Separation of the enantiomers of 2-phenylcyclopropanecarboxylate esters by capillary gas chromatography on derivatized cyclodextrin stationary phases

Summary Separation of the enantiomers of 2-phenylcyclopropanecarboxylate esters has been investigated on derivatized cyclodextrin chiral stationary phases (CD CSPs) to enable direct determination of the enantiomeric purity of the products of enantioselective cyclopropanation. Four stereoisomers of these chiral compounds could be resolved to baseline on permethylated β-cyclodextrin CSP. Some unusual phenomena, iso-enthalpy retention behavior and entropically driven chiral separation, were observed for the enantioseparation of 2-phenylcyclo-propanecarboxylates on the CD CSPs. Thermodynamic parameters were evaluated and an enthalpy-entropy compensation effect was observed forn-alkyl esters of 2-phenylcyclopropanecarboxylate separated on CD CSPs.     

Simultaneous separation and enantioseparation of thalidomide and its hydroxylated metabolites using high-performance liquid chromatography in common-size columns, capillary liquid chromatography and nonaqueous capillary electrochromatography

The separation of thalidomide (TD) and its hydroxylated metabolites including their simultaneous enantioseparation was studied using three different polysaccharide-type chiral stationary phases (CSPs) in combination with polar organic mobile phases. Three different techniques, high-performance liquid chromatography in common-size columns, capillary LC and nonaqueous capillary electrochromatography were compared in terms of separation. As this study illustrates, polar organic mobile phases represent a valuable extension for less polar and polar aqueous-organic mobile phases in combination with polysaccharide CSPs. Chiralpak AD consisting of 25% of amylose-tris(3,5-dimethylphenylcarbamate) coated on wide-pore aminopropylsilanized silica gel exhibited higher resolving ability compared to the similar cellulose derivative (Chiralcel OD) as well as to cellulose-tris(4-methylbenzoate) (Chiralcel OJ) CSPs for this particular set of chiral analytes. Baseline separation and simultaneous enantioseparation of all three compounds could be achieved under optimized separation conditions.     

淀粉及纤维素三(3-三氟甲基苯基氨基甲酸酯)手性固定相的制备及其性能评价

为了扩展多糖类手性固定相的种类,制备了基于淀粉及纤维素三(3-三氟甲基苯基氨基甲酸酯)的涂敷型手性固定相,以正己烷-异丙醇混合液为流动相,对8种手性化合物进行了高效液相色谱拆分。研究表明: 虽然与应用最广泛的分别以淀粉及纤维素三(3,5-二甲基苯基氨基甲酸酯)为手性选择因子的商品化手性柱Chiralpak AD和Chiralcel OD相比,所制备的手性固定相的手性分离能力较低,但纤维素三(3-三氟甲基苯基氨基甲酸酯)手性固定相显示出特异的手性识别能力,一些手性化合物在此固定相上得到了比在Chiracel OD上更好的分离;所制备的手性固定相的手性识别能力随流动相中异丙醇含量的降低而变好,当流动相中正己烷与异丙醇的体积比为95:5时所制备的手性固定相显示出相对较高的手性识别能力;总体来说,淀粉三(3-三氟甲基苯基氨基甲酸酯)手性固定相的手性识别能力稍强于纤维素三(3-三氟甲基苯基氨基甲酸酯)手性固定相,同时两种手性固定相的手性识别能力具有一定的互补性。     

Liquid chromatographic-mass spectrometric separation of oligoalanine peptide stereoisomers: influence of absolute configuration on enantioselectivity and two-dimensional separation of diastereomers and enantiomers

This contribution describes the chromatographic separation of peptide stereoisomers. Thereby, one focus is laid on the influence of the absolute configurations of peptide enantiomer pairs on their enantioselective separation. Three different N-terminal protecting groups and three different chiral stationary phases (CSPs) based on cinchona alkaloid derivatives were employed and oligoalanine di-, tri- and tetra-peptides were used as model set. The absolute configurations of the individual enantiomeric pairs were found to profoundly influence both the elution order and the enantioselectivity. The stereoselective molecular recognition mechanism was observed to be dependent on the combination of configuration and the chosen protecting group and CSP. As the CSPs on their own exhibited insufficient diastereoselectivity, a two-dimensional liquid chromatography-mass spectrometry (LC-MS) system was developed for the separation of both diastereomers and enantiomers of peptides in the second part of this study. Diastereomers were separated by reversed phase (RP) and the resulting enantiomeric pair fractions were transferred to a CSP for enantioseparation. All eight stereoisomers of a tripeptide (Ala-Ala-Ala) and 9 out of 10 stereoisomers of a tetrapeptide (Ala-Ala-Ala-Ala) could be successfully resolved.     

Liquid Chromatorgraphic Separation of the Enantiomers of Phenylthiohydantoin α-Amino Acids Derivatives on Polysaccharide-Based Chiral Stationary Phases

ABSTRACT

The liquid chromatographic enantioseparation of the phenylthiohydantoin (PTH) derivatives of various amino acids on four commercial polysaccharide-derived chiral stationary phases (CSPs) is described. Chiralcel OF and Chiralpak AS showed better performance than the other CSPs for resolution of the enantiomers of PTH amino acid derivatives. The enantiomers of all amino acids as their PTH derivatives were well separated on Chiralcel OF and/or Chiralpak AS. The (-)(L) or (-)-enantiomers of all analytes examined were preferentially retained on Chiralpak AS, whereas the (+)(D) or (+)-enantiomers of most of analytes were preferentially retained on Chiralcel OF.     

HPLC-MS/MS enantioseparation of triazole fungicides using polysaccharide-based stationary phases

The enantiomeric separation of 21 triazole fungicides was carried out on four polysaccharide-derived chiral stationary phases in the reversed phase separation mode using high performance liquid chromatography coupled with tandem mass spectrometry. All fungicides were detected in electrospray ionization (ESI) positive mode with selected reaction monitoring (SRM). Complete enantioseparation was achieved for 21 fungicides except for difenoconazole based on cellulose tris (3,5-dimethylphenylcarbamate) and cellulose tris (3-chloro-4-methylphenyl carbamate) columns by optimizing experimental conditions including mobile phase and column temperature. Mobile phase was 0.1% formic acid aqueous solution mixed with methanol or acetonitrile in different proportions. Among all the fungicides, 15 with two enantiomers and three with four stereoisomers (bitertanol, bromuconazole, and cyproconazole) were successfully separated at 25°C. Enantioseparation for the other three fungicides (propiconazole, triadimenol, and difenoconazole) with four stereoisomers could be achieved by changing the column temperature from 10 to 40°C. Propiconazole and triadimenol were enantioseparated on baseline at 40 and at 35°C, respectively, and difenoconazole was enantioseparated partially with the R(s) > 1.1 at 25°C. Moreover, linearities and limits of detection (LODs) of 21 fungicides except for difenoconazole were studied, showing coefficients of determination (R(2)) higher than 0.99 and LODs lower than 2.5 μg/L.     

Comparative study between the polysaccharide-based chiralcel OJ and chiralcel OD CSPSs in chromatographic enantioseparation of imidazole analogues of fluoxetine and miconazole

The enantiomeric separation of a series of imidazole analogues of Fluoxetine and Miconazole endowed with potent antifungal activity was performed using cellulose tris(4-methylbenzoate) (Chiralcel OJ) and cellulose tris(3,5-dimethylphenylcarbamate) (Chiralcel OD) as chiral stationary phases. Binary mixtures of n-hexane and alcohol as well as pure alcohols (ethanol or 2-propanol) were used as eluents. The enantiomer elution order was monitored by chiroptical detectors based on on-line optical rotation and circular dichroism measurements. For some of the compounds studied very high enantioseparation factor values (alpha > 7) on Chiralcel OJ CSP were observed. In order to study the chiroptical characteristics of the two most biologically active compounds, chromatographic resolutions were carried out on a semipreparative scale. Assignment of the absolute configuration was empirically established by comparing the CD spectra of the separated enantiomers with those obtained from the enantiomers of Miconazole.     

Applications of Cellulose-Based Chiral Stationary Phases in the Resolution of Some Beta-Adrenoceptor Antagonists

Abstract

Cellulose tris (3,5-dimethylphenyl carbamate) known as Chiralcel OD chiral stationary phase (CSP) is one of the most commonly used cellulosic CSPs which have been successfully used for separation, enantiomeric purity determination and analysis of several drug racemates including β-adrenoceptor antagonists.

Resolution of timolol, penbutolol, celiprolol and carazolol enantiomers are achieved using this CSP. A possible chiral recognition mechanism(s) for these β-adrenergic blockers and this chiral stationary phase is presented.     

Enantioselective separation and pharmacokinetic dissipation of cyflumetofen in field soil by ultra‐performance convergence chromatography with tandem mass spectrometry

Little data on the enantioselective separation of cyflumetofen exists, despite the fact that such data are essential to the assessment of the fate and potential toxic effects of cyflumetofen enantiomers. To address this issue, a simple and sensitive method for the enantioselective determination of cyflumetofen enantiomers in soil has been established using ultra performance convergence chromatography tandem triple quadrupole mass spectrometry. The effects of the chiral stationary phases, mobile phase, auto backpressure regulator pressure, column temperature, flow rate of the mobile phase, and compensation pump solvent were evaluated. The proposed method was applied to the study of the pharmacokinetic dissipation of cyflumetofen stereoisomers in soil under greenhouse conditions. The estimated half‐life of cyflumetofen isomers ranged from 12.2 to 13.6 days, and statistically significant enantioselective degradation was observed. This study not only demonstrates that there is an efficient and sensitive method for cyflumetofen enantioseparation, but also provides the first experimental evidence of the pharmacokinetic dissipation of cyflumetofen stereoisomers in the environment.     

True and false reversal of the elution order of barbiturates on a bonded cellulose-based chiral stationary phase

A set of racemic N-alkylated barbiturates were investigated for their direct enantioselective HPLC separation on a new chiral stationary phase (CSP) containing cellulose tris(3,5-dimethylphenylcarabamate) immobilized onto silica gel (Chiralpak IB) and its coated version (Chiralcel OD). They were online detected by UV and optical rotation detectors to trace the elution order of their enantiomers. Surprisingly, examples of false and true reversal of the elution order of enantiomers of barbiturates were observed and reported.     

不同载体涂敷的纤维素酯手性固定相的制备及性能

以微晶纤维素和3,5-二甲基苯基氨基甲酸酯为原料,合成了纤维素-三(3,5-二甲基苯基氨基甲酸酯)(CDMPC),将其分别涂敷于小孔硅胶(SG)、氨丙基化小孔硅胶(APS-SG)和介孔SBA-15微球上,制得3种手性固定相：SG@CDMPC(CSP1)、APS-SG@CDMPC(CSP2)及SBA-15@CDMPC(CSP3),正相条件下考察了12种中性或酸性手性化合物在自制手性固定相上的拆分效果,并与商品柱Chiralcel OD-H的拆分性能进行了对比。 6个手性化合物在CSP1上获得比在商品柱上更高的柱效,其中2个手性化合物获得比在商品柱上更高的分离因子和分离度,而CSP2和CSP3的拆分效果总体较CSP1和商品柱的差。 探讨了自制手性固定相对华法令的拆分和定量测定,华法令在CSP1上的检测限为10 μg/L,在0.05~5 g/L范围内线性关系良好。     

Chiralcel OD-RH直接拆分五味子乙素对映体

采用反相手性色谱柱Chiralcel OD-RH(纤维素3,5二甲基苯基氨基甲酸酯涂敷在5 μm硅胶上)建立了五味子乙素对映体的反相高效液相色谱拆分方法。考察了流动相组成、柱温和流速对五味子乙素手性对映体拆分的影响。以甲醇-水(90∶10)为流动相,流速0.5 mL/min,柱温20 ℃,检测波长254 nm,在Chiralcel OD-RH手性柱上成功拆分了五味子乙素对映体,其中R-构型先出峰。用lnk对1/T作图得到的Van-t Hoff曲线具有良好线性,相关系数（r）均大于0.99,计算了对映体与固定相相互作用的焓变以及焓变差值和熵变差值等热力学参数。结果显示,五味子乙素对映体的拆分过程为焓控过程,即氢键、π-π及偶极-偶极等作用方式对对映体的拆分起重要作用。     

Enantiomer separation of a novel aminothiazolecarboxamide fungicide using polysaccharide-derived chiral stationary phases

The direct enantioseparation of a novel aminothiazolecarboxamide fungicide, ethaboxam, on polysaccharide-derived chiral stationary phases (CSPs) is described. Good resolution is achieved with several polysaccharide-derived CSPs. Chiralcel OD (OD-H) and Chiralpak AS are excellent for direct enantiomer separation of ethaboxam. The elution behavior and the effects of eluent composition on the resolution of ethaboxam are also investigated. Furthermore, the mechanism for chiral recognition using molecular mechanics is discussed.     

Enantioselective separation and simultaneous determination of fenarimol and nuarimol in fruits, vegetables, and soil by liquid chromatography–tandem mass spectrometry

A method for simultaneous enantioselective determination of fenarimol and nuarimol in apple, grape, cucumber, tomato, and soil was developed using liquid chromatography–tandem mass spectrometry. The enantioseparation results of the two fungicides through three different cellulose-based chiral columns are discussed. The influence of column temperature on the resolution of the enantiomers of the two fungicides was examined. Complete enantioseparation of the two fungicides’ enantiomers was obtained on a cellulose tris(4-methylbenzoate) column (Lux Cellulose-3) at 25?°C using methanol and 0.1?% formic acid solution (80:20, v/v) as mobile phase. The linearity, matrix effect, recovery, and precision were evaluated. Good linearity was obtained over the concentration range of 1–500?μg?L^?1 for each enantiomer in the standard solution and sample matrix calibration solution. There was no significant matrix effect in apple, grape, cucumber, or tomato samples, but signal suppression was typically observed with the soil extracts. The mean recoveries, repeatability, and reproducibility were 76.5–103?%, 2.1–9.0?%, and 4.2–11.8?%, respectively. The limit of quantification for enantiomers of the two fungicides in fruits, vegetables and soil was 5?μg?kg^?1. Moreover, the absolute configuration of the enantiomers of fenarimol and nuarimol was determined from a combination of experimentally determined and predicted electronic circular dichroism spectra.

Enantioselective separation of all-E-astaxanthin and its determination in microbial sources

A method for the enantioselective separation of all-E-astaxanthin (3,3'-dihydroxy-beta,beta-carotene-4,4'-dione), an important colorant in the feed industry, was developed. Different chiral stationary phases (CSPs) such as Pirkle phases (R,R Ulmo and l-leucine), modified polysaccharides and a beta-cyclodextrin have been investigated on their separation performance of astaxanthin enantiomers. Direct resolution was only achieved employing the Chiralcel OD-RH (cellulose-tris-3,5-dimethylphenyl-carbamate) under reversed phase conditions. The chiral separation of the enantiomeric forms of astaxanthin produced in microalgae and yeasts was reported. The yeast Xanthophyllomyces sp. produces astaxanthin predominantly in the R,R configuration, whereas in the green microalgae Scenedesmus sp. astaxanthin is built primarily in the S,S form. The separation method for the identification of astaxanthin enantiomers is of great interest since astaxanthin is used as functional food additive in human nutrition. Moreover the method may be used as a food chain indicator in farmed salmon.     

Comparison of vancomycin-based stationary phases with different chiral selector coverage for enantioselective separation of selected drugs in high-performance liquid chromatography

Two vancomycin-based chiral stationary phases (CSPs) with different coverage of the chiral selector vancomycin (Chirobiotic V and Chirobiotic V2) were compared. beta-Blockers and profens, as structurally diverse groups of drugs, were chosen as analytes. Retention and enantioseparation of beta-blockers were studied in reversed-phase (RP) and polar-organic (PO) separation modes. Higher retention and better enantioresolution were obtained on the CSP with higher coverage of vancomycin in the both separation modes. Baseline separation of four beta-blockers (eight enantiomers) in the PO mode was achieved on the Chirobiotic V2 column within 15 min. The enantioseparation of profens did not bring so excellent and easy to interpret results. Higher retention of profens on the Chirobiotic V2 column was not always accompanied by an improvement of their chiral separation in the RP mode. The polar-organic mode was not suitable for these derivatives at all. The most interesting result was obtained with flobufen; its chiral center is further away from the rigid part of the molecule, which mostly causes difficulties in enantioselective recognition. Nevertheless, the enantiomers of flobufen were shown to be much better (baseline) resolved on the CSP with lower coverage of the chiral selector (Chirobiotic V).     

Enantiomers of New Synthetic Pyrrolylphenylethanoneamine Mono-Amino Oxidase Inhibitor Compounds: Analytical and Semipreparative HPLC Separations, and Chiroptical Characteristics

The polysaccharide chiral stationary phases (CSPs) Chiralcel OD and Chiralpak AD, and the brush-type (R,R)-Whelk-01 chiral stationary phases have been evaluated to separate new synthetic pyrrolylphenylethanoneamine racemic compounds, potentially monoamine oxidase (MAO) inhibitors, under various mobile phase compositions, using various temperatures. The enantioseparation was evaluated by comparing the (R,R)-Whelk-01 column performance with those of Chiralpak AD and Chiralcel OD. Significant differences were observed in their chiral recognition, as revealed from their retention, selectivity, resolution and elution order. Performances of the Chiralpak AD column were superior to those of the Chiralcel OD and (R,R)-Whelk-01 columns. Some of the racemic compounds were resolved by semipreparative chromatography on Chiralpak AD column in order to study the chiroptical proprieties of the single enantiomers.     

Comparison of the separation efficiencies of chirobiotic T and TAG columns in the separation of unusual amino acids

Two macrocyclic antibiotic type chiral stationary phases (CSPs), based on native teicoplanin and teicoplanin aglycone, Chirobiotic T and Chirobiotic TAG, respectively, were evaluated for the high-performance liquid chromatographic separation of enantiomers of 15 unnatural conformationally constrained alpha-amino acids, Phe and Tyr analogs, and 12 beta-amino acids having cycloalkane or cycloalkene skeletons. The chromatographic results are given as the retention, separation and resolution factors along with the enantioselective free energy difference corresponding to the separation of the enantiomers. It is clearly established that in most cases the aglycone is responsible for the enantioseparation of amino acids. The difference in enantioselective free energy between the aglycone CSP and the teicoplanin CSP was between 0.02 and 0.30 kcal mol(-1) for these particular amino acids. The resolution factors are higher with the aglycone CSP. Although the sugar units generally decrease the resolution of amino acid enantiomers, they can contribute significantly to the resolution of some unusual amino acid analogs. By application of these two CSPs excellent resolutions were achieved for most of the investigated compounds by using reversed phase or polar organic mobile mode systems. The separation conditions were optimized by variation of the mobile phase composition.     

Comparison of separation performance of polysaccaride-based chiral stationary phases in enantioseparation of 1-(4-chlorobenzhydryl)piperazine benzamide derivatives by HPLC

Analytical high-performance liquid chromatographic enantioseparation of 1-(4-chlorobenzhydryl) piperazine benzamide derivatives was accomplished on different chiral stationary phases. The enantiomers of the compounds were resolved by normal-phase chromatography on silica-based amylose tris(3,5-dimethylphenylcarbamate) (Chiralpak AD-H), cellulose tris(3,5-dimethylphenylcarbamate) (Chiralcel OD-H) and cellulose tris(4-methylbenzoate) (Chiralcel OJ) columns with mobile phases consisting of mixtures of n-hexane and ethanol in different proportions (90: 10, 80: 20). The mobile phase and the chiral stationary phase were varied to achieve the best resolution. The effect of the concentration of ethanol in the mobile phase was studied. The resolution obtained on the three columns was significant.     

高效液相色谱使用两种类型的纤维素-三(对甲基苯甲酸酯)固定相手性拆分非洛地平的比较

以高效液相色谱手性固定相法对非洛地平(FEL)进行手性拆分。分别采用两种类型的纤维素-三(对甲基苯甲酸酯)手性柱Chiralcel OJ-R和Chiralcel OJ-H进行比较实验,以正己烷-异丙醇(90:10, v/v)为流动相,考察了流动相、柱温对保留及手性拆分的影响。实验显示,两柱拆分FEL的van’t Hoff图均发生了转折,在高温区域为焓驱动,在低温区域为熵驱动。两柱在温度升高时拆分FEL的分离度均提高,其中OJ-H的分离度优于OJ-R。两种手性柱对FEL具有相似的拆分机理。