.

Separation of 4-substituted 5-methylpiracetam stereoisomers on polysaccharide-based chiral stationary phases

Monitoring of stereoisomer content in samples containing chiral compounds with multiple chiral centers is an important and challenging task in chiral liquid chromatography. 4-Phenyl-5-methylpiracetam, containing two chiral centers, was used as model compound to explore the stereorecognition ability of polysaccharide-based chiral selectors. Initially, the chromatographic behavior of racemic 4-phenyl-5-methylpiracetam on nineteen commercially available polysaccharide-based chiral columns was tested with a mobile phase, consisting of a mixture of ethanol and n-hexane. The obtained results were analysed, and nine chiral phases were selected for further investigation of seven newly synthesized 4-substituted 5-methylpiracetam chiral separations. Our subsequent studies showed that chiral stationary phases based on amylose tris(5-chloro-2-methylphenylcarbamate) and amylose tris[(S)-α-methylbenzylcarbamate] posess higher ability for chiral recognition of stereoisomers of the studied analytes.

HPLC and SFC Enantioseparation of (±)-Trans-β-Lactam Ureas on Immobilized Polysaccharide-Based Chiral Stationary Phases—The Introduction of Dimethyl Carbonate as an Organic Modifier in SFC

A series of nine racemic trans-β-lactam ureas were analyzed for enantiomer separation by high-performance liquid chromatography (HPLC) and supercritical fluid chromatography (SFC). The separations were performed on three immobilized polysaccharide-based chiral analytical columns (CHIRAL ART Amylose-SA, CHIRAL ART Cellulose-SB and CHIRAL ART Cellulose-SC). In HPLC mode, a normal-phase consisting of n-hexane/2-PrOH (90/10, v/v), a polar organic mobile phase consisting of 100% MeOH or 100% EtOH, and a non-standard mobile phase consisting of 100% dimethyl carbonate (DMC) were investigated. In SFC mode, the mobile phases CO2/alcohol (80/20, v/v) and CO2/DMC/alcohol (MeOH or EtOH; 70/24/6, v/v/v or 60/32/8, v/v/v) were investigated. The best achieved enantioseparation of trans-β-lactam ureas was obtained with an Amylose-SA column. We have shown that the green solvent dimethyl carbonate (DMC) can be efficiently used as a mobile phase in HPLC mode as well as in SFC mode along with the addition of polar organic modifiers (MeOH or EtOH).

High-performance liquid chromatographic enantioseparation of azole analogs of monoterpene lactones and amides focusing on the separation characteristics of polysaccharide-based chiral stationary phases

High-performance liquid chromatography-based enantioseparation of newly prepared azole analogs of monoterpene lactones and amides was studied. Effects of additives and mobile phase composition were evaluated both in normal and polar organic modes. Applying amylose tris-(3,5-dimethylphenylcarbamate) selector in normal and polar organic modes acid and base additives were found to affect the peak profiles, without significantly influencing the enantiorecognition ability of the studied selector. In most cases, differences observed in retention times and enantioselectivities were lower than 10 and 20 % under normal phase and polar organic conditions, respectively. Under normal phase conditions decreased retention was observed for all the studied analytes with increased eluent polarity. Interestingly, enantioselectivity was only slightly (<10 %) influenced by the variation in the n-hexane/2-propanol ratio between 80/20 and 20/80 v/v. In polar organic mode, five different neat solvents (acetonitrile, methanol, ethanol, 1-propanol, and 2-propanol) were tested, and the best results were obtained with acetonitrile and ethanol in the case of Lux Amylose-1 column with enantioresolutions most often above 2. Based on results obtained with amylose and cellulose-based columns the amylose tris-(3,5-dimethylphenylcarbamate) selector is found to offer a superior performance both in normal and polar organic modes. When evaluating the possible effects of the selector immobilization, no striking differences were found in the normal phase. Usually, enantioselectivities and resolutions were higher (10–20 %), while retention factors of the first peaks were lower (20–30 %), on the coated-type column. In contrast, in polar organic mode, the retention characteristics and enantiorecognition ability of the coated and immobilized selectors were heavily affected by the nature of the polar solvent.Special attention has been paid to the history-dependent behavior of polysaccharide-based selectors. A confidence interval-based evaluation is suggested to help comparison of the histereticity observed in different systems. Several examples are shown to confirm that the recently discovered hysteresis is a common characteristic of polysaccharide-based selectors.

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.

Virtual chiral recognition of eugenol derivatives on amylose tris(3-chloro-5-methylphenylcarbamate) chiral stationary phase in unusual normal-phase mode

Chromatographic enantioseparation on polysaccharide-based chiral stationary phases has undergone explosive development over the last three decades as a method for separating the enantiomers of chiral compounds on an analytical and preparative scale. In this context, understanding the nature of the intermolecular interactions involved in retention and recognition processes is an interesting scientific challenge. In the present study, three eugenol derivatives were used as chiral references to elucidate some unexplored aspects of the enantioselective and retention properties of the Chiralpak IG-U chiral stationary phase based on amylose-tris(3-chloro-5-methylphenylcarbamate).The performance of the ultra-high performance liquid chromatography chiral packing material Chiralpak IG-U was evaluated using a two-step approach. First, binary mixtures containing variable proportions of alcohol (ethanol or 2-propanol) in n-hexane were used as mobile phases and the retention factors were recorded at three different temperatures. A rational analysis of this set of chromatographic data shows the leading role played by hydrogen bond between the OH group linked to the stereogenic centre of the analytes and the active sites of the chiral chromatographic material in obtaining a high degree of enantioseparation.The retention factors were then plotted against the percentage of alcohol modifiers to obtain retention maps with a non-linear performance trend with correlation factors >0.9990.The proposed retention map model was used to extrapolate and describe virtual chiral recognition of chiral analytes on the Chiralpak IG-U chiral stationary phase under extreme elution conditions with expected run times of hundreds or thousands of years. The presented virtual chiral recognition approach is based on a generic concept and therefore opens new possibilities for understanding the performance of other polysaccharide-based chiral stationary phases.

Chromatographic Enantioseparation of Chiral Sulfoximines on Polysaccharide-Based Chiral Stationary Phases.

Chiral sulfoximines have significant roles in pharmaceutical industry and agricultural chemicals. Furthermore, chiral structurally related sulfoximines are used for their wide potential applications in some uncharted territory. However, chromatographic study on these compounds has not been systematically performed. Herein, this paper describes the enantioseparation of 12 chiral sulfoximines on polysaccharide-based chiral stationary phases (CSPs). Separation factors of chiral column, high-performance liquid chromatography parameters such as mobile phase composition and column temperature were carefully investigated. Chiralcel OJ-H column can resolve all of the 12 compounds, while Chiralpak AD-H column and Chiralpak AS-H column can separate eight and nine molecules, respectively. The sulfoximines are effectively resolved with Chiralcel OJ-H column with a mixture of n-hexane/2-propanol (80:20) as the mobile phase.

Chiral separation and molecular modeling study of decursinol and its derivatives using polysaccharide-based chiral stationary phases

Plant-based bioactive substances have long been used to treat inflammatory ailments, owing to their low toxicity and cost-effectiveness. To enhance plant treatment by eliminating undesirable isomers, optimizing the chiral separation techniques in pharmaceutical and clinical studies is important. This study reported a simple and effective method for chiral separation of decursinol and its derivatives, which are pyranocoumarin compounds with anti-cancer and anti-inflammatory properties. Baseline separation (Rs >1.5) was achieved using five different polysaccharide-based chiral stationary phases (CSPs) that differed in chiral origin, chiral selector chemistry, and preparation technique. To separate all six enantiomers simultaneously, n-hexane and three alcohol modifiers (ethanol, isopropanol, and n-butanol) were used as mobile phases in the normal-phase mode. The chiral separation ability of each column with various mobile phase compositions was compared and discussed. As a result, amylose-based CSPs with linear alcohol modifiers demonstrated superior resolution. Three cases of elution order reversal caused by modifications of CSPs and alcohol modifiers were observed and thoroughly analyzed. To elucidate the chiral recognition mechanism and enantiomeric elution order (EEO) reversal phenomenon, detailed molecular docking simulations were conducted. The R- and S-enantiomers of decursinol, epoxide, and CGK012 exhibited binding energies of –6.6, –6.3, –6.2, –6.3, –7.3, and –7.5 kcal/mol, respectively. The magnitude of the difference in binding energies was consistent with the elution order and enantioselectivity (α) of the analytes. The molecular simulation results demonstrated that hydrogen bonds, π–π interactions, and hydrophobic interactions have a significant impact on chiral recognition mechanisms. Overall, this study presented a novel and logical approach of optimizing chiral separation techniques in the pharmaceutical and clinical industries. Our findings could be further applied for screening and optimizing enantiomeric separation.

Development and validation of a chiral LC-MS method for the enantiomeric resolution of (+) and (-)-Mebeverine Hydrochloride in bulk drug by using polysaccharide-based chiral stationary phase

The aim of this study was to develop a simple, specific, sensitive and precise LC-MS method for the determination of mebeverine enantiomers in pharmaceutical formulations and it was validated as per ICH guidelines. The chromatographic separation was achieved on Phenomenex® Lux Cellulose 1 (250 mm x 4.6 mm i.d, 5μm particle size) column using mobile phase system containing acetonitrile: 10 mM ammonium acetate (85:15) at the flow rate of 0.8 mL/min. In the spectral investigation by LC-MS, the standard solution of Mebeverine showed major peak at m/z of 430.70, which was assigned to the [M+H] ion of Mebeverine. The described method was linear over the range of 15–75 ng /mL for (±) Mebeverine enantiomers with a correlation coefficient (r2 = 0.999). Detection limits and quantification limits of (+) Mebeverine and (-) Mebeverine were found to be 5 ng/mL and 15 ng/mL respectively. The recovery study of mebeverine from tablet formulation was found to be 99.16%. Mebeverine standard solution and mobile phase were found to be stable for at least 48h. The Mebeverine enantiomers were well resolved with mean retention times of about 1.16 min and 1.20 min respectively. The developed method was extensively validated and proved to be robust, accurate, precise, and suitable for analysis of Mebeverine enantiomers in tablet dosage form.

When van Deemter Goes Upside Down in Chiral Chromatography

The occurrence of convex-upward van Deemter curves is rare but not unusual in chiral liquid chromatography (LC). In this article, this behaviour, experimentally observed for the more retained enantiomer of a chiral sulfoxide on a polysaccharide-based chiral stationary phase (CSP), has been investigated from an experimental viewpoint, finding that this species is characterized by a very strong, localized adsorption on the CSP. The observation of the behaviour of other chiral sulfoxides with different chemical structures has suggested correlations between molecular properties and specific interactions on the CSP.

Enantioseparation of new axially chiral carboxylic acids on polysaccharide-based chiral stationary phases under normal phase elution conditions

In the last decade, the availability of new and versatile synthetic strategies for the preparation of substituted 4,4’-bipyridyl derivatives based on chemo- and regioselective functionalization of the 4,4’-bipyridine core has encouraged studies for exploring the bioactivity of these compounds in the fields of drug discovery and medicinal chemistry. In substituted 4,4’-bipyridines, chirality may emerge from restricted rotation induced by sterically hindered atoms or functional groups located around the 4,4’-biaryl bond (chiral axis). The first atropisomeric substituted 4,4’-bipyridine was prepared in 2008, and no asymmetric synthesis to produce pure atropisomers of chiral 4,4’-bipyridine derivatives has been available so far. Thus, in the last few years, our groups developed methods to separate atropisomers of a wide series of 4,4’-derivatives by high-performance liquid chromatography (HPLC) using polysaccharide-based chiral stationary phases (CSPs). In the frame of our interest in this field, we reported herein the synthesis of two new chiral carboxylic acids containing an axially chiral 4,4’-bipyridyl unit as source of chirality, and their HPLC enantioseparation on polysaccharide-based CSPs. In particular, the impact of analyte and CSP structures on the enantioseparation outcomes as well as mechanisms and noncovalent interactions underlying the enantioseparation were explored by using electrostatic potential analysis and molecular dynamics (MD) simulations.

Chiral separation of α-tocopherol and α-tocopheryl acetate by supercritical fluid chromatography for accurate vitamin E nutrition labeling

Separations of respective stereoisomers of α-tocopherol and α-tocopheryl acetate by supercritical fluid chromatography (SFC) using polysaccharide-based chiral stationary phases (CSP) were studied. Two separate methods have been developed for α-tocopherol and α-tocopheryl acetate with total runtime of 35 min and 15 min, respectively. Under the optimized conditions, all-rac-α-tocopherol is separated into four peaks (peak area ratio 5:1:1:1) on an amylose tris(3,5-dimethylphenylcarbamate) CSP, and all-rac-α-tocopheryl acetate is separated into 2 peaks with equal peak areas on a cellulose tris(3,5-dimethylphenylcarbamate) CSP. The characteristic peak profiles of these racemic mixtures are distinctive enough to differentiate synthetic vitamin E (racemate) from the naturally occurring vitamin E (RRR-stereoisomer only). The α-tocopherol method has been demonstrated free of interference from other natural tocopherols, such as β-, γ-, and δ-tocopherol. Evaluation of the α-tocopherol method with commercially available vitamin E dietary supplements and an infant formula showed acceptable results in the qualitative analysis of α-tocopherol. These SFC methods provide fast, simple, and “green” solutions to verify or determine the type of vitamin E for dietary supplement and food manufacturers to ensure accurate vitamin E nutrition label claims.

Hybridization of helical poly(phenylacetylene)s bearing L-proline tripeptide pendants into porous silica microspheres as a solvent-tolerable chiral stationary phase for liquid chromatography.

A novel one-handed helical copoly(phenylacetylene) (CPA) bearing L-proline tripeptide pendants and a few triethoxysilyl residues was synthesized and hybridized into SiO2 porous microspheres (PMSs) during microsphere growth through the hydrolytic polycondensation of ethoxysilyl groups. Nuclear magnetic resonance and Fourier transform infrared spectroscopy results verified the successful preparation of CPA and its hybrid product using SiO2 PMSs. The chiral recognition ability of the resulting CPA with a hybridized-type chiral stationary phase (HCSP) for high-performance liquid chromatography (HPLC) was investigated, revealing its high recognition ability for selected racemates. Moreover, the HCSP showed good solvent tolerability, thus broadening the selection of suitable eluents. The separation effect of the HCSP for the racemate N,N-diphenylcyclohexane-1,2-dicarboxamide (7) improved significantly after introducing CHCl3 in the eluent, resulting in separation factors equivalent or superior to common commercially available polysaccharide-based chiral stationary phases. The proposed preparation strategy provides a new and valuable method for obtaining poly(phenylacetylene)-based HCSPs suitable for a wide range of applications and eluent conditions.

Novel Gatifloxacin3-Carboxamide Derivatives as Anti-Tumor Agents: Synthesis, Enantioseparation, and Molecular Docking

Background:: The drug's affinity to the identified target (protein/enzyme) is a critical characteristic in the development of a novel drug. Fluoroquinolone derivatives with a carboxylic group change have improved antimicrobial and anticancer activity while maintaining antibacterial activity similar to parent drugs. Aim:: The rationale upon which synthesis of the new compounds, evaluation of their anticancer activity with in silico study, and suggestion of their mechanism of action is presented in this paper. Methods:: This part describes the practical procedures used for the synthesis of four new gatifloxacin 3-carboxamide derivative, with their spectral data (UV-vis, IR, and 1H-NMR). The enantiosaparation and docking studies are presented and discussed. Results:: Four gatifloxacin 3-carboxamide derivatives were enantioseparated using a high-performance liquid chromatography approach using two distinct polysaccharide-based chiral stationary phases (CSPs). The baseline enantioseparation of all derivatives evaluated in this study was achieved using both coated and immobilized amylose columns. In silico molecular docking study, revealed that all compounds showed good docking score. Conclusion:: The novel Fluoroquinolone caboxamides derivatives could be repositioned as DNA topoisomerase II inhibitors, allowing them to be employed as anticancer agents, according to our in silico study. Experiments in vitro and in vivo are required to confirm their efficacy.

Two-Dimensional Chiral HPLC Analysis of Lactate, Hydroxybutyrates and Malate in Human Plasma

For the simultaneous determination of lactate (LA), 2-hydroxybutyrate (2HB), 3-hydroxybutyrate (3HB) and malate (MA) enantiomers, a new separation technique in a two-dimensional high-performance liquid chromatography (2D-HPLC) system following the fluorescence derivatization with 4-nitro-7-piperazino-2,1,3-benzoxadiazole has been developed. The 2D-HPLC system was composed of the reversed-phase (1D) and enantioselective (2D) separations. In the first dimension, the target hydroxy acids were separated as their D plus L mixtures on a Singularity RP18 column (1.0 mm i.d. x 250 mm), and the enantiomers were separated in the second dimension using a polysaccharide-based chiral stationary phase, Chiralpak IG (2.0 mm i.d. x 250 mm). By using the Chiralpak IG column, the LA, 2HB, 3HB and MA enantiomers were separated with resolution values of 3.47, 3.63, 6.81 and 3.72, respectively. The developed 2D-HPLC system was applied to human plasma, and trace levels of D-LA and L-3HB in addition to their major antipodes were determined. The acquired %D of LA (the percentage of D-LA over total LA) and %L of 3HB (the percentage of L-3HB over total 3HB) were 1.0 and 2.7, respectively. For 2HB, only the L-form was detected, while the MA enantiomers were not found in the human plasma.

Enantioseparation of syn- and anti-3,5-Disubstituted Hydantoins by HPLC and SFC on Immobilized Polysaccharides-Based Chiral Stationary Phases

The enantioseparation of syn- and anti-3,5-disubstituted hydantoins 5a–i was investigated on three immobilized polysaccharide-based columns (CHIRAL ART Amylose-SA, CHIRAL ART Cellulose-SB, CHIRAL ART Cellulose-SC) by high performance liquid chromatography (HPLC) using n-hexane/2-PrOH (90/10, v/v) or 100% dimethyl carbonate (DMC) as mobile phases, respectively, and by supercritical fluid chromatography (SFC) using CO2/alcohol (MeOH, EtOH, 2-PrOH; 80/20, v/v) as a mobile phase. The chromatographic parameters, such as separation and resolution factors, have indicated that Amylose-SA is more suitable for enantioseparation of the most analyzed syn- and anti-3,5-disubstituted hydantoins than Celullose-SB and Cellulose-SC in both HPLC and SFC modalities. All three tested columns showed better enantiorecognition ability toward anti-hydantoins compared to syn-hydantoins, both in HPLC and SFC modes. We have demonstrated that environmentally friendly solvent DMC can be efficiently used as the mobile phase in HPLC mode for enantioseparation of hydantoins on the immobilized polysaccharide-based chiral stationary phases.

The separation of several organophosphate pesticides on immobilized polysaccharide chiral stationary phases.

While not initially a focus or priority, in recent decades, an emphasis has been placed on the activity of individual enantiomers of widely used pesticides. Of particular note are organophosphorus‐based pesticides like fenamiphos and profenofos, as examples. This work explores the enantioselective high‐performance liquid chromatography (HPLC) separations of seven such organophosphorus pesticides (OP's) on the library of immobilized polysaccharide‐based chiral stationary phases (CSPs) with normal phase hexane/alcohol mixtures. Further exploration of the effect of mobile phase strength and temperature on several of the separations was performed using simple factorial design. Equivalent retention of the first eluting enantiomer of several combinations of temperature and mobile phase was compared for peak shape, selectivity, and resolution. Similarly, equivalent selectivity of several combinations of temperature and mobile phase was compared for peak shape, retention of the first eluting enantiomer, and resolution. The results of this study make available several new chiral separations of the OPs included in the work that were not previously documented, including separations on the three most recently commercialized phases, Chiralpak IH, IJ, and IK. Additionally, sufficient understanding was obtained to be able to predict the trade‐off of resolution, analysis time, peak sharpness (and thus improve limit‐of‐detection [LOD]/limit‐of‐quantification [LOQ]), robustness, and convenience of conditions for further application optimization.

Supercritical fluid chromatography for separation of chiral planar metallocenes

Unsymmetrically disubstituted metallocene derivatives, characterized as the first sandwich structure, have found interest in asymmetrical synthesis and in medicinal chemistry as well. Besides, they present a particular case of chirality. Twenty original and six commercially available molecules presenting either i) a planar chirality or ii) an asymmetrical carbon containing group or iii) being symmetrically substituted were analyzed in supercritical fluid chromatography on eleven polysaccharide-based chiral stationary phases with carbon dioxide containing 30% of methanol or 2-propanol as a co-solvent mobile phase. A basic additive, either diethylamine, triethylamine or n-butylamine was also required at 1% to the co-solvent for elution. While some of the tested chiral stationary phases provided enantioseparation for the racemates, chlorinated cellulosic phases proved to be both highly retentive and highly enantioselective towards these particular species with the highest rate of success compared to their non-chlorinated counterparts. For instance, the resolution value was equal to 14.1 for one ferrocene derivative in one-hour analysis time on cellulose tris(3,5-dichlorophenylcarbamate) column with 30% 2-propanol/1% n-butylamine while a single peak was observed under the same conditions on cellulose tris(3,5-dimethylphenylcarbamate) column. Experimental parameters were arbitrarily set at 150 bar outlet pressure, 40 °C temperature and 3 mL/min flow-rate.