Enantiomer separation of pharmaceuticals by capillary gas chromatography with novel chiral stationary phases

New chiral stationary phases of polydimethylsiloxane anchored with (S)-(-)-t-leucine derivatives were provided for use in enantiomer separation of pharmaceuticals by capillary gas chromatography. Fifteen pharmaceuticals were separated into their enantiomeric pairs by converting them into pentafluoropropionyl and heptafluorobutyryl derivatives. The separation factor and resolution obtained from the new phases were superior to those from the conventional Chirasil-Val capillary column.     

Quantification of D‐Asp and D‐Glu in rat brain and human cerebrospinal fluid by microchip electrophoresis

A microchip electrophoresis (MCE) method with LIF detection was presented for quantification of D ‐aspartic acid (D ‐Asp) and D ‐glutamate (D ‐Glu) in biological samples. D ‐Asp and D ‐Glu were determined after precolumn derivatization with FITC. The chiral separation was performed on a glass/PDMS hybrid microfluidic chip using γ‐CD as chiral selector in the running buffer. High sensitive detection was obtained by the LIF detection. The LODs (S/N = 3) for D ‐Asp and D ‐Glu were 6.0×10^–8 and 4.0×10^–8 M, respectively. Using this method, the levels of D ‐Asp and D ‐Glu in rat brain and human cerebrospinal fluid (CSF) were determined.     

手性冠醚聚硅氧烷固定相的制备及其气相色谱性能

以Ｄ－甘露醇和）＋）－２－氨基－１－丁醇为手性源，合成了两种含末端烯基的手性冠醚。通过硅氢加成反应制备了两种新型手性冠醚聚氧烷相色谱固定相ｃｈｉｒａｓｉｌ－ｍａｎ－１８Ｃ６－２５和ｃｈｉｒａｓｉｌ－ａｚａ－１５Ｃ－２５。     

(S)-(-)-alpha,alpha-Di(2-naphthyl)-2-pyrrolidinemethanol, a useful tool to study the recognition mechanism in chiral ligand-exchange chromatography

A dynamic coating of the RP-18 carbon chain layers with the new chiral selector (S)-(-)-alpha,alpha-di(2-naphthyl)-2-pyrrolidinemethanol allowed the formation of a mixed chiral stationary phase that has been used in the separation of a selected set of amino acid racemates. Both a representative model and classification structure-property relationship studies have been performed in order to study the contribution of hydrophobic, bulky and electron-donating groups in the side chain of the chiral selector to the mechanism of chiral recognition.     

Chiral separation of disease biomarkers with 2‐hydroxycarboxylic acid structure

Chiral 2‐hydroxycarboxylic acids are compounds that have been linked to particular diseases and are putative biomarkers with some diagnostic potential. The importance of identifying whether a particular enantiomer is related to certain diseases has been encouraged recently. However, in many cases it has not yet been elucidated whether there are stereochemical implications with respect to these biomarkers and whether their enantioselective analysis provides new insights and diagnostic potential. In this study 13 disease‐related chiral 2‐hydrocarboxylic acids were studied for their chiral separation by high‐performance liquid chromatography on three cinchona alkaloid‐derived chiral stationary phases. From a subgroup of eight 2‐hydroxymonocarboxylic acids, baseline resolution could be achieved and inversion of elution order by exchanging tert‐butylcarbamoyl quinidine chiral stationary phase (Chiralpak QD‐AX) for the corresponding quinine analogue (Chiralpak QN‐AX) is shown for seven of them. Furthermore, conditions for chiral separation of the 2‐hydroxydicarboxylic acids, citramalic acid, 2‐isopropylmalic acid, and 2‐hydroxyadipic acid are reported and compared to the previous reported conditions for 2‐hydroxyglutaric acid and malic acid.     

Enantiomeric determination, validation and robustness studies of racemic citalopram in pharmaceutical formulations by capillary electrophoresis

A chiral capillary electrophoresis (CE) method has been developed allowing the enantiomeric separation of racemic citalopram (R-(-) and S-(+) citalopram) using as chiral selector carboxymethyl-gamma-cyclodrextrin (CM-gamma-CD). The influence of chemical and instrumental parameters on the separation such as cyclodextrin (CD) and buffer concentrations, buffer pH, voltage, injection pressure, ..., was investigated. Good chiral separation of the racemic mixture was achieved in less than 4 min using a fused-silica capillary and as background electrolyte (BGE) a phosphate buffer solution (20 mM, pH 7) containing 0.15% (w/v) of CM-gamma-CD as chiral selector. The separation was driven in normal polarity mode at 15 degrees C, 30 kV and hydrodynamic injection. In order to validate the method, the stability of the solutions, precision (repeatability, reproducibility and F-Snedecor test), linearity (Lack of Fit and ANOVA tests) accuracy (98-101%), detection and quantitation limits (0.06 and 0.2 mg L(-1), respectively), on a selected analytical placebo, were examined. Besides, a robustness test was performed using the Plackett-Burman fractional factorial experimental design using a matrix of 15 experiments for seven factors (internal parameters) with a statistical treatment suggested by Youden and Steinner. The proposed method is fast, sensitive, inexpensive and, besides, it has been evaluated by means of an extensive validation study and an exhaustive robustness test. The scope of this validated and robust method has been proved in the analysis of four pharmaceutical formulations; two of them (recently available in Spain), which just contained S-(+)-citalopram (escitalopram) as active principle. Recoveries between 101 and 103%, with regard to their nominal contents were obtained. In the other two pharmaceutical ones, the method provided the separation and quantification of both chiral isomers in the existing racemic mixture.     

Separation and determination of some stereoisomers by capillary gel electrophoresis with cyclodextrin incorporated in polyacrylamide gel

Capillary gel electrophoresis (CGE) was successfully applied to the separation of optically active isomers and position isomers by incorporating a suitable cyclodextrin chiral selector in polyacrylamide gel. A commercially available ss-cyclodextrin (ss-CD) was used for enantioselectivity towards o-, m- and p-nitrobenzoic acid, o-, m- and p-hydroxybenzoic acid, o-, m- and p-toluic acid and the optical isomers of dansyl-D,L-leucine and R,S-1,1'-binaphthyl-2,2-dihydrogenphosphate. Especially the effect of organic solvents, such as acetonitrile, methanol, dimethylsulphoxide and others were examined in detail. The resolution varied to some extent with the addition of the organic solvent to the polyacrylamide gel and the running buffer solution. The possible mechanism has also been discussed. In addition, quantitative aspects of the separation of stereoisomers using CGE have been studied, showing that both the resolution and accuracy of the determinations were affected by the ratio of the enantiomers.     

Use of cyclodextrin‐modified gold nanoparticles for enantioseparations of drugs and amino acids based on pseudostationary phase‐capillary electrochromatography

The application of chemical‐modified gold nanoparticles (GNPs) as chiral selector for the enantioseparation based on pseudostationary phase‐CEC (PSP‐CEC) is presented. GNPs modified by thiolated β‐CD were characterized by NMR and FT‐IR. The nanoparticle size was determined to be of 9.5 nm (+2.5 nm) by Transmission Electron Microscopy (TEM) and UV spectra. Four pairs of dinitrophenyl‐labeled amino acid enantiomers (DL‐Val, Leu, Glu and Asp) and three pairs of drug enantiomers (RS‐chlorpheniramine, zopiclone and carvedilol) were analyzed by using modified GNPs as the chiral selector in PSP‐CEC. Good theoretical plate number (up to 2.4×10⁵ per meter) and separation resolution (up to 4.7) were obtained even with low concentration of modified GNPs (0.8–1.4 mg/mL). The corresponding concentration of β‐CD in the buffer was only 0.30?0.53 mM, which was much lower than the optimum concentration of 15 mM if pure β‐CD was used as chiral selector. Our results showed that thiolated β‐CD modified GNPs have more sufficient interaction with the analytes, resulting in significant enhancement of enantioseparation. The study shed light on potential usage of chemical modified GNPs as chiral selector for enantioseparation based on PSP‐CEC.     

高效液相色谱-串联质谱法分析毛发中甲基苯丙胺和苯丙胺手性对映异构体

建立了高效液相色谱-串联质谱（HPLC-MS/MS）分析毛发中甲基苯丙胺与苯丙胺对映异构体的手性分离方法。采用SUPELCO Astec CHIROBIOTIC^® V2手性液相色谱柱,以甲醇-含0.1%（v/v）甲酸的20 mmol/L乙酸铵水溶液（99：1,v/v）为流动相进行手性分离。结果表明,甲醇高温水浴超声法能较好地提取苯丙胺类化合物,且峰形较好（拖尾因子>0.95）。S-（+）-甲基苯丙胺、R-（-）-甲基苯丙胺、S-（+）-苯丙胺和R-（-）-苯丙胺在15~300 ng/mg范围内线性关系良好,相关系数均大于0.99;甲基苯丙胺和苯丙胺的检出限分别为0.1 ng/mg和0.15 ng/mg,定量限分别为0.4 ng/mg和0.5 ng/mg;日内精密度均≤6.8%,日间精密度均≤11.4%。采用所建方法对50余嫌疑人毛发进行手性分析,检出单一S-（+）-甲基苯丙胺和S-（+）-苯丙胺的占70%,同时检出S-（+）-甲基苯丙胺、R-（-）-甲基苯丙胺、S-（+）-苯丙胺和R-（-）-苯丙胺的占18%。该法简单快速,精密度好,可为实际法医毒物鉴定案例中的毛发手性分析提供技术支持与科学依据。     

单细胞中D-天冬氨酸和D-谷氨酸的毛细管电泳分析

建立了一种毛细管电泳-激光诱导荧光检测单个神经细胞中D-天冬氨酸和D-谷氨酸的方法.以萘二甲醛(NDA)为衍生试剂,β-环糊精(β-CD)和脱氧胆酸钠(SDC)为拆分体系,对16对氨基酸对映体的NDA衍生物进行了手性拆分研究.考察了蛋白氨基酸和一些胺对检测D-天冬氨酸和D-谷氨酸的影响,并确立了最佳分离条件,从而建立了单细胞中D-天冬氨酸和D-谷氨酸的检测方法,并对海兔的单个神经细胞中D-天冬氨酸和D-谷氨酸进行了检测.     

CdS纳米粒子与半胱氨酸相互作用的研究

合成了粒径均匀和分散性好的CdS纳米粒子.通过改变CdS纳米粒子及半胱氨酸的浓度、体系的pH值及CdCl2和CH3CSNH2摩尔比等实验条件跟踪监测了CdS纳米粒子光谱性质的变化,探讨了CdS纳米粒子与半胱氨酸之间的相互作用及化学反应机理.     

(R)‐N,N,N‐Trimethyl‐2‐Aminobutanol‐Bis(Trifluoromethane‐Sulfon)Imidate Chiral Ionic Liquid Used as Chiral Selector in HPCE,HPLC, and CGC

Abstract

In this work, the (R)‐N,N,N‐trimethyl‐2‐aminobutanol‐bis(trifluoromethanesulfon)imidate chiral ionic liquid was first used in chromatography and exhibited a excellent chiral recognition ability in high performance capillary electrophoresis (HPCE), high performance liquid chromatography (HPLC), and capillary gas chromatography (CGC), which also showed for the first time that chrial ionic liquid was an effective chiral selector in HPCE and HPLC. The compounds that have been separated using this chiral ionic liquid at least included alcohol, amine, acid, and amino acid, et al. enantiomers. As the chiral ionic liquid can be easily synthesized from relatively inexpensive materials, it should have a great potentiality for chiral separation in chromatographic science.     

Chiral analysis of baclofen by alpha-cyclodextrin-modified capillary electrophoresis and laser-induced fluorescence detection

An enantioselective method for baclofen (4-amino-3-p-chlorophenylbutyric acid) based on capillary electrophoresis (CE) separation and laser-induced fluorescence (LIF) detection has been developed. Naphthalene-2,3-dicarboxaldehyde (NDA) was used for precolumn derivatization of the nonfluorescent drug. alpha-Cyclodextrin (alpha-CD) was included in the buffer as a chiral selector for the separation of NDA-labeled S-(+)- and R-(-)-baclofen. Optimal resolution and detection were obtained with an electrophoretic buffer of 50 mM sodium borate (pH 9.5) containing 7 mM alpha-CD and a He-Cd laser (lambda ex = 442 nm, lambda em = 500 nm). Combined with a simple cleanup procedure, this method can be applied to the analysis of baclofen enantiomers in human plasma. The relative standard deviation (RSD) values on peak areas of a plasma sample containing 1.0 microM racemic baclofen were 6.4 and 4.9% (n = 8) for the S-(+)- and R-(-)-enantiomer, respectively. The RSD value on migration times of both enantiomers was 0.5% (n = 8). Calibration graphs for S-(+)- and R-(-)-baclofen in plasma showed a good linearity (r > or = 0.999) in the concentration range of 0.1-2.0 microM. The limit of detection of baclofen in plasma was about 10 ng/mL.     

Open tubular layer of S‐ofloxacin imprinted polymer fabricated in silica capillary for chiral CEC separation

An open tubular molecule imprinted polymer (OT‐MIP) capillary column has been prepared for chiral separation of ofloxacin enantiomers in CEC. The S‐ofloxacin imprinted OT column was fabricated by thermally initiated non‐covalent polymerization procedure inside a pretreated and silanized fused silica capillary. The template molecule was incorporated with methacrylic acid (MAA), ethylene glycol dimethacrylate (EDMA) and 4‐styrenesulfonic acid (4‐SSA) and dissolved in a porogen mixture of ACN/2‐propanol (9:1). The separation efficiency of the 4‐SSA MIP column was found quite better than that of the MIP column without 4‐SSA. It has been demonstrated that our OT‐MIP column can separate ofloxacin enantiomers with excellent chiral separation efficiency after tuning the various chromatographic conditions. The optimized chromatographic eluent was 85:15, v/v%, ACN/60 mM sodium acetate at pH 7. The separation efficiency and selectivity of chiral separation of this study were far better than those obtained by previous methods for chiral separation of R‐ and S‐ofloxacin.     

Chiral ionic liquids for enantioseparation of pharmaceutical products by capillary electrophoresis

A chiral ionic liquid (IL), S-[3-(chloro-2-hydroxypropyl)trimethylammonium] [bis((trifluoromethyl)sulfonyl)amide] (S-[CHTA](+)[Tf(2)N](-)), which can be easily and readily synthesized in a one-step process from commercially available reagents, can be successfully used both as co-electrolyte and as a chiral selector for CE. A variety of pharmaceutical products including atenolol, propranolol, warfarin, indoprofen, ketoprofen, ibuprofen and flurbiprofen, can be successfully and baseline separated with the use of this IL as electrolyte. Interestingly, while S-[CHTA](+)[Tf(2)N](-) can also serve as a chiral selector, enantioseparation cannot be successfully achieved with S-[CHTA](+)[Tf(2)N](-) as the only chiral selector. In the case of ibuprofen, a second chiral selector, namely a chiral anion (sodium cholate), is needed for the chiral separation. For furbiprofen, in addition to S-[CHTA](+)[Tf(2)N](-) and sodium cholate, a third and neutral chiral selector, 1-S-octyl-beta-d-thioglucopyranoside (OTG), is also needed. Due to the fact that the chirality of this chiral IL resides on the cation (i.e., -[CHTA](+)), and that needed additional chiral selector(s) are either chiral anion (i.e., cholate) or chiral neutral compound (OTG), the results obtained seem to suggest that additional chiral selector(s) are needed to provide the three-point interactions needed for chiral separations.     

Determination of neurotransmitters in PC 12 cells by microchip electrophoresis with fluorescence detection

A sensitive fluorescence detection system with an Hg-lamp as the excitation source and a photon counter as the detector for microchip CE (MCE) has been developed. O-Phthaldialdehyde (OPA, lambda(ex) = 340 nm) was employed to label the catecholamine neurotransmitters such as dopamine (DA), norepinephrine (NE), and amino acid neurotransmitters including alanine (Ala), taurine (Tau), glycine (Gly), glutamic acid (Glu), and aspartic acid (Asp). The separation of seven derivatized neurotransmitters was successfully performed in MCE and the detection limits (S/N = 3) for DA, NE, Ala, Tau, Gly, Glu, and Asp were 0.85, 0.49, 0.23, 0.15, 0.13, 0.18, and 0.29 fmol, respectively. The system was then successfully applied for separation and determination of neurotransmitters in rat pheochromocytoma (PC 12) cells, and the average amounts of analyte per cell from a cell population were 2.5 fmol for DA, 3.3 fmol for Ala, 8.2 fmol for Tau, 4.0 fmol for Gly, and 1.9 fmol for Glu, respectively. By single-cell injection mode, electrophoresis separation and quantitative measurement of Glu in individual PC 12 cells was obtained. The average value of Glu per cell from single PC 12 cells analysis was found to be 3.5 +/- 3.1 fmol.     

分子对接预测手性化合物在蛋白质固定相色谱柱上的保留行为

利用分子对接技术预测了2种蛋白质固定相分别与4对手性化合物的相互作用情况。 结果表明,预测结合自由能(ΔG)的大小与对映体（R-(+)型和S-(-)型）的出峰顺序一致;结合自由能差值的绝对值(Δ(ΔG))与实验分离因子(α)大小顺序一致。 说明分子对接可以反映蛋白质对不同的手性化合物的识别能力和化合物R-(+)型和S-(-)型的出峰顺序。     

Effect of Chiral Additives in the Preparation of Cellulose-Based Chiral Stationary Phases in HPLC, and Effect on Enantiomer Resolution

Chiral stationary phases (CSPs) for high-performance liquid chromatographic (HPLC) have been prepared by coating silica gel with cellulose tribenzoate or cellulose trisphenylcarbamate. The effect of chiral additives on preparation of the CSPs was studied with (+)-l-mandelic acid, (−)-2-phenyl-1-propanol, (+)-1-phenyl-1,2-ethanediol and (−)-1-(1-naphthyl)ethanol as chiral additives for cellulose tribenzoate and (−)-2-phenyl-1-propanol and (+)-phenylsuccinic acid as chiral additives for cellulose trisphenylcarbamate. The results showed that chiral recognition by these stationary phases was increased in comparison with the original CSPs, especially the resolution (R _S) obtained. The method can be used to improve the efficiency of enantiomer separation by silica gel stationary phases coated with polymers.     

Resolution of beta-amino acids on a high performance liquid chromatographic doubly tethered chiral stationary phase containing N-CH3 amide linkage based on (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid

A doubly tethered chiral stationary phase (CSP) containing N-CH(3 )amide linkage based on (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid was applied to the resolution of various beta-amino acids. The chiral recognition behaviors for the resolution of beta-amino acids on the doubly tethered CSP were consistent with those on the corresponding singly tethered CSP while the chiral recognition ability of the doubly tethered CSP was generally greater in terms of both the separation (alpha) and the resolution factors (R(S)) than that of the corresponding singly tethered CSP. From these results, it was concluded that attaching the second tethering group to silica gel through a carbon atom of the first tethering group of the CSP improves the chiral recognition ability for the resolution of beta-amino acids without any change in the chiral recognition mode. The retention factors (k(1)) on the doubly tethered CSP were larger than those on the corresponding singly tethered CSP and these retention factors were found to be controllable with the variation of the type and the content of the organic and/or acidic modifier in the aqueous mobile phase without significant change in the separation and the resolution factors.     

Chiral characterization of deprenyl-N-oxide and other deprenyl metabolites by capillary electrophoresis using a dual cyclodextrin system in rat urine

A chiral capillary electrophoresis method has been developed for the simultaneous separation of the enantiomers of deprenyl and eight of its metabolites, among them the recently described metabolite deprenyl-N-oxide. Although heptakis-(2,6-di-O-methyl)-beta-cyclodextrin (DIMEB) was suitable for the enantioresolution of deprenyl and its dealkylated derivatives, the enantiomers of deprenyl-N-oxide were just partly resolved. Carboxymethyl-beta-cyclodextrin (CMBCD) in as low as 2 mM concentration was capable of the enantiomer separation of all the nine examined compounds, however co-migration of 1R,2S-(-)-norephedrine and 1R,2R-(-)-pseudoephedrine, as well as 1S,2R-(+)-ephedrine and R-(-)-amphetamine was observed. This problem could be overcome by the use of a dual cyclodextrin system containing 4 mM DIMEB in addition to 2 mM CMBCD; simultaneous separation of all the compounds could be achieved. The optimized method was used for the analysis of rat urine samples after 10 days of treatment of animals with either R-(-)- or S-(+)-deprenyl. The stereospecific biotransformation of both deprenyl enantiomers was confirmed, and the stereoselectivity of N-oxide formation was demonstrated.