The adsorption of Naproxen enantiomers on the chiral stationary phase Whelk-O1 under reversed-phase conditions: The effect of buffer composition

The adsorption of the Naproxen enantiomers on the chiral stationary phase (S,S)-Whelk-O1 from methanol–water 80:20 (v/v) solutions modified with the addition of acetic acid or an acetic acid–sodium acetate buffer was studied using elution chromatography. Adsorption was found to be best accounted for by a two-site model assuming different retention mechanisms for the two enantiomers. Under experimental conditions causing a considerable degree of solute dissociation, strong distortion of overloaded band profiles is observed. This phenomenon is explained by the superimposition of the adsorption and the dissociation equilibria. The effect of the buffer composition on the retention is discussed and the results compared with previous ones obtained with the same system. The proposed model explains all the principal features of the adsorption of Naproxen on Whelk-O1 that were found earlier. Moreover this model applies well in a wider range of buffer concentrations, encompassing both the eluents in which solute dissociation is suppressed and those in which dissociation is significant.     

The study of enantioseparation of zolmitriptan on vancomycin-bonded chiral stationary phase

In this study, the chiral stationary phase was prepared by bonding vancomycin to 5 microm spherical silica gel according to "one-pot" synthetic strategies, and used to separate the enantiomers of zolmitriptan under polar ionic mode. The influences of mobile phase composition, such as the concentration and ratio of glacial acetic acid (HOAc) and triethylamine (TEA), on the enantioseparation were investigated, and the chiral recognition mechanism is discussed. It was found experimentally that the retention factors were increased with the increase of the HOAc/TEA concentration in a certain extent, and the ionic interactions, hydrogen bondings, and steric interactions may play key role together. The method is suitable for baseline separation of zolmitriptan enantiomers.     

The Separation of Alanine Enatiomer Derivatives by the Proton‐Inhibition Method

Better peak shapes and complete separation of amino‐3,5‐dinitro derivatives by (S)‐N‐(2‐naphthyl)alanine derived chiral stationary phase (CSP) is achieved by adding a trace amount of acetic acid in the mobile phase. This method provides an indication of its broad applicability on direct separation of a series of amino‐containing enantiomers on CSP. In addition, the reversed elution order was obtained on its enatiomeric CSP.     

Direct high-performance liquid chromatography enantioseparation of terazosin on an immobilised polysaccharide-based chiral stationary phase under polar organic and reversed-phase conditions

High-performance liquid chromatography (HPLC) enantioseparation of terazosin (TER) was accomplished on the immobilised-type Chiralpak IC chiral stationary phase (CSP) under both polar organic and reversed-phase modes. A simple analytical method was validated using a mixture of methanol–water–DEA 95:5:0.1 (v/v/v) as a mobile phase. Under reversed-phase conditions good linearities were obtained over the concentration range 8.76–26.28 μg mL⁻¹ for both enantiomers. The limits of detection and quantification were 10 and 30 ng mL⁻¹, respectively. The intra- and inter-day assay precision was less than 1.66% (RSD%). The optimised conditions also allowed to resolve chiral and achiral impurities from the enantiomers of TER. The proposed HPLC method supports pharmacological studies on the biological effects of the both forms of TER and analytical investigations of potential drug formulations based on a single enantiomer. At the semipreparative scale, 5.3 mg of racemic sample were resolved with elution times less than 12 min using a mobile phase consisting of methanol–DEA 100:0.1 (v/v) and both enantiomers were isolated with a purity of ≥99% enantiomeric excess (ee). The absolute configuration of TER enantiomers was assigned by comparison of the measured specific rotations with those reported in the literature.     

手性流动相添加剂法拆分比索洛尔对映体

以羧甲基-β-环糊精作为手性流动相添加剂,建立了高效液相色谱拆分比索洛尔对映体的方法。系统考察了手性添加剂的种类及浓度、流动相中甲醇的含量、pH值和流速等因素对拆分的影响。色谱分离条件:流动相甲醇∶乙腈∶水为20∶67∶13(V/V/V),羧甲基-β-环糊精浓度为0.5g.L-1,pH值为4.07(以三乙胺-冰乙酸调节),流速为0.3mL.min-1,检测波长223nm,对映体得到基线分离,分离度为1.89。     

异喹啉酸衍生物刷型手性键合固定相的制备及在联萘酚衍生物拆分中的应用

在(S)-THIQCA环上引入π 酸基团, 制备了一种新型的刷型手性固定相(CSP), 并用于联萘酚及其衍生物的拆分, 探讨了改性剂对色谱行为的影响.     

氨基酸衍生物对映体的高效液相色谱手性分离

通过在流动相中使用酸性添加剂,在由(S)-N-(2-萘基)丙氨酸衍生而成的手性固定相上直接分离氨基酸的3,5-二硝基苯甲酰衍生物,获得非常理想的分离效果。并在此工作的基础上对手性识别机理进行了初步探讨。另外,通过在不同构型的手性固定相上分离相同的溶质,证明在结构相同、构型相反的手性固定相上,对映体的出峰顺序是相反的。     

Chromatographic separation and enantiomeric resolution of flurbiprofen and its major metabolites

Summary The chromatographic separation and resolution of the enantiomers of flurbiprofen and its two major metabolites, 4′-hydroxyflurbiprofen and 3′-hydroxy-4′-methoxyflurbiprofen was investigated using four different approaches: reversed-phase HPLC after pre-column derivatization with (R)-1-(naphthen-1-yl)ethylamine; reversed-phase HPLC using hydroxypropyl-β-cyclodextrin as a chiral mobile phase additive; chiral-phase HPLC using either an α₁-acid glycoprotein CSP (Chiral-AGP) or an amylose tris(3,5-dimethylphenylcarbamate) CSP (Chiralpak AD). Of all the approaches, only the direct method using the Chiralpak AD CSP demonstrated separation and enantiomeric resolution of all three analytes within an acceptable run time of 45 minutes. Enantiomeric resolution values of 1.67,3.67 and 3.44 were obtained for flurbiprofen, 4′-hydroxyflurbiprofen and 3′-hydroxy-4′-methoxyflurbiprofen respectively. Semi-preparative isolation of the individual enantiomers of both metabolites, followed by CD analysis, revealed that the elution order on the AD CSP wasR-beforeS-enantiomer for both metabolites and the same as that observed for flurbiprofen. The metabolite elution order was subsequently confirmed on the analysis of urine samples obtained from a healthy volunteer following oral administration of the individual drug enantiomers.     

Separation of the enantiomers of tebuconazole and its potential impurities by high-performance liquid chromatography with a cellulose derivative-based chiral stationary phase

Summary The high-performance liquid chromatographic resolution of the enantiomers of tebuconazole, a new anti-fungal agent with one chiral center, and the enantiomers of some impurities in technical tebuconazole, has been studied on a chiral stationary phase prepared by coating aminopropylated silica gel with celluloseris(3,5-dimethylphenylcarbamate). The effects of solute structure and the amount of the organic mobile-phase modifier, 2-propanol, on retention and resolution were studied. Under optimum conditions excellent enantiomer separations were achieved for tebuconazole and its impurities. As far as we are aware this is the only liquid chromatographic system enabling discrimination of the enantiomers of all of the racemates discussed in this paper.     

Covalently bonded DNA aptamer chiral stationary phase for the chromatographic resolution of adenosine

In this work, a target-specific aptamer chiral stationary phase (CSP) based on the oligonucleotidic selector binding to silica particles through a covalent linkage was developed. An anti-d-adenosine aptamer was coupled, using an in-situ method, by way of an amide bond to macroporous carboxylic acid based silica. Frontal chromatography analysis was performed to evaluate the column properties, i.e., determination of the stationary phase binding capacity and the dissociation constant of the target-immobilized aptamer complex. It was found that such covalent immobilization was able to maintain the aptamer binding properties at a convenient level for an efficient enantioseparation. Subsequently, the separation of adenosine enantiomers was investigated under different operating conditions, including changes in the eluent’s ionic strength and the proportion of organic modifiers as well as column temperatures. It was demonstrated that, under various conditions of use and storage, the present CSP was stable over time.     

含磷手性化合物在多聚糖类手性固定相上的手性分离

在纤维素 三(3,5 二甲基苯基氨基甲酸酯)(ChiralcelOD)和直链淀粉 三(3,5 二甲基苯基氨基甲酸酯)(ChiralpakAD H)手性固定相上,采用高效液相色谱正相条件,分离了系列含磷手性化合物。考察了流动相中有机改性剂的种类及浓度对手性分离的影响;研究了化合物的结构与保留及对映体选择性的关系;并探讨了手性识别机理。     

Kinetic and equilibrium study of the enantioseparation of paroxetine intermediate on amylose and tartaric acid-based chiral stationary phases

trans-(-)-Paroxetine is a selective 5-hydroxytryptamine (5-HT) reuptake inhibitor currently used as an antidepressant. trans-(+/-)-3-Ethoxycarbonyl-4-(4'-fluorophenyl)-1-methylpiperidine-2,6-dione is an important intermediate of trans-(-)-paroxetine. It was separated on amylose and tartaric acid-based chiral stationary phases by HPLC. The equilibrium constants and overall mass transfer coefficients together with the axial dispersion coefficients were experimentally determined by moment analysis based on the lumped kinetic model of chromatography. In case of Kromasil CHI-TBB, the equilibrium constants measured were found to be 8.36 and 9.37 for trans-(+) and trans-(-) enantiomers, respectively. For Chiralpak AD-H, the equilibrium constants were 6.68 and 4.13 for trans-(+) and trans-(-) enantiomers, respectively. The axial dispersion coefficients of both enantiomers on Kromasil CHI-TBB column were about one order of magnitude greater than on Chiralpak AD-H. Fast kinetics of mass transfer in both chiral stationary phases was observed. Their overall mass transfer coefficients on Kromasil CHI-TBB and Chiralpak AD-H were 32.12, 33.18, 26.50, 46.85 s(-1) for trans-(+) and trans-(-) enantiomers, respectively. The parameters obtained were utilized to simulate the elution profiles, and the simulated and experimental results match well, which confirmed that the parameters obtained in this study were valid.     

Validated HPLC Method for Separation and Determination of Terbutaline Enantiomers

Abstract

A simple, rapid, and validated method for separation and determination of terbutaline enantiomers was developed. Terbutaline was separated and determined on a Vancomycin Chirobiotic V column (250 × 4.6 mm), using a mixture of methanol, acetic acid, and triethylamine (100:0.1:0.1% v/v/v) as a mobile phase at 20°C and at a flow rate of 1 ml/min. The UV detector was set to 276 nm. Acetyl salicylic acid (aspirin) was used as an internal standard. The applied high-performance liquid chromatography (HPLC) method allowed separation and quantification of terbutaline enantiomers with good linearity (r > 0.999) in the studied range. The relative standard deviations (RSD) were 1.10 and 1.32% for the terbutaline enantiomers with accuracy of 99.80 and 99.55. The limit of detection and limit of quantification of terbutaline enantiomers were found to be 0.05 and 0.10 µg · ml^?1, respectively. The method was validated through the parameters of linearity, accuracy, precision, and robustness. The HPLC method was applied for the quantitative determination of terbutaline in pharmaceutical formulations.     

三唑类杀菌剂己唑醇外消旋体的手性拆分研究

以正己烷为流动相，添加一定比例的异丙醇作为改性剂，在纤维素—三(3，5—二甲基苯基氨基甲酸酯)(CDMPC)手性固定相上，实现了对己唑醇光学异构体的高效液相色谱直接拆分，研究了流动相中异丙醇的比例对分离效果的影响，优化了色谱拆分条件，进行了机理的初步探讨。     

A new gas chromatographic stationary phase: Polysiloxane with β-cyclodextrin side chain for the separation of chiral and positional isomers

Summary A new stationary phase [bikis(2,6-di-O-pentyl-3-O-hex-6-enyl)-pentakis(2,6-di-O-pentyl-3-O-methyl)-β-CD-polysiloxane] was synthesized and successfully applied in GC for the separation of chiral and achiral isomers. It possesses high column efficiency and exhibits excellent separation ability for disubstituted benzenes. Some typical enantiomers and optical isomers are well separated. The separation behavior of this new phase is characterized and discussed.     

Direct separation of the enantiomers of cetirizine and related compounds by reversed-phase chiral HPLC

Summary Direct separations of the enantiomers of cetirizine and related compounds have been achieved by reversed-phase HPLC on the Chiralcel OD-R, a polysaccharide-derived chiral stationary phase; the mobile phase was usually perchlorate solution supplemented with acetonitrile. Resolution of the enantiomers of cetirizine and related compounds was good. The effect of the acetonitrile content of the mobile phase was investigated, and the effect of the structure of the chiral compounds on their behavior on the Chiralcel OD-R column is discussed.     

Synthesis and Evaluation of a Synthetic Polymeric Chiral Stationary Phase for LC Based on the N, N′-[(1R,2R)-1,2-Diphenyl-1,2-Ethanediyl]bis-2-Propenamide Monomer

A synthetic polymeric chiral stationary phase for liquid chromatography based on N, N′-[(1R,2R)-1,2-diphenyl-1,2-ethanediyl]bis-2-propenamide monomer was prepared via a simple solution initiated radical polymerization. This stable chiral stationary phase showed enantioselectivities for a large number of racemates in polar organic and normal phase modes and high sample loading ability. However, none of the generated data has been optimized in terms of column performance. Different enantioselectivities were observed on this new chiral stationary phase compared with the commercial polymeric chiral stationary phase based on N-(2-acryloylamino-(1R,2R)-cyclohexyl)-acrylamine monomer. Consequently, these two chiral stationary phases are considered complementary to one another. Furthermore they utilize the same mobile phase and optimization procedures. This polymeric chiral stationary phase appears to be useful for preparative separations since high amounts of analyte can be injected without loosing enantioselectivity.     

Separation of α-cyclohexylmandelic acid enantiomers using biphasic chiral recognition high-speed counter-current chromatography

This work concentrates on a chiral separation technology named biphasic recognition applied to resolution of α-cyclohexylmandelic acid enantiomers by high-speed counter-current chromatography (HSCCC). The biphasic chiral recognition HSCCC was performed by adding lipophilic (−)-2-ethylhexyl tartrate in the organic stationary phase and hydrophilic hydroxypropyl-β-cyclodextrin in the aqueous mobile phase, which preferentially recognized the (−)-enantiomer and (+)-enantiomer, respectively. The two-phase solvent system composed of n-hexane-methyl tert-butyl ether–water (9:1:10, v/v/v) with the above chiral selectors was selected according to the partition coefficient and separation factor of the target enantiomers. Important parameters involved in the chiral separation were investigated, namely the types of the chiral selectors (CS); the concentration of each chiral selector; pH of the mobile phase and the separation temperature. The mechanism involved in this biphasic recognition chiral separation by HSCCC was discussed. Langmuirian isotherm was employed to estimate the loading limits for a given value of chiral selectors. Under optimum separation conditions, 3.5–22.0 mg of α-cyclohexylmandelic acid racemate were separated using the analytical apparatus and 440 mg of racemate was separated using the preparative one. The purities of both of the fractions including (+)-enantiomer and (−)-enantiomer from the preparative CCC separation were over 99.5% determined by HPLC and enantiomeric excess reached 100% for the (±)-enantiomers. Recovery for the target compounds from the CCC fractions reached 85–88% yielding 186 mg of (+)-enantiomer and 190 mg of (−)-enantiomer. The overall experimental results show that the HSCCC separation of enantiomer based on biphasic recognition, in which only if the CSs involved will show affinity for opposite enantiomers of the analyte, is much more efficient than the traditional monophasic recognition chiral separation, since it utilizes the cooperation of both of lipophilic and hydrophilic chiral selectors.     

Rapid Supercritical Fluid Chromatography Method for Separation of Chlorthalidone Enantiomers

Supercritical fluid chromatography employing chiral stationary phases is a popular separation technique to perform enantioselective separations. The main advantages of supercritical fluid chromatography are low analysis time, low consumption of organic modifiers, and therefore lower costs and higher environmental friendliness. A novel method for the separation of chlorthalidone enantiomers, widely used diuretic drug, is reported that clearly demonstrates the advantages of supercritical fluid chromatography. The effects of the amount and type of organic modifiers, temperature, and back pressure on enantioselectivity and resolution of the enantiomers were evaluated. The baseline separation was achieved in less than 2.5 min in the optimized system composed of Chiralpak AD column, mobile phase CO₂/MeOH 50/50 (v/v), temperature 40°C, a flow rate of 4.0 mL/min, and 120 bar back pressure. Moreover, enantiomers of chlorthalidone were determined in two commercially available pharmaceuticals. The proposed method may be easily transferred to a semi-preparative scale.     

Preparation of a new chiral stationary phase for HPLC based on the (R)- 1-phenyl-2-(4-methylphenyl)ethylamine amide derivative of (S)-valine and 2-chloro-3,5-dinitrobenzoic acid: enantioseparation of amino acid derivatives and pyrethroid insecticides

A novel chiral stationary phase (CSP) for HPLC was prepared by bonding (R)-1-phenyl-2-(4-methylphenyl)ethylamine amide derivative of (S)-valine to aminopropyl silica gel through a 2-amino-3,5-dinitro-1-carboxamido-benzene unit. The CSP was used for the separation of some amino acid derivatives and pyrethroid insecticides by chiral HPLC. Satisfactory baseline separation required optimization of the variables of mobile phase composition. Use of dichloromethane as modifier in the mobile phase gave baseline separations of amino acid derivatives. The two enantiomers of fenpropathrin and four stereoisomers of fenvalerate were baseline separated using hexane-dichloromethane-ethanol as mobile phase. The results show that the enantioselectivity of the new CSP is better than Pirkle type 1-A column for these compounds. Only partial separations were observed for the stereoisomers of cypermethrin and cyfluthrin, which gave even and eight peaks, respectively.