Investigation on chiral capillary columns and their application in separation of enantiomers

Six chiral diamide stationary phases (CSPs), namely N-(3-carbobenzoxypropionyl)-L-Val-tert-butylamide (CSP-1), N-undecenoyl-L-Val-S-α-phenylethylamide (CSP-2), N-undecenoyl-L-Val-R-α-phenylethylamide (CSP-3), OV-225-L-Val-tert-butylamide (CSP-4), XE-60-L-Val-tert-butylamide (CSP-5) and polycyanoethyl vinyl siloxane-L-Val-tert-butylamide (CSP-6), were inves-tigated and CSP-6 was crosslinked within narrow bore (70 μm) fused silica capillary columns. Theseparation of amino acid enantiomers on this narrow bore column by gas chromatography (GC) isillustrated.     

The separation of racemic crystals into enantiomers by chiral block copolymers

A series of chiral double hydrophilic block copolymers (DHBCs) was synthesized and employed as additives in the crystallization of calcium tartrate tetrahydrate (CaT). We found that appropriate polymers can slow down the formation of the thermodynamically most stable racemic crystals as well as the formation of one of the pure enantiomeric crystals so that chiral separation by crystallization occurs even when racemic crystals can be formed. In addition, the presence of DHBCs results in major modifications of crystal morphology, creating unusual morphologies of higher complexity. Our study demonstrates the potential application of chiral DHBCs in the control of chirality throughout crystallization, in particular for racemic crystal systems, and also shows that enantiomeric excess of one enantiomer can be maximized by the kinetic control of crystallization.     

Streptavidin chiral stationary phase for the separation of adenosine enantiomers

In this paper, a microbore column packed with streptavidin particles was used, at various temperatures (0-24 degrees C), to separate the adenosine enantiomers by HPLC. Using an aqueous mobile phase, the apparent enantioseparation was high for a small molecule, varying from 11.5 at 0 degrees C to 6.2 at 24 degrees C. From the experiments carried out with a streptavidin-biotin complex stationary phase, it was demonstrated that the blockage of the biotin sites of the immobilized streptavidin was responsible for a strong decrease in the enantioselectivity via a direct and/or an indirect effect. From the analysis of the concentration dependencies of the solute retention factor, it was also shown that a reduction of the D-adenosine specific binding sites occurred at the lowest temperature. The thermodynamic parameters determined from the van't Hoff plots indicated that the D-adenosine binding to the streptavidin specific sites was enthalpically driven.     

High-performance liquid chromatographic separation of imidazolinone herbicide enantiomers and their methyl derivatives on polysaccharide-coated chiral stationary phases

Many chiral pesticides exhibit enantioselectivity in biotransformation and ecotoxicity in the environment. A significant class of chiral pesticides is imidazolinone herbicides, of which enantioselectivity has not been well studied. Development of efficient chiral separation methods is the first step for allowing characterization of enantioselectivity in environmental processes. In this study, we attempted to resolve enantiomers of imidazolinone herbicides using reversed-phase and normal-phase high-performance liquid chromatography with polysaccharide-type chiral columns. Enantiomers of imazethapyr, imazaquin, and imazamox were separated on a Chiralcel OD-R column using 50mM phosphate buffer-acetonitrile as mobile phase. Enantiomers of imazapyr, imazapic, imazethapyr, imazamox and imazaquin were resolved on a Chiralcel OJ column using n-hexane (0.1% trifluoroacetic acid)-alcohol as mobile phase. The enantiomers of five methyl derivatives of imidazolinone herbicides were also resolved on the Chiralcel OJ column. The Deltak' values revealed a structure-enantioselectivity relationship for the separation behaviors of the enantiomers on the OJ column. The described method was successfully applied for chiral analysis of two imidazolinone herbicides (imazapyr and imazaquin) in spiked soil samples.     

Optimized separation of pesticide enantiomers by chiral high-performance liquid chromatography

Summary A computer-assisted method is described for optimization of multi-component, mobile phase selection for separating enantiomers of four pesticides in normal-phase HPLC. The method is based on the triangle, solvent-selection concept using a statistical scanning method. The optimization of the separation over the experimental region is based on a special polynomial estimation from seven experimental runs, and resolution (R_s) is used as the selection criterion. Excellent agreement was obtained between predicted and experimental data.     

手性金属有机骨架材料的合成及其在对映异构体选择性分离中的应用

手性现象在自然界中广泛存在,手性分离在药物研发、农用化学、药理学、环境科学和生物学等诸多领域具有重要意义。手性金属有机骨架化合物材料(MOFs)是一类具有特殊拓扑结构和可设计的孔道结构的新型多孔材料,加之其比表面积高、孔隙率大、热稳定性良好和溶剂耐受性好等特性,使得MOFs在分析化学领域的应用与研究日益深入。本文简要综述了手性MOFs的合成方法,着重讨论了手性MOFs在对映异构体选择性分离方面的应用及相关机理,最后对该类材料的发展前景做了展望。     

Liquid chromatographic separation of enantiomers using chiral additives in the mobile phase

Addition of an optically active compound to the mobile phase is an attractive method for resolving enantiomers in liquid chromatography. The technique is practical, easy to use and allows rapid screening for new chiral complexing agents as well as for optimal separation conditions.     

手性流动相添加剂法拆分盐酸氯丙那林对映体

盐酸氯丙那林(Clorprenaline hydrochloride)其化学名为α-[[(1-甲基乙基)氨基]甲基]-2-氯-苯甲醇盐酸盐,分子中含有一个手性碳原子,分子式见图1.临床上使用的是盐酸氯丙那林外消旋体,可用于支气管哮喘、哮喘型支气管炎、慢性支气管炎合并肺气肿,可止喘并改善肺功能.     

Some aspects of the preparative separation of enantiomers on chiral stationary phases

Summary In preparative column liquid chromatography, it is necessary to work with conditions of mass overload to obtain high throughput per unit time. The influence of sample mass and of eluent composition on the separation of R,S-1-(1-naphthylethyl)propylamide on chiral 3,5-dinitrobenzoylphenylglycine-silica (Pirkle type stationary phase) was investigated. At a sample load of 200μg of racemate per gram of stationary phase, the column becomes overloaded. At higher sample loads the peaks become triangular; therefore the first peak is always pure up to loads of 10mg g⁻¹, although resolution is low. The purity of the second peak depends on sample mass, but not on the strength (polarity) of the mobile phase. This is due to the effect that peak width, as well as resolution, decrease as the polarity of the eluent increases. In certain cases the polarimeter, used as a detector, can give more information on peak purity than the UV detector.     

立体选择性萃取分离反式DV菊酸对映体

研究了反式DV菊酸对映体在含有手性选择体酒石酸酯的水-有机相双相体系中的萃取分配行为,考察了有机稀释剂种类、酒石酸酯的浓度、温度、水相的pH值、酒石酸酯烷基链长度对分配系数(D)和分配因子(α)的影响.研究表明:三氯甲烷作稀释剂时萃取分离效果较好;温度升高使分配系数增大,分离因子减小;分配系数随pH的升高而降低,随着酒石酸酯浓度的增大而增大,分离因子随pH的升高和酒石酸酯浓度的增大先增加后降低,pH和酒石酸酯浓度分别为4.50和0.40mol/L时取得较好的分离效果;取代烷基链长对分配系数(D)和分离因子(α)亦有较大影响.     

酒石酸酯立体选择性萃取分离功夫菊酸对映体

研究了功夫菊酸对映体在含有手性选择剂酒石酸酯的水-有机相双相体系中的萃取分配行为,考察了水相的pH、酒石酸酯的浓度、磷酸盐浓度、温度和酒石酸酯烷基链长度对分配系数(K)和分离因子(α)的影响.研究结果表明:分配系数(K)随pH的升高而降低,随着酒石酸酯浓度的增大而增大,分离因子(α)随pH的升高和酒石酸酯浓度的增大先增加后降低,pH和酒石酸酯浓度分别为5.50和0.30 mol/L时取得较好的分离效果;分配系数(K)和分离因子(α)都随磷酸盐浓度增大而减小;温度、取代烷基链长对分配系数(K)和分离因子(α)亦有较大影响.     

First synthesis of enantio-uracil dinucleotide, comparison of physicochemical properties of their enantiomers, and separation by chiral column chromatography

Enantio-uracil dinucleotide 5, which consists of two l-uridylic acids and one pyrophosphate, was synthesized for the first time in our laboratory. Benzolyated l-uridine was prepared by a stereoselective glycosylation of silylated uracil with l-1-O-acetyl-2,3,5-tri-O-benzoylribose (l-ABR 7). After deprotection, l-uridine 9 was converted to P¹,P⁴-di(l-uridine 5′-) tetraphosphate tetrasodium salt (l-UP₄U 5) by treatment of l-UMP morpholidate 10c with triethylammonium pyrophosphate (TEA-PPi 11b). Spectral data of synthesized l-UP₄U 5 are given in the references. All spectral data were identical with those of UP₄U 3 except the specific rotation, which showed a positive value compared to UP₄U 3 having a negative value. Furthermore, the separation by chiral column chromatography was investigated.     

Direct chiral separation of caderofloxacin enantiomers by HPLC using a glycoprotein column

The enantiomers of caderoflxacin (CS-940), the new antibacterial fluoroquinolone compound, were separated on the commercially available α-acid glycoprotein-coated chiral stationary phase (Chiral-AGP) using the mobile phase of IPA: 0.15 M NaH₂PO₄ + Et₃N (pH 7.9) = 3: 97 at 0.8 mL/min with UV detection at 282 nm. The chromatographic behavior of caderofloxacin enantiomers was investigated by varying the mobile phase conditions. The chiral assay method was validated and used to determination of (R)-Caderofloxacin in (S)-Caderofloxacin raw material samples.     

Kinetic study on reactive extraction for chiral separation of phenylsuccinic acid enantiomers

The kinetics of the extraction of phenylsuccinic acid (PSA) enantiomers by hydroxypropyl-β-cyclodextrin (HP-β-CD) in a modified Lewis cell was studied, in which HP-β-CD dissolved in 0.1 mol L^?1 NaH₂PO₄/H₃PO₄ buffer solution (pH = 2.5) was selected as the chiral extractant. PSA enantiomers were extracted from organic phase to aqueous phase in the extraction module. The theory of extraction accompanied by a chemical reaction has been used to obtain the intrinsic kinetics of this extraction module. The different parameters affecting the extraction rate such as agitation speed, interfacial area, initial concentration of PSA enantiomers in organic phase as well as HP-β-CD concentration in aqueous phase were separately studied. The experimental results demonstrate that the extraction reactions are fast. The reactions were found to be first order with respect to PSA and second order with respect to HP-β-CD with forward rate constants of 3.4 × 10^?2 m⁶ mol^?2 s^?1 for R-PSA and 9.96 × 10^?3 m⁶ mol^?2 s^?1 for S-PSA. These data will be useful in the design of extraction processes.     

反应萃取手性分离苯基琥珀酸对映体动力学研究

通过恒界面池研究了羟丙基-β-环糊精(HP-β-CD)萃取苯基琥珀酸对映体(PSA)动力学.采用伴随化学反应的萃取理论获得萃取动力学.实验分别考察了搅拌速率、界面面积、对映体浓度和萃取剂浓度等条件对PSA对映体萃取动力学的影响.实验结果表明:HP-β-CD萃取PSA对映体的反应为快反应;对对映体反应是一级反应,对萃取剂反应是二级反应;R-PSA,S-PSA反应速率常数分别为3.4×10-2m6mol-2s-1,9.96×103m6mol-2s-1.这些数据对萃取过程的设计是很重要的.     

Hybridation of different chiral separation techniques with ICP-MS detection for the separation and determination of selenomethionine enantiomers: chiral speciation of selenized yeast

Enantioseparation and determination of selenomethionine enantiomers in selenized yeast was investigated using chiral separation techniques based on different principles, coupled on-line to inductively coupled plasma mass spectrometry (ICP-MS) for selenium-specific detection. High performance liquid chromatography (HPLC) on a beta-cyclodestrin (beta-CD) column, cyclodextrin-modified micellar electrokinetic chromatography (CD-MEKC), gas chromatography (GC) on a Chirasil-L-Val column, and HPLC on a Chirobiotic T column have been investigated as the chiral separation techniques. For HPLC separation on the beta-CD column, and also for CD-MEKC, selenomethionine enantiomers were derivatized with NDA/CN(-). For chiral separation by GC, selenomethionine enantiomers were converted into their N-trifluoroacetyl (TFA)-O-alkyl esters. The developed hybridation methodologies are compared with respect to enantioselectivity, sensitivity and analysis time. The usefulness of the best-suited method [HPLC (Chirobiotic T)-ICP-MS] was demonstrated by its application to the successful chiral speciation of selenium and D-and L-selenomethionine content determination in selenized yeast.     

Reversed-phase liquid chromatographic separation of enantiomers on polysaccharide type chiral stationary phases

The direct chiral separation by chiral stationary phases (CSPs) is one of the most important techniques to analyze enantiomeric purity as well as to get enantiomerically pure material quickly. Among various types of CSPs, polysaccharide type CSPs are well known by their versatility and durability. They are not only effective under normal-phase conditions, but also under reversed-phase conditions. In order to get a good separation under the reversed-phase conditions, it is the key to choose an appropriate mobile phase. For example, a simple mixture of water/acetonitrile or water/methanol are sufficient for a neutral analyte, while it is necessary to use an acidic solution instead of water for an acidic analyte and a solution of a chaotropic salt (or a basic solution) for a basic analyte, respectively. The paper also presents lists of more than 350 separation examples that include 22 validated methods for drug analyses from serum, plasma, or urine samples on polysaccharide type CSPs under reversed-phase conditions.     

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.     

Total synthesis of (±)-tangutorine and chiral HPLC separation of enantiomers

The first total synthesis of racemic tangutorine, a novel indole alkaloid, was performed in 7 steps. The key reactions, dithionite reduction and acidic cyclization provided easy access with good yields to the tangutorine skeleton. Comprehensive NMR spectroscopic data of new compounds are given. Chiral HPLC separation of enantiomers is reported.