Cellulose-based Chiral Stationary Phase Research Articles

Chemoenzymatic Synthesis of Optically Active Ethereal Analog of iso-Moramide-A Novel Potentially Powerful Analgesic †.

To develop potent and safer analgesics, we designed and synthesized a novel enantiomerically enriched ethereal analog of (R)-iso-moramide, namely 2-[(2R)-2-(morpholin-4-yl)propoxy]-2,2-diphenyl-1-(pyrrolidin-1-yl)ethan-1-one. The titled active agent can potentially serve as a powerful synthetic opiate with an improved affinity and selectivity toward opioid receptors (ORs). This hypothesis was postulated based on docking studies regarding the respective complexes between the designed ligand and µ-OR, δ-OR, and κ-OR. The key step of the elaborated asymmetric synthesis of novel analog involves lipase-catalyzed kinetic resolution of racemic 1-(morpholin-4-yl)propan-2-ol, which was accomplished on a 10 g scale via an enantioselective transesterification employing vinyl acetate as an irreversible acyl donor in tert-butyl methyl ether (MTBE) as the co-solvent. Next, the obtained homochiral (S)-(+)-morpholino-alcohol (>99% ee) was functionalized into corresponding chloro-derivative using thionyl chloride (SOCl2) or the Appel reaction conditions. Further transformation with N-diphenylacetyl-1-pyrrolidine under phase-transfer catalysis (PTC) conditions using O2-saturated DMSO/NaOH mixture as an oxidant furnished the desired levorotatory isomer of the title product isolated in 26% total yield after three steps, and with 89% ee. The absolute configuration of the key-intermediate of (R)-(–)-iso-moramide was determined using a modified form of Mosher’s methodology. The preparation of the optically active dextrorotatory isomer of the titled product (87% ee) was carried out essentially by the same route, utilizing (R)-(–)-1-(morpholin-4-yl)propan-2-ol (98% ee) as a key intermediate. The spectroscopic characterization of the ethereal analog of iso-moramide and the enantioselective retention relationship of its enantiomers using HPLC on the cellulose-based chiral stationary phase were performed. Moreover, as a proof-of-principle, single-crystal X-ray diffraction (XRD) analysis of the synthesized 2-[(2R)-2-(morpholin-4-yl)propoxy]-2,2-diphenyl-1-(pyrrolidin-1-yl)ethan-1-one is reported.

Chiral LC method development: Stereo-selective separation, characterization, and determination of cabotegravir and related RS, RR, and SS isomeric impurities on coated cellulose-based chiral stationary phase by HILIC-LC and LC-MS

The first, sensitive, and rapid chiral method was developed for enatioseperations and determination of cabotegravir and its enantiomeric impurities by using HPLC and LC-MS. Cabotegravir is an antiretroviral medication used for the treatment of HIV/AIDS approved by the food and drugs administration (FDA) in the year 2021. The cabotegravir chiral separation was achieved on the coated cellulose-tris (4-chloro-3-methyl phenyl carbamate) (CHIRALCEL OX-3R) column in HILIC mode and the total run time is less than 15 min. The effects of mobile phase composition, elution mode, and percentage of organic modifier as well as the effect of mobile phase-additives and column temperature were investigated on selectivity, resolution, and peak symmetry. The mobile phase consisted of acetonitrile and water with 0.1% (v/v) addition of formic acid additive with the flow rate of 1 mLmin−1. UV detection was carried out at 220 nm. The calibration curves of cabotegravir and its enantiomers were linear over the concentration range of 0.04–1.125 µgmL−1. The limits of detection and quantification for cabotegravir and its enantiomer (RS isomer) were ≤ 0.02 and ≤ 0.06, and the RR and SS-isomers limits were ≤ 0.02 and 0.03 µgmL−1 respectively. It was demonstrated that the proposed method is selective, precise, and robust. Finally, the validated method was applied for the determination and identification of cabotegravir and its chiral enantiomers in the bulk drugs by using HPLC and LC-MS techniques.

Comparative study on retention behaviour and enantioresolution of basic and neutral structurally unrelated compounds with cellulose-based chiral stationary phases in reversed phase liquid chromatography-mass spectrometry conditions

A comparative study on the retention behaviour and enantioresolution of 54 structurally unrelated neutral and basic compounds using five commercial cellulose-based chiral stationary phases (CSPs) and hydro-organic mobile phases compatible with MS detection is performed. Four phenylcarbamate-type cellulose CSPs (cellulose tris(3,5-dimethylphenylcarbamate), Cell1; cellulose tris(3-chloro-4-methylphenylcarbamate), Cell2; cellulose tris(4-chloro-3-methylphenylcarbamate), Cell4 and cellulose tris(3,5- dichlorophenylcarbamate), Cell5) and one benzoate-type cellulose CSP (cellulose tris(4-methylbenzoate), Cell3) are assayed. Mobile phases consist of binary mixtures of methanol (30–90% MeOH) or acetonitrile (10-98% ACN) with 5 mM ammonium bicarbonate (pH = 8.0).The existence of reversed phase (RPLC) and hydrophilic interaction liquid chromatography (HILIC) retention behaviour domains is explored. In MeOH/H2O mobile phases, for all compounds and CSPs, the typical RPLC retention behaviour is observed. When using ACN/H2O mobile phases, for all compounds in all CSPs (even in the non-chlorinated CSPs) a U-shaped retention behaviour depending on the ACN/H2O content is observed which indicates the coexistence of the RPLC- (< 80% ACN) and HILIC- (∼80–98% ACN) domains. The magnitude of retention changes in both domains is related to the hydrophobicity of the compound as well as to the nature of the CSP.The study of the effect of the nature and concentration of the organic solvent, as well as the nature of the CSP on the enantioresolution reveals that: (i) the use of MeOH/H2O or ACN/H2O greatly affects the enantioselectivity and enantioresolution degree of the chromatographic systems, being, in general, better the results obtained with ACN/H2O mobile phases. (ii) The ACN-RPLC-domain provides much better enantioresolution than HILIC-domain. (iii) Cell2, especially with ACN/H2O mobile phases, is the CSP that allows baseline enantioresolution for a higher number of compounds. (iv) Phenylcarbamate-type CSPs do not offer clear complementary enantioselectivity to that of Cell2. (v) Cell3 is the only CSP that provides marked complementary enantioselectivity to that of Cell2, almost orthogonal in MeOH/H2O mobile phases.

Liquid chromatography enantiomeric separation of chiral ethanolamine substituted compounds.

Eleven racemic ethanolamine derivatives were prepared, and their enantiomers were separated using liquid chromatography with various chiral columns. These derivatives included chiral vicinal amino alcohols, β-hydroxy ureas, β-hydroxy thioureas, and β-hydroxy guanidines, all of which are present in many active pharmaceutical ingredients. The screening study was performed with six chiral stationary phase containing columns, including four recently introduced superficially porous particles bonded with two macrocyclic glycopeptides, a cyclodextrin derivative and a cyclofructan derivative. The two remaining columns contained chiral stationary phases, based on either a cellulose derivative or derivatized amylose, both bonded to fully porous particles. The cyclodextrin and cellulose-based chiral stationary phases proved to be the most broadly effective selectors and were able to separate 8 and 7 of the 11 tested compounds, respectively. With respect to analyte structural features, marked differences in enantiorecognition were observed between compounds containing phenyl and cyclohexyl groups adjacent to the stereogenic center. Additionally, replacing a small electronegative oxygen atom by a larger and less electronegative sulfur atom induced a significant difference in chiral recognition by the cellulose derivative as well as by the vancomycin-based chiral selectors.

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.

Original enantioseparation of illicit fentanyls with cellulose-based chiral stationary phases under polar-ionic conditions

Fentanyl analogues used in therapy and a range of highly potent non-pharmaceutical fentanyl derivatives are subject to international control, as the latter are increasingly being synthesized illicitly and sold as ‘synthetic heroin’, or mixed with heroin. A significant number of hospitalizations and deaths have been reported in the EU and USA following the use of illicitly synthesized fentanyl derivatives.It has been unequivocally demonstrated that the enantiomers of fentanyl derivatives exhibit different pharmaco-toxicological profiles, which makes crucial to avail of suitable analytical methods enabling investigations at a “stereochemical level”.Chromatographic methods useful to discriminate the enantioseparation of fentanyls and their derivatives are still missing in the literature. This is the first study in which the enantioseparation of four fentanyl derivatives, that is, (±)-trans-3-methyl norfentanyl, (±)-cis-3-methyl norfentanyl, β-hydroxyfentanyl, and β-hydroxythiofentanyl, has been obtained under polar-ionic conditions. Indeed, the use of ACN-based mobile phases with minor amounts of either 2-propanol or ethanol (plus diethylamine and formic acid as ionic additives) allowed obtaining enantioseparation and enantioresolution factors up to 1.83 and 7.02, respectively.For the study, the two chiral stationary phases cellulose tris(3-chloro-4-methylphenylcarbamate) and cellulose tris(4-chloro-3-methylphenylcarbamate) were used, displaying a remarkably different performance towards the enantioseparation of (±)-cis-3-methyl norfentanyl.Chiral LC analyses with a high-resolution mass spectrometry detector were also carried out in order to confirm the obtained data and demonstrate the suitability and compatibility of the optimized mobile phases with mass spectrometric systems.

Analysis of Orphenadrine Citrate in Various Chiral Stationary Phases: A Comparative Study

Background: Polysaccharide based chiral stationary phases (CSPs) were used to perform enantiomeric separation of Orphenadrine Citrate by Ultra-Fast Liquid Chromatography (UFLC) technique. Trials were conducted using the polar mode, reverse phase mode and normal phase mode. Amylose and Cellulose-based CSPs were used for the same. Materials and Methods: Eight Amylose-based CSPs and four Cellulose-based CSPs were used in the reverse phase mode. Five Amylose-based CSPs and two Cellulose-based CSPs were used in polar mode. The only Cellulose-based CSP used in the normal phase mode could effectively separate Orphenadrine Citrate enantiomers with a good resolution. Results and Discussion: Successful enantioseparation was obtained using Chiralcel OD-H containing Cellulose tris (3, 5-dimethylphenylcarbamate) as a chiral selector and n-hexane: Ethanol: Diethylamine (95: 05: 0.1, v/v/v) as the mobile phase. The developed method was validated in accordance with ICH guidelines (Q2R1). Conclusion: The proposed objectives were successfully accomplished as the developed method could effectively resolve Orphenadrine Citrate enantiomers.

Effect of solvents on the chiral recognition mechanisms of immobilized cellulose-based chiral stationary phase

The effect of solvents on the enantioselectivities of four structurally similar chiral solutes with a cellulose derivative–based chiral stationary phase, Chiralpak IB, were studied using acetone (AC), 2-propanol (IPA), and tert-butanol (TBA) separately as polar modifiers. The enantioselectivities α of benzoin and methyl mandelate decrease with an increase in modifier concentration CM, whereas the enantioselectivity of pantolactone increased with increasing AC concentration. These results were attributed to the heterogeneous adsorption mechanisms of enantiomers. To interpret the dependence of enantioselectivity on modifier content, an enantioselectivity model based on a two-site adsorption model was proposed. The dependence of α on CM was inferred to be mainly due to the distinct modulating effects of modifier concentration on the two adsorption sites: the nonselective type-I site and enantioselective type-II site. The model fitted the benzoin data satisfactorily over a wide TBA concentration range. The retention factors as a function of TBA concentration were successfully deconvoluted for each site. With the use of the proposed model, it was inferred that the chiral recognitions of benzoin and methyl mandelate were mainly achieved by the presence of an aromatic group adjacent to the hydroxyl group. When using IPA and TBA separately as modifiers, the presence of an aromatic group adjacent to the ketone group mainly contributed to the nonselective π interactions and enantioselective steric interactions, respectively. These results, along with those of the modifier adsorption isotherms, determined using the perturbation method, as well as the retention behaviors of various achiral solutes, indicate that the molecular recognition mechanism of IB sorbent is highly sensitive to the adsorbate's molecular geometry. The molecular environment of the sorbent can be controlled using different modifiers, leading to distinct adsorption and retention mechanisms.

Enantioseparation and molecular modeling study of eight psychoactive drugs on a coated polysaccharide-based chiral stationary phase.

The enantioseparation of eight psychoactive drugs has been firstly performed on a coated cellulose-based chiral stationary phase (Chiralcel OJ-H). To obtain optimum separation conditions, the influences of alcohol modifiers and basic/acidic additives have been studied. As a result, except for the partial separation of oxybutynin enantiomers, the other seven drug enantiomers, including mirtazapine, sulpiride, promethazine, citalopram, oxazepam, donepezil, and cyamemazine, have been completely separated. Additionally, for gaining a better insight into the chiral recognition mechanisms, molecular docking was carried out using the Autodock software. Herein, binding energy and conformations of the chiral stationary phase complexes were provided, and it was found that the distinction in enantiomeric conformation determined the number and strength of intermolecular interactions between analytes and chiral stationary phase which resulted in the difference in binding energies of two enantiomers, and ultimately led to the different migration. These modeling results were in accordance with the observed enantioseparation results in high performance liquid chromatography experiments. At last, chiral separation mechanisms have been discussed in detail, and it has been confirmed that hydrogen bond, π-π, hydrophobic interactions, and some special interactions synergistically contributed to the enantioseparation of psychoactive drugs.

Chiral Separation of Non-Nucleoside Reverse Transcription Inhibitor Efavirenz by HPLC on Cellulose-Based Chiral Stationary Phase

A stereospecific HPLC method for the separation of efavirenz (EFZ) enantiomers in bulk drug and formulations was developed and validated on a normal-phase cellulose derivatized chiral column. The effect of organic modifiers, namely, 2-propanol, ethanol and trifluoroacetic acid in mobile phase was optimized to obtain the best enantiomeric separation. The retention times of (R)-EFZ and (S)-EFZ were observed to be 7.5 and 9.2 min, respectively. The calibration curve was found to be linear over the concentration range of 200 - 6210 ng/mL with a determination coefficient (R 2 ) of 0.9999 for the (R)-isomer. The limit of detection (LOD) and limit of quantification (LOQ) were calculated to be 66 ng/mL and 200 ng/mL, respectively. The proposed method was found to be accurate, precise and suitable for the separation and quantification of unwanted (R)-EFZ in active pharmaceutical ingredients (API). The analytical results were supported by statistical parameters. The proposed method could be successfully applied to the enantiomeric purity analysis of EFZ in bulk drug samples and formulations.

Direct separation of the enantiomers of ramosetron on a chlorinated cellulose-based chiral stationary phase in hydrophilic interaction liquid chromatography mode.

Ramosetron is an enantiopure active pharmaceutical ingredient marketed in Japan since 1996 and later in a few Southeast Asian countries predominantly as an antiemetic for patients receiving chemotherapy. In this study, a simple and rapid high-performance liquid chromoatography method for the separation of ramosetron and its related enantiomeric impurity by using hydrophilic interaction liquid chromatography mode is presented. Chiral resolution was performed on an analytical column (100mm × 4.6mm id) packed with 3 μm particles of cellulose-based Chiralpak IC-3 chiral stationary phase. Using a mobile phase containing acetonitrile-water-diethylamine (100:10:0.1, v/v/v) and setting the column temperature at 35°C, the resolution value was 7.35. At a flow rate of 1mL/min, the enantioseparation was completed within 5min. The proposed method was partially validated and it has proven to be sensitive with limit of detection and limit of quantitation of the (S)-enantiomer impurity of 44.5 and 133.6ng/mL.

Regioselectively substituted cellulose mixed esters synthesized by two-steps route to understand chiral recognition mechanism and fabricate high-performance chiral stationary phases

It is challenging to design and fabricate new and high-performance cellulose-based chiral stationary phases (CSPs), due to the indistinct chiral recognition mechanism and the inherent difficulty to control the structure of cellulose derivatives. Herein, taking advantage of the high regioselective benzoylation of cellulose in 1-allyl-3-methylimidazolium chloride, a series of regioselectively substituted cellulose mixed esters, cellulose 6-benzoate-2,3-phenylcarbamate, are directly obtained by a facile two-steps route without protecting and deprotecting process. The resultant cellulose mixed esters exhibit high chiral recognition capability. In particular, when the benzoate group has an electron-donating substituent on phenyl ring, such as 4-tert-butyl group, the corresponding regioselectively substituted cellulose mixed esters have much better enantioseparation capability than cellulose tri(3,5-dimethylphenylcarbamate), which is commercially available as Chiralcel OD column, one of the most powerful CSPs. More importantly, via adjusting the chemical structure of cellulose derivatives and adding a post-treatment process to optimize their chiral recognition properties, the chiral recognition mechanism is clearly revealed. The synergy of the hydrophobic helical conformation, weak hydrogen-bond donating ability and appropriate distribution of substituents of cellulose derivatives is essential to fabricate high-performance CSPs.

HPLC Enantioseparations with Polysaccharide-Based Chiral Stationary Phases in HILIC Conditions.

In contrast to achiral hydrophilic interaction liquid chromatography (HILIC), which is a popular and largely applied technique to analyze polar compounds such as pharmaceuticals, metabolites, proteins, peptides, amino acids, oligonucleotides, and carbohydrates, the introduction of the HILIC concept in enantioselective chromatography has been relatively recent and scarcely debated. In this chapter, the HILIC enantioseparations carried out on polysaccharide-based chiral stationary phases are grouped and discussed. Another objective of this chapter is to provide a comprehensive overview and insight into the experimental conditions needed to operate under HILIC mode. Finally, to stimulate and facilitate the application of this chromatographic technique, a detailed experimental protocol of a chiral resolution on a chlorinated cellulose-based chiral stationary phase under HILIC conditions is described.

A facile and efficient method to fabricate high-resolution immobilized cellulose-based chiral stationary phases via thiol-ene click chemistry

Abstract Immobilized chiral stationary phases (CSPs) have attracted much attention because of strong solvent resistance and selection of wide range of eluents. In this work, a facile, efficient and engineering method is developed to fabricate high-resolution immobilized cellulose-based CSPs. A controllable amount of acrylate groups, the key to dominate the immobilization degree, is introduced into cellulose chains to obtain cellulose mixed esters with well-defined structure by homogeneous esterification reaction. Subsequently, via simple, efficient, and highly selective thiol-ene click reaction, cellulose mixed esters were chemically bonded onto thiol-modified silica gel to obtain immobilized cellulose-based CSPs, C-AC5-N95 and C-AC25-N75. Due to the stable “C S C” crosslinking bonds, the resultant immobilized CSPs exhibit strong solvent resistance, thus they can be used in a wide range of eluents, including normal-phase non-standard solvents and reversed-phase solvents. They withstand even strong solvents of cellulose derivatives, such as hot pyridine, chloroform, DMF and DMSO. More importantly, the immobilized CSPs C-AC5-N95 displays excellent chiral recognition capability, which is similar with, or even better than, that of coated CSPs.

Enantioseparation of fluorinated 3-arylthio-4,4’-bipyridines: Insights into chalcogen and π-hole bonds in high-performance liquid chromatography

A chalcogen bond (ChB) is a σ-hole-based noncovalent interaction between a Lewis base and an electrophilic element of Group VI (O, S, Se, Te), which behaves as a Lewis acid. Recently, we demonstrated that halogen bond, the more familiar σ-hole-based interaction, is able to promote the enantioseparation of chiral compounds in HPLC environment. On this basis, an investigation to detect ChBs, functioning as stereoselective secondary interactions for HPLC enantioseparations, was started off and the results of this study are described herein. Our investigation also focused on the impact of the perfluorinated aromatic ring as a π-hole donor recognition site. For these purposes, seven atropisomeric fluorinated 3-arylthio-4,4’-bipyridines were designed, synthesized and used as potential ChB donors (ChBDs) with two cellulose-based chiral stationary phases (CSPs) containing carbonyl groups as ChB acceptors (ChBAs). In addition, one and two analogues lacking fluorine and sulphur, respectively, were prepared as terms of comparison. The design of the test analytes was computationally guided. In this regard, electrostatic potentials (EPs) associated with σ- and π-holes were computed and the atomic contributions to the sulphur EP maxima were derived using a molecular space partitioning in terms of Bader’s atomic basins. This procedure is akin to the Bader-Gatti electron density source function (SF) decomposition, yet suitably extended to the EP field. For five 3-substituted-4,4’-bipyridines, thermodynamic parameters were derived from van’t Hoff plots. Finally, the use of molecular dynamic (MD) simulation to model ChB in cellulose-analyte complexes was explored. Evidences that σ-hole and π-hole interactions can jointly drive HPLC enantioseparations through recognition sites generated by electronic charge depletion emerged from both experimental results and theoretical data.

Trimeprazine is enantioselectively degraded by an activated sludge in ready biodegradability test conditions

A great number of available pharmaceuticals are chiral compounds. Although they are usually manufactured as racemic mixtures, they can be enantioselectively biodegraded as a result of microbial processes. In this paper, a biodegradability assay in similar conditions to those recommended in OECD tests of enantiomers of trimeprazine (a phenothiazine employed as a racemate) is carried out. Experiments were performed in batch mode using a minimal salts medium inoculated with an activated sludge (collected from a Valencian Waste Water Treatment Plant, WWTP) and supplemented with the racemate. The concentration of the enantiomers of trimeprazine were monitored by means of a chiral HPLC method using a cellulose-based chiral stationary phase and 0.5 M NaClO4/acetonitrile (60:40, v/v) mobile phases. Experiments were performed at three concentration levels of the racemate. In parallel, the optical density at 600 nm (OD600) was measured to control the biomass growth and to connect it with enantioselectivity. The calculated enantiomeric fractions (EF) offer the first evidence of enantioselective biodegradation of trimeprazine. A simplified Monod equation was used as a curve fitting approach for concentration (S), biodegradation (BD), and for the first time, EF experimental data in order to expand the usefulness of the results. Precision studies on S (repeatability conditions) and, for the first time, EF (intermediate precision conditions) were also performed.

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.

Development of a high-performance liquid chromatography method for the simultaneous determination of chiral impurities and assay of (S)-clopidogrel using a cellulose-based chiral stationary phase in methanol/water mode.

A simple reversed-phase high-performance liquid chromatography method for the chiral separation of the active pharmaceutical ingredient (S)-clopidogrel has been developed on the cellulose-based Chiralcel OJ-RH chiral stationary phase. The S enantiomer was baseline resolved from its R impurity (impurity C) with a mobile phase consisting of methanol/water (100:15) without any interference coming from the other two potential chiral impurities A and B. The enantio- and chemoselective method was partially validated and compared with that reported in the United States Pharmacopoeia for the drug product. The versatility of the Chiralcel OJ-RH allowed separating the enantiomers of the impurity B also under normal phase and setting up an efficient strategy to convert the racemic sample into the enantiomeric S form on a semipreparative scale.

Enantioselective separation of racemates using CHIRALPAK IG amylose-based chiral stationary phase under normal standard, non-standard and reversed phase high performance liquid chromatography

We have previously reported on the solvent versatility of immobilized amylose and cellulose-based chiral stationary phases in enantioselective liquid chromatographic separation of racemates. The studies were mainly focusing on the tris substituted 3,5-dimethylphenylcarbamate polysaccharide-based chiral stationary phases namely CHIRALPAK IA® [Amylose tris (3,5-dimethylphenylcarbamate)] or ADMPC and CHIRALPAK IB® [Cellulose tris (3,5-dimethylphenylcarbamate)] or CDMPC. Here we focus on the application of the recently introduced amylose tris (3-chloro-5-methylphenylcarbamate) or ACMPC and brand name CHIRALPAK IG® with a chlorine substituent replacing the methyl group in CHIRALPAK IA®. This was investigated for the enantioslective separation of different classes of pharmaceuticals namely β- and α-blockers, anti-inflammatory and antifungal drugs, norepinephrine-dopamine reuptake inhibitor, catecholamines, sedative hypnotics, anti-histaminics, anticancer drugs, antiarrhythmic drugs, flavonoids, amino acids, alpha-2 adrenergic agonist, adrenaline and miscellaneous.A brief comparison between CHIRALPAK IG® and CHIRALPAK IA® under normal standard, non-standard and reversed mobile phase is demonstrated. The results revealed the versatility of the CHIRALPAK IG® column, its compatibility with a wide ranges of solvent and operation modes and its ability to separate chiral compounds not separated with other amylose based chiral stationary phases.

Controlled synthesis, immobilization and chiral recognition of carboxylic acid functionalized cellulose tris(3,5-dimethylphenylcarbamate)

Traditional cellulose-based chiral stationary phases (CSPs) are prepared by physically coating cellulose derivatives onto substrates and only compatible with a very limited range of solvents as the mobile phase. Therefore, chemical immobilization of cellulose derivatives onto silica gel has been efficiently applied to improve the solvent compatibility of cellulose-based CSPs. Here we developed a novel approach to homogeneously modifying cellulose tris(3,5-dimethylphenylcarbamate) (CDMPC). A series of carboxylic acid functionalized CDMPCs (CC-Xs) with controlled amounts and randomly distributed carboxylic acid groups was synthesized. CC-Xs were effectively immobilized onto amine-modified silica gel to afford immobilized CSPs. Compared to coated-type CSPs, immobilized CSPs significantly improved the solvent compatibility while maintaining similar chiral recognition abilities, but the introduction of excessive functional groups led to a deteriorated performance for columns. Moreover, a commercial drug, atenolol, was also sufficiently separated on the immobilized CSPs.