On the use of dispersed nanoparticles modified with single layer beta-cyclodextrin as chiral selecor to enhance enantioseparation of clenbuterol with capillary electrophoresis

A new strategy for chiral separation by capillary electrophoresis employing modified-nanoparticles as chiral selector is described for clenbuterol analysis. Nanoparticles modified with β-cyclodextrin (β-CD) form a large surface area platform to serve as a pseudostationary chiral phase, which can be applied for the enhancement of the enantioseparation. The application of four kinds of nanoparticles was investigated (multi-walled nanotubes (MWNTs), polystyrene (PS), TiO₂ and Al₂O₃) modified with single layer β-CD as chiral selector in the enantioseparation of clenbuterol by capillary electrophoresis (CE). Successful clenbuterol enantioseparation could be achieved with the β-CD-modified MWNTs as chiral selector. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) confirmed the β-CD modification of the nanoparticles. The effects of nanoparticles, surfactant, chiral selector (β-CD) and run buffer were studied in relation to the enantiomeric separation of clenbuterol. This study opens attractive perspectives for the use of modified nanoparticles for chiral separational purposes in CE.     

毛细管区带电泳对手性药物盐酸美西律和盐酸异博定的对映体分离

应用环糊精-毛细管区带电泳体系对手性药物盐酸美西律和盐酸异博定的对映体分离进行了研究。结果表明, 在所研究的手性选择剂α-环糊精, β-环糊精, 二甲基-β-环糊精, 羟丙基β-环糊精和γ-环糊精中, 羟丙基β-环糊精对所研究的手性药物分离效果较好。对盐酸美西律和盐酸异博定的最佳羟丙基-β-环糊精浓度分别为30mmol/L和9mmol/L, 最佳缓冲溶液浓度为100mmol/L Tris-H3PO4(pH2.3)。向缓冲溶液中加入0.05%羟丙基纤维素(HPLC)可改善分离。盐酸美西律获得了接近基线的手性分离, 而盐酸异博定亦获得了较好的分离。     

Evaluation of the enantioselectivity of glycogen-based dual chiral selector systems towards basic drugs in capillary electrophoresis

Several chiral reagents including cyclodextrins (CDs) and derivatives, crown ethers, proteins, chiral surfactants and polymers have been involved in dual selector systems for enantioseparation of a series of chiral compounds by capillary electrophoresis (CE). In comparison to the chiral reagents above-mentioned, there is no report concerning the use of polysaccharides in dual chiral CE system. In this paper we first investigate the enantioselectivity of polysaccharide-based dual selector systems towards some chiral drugs. During our recent work, glycogen belonging to the class of branched polysaccharides has been used as a novel chiral selector in CE. In this study, three glycogen-based dual chiral CE systems have been established for enantiomeric separations of several racemic basic drugs consisting of duloxetine, cetirizine, citalopram, sulconazole, laudanosine, amlodipine, propranolol, atenolol and nefopam. These three dual systems combined glycogen (neutral polysaccharide) with chondroitin sulfate A (CSA, ionic polysaccharide), β-CD and HP-β-CD, respectively. It was found that the dual system of glycogen/CSA exhibited good enantioselective properties toward the tested drugs. More importantly, compared to the single selector systems, synergistic effect was observed when glycogen was used with CSA for most of the analytes. This indicated the enhancement of enantioseparation observed for these analytes in glycogen/CSA system might be due to some favorable interaction effects between glycogen and CSA. Moreover, in order to evaluate the stereoselectivity of glycogen/CSA, the influences of buffer pH and selector concentration on enantioseparation of the studied drugs were also investigated.     

加压毛细管电色谱法分离1-甲基-3-苯基丙胺对映体

运用毛细管电色谱(pCEC)模式,以羟丙基-β-环糊精(HP-β-CD)作为手性选择剂,对1-甲基-3-苯基丙胺对映体进行手性分离。1-甲基-3-苯基丙胺对映体在最佳的条件下如:手性选择剂浓度10g/L、流动相配比:V(乙腈)∶V(磷酸盐体系)=60∶40溶液(5mmol/L)、背景电解质pH=7.6、柱温16℃和分离电压10kV达到了基线分离,该方法重现性好、简便、快捷。     

Comparative NMR and MS studies on the mechanism of enantioseparation of propranolol with heptakis(2,3-diacetyl-6-sulfo)-β-cyclodextrin in capillary electrophoresis with aqueous and non-aqueous electrolytes

In our recent studies, the reversal of the enantiomer migration order (EMO) was observed with heptakis (2,3-dimethyl-6-sulfo)-β-CD (HDMS-β-CD) when aqueous electrolyte was changed with nonaqueous electrolyte in CE. One-dimensional rotating frame nuclear Overhauser effect spectroscopy experiments prevailed that an inclusion complex was formed between the analyte and the chiral selector in the aqueous buffer, whereas an external complex resulted when a methanolic electrolyte was employed. In the case of the similarly substituted heptakis (2,3-diacetyl-6-sulfo)-β-CD (HDAS-β-CD), the external complex was observed in the aqueous buffer but an inclusion complex was formed in methanolic electrolyte. In contrast to heptakis (2,3-dimethyl-6-sulfo)-β-CD, no reversal of the enantiomer migration order was observed with HDAS-β-CD. In the present study, further mechanisms of enantioselective recognition and separation of propranolol enantiomers with HDAS-β-CD were investigated by using different techniques of nuclear magnetic resonance spectroscopy and high-resolution mass spectrometry. To the best of our knowledge, enantioselective nuclear Overhauser effect was observed for the first time in this study.     

毛细管电泳法和高效液相色谱法拆分联萘二酚酸对映体

采用毛细管电泳法和高效液相色谱法直接拆分2,2′-二羟基-1,1′-联二萘-3,3′-二甲酸(HBNC)对映体.以四种不同的β-环糊精为手性添加剂,考察环糊精的种类与浓度、缓冲液pH值及浓度、分离电压、温度等因素对HBNC分离的影响.结果表明:采用10 mmol/L磺丁基醚-β-环糊精+20 mmol/L磷酸盐缓冲液(pH=7.0),20 kV分离电压,HBNC对映体在20 min内达到基线分离,分离度达到3.31.采用(S)-叔-亮氨酸基-(S)-1-(α-萘基)乙胺手性柱,正己烷-乙醇-三氟乙酸(97∶3∶0.2,V/V)流动相,HBNC对映体在40 min内也基本达到基线分离.     

Enantiomeric separation of (R, S)-naproxen by recycling high speed counter-current chromatography with hydroxypropyl-β-cyclodextrin as chiral selector

Recycling high speed counter-current chromatography (HSCCC) was successfully applied to resolution of (R, S)-naproxen (NAP) using hydroxypropyl-β-cyclodextrin (HP-β-CD) as chiral selector. The two-phase solvent system composed of n-hexane-ethyl acetate-0.1 mol L(-1) phosphate buffer solution with pH=2.67 (8:2:10, v/v/v) was selected. Influence factors for the chiral separation process were investigated, including concentration of HP-β-CD, equilibrium temperature and pH of aqueous phase. Suitable elution mode was selected for HSCCC enantioseparation of (R, S)-NAP. Under optimum separation conditions, 29 mg of (R, S)-NAP was separated using preparative recycling HSCCC with the molar ratio HP-β-CD/NAP racemate 83:1. Technical details for recycling elution mode were discussed as for chiral HSCCC separation. The purities of both (S)-NAP and (R)-NAP were over 99.5% as determined by HPLC. Enantiomeric excess of (S)-NAP and (R)-NAP reached 99.4%. Recovery for NAP enantiomers from HSCCC fractions was 82-89%, yielding 13 mg of (S)-NAP and 12 mg of (R)-NAP.     

Computer-aided molecular modeling study of enantioseparation of iodiconazole and structurally related triadimenol analogues by capillary electrophoresis: Chiral recognition mechanism and mathematical model for predicting chiral separation

Chiral separation of iodiconazole, a new antifungal drug, and 12 new structurally related triadimenol analogues had been developed by capillary electrophoresis (CE) using hydroxypropyl-γ-cyclodextrin (HP-γ-CD) as the chiral selector. The effect of structural features of analytes on Δt and R_s was studied under the optimum separation conditions. Using molecular docking technique and binding energy calculations, the inclusion process between HP-γ-CD and enantiomers was investigated and chiral recognition mechanisms were discussed. The results suggest that hydrogen bonding between fluorine at position 4 of the phenyl group beside the chiral carbon and the hydroxyl group on the HP-γ-CD rim and face to face π–π interactions between two phenyl rings highly contributed to the enantiorecognition process between HP-γ-CD and iodiconazole. The N-methyl group beside chiral carbon also played an important role in enantiomeric separation. Additionally, the big difference in binding energy (ΔΔE) highly contributed to good separation in the presence of HP-γ-CD chiral selector, which may be a helpful initial guide for chiral selector selection and predicting the result of enantioseparation. Furthermore, the new mathematical equation established based on the results of molecular mechanics calculations exhibited good capability in predicting chiral separation of these triadimenol analogues using HP-γ-CD mediated CE.     

Enantioseparation Of Aromatic Dipeptides Using Carboxymethyl-β-Cyclodextrin Polymer As Chiral Selector By Capillary Electrophoresis

ABSTRACT

Chiral separation of peptides is of interest because of the different biological activity of enantiomers. In this report, several underivatized dipeptides with benzene moieties were optically resolved by employing carboxymethyl-β-cyclodextrin polymer(CM-β-CD polymer) as chiral selector. The effects of different cyclodextrin types, selector concentration, buffer pH, and organic additive were examined. Selector concentration and buffer pH played significant roles in resolution. Enantioseparation was found to be negatively influenced by adding the organic additive into running buffer and even completely lost at the organic additive content of 16%. It was also noted that the dipeptides with short chain in the vicinity of the second chiral carbon atom showed better chiral resolution by using CM-β-CD polymer than by using either carboxyethyl-β-CD or succinylated-β-CD. Simultaneous chiral separation of a mixture of DL-Ala-DL-Phe and DL-Leu-DL-Phe was also obtained using 27 mg/ml CM-β-CD polymer in the running buffer at pH5.12.     

新型三唑类抗真菌活性化合物毛细管电泳手性拆分及手性识别机理分子模拟研究

研究了7种新型三唑类抗真菌活性化合物的毛细管电泳法手性分离,利用计算机辅助分子模拟技术研究拆分机理。考察了8种中性环糊精手性添加剂,只有2,6-二甲基-β-环糊精对7种活性化合物都有手性识别能力。在30mmol/L NaH2PO4缓冲液中含2,6-二甲基-β-环糊精30mmol/L,用H3PO4调至pH 2.2,温度20℃,电压20kV,在此条件下7种活性化合物都能达到手性分离,其中4种活性化合物能达到基线分离(Rs>1.5)。应用计算机辅助分子模拟软件Discovery Studio 2.5/Sybyl/Gold模拟2,6-二甲基-β-环糊精与7种活性化合物主客体包结过程,并计算相互结合能,探讨手性识别机理,发现拆分结果与结合能的差异有关,结合能差异越大拆分结果越好。     

Separation of enantiomers of ephedrine by capillary electrophoresis using cyclodextrins as chiral selectors: comparative CE, NMR and high resolution MS studies

The enantiomer migration order (EMO) of ephedrine was investigated in the presence of various CDs in CE. The molecular mechanisms of chiral recognition were followed for the ephedrine complexes with native α- and β-CD and heptakis(2,3-di-O-acetyl-6-O-sulfo)-β-CD (HDAS-β-CD) by CE, NMR spectroscopy and high-resolution MS. Minor structural differences were observed between the complexes of ephedrine with α- and β-CD although the migration order of enantiomers was opposite when these two CDs were applied as chiral selectors in CE. The EMO was also opposite between β-CD and HDAS-β-CD. Significant structural differences were observed between ephedrine complexes with the native CDs and HDAS-β-CD. The latter CD was advantageous as chiral CE selector not only due to its opposite electrophoretic mobility compared with that of the cationic chiral analyte, but also primarily due to its enhanced chiral recognition ability towards the enantiomers of ephedrine.     

Borate Complexation and Mixed Cyclodextrin Additives for Chiral Separation of Propranolol and Its Metabolites by Capillary Electrophoresis

A buffer system of borate with charged (carboxymethyl-β-CD) and uncharged (β-CD) cyclodextrins (CDs) was employed in the chiral resolution and separation of propranolol and its selected major metabolites. By appropriate choice of buffer and additive conditions, chiral resolution of all of the compounds studied was achieved in a single analysis, where near baseline resolution was found for the difficult to resolve propranolol-glycol (Pr-glycol). This has not been observed in previous studies of propranolol and its metabolites.     

Analysis of enantiomers in biological matrices by charged cyclodextrin-mediated capillary zone electrophoresis in column-coupling arrangement with capillary isotachophoresis

The possibility to apply charged chiral selector as buffer additive in capillary zone electrophoresis (CZE) on-line coupled with capillary isotachophoresis (CITP) was studied. Enantioseparations and determinations of trace (ng/ml) antihistaminic drugs [pheniramine (PHM), dimethindene (DIM), dioxopromethazine (DIO)] present in samples of complex ionic matrices (urine) served as model examples. A negatively charged carboxyethyl-β-cyclodextrin (CE-β-CD) was used as a chiral selector in analytical CZE stage following upon a sample pretreatment by CITP (preconcentration of the analytes from 5 to 20-times diluted urine samples, partial sample clean up removing macroconstituents from the sample matrices). A high recognition capability of the oppositely charged CE-β-CD was demonstrated by enantioselective retardation of the drugs in presence of micro-and semi-macroconstituents migrating in CZE stage and detectable by UV detector. In this way, enantiomers of the drugs could be easily separated and determined. Due to lack of interferences between the drugs and sample-matrix constituents in presence of charged CE-β-CD, demands on both spacers in CITP step and multiple column-switching were minimized. CITP-CZE method with charged selector appeared to be a useful analytical approach for the trace enantiomers in complex ionic matrices as it combined enhanced separation selectivity and sample loadabitlity with high separation efficiency and provided favorable performance parameters including sensitivity, linearity, precision, accuracy/recovery and robustness with minimal demands on sample preparation. Analysis of urine sample taken from a patient treated by PHM, showing concentration profile of PHM enantiomers and their metabolites, illustrated potentialities of the method in clinical research.     

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.     

基于非手性离子液体的毛细管电泳法拆分3种手性药物

建立了以非手性离子液体1-正丁基-3-甲基咪唑氯(［BMIM］Cl)为手性分离的添加剂、β-环糊精作为手性选择剂的毛细管区带电泳(CZE)分离扑尔敏、氯霉素前体和氧氟沙星3种对映体的方法,并与未添加［BMIM］Cl的CZE分离情况进行了对比研究。发现［BMIM］Cl对手性药物的拆分有协同作用,不仅能够增加对映体的分离度,还能有效地抑制毛细管内壁对样品分子的吸附作用,改善峰形。采用离子液体辅助手性选择剂(尤其是环糊精)的CZE改进方法,为其他毛细管电泳难以分离的手性药物的分离分析提供了新的方法。     

Synthesis and application of a novel single-isomer mono-6-deoxy-6-(3R,4R-dihydroxypyrrolidine)-β-cyclodextrin chloride as a chiral selector in capillary electrophoresis

A novel positively charged single-isomer of β-cyclodextrin, mono-6-deoxy-6-(3R,4R-dihydroxypyrrolidine)-β-CD chloride (dhypy-CDCl), was synthesized and employed as a chiral selector for the first time in capillary electrophoresis (CE) for the enantioseparation of anionic and ampholytic acids. The effects of the running buffer pH, chiral selector concentration, analyte structure and organic modifier on the enantioseparation were studied in detail. The chiral selectivity and resolution for most of the studied analytes decreased as the buffer pH increased in the range of 6.0–9.0. Increasing selector concentration led to decreased effective mobility, increased chiral selectivity and resolution for most of the studied analytes. Moreover, the hydroxyl groups located on the dihydroxypyrrolidine substituent of the dhypy-CDCl could have influence on the chiral separation.     

Enantiomeric Separation of β-Amino Alcohols by Capillary Electrophoresis Using DM-β-CD as Chiral Selector

Enantiomeric separations of several β-amino alcohol drugs, i.e., phenylephrine, epinephrine, norepinephrine, synephrine, and chlorprenaline were performed by capillary electrophoresis using DM-β-CD as a chiral selector. Five test solutes were baseline resolved in six minutes. The effects of DM-β-CD concentration, pH value, ionic strength of the buffer, and the type of β-CDs on resolution were investigated. The results indicated that DM-β-CD is suitable for enantiomeric separation of β-amino alcohols containing a phenyl group on the chiral atom. Enantiorecognition mechanisms for test solutes are also discussed.     

Enantioseparation of Reduced Haloperidol by Capillary Zone Electrophoresis with Dimethyl-β-Cyclodextrin

Chiral separation of reduced haloperidol (RHP), an optically active metabolite from haloperidol, by capillary electrophoresis is described. RHP was separated on an uncoated capillary with dimethyl-β-cyclodextrin (dimethyl-β-CD) in Tris phosphate buffer using PEG 6000 as an organic additive. Several parameters affecting the separation of RHP were studied, including pH and concentration of buffer, buffer additive, and concentration of chiral selector. The migration order of the resolved RHP was assigned with reference RHP enantiomers.     

Influence of the Buffer Organic Cation on the Chiral Separation of Some Basic Drugs by Capillary Zone Electrophoresis

This paper addresses the influence of small organic cations in the background electrolyte (BGE) on chiral separation by capillary zone electrophoresis (CZE). Seven basic drugs, viz. alprenolol, amphetamine, anisodamine, isoprenaline, pinacidil, synephrine, and verapamil were used as test compounds with hydroxylpropyl-β-cyclodextrin (HP-β-CD) as the chiral selector. Resolution of the chiral test compounds was studied at pH 2.5 in the presence of Tris, ethanolamine, diethanolamine, triethanolamine, diethylamine, and triethylamine, which exist in their cationic forms at this pH value. Among the six cationic additives studied, triethylamine is most effective in enhancing resolution. A tentative mechanism of the effect is proposed.     

Separation of chiral drugs with sulfobutylether-β-cyclodextrin bycapillary zone electrophoresis

IntroductionChaedcyclodextrlnswerefirstIntroducedby几rabelforchlralseparationofamlnoacids,andthechargedCDcommonlyusednowdaysarecarboxymethyl－p－CD（CM－p－CD）,p－CD－phosphate,Y－CD－phosphate,sulfobutylether－p－cyclodextrln（SBE－p－CD）etc．...