Derivatized Cellulose Chiral Stationary Phases Research Articles

Enantioseparation and molecular modeling study of chiral amines as three naphthaldimine derivatives using amylose or cellulose trisphenylcarbamate chiral stationary phases.

This study describes the enantioseparation of three chiral amines as naphthaldimine derivatives, using normal phase HPLC with amylose and cellulose tris(3,5-dimethylphenylcarbamate) chiral stationary phases (CSPs). Three chiral amines were derivatized using three structurally similar naphthaldehyde derivatizing agents, and the enantioselectivity of the CSPs toward the derivatives was examined. The degree of enantioseparation and resolution was affected by the amylose or cellulose-derived CSPs and aromatic moieties as well as a kind of chiral amine. Especially, efficient enantiomer separation was observed for 2-hydroxynapthaldimine derivatives on cellulose-derived CSPs. Molecular docking studies of three naphthaldimine derivatives of leucinol on cellulose tris(3,5-dimethylphenylcarbamate) were performed to estimate the binding energies and conformations of the CSP-analyte complexes. The obtained binding energies were in good agreement with the experimentally determined enantioseparation and elution order.

Towards enantioselective ultrahigh performance liquid chromatography-mass spectrometry-based metabolomics of branched-chain fatty acids and anteiso-fatty acids under reversed-phase conditions using sub-2-μm amylose- and cellulose-derived chiral stationary phases.

Branched-chain fatty acids (BCFAs) are mostly saturated fatty acids with one or more methyl, seldom ethyl, branches in the alkyl chain. They are derived from branched-chain amino acids, ruminant-derived food, or biosynthetic side products of acetyl-CoA carboxylase. They possess iso- (branching at penultimate carbon) and anteiso-fatty acid structure (branching at antepenultimate carbon) or are branched at any other position of the carbon chain. Except for iso-fatty acids, BCFAs are chiral. They are commonly analyzed by GC-MS, while there is a lack of enantioselective LC-MS methods. In this work, we present a methodology for targeted enantioselective UHPLC-ESI-MS/MS metabolomics of BCFAs. It makes use of precolumn derivatization with 1-naphthylamine and reversed-phase elution conditions. A homologous series of short BCFA analytes with distinct chain lengths (having up to eight carbon atoms), branching type (methyl or ethyl), and position of branching (2, 3, and 4, anteiso and iso) has been systematically studied on six commercially available polysaccharide UHPLC columns. Chiralpak IB-U exhibited the highest and broadest enantioselectivity while IH-U maintained enantioselectivity also for BCFAs with chirality distant from the carboxylic function (i.e., with other branching than in 2-position). The method was used to assign the absolute configuration of a 4-methylhexanoic acid side chain of a natural product from Streptomyces sp. SHP 22-7. The potential of the corresponding UHPLC-ESI-QTOF-MS/MS assay for analyzing stereoselectively BCFAs and other short organic acids by untargeted analysis in human urine was further elucidated in a preliminary proof-of-principle test.

Immobilized Cellulose-Based Chiralpak IC Chiral Stationary Phase for Enantioseparation of Eight Imidazole Antifungal Drugs in Normal-Phase, Polar Organic Phase and Reversed-Phase Conditions Using High-Performance Liquid Chromatography

Due to the remarkable enantioselective performances of polysaccharide derivatives, immobilized cellulose-based columns have high enantioseparation ability, which can be applied under various mobile phase conditions. In the present work, a cellulose-derived chiral stationary phase (CSP), namely Chiralpak IC was evaluated for enantioseparation of eight imidazole antifungal drugs (miconazole, econazole, isoconazole, sulconazole, butoconazole, fenticonazole, sertaconazole, and ketoconazole) in three mobile phase modes: normal-phase mode, polar organic mode and reversed-phase mode. The factors that affected the enantioseparation were investigated and optimized. Results indicated that the Chiralpak IC column possessed good enantioselectivity in three modes, with all analytes being successfully resolved. In addition, the mechanism of enantioseparation was preliminarily discussed based on the molecular structures and retention behavior of the enantiomers.

Liquid Chromatographic Enantiomeric Separation of Chiral Aliphatic Amines Using 2-Hydroxynaphthaldehyde as a Derivatizing Agent on Polysaccharide-Derived Chiral Stationary Phases

A new liquid chromatographic enantiomer separation of chiral amines as 2-hydroxynaphthaldimine derivatives on several coated and immobilized chiral stationary phases (CSPs) derived from polysaccharides is described. 2-Hydroxynaphthaldehyde was introduced as a derivatizing agent for the enantiomeric separation of chiral aliphatic amines under the normal phase conditions, and was found to both enhance detection sensitivity and provide suitable interaction sites for enantiodiscrimination. Cellulose-derived CSPs, in general, exhibited better enantiomeric separation than amylose-derived CSPs. Amongst the examined six covalently bonded and four coated-type CSPs, covalently bonded Chiralpak IC, which contains a cellulose-based chiral selector, showed the best enantioseparation. The method was applied to the determination of the enantiomeric purity of commercially available (R)- and (S)-leucinol. The enantiomeric impurities of the investigated analytes procured from two suppliers were found to be 0.06–1.20%. The developed analytical method was also validated in accordance with ICH guidelines and proved to be enantioselective, sensitive and effective for the enantiomeric separation of chiral aliphatic amines as 2-hydroxynaphthaldimine derivatives under ultraviolet detection.

HPLC Enantioseparation of Menthol with Non-ultraviolet Detectors and Effect of Chromatographic Conditions

Menthol has been widely used in pharmaceuticals, food industry, oral health care products, cosmetic industry, and tobacco products, and its HPLC chiral separation has been less reported till now. Herein, a simple and direct method has been developed for separation of menthol by normal-phase HPLC coupled with refractive index detector and/or optical rotation detector, in which special sample pretreatment and derivatization were not required. The effects of chiral stationary phases, alcoholic modifiers, column temperature, and injection amount were studied in detail. The amylose tris(3,5-dimethylphenylcarbamate)-coated chiral stationary phase showed the best separation performance for menthol with the resolution of 2.84. Through the optical rotation detector, (+)-menthol was first eluted on the amylose-based chiral stationary phase in the hexane-2-propanol mixture, but later eluted on the cellulose-derived chiral stationary phases in the same mobile phase. In addition, retention and resolution of menthol displayed an upward trend along with the content of 2-propanol and column temperature reduction. Chiral separation of menthol could be attributed to an enthalpically driven process, since ΔΔH (− 3.04 kJ mol− 1) and ΔΔS* (− 8.57 J mol− 1 K− 1) for two enantiomers were negative in the experimental temperature range. Moreover, the limits of detection and quantitation for the menthol enantiomers with the refractive index detector were similar to the optical rotation detector. These results would provide useful information for direct resolution for chiral compounds without typical chromophoric groups.

Efficient preparative separation of β-cypermethrin stereoisomers by supercritical fluid chromatography with a two-step combined strategy.

An efficient two-step method has been developed for the separation of β-cypermethrin stereoisomers by supercritical fluid chromatography with polysaccharide chiral stationary phases. With respect to retention, selectivity, and resolution of β-cypermethrin, the effects of chiral stationary phases, cosolvents, mobile phases, and column temperature have been studied in detail. Through a two-step separation, β-cypermethrin was firstly separated by using a cellulose-derived chiral stationary phase to obtain two stereoisomeric pairs, and further resolved on an amylose-based chiral stationary phase to produce four enantiopure stereoisomers. The electronic circular dichroism patterns of the first- and the third-eluted isomers in methanol solution showed the mirror image of each other in the wavelength range 200∼300nm, indicating that they were a pair of enantiomers. Moreover, the second- and the fourth-eluted isomers were also enantiomers. This proposed two-step strategy showed low solvent consumption, fast separation speed, and high-purity, which may provide an effective approach for preparative separation of compounds with multiple chiral centers and difficult-to-separate multicomponent samples.

Liquid chromatographic enantiomer separation of 1-naphthylamides of chiral acids using several amylose- and cellulose-derived chiral stationary phases.

The liquid chromatographic enantiomer separation of various chiral acids as 1-naphthylamides was performed using several chiral stationary phases (CSPs). The CSPs used in this study were six covalently bonded and four coated type CSPs derived from amylose and cellulose derivatives as chiral selectors. The degree of enantioseparation is affected by the structure of chiral acids and the CSPs used, which have different chiral selectors and types of immobilization. For the enantiomer resolution of chiral acids as 1-naphthylamide derivatives, the performance of the coated type Lux Cellulose-1 was superior to those of the other CSPs, except for 2-aryloxypropionic acid derivatives. Owing to the strong ultraviolet absorbance of the 1-naphthyl group, the convenient analytical method developed and validated in this study could be expected to be very useful for the enantiomer separation of various chiral acids as 1-naphthylamide derivatives using polysaccharide-derived CSPs.

Chiral separation and determination of enantiomeric purity of the pharmaceutical formulation of cefadroxil using coated and immobilized amylose-derived and cellulose-derived chiral stationary phases

Background and objectives In the present article, we describe the development of a simple, direct, and isocratic high-performance liquid-chromatographic method for chiral separation and the determination of the enantiomeric purity of cefadroxil. Cefadroxil has three chiral centers; the existence of eight different stereoisomers is possible. Only one of these isomers is currently under development as an antibiotic agent and, consequently, the other seven isomers are considered as unwanted chiral impurities.Materials and methods An analytical chiral separation was carried out to check its enantiomeric purity. The separation was carried out by exploiting the high efficiency of several coated/immobilized cellulose and amylose chiral stationary phases under normal-phase and polar-organic modes. The effects of type and concentration of the alcoholic modifiers, 2-propanol and ethanol, on the separation of stereoisomers were studied for optimum resolution.Results and conclusion Complete baseline separation of stereoisomers with good resolution was achieved within 40 min under normal-phase mode on Chiralpak IB column using hexane–2-propanol (60 : 40 v/v) as the mobile phase, without any organic additives, at a flow rate of 0.4 ml/min at 25°C and with the ultraviolet detection set at 268 nm. This process was found to be suitable for rapid enantiomeric purity analysis and a quality control of cefadroxil in pharmaceutical formulations without interference of the excipients. The chiral recognition mechanisms of separation were also discussed.

Synthesis and enantioseparation behaviors of novel immobilized 3,5-dimethylphenylcarbamoylated polysaccharide chiral stationary phases

Two new polysaccharide-derived chiral selectors, namely, 6-azido-6-deoxy-3,5-dimethylphenylcarbamoylated amylose and 6-azido-6-deoxy-3,5-dimethylphenyl carbamoylated cellulose, were synthesized under homogeneous conditions and immobilized onto aminized silica gel by the Staudinger reaction, resulting in two new immobilized polysaccharide chiral stationary phases (CSPs). Their enantioseparation performances were investigated under normal-phase mode by HPLC. Among 17 analytes, baseline separations of 12 pairs of enantiomers are achieved on the immobilized cellulose CSP, which demonstrates that this new cellulose material exhibits almost the same enantioseparation performance as the coated cellulose CSP. In addition, the amylose-derived CSP presents limited enantiorecognition ability but certain complementarity with the immobilized and coated cellulose-based materials. Neither metolachlor nor paclitaxel side chain acids are separated on two cellulose-derived CSPs, but effective separations are obtained on the immobilized amylose column.

Practical access to the proline analogs (S,S,S)‐ and (R,R,R)‐2‐methyloctahydroindole‐2‐carboxylic acids by HPLC enantioseparation

An efficient methodology for the preparation of the α-tetrasubstituted proline analog (S,S,S)-2-methyloctahydroindole-2-carboxylic acid, (S,S,S)-(αMe)Oic, and its enantiomer, (R,R,R)-(αMe)Oic, has been developed. Starting from easily available substrates and through simple transformations, a racemic precursor has been synthesized in excellent yield and further subjected to HPLC resolution using a cellulose-derived chiral stationary phase. Specifically, a semipreparative (250 mm × 20 mm ID) Chiralpak® IC column has allowed the efficient resolution of more than 4 g of racemate using a mixture of n-hexane/tert-butyl methyl ether/2-propanol as the eluent. Multigram quantities of the target amino acids have been isolated in enantiomerically pure form and suitably protected for incorporation into peptides.

Enantioseparation of 1-phenyl-1-propanol on cellulose-derived chiral stationary phase by supercritical fluid chromatography: II. Non-linear isotherm

The separation of the enantiomers of 1-phenyl-1-propanol by supercritical fluid chromatography on a chiral stationary phase, which consists of cellulose tris (3,5-dimethylphenylcarbamate) coated on a silica support (Chiralcel-OD), is studied under overloaded, non-linear chromatographic conditions. Pulse experiments are performed at a temperature of 30 ° C using supercritical CO 2 modified with methanol as a mobile phase. The parameters of the binary Langmuir adsorption isotherm are determined by the inverse method, comparing experimental and simulated peak responses. Isotherm parameters are derived for modifier concentrations between 1 and 5% (w/w) and operating pressures between 125 and 185 bar, and the dependency of the isotherm parameters, namely the Henry constant and the saturation capacity, on operating conditions is investigated.

Synthesis of the four stereoisomers of cyclobutane analogues of phenylalanine in enantiomerically pure form

All stereoisomers of 1-amino-2-phenylcyclobutanecarboxylic acid—c 4Phe—have been synthesized and the series c n Phe has thus been completed. The use of two different strategies based on a cyclization reaction, starting from ethyl isocyanoacetate and dialkyl malonate, respectively, gave both cis-c 4Phe and trans-c 4Phe in racemic form. HPLC resolution of one of the intermediates using a cellulose-derived chiral stationary phase allowed the isolation of the corresponding enantiomerically pure N-protected amino acids, prepared for incorporation into peptides. The relative stereochemistry of enantiopure compounds has been unambiguously assigned.

Synthesis of enantiomerically pure cis- and trans-cyclopentane analogues of phenylalanine

For the first time, all stereoisomers of 1-amino-2-phenylcyclopentanecarboxylic acid—c 5Phe—have been synthesised. A Strecker reaction on 2-phenylcyclopentanone and further transformations of each amino nitrile into the amino acid provides cis-c 5Phe and trans-c 5Phe with high efficiency. A divergent synthetic route was then developed to obtain the target compounds cis- and trans-c 5Phe in their racemic form. The preparation of the final enantiomerically pure amino acids and their corresponding N-protected derivatives was also achieved by HPLC resolution of one of the intermediates using a cellulose-derived chiral stationary phase. The relative stereochemistry of each amino acid and its precursors have been unambiguously assigned.

Enantiomeric resolution of new aromatase inhibitors by liquid chromatography on cellulose chiral stationary phases

Analytical HPLC methods using derivatized cellulose chiral stationary phases were developed for the direct enantioseparation of substituted [1-(imidazo-1-yl)-1-phenylmethyl)]-benzothiazolinone and benzoxazolinone derivatives with one chiral center. Those analogues of fadrozole constitute new potent nonsteroidal inhibitors of aromatase (P450 arom). The separations were made using normal phase methodology with a mobile phase consisting of n-hexane-alcohol (ethanol, 1-propanol, or 2-propanol) in various proportions, and a silica-based cellulose tris-3,5-dimethylphenylcarbamate (Chiralcel OD-H), or tris-methylbenzoate (Chiralcel OJ). The effects of concentration of various aliphatic alcohols in the mobile phase were studied. A better separation was achieved on cellulose carbamate phase compared with the cellulose ester phase. The effects of structural features of the solutes along with the temperature of the column on the discrimination between the enantiomers were examined. Baseline separation (Rs > 1.5) was easily obtained in many cases.

Separation of the enantiomers of 4-aryl-7,7-dimethyl- and 1,7,7-trimethyl-1,2,3,4,5,6,7,8-octahydroquinazoline-2,5-diones by chiral HPLC

Analytical HPLC methods using derivatized cellulose chiral stationary phases have been developed for separation of the enantiomers of 25 racemic 4-aryl-7,7-dimethyl- or 1,77-trimethyl-1,2,3,4,5,6,7,8-octahydroquinazoline-2,5-diones, condensed derivatives of dihydropyrimidines. The enantiomers of the compounds were resolved by normal-phase chromatography on silica-based cellulose tris(3,5-dimethylphenylcarbamate) (Chiralcel OD) and amylose tris(3,5-dimethylphenylcarbamate) (Chiralpak AD) columns with mobile phases consisting of mixtures ofn-hexane and an alcohol (2-propanol, ethanol, or methanol) in different proportions. The mobile phase and the chiral stationary phase were varied to achieve the best resolution. The effect of the concentration of alcohol in the mobile phase was studied. The resolution obtained on the two columns was complementary.

Nucleophilic aromatic substitution on 1-alkoxy-2-nitronaphthalene by 1-naphthyl Grignard reagents for the synthesis of 2-nitro-1,1′-binaphthyls

Treatment of 1-methoxy-2-nitronaphthalene with 1-naphthyl- and 2-methoxy-1-naphthylmagnesium bromide in diethyl ether–benzene at room temperature provides a facile entry to the corresponding 2-nitro-1,1′-binaphthyls in high yields. Induction of axial chirality into the binaphthyl bond has been achieved by using 1-menthoxy-2-nitronaphthalene as the substrate, giving 2-methoxy-2′-nitro-1,1′-binaphthyl of 78% ee. Also reported is the optical resolution of 2-amino-1,1′-binaphthyls, which can be easily prepared by reduction of the 2-nitro-1,1′-binaphthyls, by preparative LC on a cellulose-derived chiral stationary phase, or on silica gel after conversion into the diastereomeric menthyl carbamates.

Absolute configuration in 4-alkyl- and 4-aryl-3,4-dihydro-2(1H)-pyrimidones: a combined theoretical and experimental investigation.

Structural features (orientation of the carboxyl group, ring puckering), electronic absorption, and circular dichroism spectra of 4-alkyl- and 4-aryl-dihydropyrimidones 1-5 are calculated by semiempirical (AM1, INDO/S), ab initio (HF/6-31G, CIS/6-31G, RPA/6-31G), and density functional theory (B3LYP/6-31G) methods. These calculations allow an assignment of the absolute configuration by comparison of simulated and experimental CD spectra. Although the ab initio methods greatly overestimate electronic transition energies, the general appearance of the experimental CD spectra is quite nicely reproduced by these calculations. Thus, comparison of experimental with calculated CD spectra is a reliable tool for the assignment of the absolute configuration. For 4-methyl derivatives 1, the first enantiopure DHPM examples with no additional aromatic substituent, the stereochemistry at C4 provided by the theoretical results is confirmed by X-ray structure determination of the diastereomeric salt 6. Additional support is the consistent HPLC elution order found for all investigated DHPMs on a cellulose-derived chiral stationary phase.

Direct separation of the stereoisomers of methoxytetrahydronaphthalene derivatives, new agonist and antagonist ligands for melatonin receptors, by liquid chromatography on cellulose chiral stationary phases

Analytical HPLC methods using derivatized cellulose chiral stationary phases were developed for the direct separation of the stereoisomers of disubstituted tetralin derivatives with two chiral centers, new agonist and antagonist ligands for melatonin receptors. The separations were made using normal-phase methodology with a mobile phase consisting of n-hexane–alcohol (methanol, ethanol, 1-propanol or 2-propanol) in various proportions, and a silica-based cellulose tris-3,5-dimethylphenylcarbamate (Chiralcel OD-H), or tris-methylbenzoate (Chiralcel OJ). The effects of concentration of various aliphatic alcohols in the mobile phase were studied. A better separation was achieved on cellulose carbamate phase compared with the cellulose ester phase. The effects of structural features of the solutes on the discrimination between the stereoisomers were examined. Baseline separation ( R s >1.5) was easily obtained in many cases.

Studies on synthesis, chromatographic resolution, and antiinflammatory activities of some 2-thioxo-1,2,3,4-tetrahydropyrimidines and their condensed derivatives.

In this study, the synthesis of some new 2-thioxo-1,2,3,4-tetrahydropyrimidines and their condensed derivatives, thiazolo[3,2-a]pyrimidines, are described. The structures of the compounds were confirmed by 1R, 1H-NMR, 13C-NMR, and mass spectroscopy. The direct high-performance liquid chromatographic separation of the compounds on derivatized cellulose chiral stationary phases such as cellulose tris(3,5-dimethylphenylcarbamate) (OD), cellulose tris(4-methylphenylcarbamate) (OG), and cellulose tris(4-methylbenzoate) (OJ) was studied. All of the compounds were screened for their antiinflammatory activity and also investigated histopathologically. Compounds 3 and 1a were found to be the most promising antiinflammatory agents in this group.

Chiral resolution of the enantiomers of 7-chloro-3-methyl-3,4-dihydro-2H-1,2,4-benzothiadiazine 1,1-dioxide using high-performance liquid chromatography on cellulose-based chiral stationary phases

Analytical high-performance liquid chromatography (HPLC) methods using derivatized cellulose chiral stationary phases (CSPs) were developed for the separation of the enantiomers of 7-chloro-3-methyl-3,4-dihydro-2H-1,2,4-benzothiadiazine 1,1-dioxide ((±) IDRA21). In previous studies, (±) IDRA21 has been found to have an interesting inhibitory effect on the desensitization of α-amino-2,3-dihydro-5-methyl-3-oxo-4-isoxazolepropanoic acid (AMPA) receptor and improve cognition in animals. This compound posses one chiral carbon atom, but very little information has been reported on the stereoselectivity of his activity. Therefore resolution of the enantiomers of this compound and subsequent identification of stereospecifity in his pharmacological actions are clearly matters of interest. The resolution were made under normal- and reversed-phase conditions using a mobile phase consisting of n-hexane:2-propanol (70/30, v/v) and water:acetonitrile (60/40, v/v) respectively, and a CSP of silica-based cellulose tris-3,5-dimethyl-phenylcarbammate (Chiralcel OD and Chiracel OD-R). The enantiomeric nature of eluates was confirmed by circular dichroism (CD) spectra. A baseline separation ( R s>1.5) was obtained in both cases. Furthemore the isolation of optical isomers of (±) IDRA21 was perfomed using a semipreparative column packed with the same cellulose OD CSP.