Direct optical resolution of the enantiomers of axially chiral compounds by high-performance liquid chromatography on cellulose tris-(3,5-dimethylphenylcarbamate) stationary phase

Summary The enantiomeric separation of nineteen biphenyl dimethyl dicarboxylate derivatives has been examined by HPLC on a chiral statonary phase prepared by coating aminopropylated silica gel with cellulose tris-(3,5-dimethylphenylcarbamate). It was found that trifluoroacetic acid (TFA) has a dominant effect on chiral separation for acidic compounds. The percentage of 2-propanol in the mobile phase does not have a large effect on the anantioselectivity but the separation was dramatically influenced by the kind of alcohol in the mobile phase. The effect of temperature on the chiral separation is also discussed. Most of the enantiomers investigated could be resolved satisfactorily.     

Enantioseparation of Novel Chiral Tetrahedral Clusters on an Amylosoe Tris-（3,5-dimethylphenylcarbamate） Chiral Stationary Phase by Normal Phase HPLC

Amylose tris(3,5-dimethylphenylcarbamate) (ADMPC) coated on a kind of small particle silica gel was prepared. On this ADMPC chiral stationary phase (CSP), the direct enantiomeric separation of six novel chiral transition metal tetrahedral clusters has firstly been achieved using n-hexane as the mobile phase containing various alcohols as modifiers. The effect of mobile phase modifiers and the structural variation of the solutes on their retention factors (k‘) and resolutions (Rs) were investigated. The result suggests that not only the structure and concentration of alcohol in mobile phase, but also the structural differences in racemates can have a pronounced effect on enantiomeric separation. ADMPC-CSP is a suitable CSP for the optical resolution of chiral tetrahedral cluster by HPLC.     

Application and comparison of immobilized and coated amylose tris-(3,5-dimethylphenylcarbamate) chiral stationary phases for the enantioselective separation of beta-blockers enantiomers by liquid chromatography

A direct liquid chromatographic enantioselective separation of a set of β-blocker enantiomers on the new immobilized and conventional coated amylose tris-(3,5-dimethylphenylcarbamate) chiral stationary phases (Chiralpak IA and Chiralpak AD, respectively) was studied using methanol as mobile phase and ethanolamine as an organic modifier (100:0.1, v/v). The separation, retention and elution order of the enantiomers on both columns under the same conditions were compared. The effect of the immobilization of the amylose tris-(3,5-dimethylphenylcarbamate) chiral stationary phase on silica (Chiralpak IA) on the chiral recognition ability was noted when compared to the coated phase (Chiralpak AD) which possesses a higher resolving power than the immobilized one (Chiralpak IA). A few racemates, which were not or poorly resolved on the immobilized Chiralpak IA were most efficiently resolved on the coated Chiralpak AD. However, the immobilized phase withstand solvents like dichloromethane when used as an eluent or as a dissolving agent for the analyte. The versatility of the immobilized Chiralpak IA in monitoring reactions performed in dichloromethane using direct analysis techniques without further purification, workup or removal of dichloromethane was studied on a representative example consisting of the lipase-catalyzed irreversible transesterification of a β-blocker using either vinylacetate or isopropenyl acetate as acyl donor in dichloromethane as organic solvent.     

纤维素-三（3,5-二甲苯基氨基甲酸酯）手性固定相拆分氨鲁米特对映体

以纤维素-三（3,5-二甲苯基氨基甲酸酯）为手性固定相（Chiralcel OD-H）在高效液相色谱上拆分了氨鲁米特对映体。通过测定氨鲁米特在正己烷/乙醇和正己烷/异丙醇中的溶解度,优选了对样品溶解度大的流动相体系,并考察了流动相添加剂乙醇胺对拆分效果的影响。在此基础上进一步研究了流动相中乙醇含量、柱温和进样量对分离因子、分离度、不对称因子和理论板数的影响,从而确定了最佳的拆分条件：固定相为Chiralcel OD-H,流动相为正己烷/乙醇/乙醇胺（体积比为30：70：0.1）,柱温25℃。本文所得结果可为工业放大提供基础数据。     

Reversed-phase separations on cellulose tris(3,5-dimethylphenylcarbamate) chiral stationary phase

Summary The chiral separation of eight racemic compounds has been investigated on a cellulose tris(3,5-dimethylphenylcarbamate) chiral column under reversed-phase conditions. The discrimination mechanism under reversed-phase conditions is discussed. Addition of acid to the mobile phase is necessary for resolution of acidic racemic compounds. The presence of ion-pair reagent in the mobile phase is a key factor in the resolution of basic racemic compounds. Retention of the racemates is also affected by addition of acid or salt. The anion in buffer not only interacts with the racemete, but also with the polysaccharide derivative on the silica gel surface.     

Enantioseparation of Novel Chiral Tetrahedral Clusters on an Amylose Tris-(3,5-dimethylphenylcarbamate) Chiral Stationary Phase by Normal Phase HPLC

Introduction In recent years, chiral transition metal cluster has at-tracted a great deal of interests due to its potential ap-plication in asymmetric catalytic reaction.1-3 Producing catalysis for asymmetric induction using a rigid chiral framework would not only bring a basically conceptual breakthrough in the asymmetric catalysis, but also en-rich the methodology in the design of new chiral cata-lysts.4 So far, a lot of chiral clusters have been re-ported,5-9 but only a few of them have bee…     

几种新的外消旋过渡金属簇合物在纤维素衍生的高效液相色谱手性固定相上的直接拆分

正相条件下,在自制的涂敷型纤维素-三(3,5-二甲基苯基氨基甲酸酯)手性固定相上,首次直接拆分了几种新的外消旋过渡金属簇合物,考察了流动相中极性添加剂对手性拆分的影响.结果发现不仅不同立体结构的醇对手性簇合物的选择性不同,而且手性簇合物四面体骨架的四个顶点上的原子及与之配位的基团,对它们的色谱行为都有重要的影响.     

氟环唑外消旋体在纤维素-三(3,5-二甲基苯基氨基甲酸酯)手性固定相上的高效液相色谱法拆分

在纤维素-三(3,5-二甲基苯基氨基甲酸酯)（CDMPC）手性固定相上,分别采用正相、反相及极性有机相色谱模式对氟环唑外消旋体进行了拆分,并考察了流动相组成在手性识别中对手性分离的影响。氟环唑在Chiralcel OD-H手性色谱柱（填充CDMPC手性固定相）上采用反相色谱模式,以甲醇-水(体积比为80∶20)为流动相,获得了最佳的拆分,其两对对映异构体的分离度Rs分别为1.64和6.50。     

Enantioseparation of novel chiral tetrahedrane-type clusters on an amylose tris (Phenylcarbamate) chiral stationary phase

Summary Amylose tris(phenylcarbamate) (ATPC) coated on a small particle silica gel was prepared. This ATPC chiral stationary phase (ATPC-CSP) was found to be useful for the enantiomeric separation of some novel chiral tetrahedrane-type clusters. Moreover, the influence of mobile phase modifier and of the structure of chiral tetrahedrane-type clusters on the chiral separation and retention were investigated. The results suggest that not only the structure and concentration of alcohol in mobile phase, but also the subtle structural differences in racemates can have a pronounced effect on enantiomeric separation and retention.     

高效液相色谱手性固定相法直接拆分外消旋雷诺嗪

在反相以及正相争件下，利用自制的涂敷型纤维素-三（3，5-二甲基苯基氨基甲酸酯）手性固定相直接拆分了外消旋雷诺嗪，并考察了不同流动相对手性拆分的影响，特别是醇类物质对拆分影响。结果表明，醇的立体结构、极性对雷诺嗪的手性拆分均有影响。实验结果显示无论在正相条件下还是在反相条件下，涂敷型纤维素-三（3，5-二甲基苯基氨基甲酸酯）手性固定相均可以很好的拆分外消旋体雷诺嗪。     

Enantioseparation on cellulose dimethylphenylcarbamate-modified zirconia monolithic columns by reversed-phase capillary electrochromatography

This work reports the preparation of monolithic zirconia chiral columns for separation of enantiomeric compounds by capillary electrochromatography (CEC). Using sol–gel technology, a porous monolith having interconnected globular-like structure with through-pores is synthesized in the capillary column as a first step in the synthesis of monolithic zirconia chiral capillary columns. In the second step, the surface of the monolith is modified by coating with cellulose tris(3,5-dimethylphenylcarbamate) (CDMPC) as the chiral stationary phase to obtain a chiral column (CDMPCZM). The process of the preparation of the zirconia monolithic capillary column was investigated by varying the concentrations of the components of the sol solution including polyethylene glycol, water and acetic acid. CDMPCZM is mechanically stable and no bubble formation was detected with the applied current of up to 30 μA. The enantioseparation behavior of the CDMPCZM columns was investigated by separating a set of 10 representative chiral compounds by varying the applied voltage and pH and organic composition of the aqueous organic mobile phases.     

Enantioseparation of 15 organic phosphonate esters on the cellulose tris(3,5-dimethylphenyl carbamate) chiral stationary phase by HPLC

A series of 15 organic phosphonate esters enatiomers containing a carbon atom as a chiral center have been separated on the cellulose tris(3,5-dimethylphenyl carbamate) chiral stationary phase (CSP) in the normal phase by high performance liquid chromatography (HPLC). Both the capacity factor (k) and separation factor () of all solutes are presented. The influence of the substitutional group on the benzene ring attached to the chiral carbon atom and the steric hindrance of alkoxyl of the phosphonate ester on the chiral separation are discussed. Based on and different structure parameters, good agreement between the predicted values and the experimental ones is obtained. The most characteristic parameter influencing the chromatographic separation is chosen from many structure parameters by linear regression method of QSAR software. The probable mechanism of the chiral recognition is proposed.     

Enantiospecific resolution of rabeprazole by liquid chromatography on amylose-derived chiral stationary phase using photo diode array and polarimetric detectors in series

A simple and rapid liquid chromatographic method for enantioselective separation and determination of R-(+) and S-(−) enantiomers of rabeprazole in drugs and pharmaceuticals using photo diode array (PDA) and polarimetric detectors connected in series was developed. Chiralpak AD-H (250 mm × 4.6 mm) 5 μm column packed with amylose tris(3,5-dimethylphenyl carbamate) as a stationary phase and the mobile phase containing n-hexane:ethanol:2-propanol(75:15:10, v/v/v) in an isocratic mode has yielded baseline separation with resolution greater than 3.0 at 40 °C. Effects of ethanol, 2-propanol and temperature on separation were studied for optimum resolution. Lansoprazole sulphone was used as an internal standard (IS) for quantitative determination of individual enantiomers in bulk drugs as well as pharmaceutical formulations. The method was validated in terms of accuracy, precision and linearity according to ICH guidelines. The linearity of the method was studied in the range of 0.5-50 μg/ml and the r² was >0.9997. The inter- and intra-day precision of assay were determined (R.S.D. < 1%) and the recoveries were in the range of 99.63-100.22% with <1% R.S.D. The limits of detection (LOD) and quantification (LOQ) were 0.02 μg/ml and 0.07 μg/ml for both the enantiomers, respectively.     

Evaluation of the chiral recognition properties as well as the column performance of four chiral stationary phases based on cellulose (3,5-dimethylphenylcarbamate) by parallel HPLC and SFC

The performance of four commercially available cellulose tris(3,5-dimethylphenylcarbamate) based chiral stationary phases (CSPs) was evaluated with parallel high performance liquid chromatography (HPLC) and super critical fluid chromatography (SFC). Retention, enantioselectivity, resolution and efficiency were compared for a set of neutral, basic and acidic compounds having different physico-chemical properties by using different mobile phase conditions. Although the chiral selector is the same in all the four CSPs, a large difference in the ability to retain and resolve enantiomers was observed under the same chromatographic conditions. We believe that this is mainly due to differences in the silica matrix and immobilization techniques used by the different vendors. An extended study of metoprolol and structure analogues gave a deeper understanding of the accessibility of the chiral discriminating interactions and its impact on the resolution of the racemic compounds on the four CSPs studied. Also, a clear difference in enantioselectivity is observed between SFC and LC mode, hydrogen bonding was found to play an important role in the differential binding of the enantiomers to the CSPs.     

联苯类对映体在纤维素类手性固定相上的高效液 相色谱法直接拆分

涂敷纤维素-三(3,5-二甲基苯基氨基甲酸酯)于自制的球形氨丙基硅胶上,制备了手性固定相。用该固定相直接拆分了一系列外消旋联苯类保肝药物。考察了柱温和流动相中乙醇含量对样品的保留和立体选择性的影响,升高柱温或增大流动相中乙醇含量都会使对映体的保留因子和分离因子降低。氨考察榈的分离因子的对数与温度的倒数成线性关系。确定了对映体从流动相传递到固定相的吉布斯自由能变之差值、焓变之差值及熵变之差值。     

Resolution of naftopidil and bufuralol enantiomers by high-performance liquid chromatography on cellulose tris-(3,5-dimethylphenyl carbamate) column

The liquid Chromatographic resolution of the racemic cardiovascular drugs naftopidil and bufuralol to their corresponding enantiomers was achieved on cellulose tris-(3,5-dimethylphenyl carbamate) chiral stationary phase known as Chiralcel OD. The chiral recognition mechanism(s) involved between the chiral stationary phase and these drugs, which include hydrogen bonding, intercalative interactions, and steric interactions, among other factors, were discussed.     

L-N-(3,5-Dimethoxybenzoyl)isoleucine chiral stationary phase for separation of enantiomers by HPLC

Summary L-N-(3,5-dimethoxyoxybenzoyl)isoleucine, ionically bonded to γ-aminopropyl silica, has been tested as a chiral stationary phase for the separation of racemates by HPLC. The phase shows good selectivity towards different types of racemates and in particular for those having an electron-poor aromatic group in their molecule. The separation of benzoin racemate can be achieved on the developed chiral phase with an α value of 1.10.     

A novel stability-indicating HPLC method for the determination of enantiomeric purity of eluxadoline drug: Amylose tris(3,5-dichlorophenyl carbamate) stationary phase

A simple and sensitive stability-indicating chiral HPLC method has been developed and validated per International Conference on Harmonization guidelines for the determination of enantiomeric purity of eluxadoline (Exdl). The impact of different mobile phase compositions and chiral stationary phases on the separation of Exdl enantiomer along with process- and degradation-related impurities has been studied. Homogeneity of Exdl and stable results of Exdl enantiomer in all degraded samples reveal the fact that the proposed method was specific (stability indicating). Amylose tris(3,5-dichlorophenyl carbamate) stationary phase column Chiralpak IE-3 (150 × 4.6 mm, 3 μm) provided better resolution with polar organic solvents than cellulose derivative, crown ether, and zwitterion stationary phases and nonpolar solvents. The mobile phase consisted of acetonitrile, tetrahydrofuran, methanol, butylamine, and acetic acid in the ratio of 500:500:20:2:1.5 (v/v/v/v/v). Isocratic elution was performed at a flow rate of 1.0 mL/min, column temperature of 35°C, injection volume of 10 μL, and UV detection of 240 nm. The United States Pharmacopeia (USP) resolution of the Exdl enantiomer was found to be more than 4.0 within a 65-min run time. Exdl enantiomer detector response linearity over the concentration range of 0.859–4.524 μg/mL was found to be R² = 0.9985. The limit of detection, limit of quantification, and average percentage recovery values were established as 0.283 μg/mL, 0.859 μg/mL, and 96.0, respectively.     

Separation of Enantiomers of N-Protected Non-Protein Amino Acid Esters by Chiral High-Performance Liquid Chromatography

The high-performance liquid chromatographic separation of enantiomers of N-protected non-protein amino acid esters was investigated by using a cellulose tris(3,5-dimethylphenylcarbamate) chiral stationary phase column (Daicel Chiracel OD). The effect of the N-protecting groups and the ester groups on chiral discrimination was examined. The benzyloxycarbonyl (Z), 4-methoxybenzyloxycarbonyl, and 9-fluorenylmethoxycarbonyl derivatives gave good enantiomeric separations, while the formyl and t-butoxycarbonyl groups marred them. Almost all the alkyl esters examined and the benzyl ester gave enantiomeric separations better than or of the same order as the methyl ester. The N-Z-protected methyl esters of a number of non-protein -amino acids were well resolved using hexane–2-propanol as a mobile phase. The resolution of -amino acid derivatives was inferior to that of the isomeric -amino acid derivatives.