毛细管区带电泳法拆分手性药物环扁桃酯

近年来,随着不同种类的手性添加剂[1]在毛细管电泳(CZE)中的使用,毛细管电泳越来越显示出其强有力的手性拆分性能。具有特殊笼状结构并含有多个手性中心的环糊精及其衍生物是毛细电泳手性分离研究中最常采用的手性添加添[2-4]。本文合成了环糊精衍生物单3 O 苯基胺甲酰基 β CD[2]并以之作为手性选择剂分离了β CD及手性药物环扁桃酯。1　实验部分932 3 HVPS高压电源(山东省化工研究院),DD 2000型可调波长紫外检测器(中国科学院大连化学物理研究所),XWT型记录仪(上海大华仪表厂),pHS 25型酸度计(上海雷磁仪器厂),石英毛细管45cm…     

Enantiomeric separation by capillary electrophoresis with an electroosmotic flow-controlled capillary

Perfect control of electroosmotic flow (EOF) was achieved by dovetailing successive multiple ionic-polymer layer (SMIL) coated capillaries. The direction and magnitude of the EOF was perfectly controllable over the pH range 2-13. Zone diffusion was not observed, even if the inner wall of the dovetailed capillary was discontinuous, or if the sample zone passed through the connected part of the capillary because the RSDs of migration time, theoretical plates, symmetry factor and S/N of the marker were almost the same when seamless capillary and dovetailed capillary were compared. The dovetailed capillary was applied to cyclodextrin modified capillary zone electrophoresis. The control of the EOF enabled us to control both the resolution and the migration order of the enantiomers. The migration time was also controllable and, therefore, the best condition between separation and migration time could be determined by controlling the EOF. Partial filling affinity electrokinetic chromatography with a protein used as a chiral selector was also studied. The migration of the pseudostationary phase was controllable by EOF, and detection of the solute at 214 nm was possible. Therefore, the EOF-controlled dovetailed capillary has great potential to expand the application of the separation technique.     

Enantiomeric separation of racemic clenbuterol by capillary zone electrophoresis

A method for capillary electrophoretic enantiomeric separation of a racemic clenbuterol has been established with hydroxypropyl-β-cyclodextrin as the chiral selector. General equations and data analysis are presented to relate mobility to the equilibrium constants in simple binding equilibria and used to determine binding constants and thermodynamic parameters for host-guest complexation of clenbuterol enantiomers with hydroxypropyl-β-cyclodextrin as a selector. The effects of β-cyclodextrin type and concentration, buffer type, concentration and pH, as well as separation voltage and capillary temperature were investigated in detail. A maximal resolution of 6.78 was obtained. The binding constants of the host-guest complex of clenbuterol enantiomers with hydroxypropyl-β-cyclodextrin, K _R-CD and K _S-CD are 22.50 and 43.09 l mol^-1, respectively.     

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。     

Enantiomeric separation of omeprazole and its metabolite 5-hydroxyomeprazole using non-aqueous capillary electrophoresis

This study demonstrates the development and validation of a non-aqueous capillary electrophoresis (NACE) method for enantiomeric determination of omeprazole and its metabolite 5-hydroxyomeprazole. Heptakis-(2,3-di-O-methyl-6-O-sulfo)-beta-cyclodextrin (HDMS-beta-CD) was chosen as the chiral selector in an ammonium acetate buffer acidified with formic acid in methanol. Parameters such as CD concentration, concentration of buffer electrolyte, voltage and temperature were studied in order to optimize both the enantioresolution and migration times. An experimental design was utilized for method optimization, using software Modde 5.0. Validation of the developed method showed good linearity, which was tested over a concentration range of 2.5-500 microM. The regression coefficients for S-omeprazole, S-5-hydroxyomeprazole, R-omeprazole and R-5-hydroxyomeprazole were between 0.996 and 0.997. The limits of detection for the four enantiomers were in the range from 45 to 51microM and the limits of quantification were between 149 and 170 microM with UV detection at 301nm. Using a reduced temperature of 16 degrees C gave improved resolution values, reproducibility and also decreased the occurrence of current loss within the capillary. RSD values for peak migration time were calculated to be between 0.41 and 1.48% using an inter-day study.     

Enantiomeric separation of neutral hydrophobic dihydrofuroflavones by cyclodextrin-modified micellar capillary electrophoresis

The enantiomeric separations of several very hydrophobic dihydrofuroflavones were performed and optimized using cyclodextrin-modified micellar capillary electrophoresis. Overall, the greatest enantiomeric peak-to-peak separations for the greatest number of flavones were obtained with hydroxypropyl-gamma-cyclodextrin. The effects of cyclodextrin and sodium dodecyl sulfate concentration and pH were examined in order to optimize the separation conditions. The ratio of surfactant-to-cyclodextrin concentration affected the chiral discrimination of the system significantly, with increases in the derivatized cyclodextrin concentration generally enhancing resolution. Higher efficiencies were obtained with lower concentrations of surfactant and cyclodextrin, although enantioseparation optimization often required higher concentrations to be used. A highly acidic pH was necessary to effectively suppress the electroosmotic flow when operating in the reversed polarity mode. Experiments utilizing the normal polarity mode and higher pH produced no separations.     

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.     

Enantiomeric separation of furan derivatives and fused polycycles by cyclodextrin-modified micellar capillary electrophoresis

The enantiomeric separations of highly hydrophobic furan derivatives and polycycles were performed and optimized using CD-modified micellar CE. The most effective chiral selector for the enantiomeric separation of these analytes was hydroxypropyl-gamma-CD. The effects of CD and SDS concentration and organic modifier were examined in order to optimize the separation conditions. The ratio of CD to surfactant concentration affected the enantiomeric separation significantly, with increases in the derivatized CD concentration generally enhancing resolution. Addition of an organic solvent modifier to the run buffer served to increase the analytes' solubility and enhance the separation efficiency. A highly acidic pH was necessary to effectively suppress the EOF when operating in the reverse polarity mode.     

Enantiomeric separations by nonaqueous capillary electrophoresis

This paper reviews the recent advances in enantioseparations by nonaqueous capillary electrophoresis (NACE) and the effect of organic solvents on mobility of enantiomers, separation selectivity and resolution. In general, the enantioseparation systems in NACE are similar to those of aqueous capillary electrophoresis (CE) except pure organic solvents are used. The influence of important parameters such as concentration and type of chiral selectors, apparent pH, ionic strength, temperature, and control of electroosmotic flow is discussed. In addition, the reported applications of NACE separations of racemates are presented.     

Enantiomeric and isomeric separation of herbicides using cyclodextrin-modified capillary zone electrophoresis

Cyclodextrin-modified capillary zone electrophoresis (CD-CZE) was applied successfully to the enantiomeric and isomeric separation of three herbicides (imazaquin, diclofop and imazamethabenz). Commercially available cyclodextrins were evaluated for separation of the enantiomers and isomers of the three herbicides having varied molecular structures. The enantiomers of imazaquin and diclofop, and the isomers of imazamethabenz could be resolved with a resolution of ≥1.5. The resolution was found to depend on pH of the run buffer, cyclodextrin type and cyclodextrin concentration. By employing mixed cyclodextrins in the running buffer, the three herbicides were simultaneously separated in a single run. In addition, rapid (less than 3 min) enantiomeric separation is demonstrated using imazaquin as a model herbicide. The reported capillary electrophoresis (CE) methods are simple, rapid, efficient and reproducible and our results demonstrate that CE provides a powerful analytical tool for enantiomeric and isomeric separation of herbicides.     

Enantiomeric screening of racemic citalopram and metabolites in human urine by entangled polymer solution capillary electrophoresis: an innovatory robustness/ruggedness study

Several CE methods have been developed to achieve the chiral separation of citalopram (CIT) and its metabolites demethylcitalopram (DCIT), didemethylcitalopram (DDCIT), and citalopram N-oxide (CIT-NO). All of these compounds were present as racemic mixtures. The best method, which led to the first ever chiral screening of CIT, DCIT, DDCIT, and CIT-NO, involved the use of carboxymethyl-gamma-CD (CM-gamma-CD) and the entangled polymer hydroxypropylmethylcellulose (HPMC) as chiral and selectivity additives, respectively, in the buffer system. In an effort to improve the selectivity and sensitivity of the method, the chemical and instrumental parameters were optimized. The best conditions were short-end anodic hydrodynamic injection (6 s, 0.7 psi); as BGE pH 5, 20 mM phosphate buffer, 0.2% w/v CM-gamma-CD, 0.05% w/v HPMC; voltage of 28 kV with a ramp applied (0.4 s); cartridge temperature of 20 degrees C; detection at 205 nm. In addition, a simple and rapid achiral CE method for the determination of citalopram propionic acid (CIT-PA, the only anionic metabolite of CIT) is also reported for the first time. Prior to the electrophoretic procedure it was necessary to apply an extraction and preconcentration step to obtain analytes from the human urine samples. This was achieved using an optimized SPE process. Moreover, an innovatory experimental and statistical design approach, which involves the simultaneous evaluation of the global robustness and ruggedness effects, was applied. Both of the proposed methods proved to be very useful in the chiral pharmacokinetic screening of CIT and related metabolites in clinical human urine samples.     

Enantiomeric separation of citalopram base by supercritical fluid chromatography

The chiral separation of citalopram base by supercritical fluid chromatography on a semipreparative Chiralpak AD column was studied with the use of three alcohol‐type modifiers (methanol, ethanol, and 2‐propanol) with different volume percentages (5, 10, and 15%). The best separation was achieved when 10% 2‐propanol was used in the presence of 0.1% diethylamine as additive. Under these conditions, the resolution reached 2.15 and the selectivity was 1.388. In addition, other parameters that affected the retention and separation properties, i.e. temperature, pressure, and density, were studied in detail. At the same pressure, a decrease in the temperature improved the enantioselectivity as the experimental temperature range was below the isoelution temperature. However, the temperature dependence of the retention factor was complicated. As a rule, the retention factor decreased when the temperature increased at the same density. A satisfactory regression of the logarithm of the retention factor versus density and temperature was obtained using a simplified lattice‐fluid model. Surprisingly, the relationship between the Henry constant and density can be accurately correlated by using the same quadratic equation.     

Enantiomeric separation of glycyl dipeptides by capillary electrophoresis with cyclodextrins as chiral selectors

Uncharged cyclodextrins were tested as chiral selectors for the enantiomeric separation of 13 glycyl dipeptides with capillary electrophoresis. Initial experiments were performed on 10 mmol/L of a cyclodextrin in 0.1 mol/L phosphoric acid -0.088 mol/L triethanolamine. Some of the resolved dipeptides were nonaromatic, which is noteworthy since, to our knowledge, no examples of the separation of small, nonaromatic molecules have been published. Mobility difference plots for Gly-DL-Leu and Gly-DL-Phe with heptakis(2,6-di-O-methyl)-beta-cyclodextrin showed relatively flat profiles in a large concentration range, which is an advantage for the development of robust quantitative analytical methods. The use of a background electrolyte (BGE) solution with pH 3.0 gave irreproducible results for two of the dipeptides, the acidic Gly-DL-Asp and Gly-DL-Glu; this pH is not advisable for the development of robust methods for these two peptides. The need for purer chiral selectors was demonstrated by comparing different batches of heptakis(2,6-di-Omethyl)-beta-cyclodextrin from the same supplier. A BGE consisting of malonic acid and triethanolamine was introduced to give better buffer capacity than the original BGE at pH 3.0.     

Enantiomeric separation of synthetic 2,3-dihydroxy-3-phenylpropionate compounds by beta-cyclodextrin-modified capillary electrophoresis

A new capillary electrophoretic method was developed for enantiomeric separation and optical impurity analysis of three synthetic 2,3-dihydroxy-3-phenylpropionate compounds using native beta-cyclodextrin (beta-CD) as chiral selector and borate as a background electrolyte. The separation was carried out in uncoated capillary (58.5 cm x 75 microm I.D., effective length 48.5 cm). The results showed that beta-CD as the chiral selector exhibited good enantioselectivity and the baseline separation was obtained at pH 9.8, 200 mM borate buffer containing 1.7% beta-CD at applied voltage 15 kV and capillary temperature 20 degrees C within 15 min. The precision of each tested compound was less than 1.0% at migration time and 5.0% in corrected peak area and the accuracy of the method was in the range of 98.7-105%. Furthermore, the developed method was successfully applied to the determination of the undesirable trace (2S,3R)-(+)-form impurity in the synthetic (2R,3S)-(-)-2,3-dihydroxy-3-phenylpropionate samples.     

Enantiomeric separation by capillary electrophoresis using a crown ether as chiral selector.

This paper reviews chiral separations of primary amines by capillary electrophoresis and crown ether as chiral selector. Two possible mechanisms of chiral recognition by host-guest complexation are discussed: (i) The substituents of the crown ether act as barriers for the guest compounds, and (ii) lateral electrostatic interactions between host and guest occur. Experimental conditions affecting the separation are discussed in detail. A literature overview of practical applications is presented as well. More than 80 different primary amines were analyzed, whereupon the majority could be resolved using a screening method. It is shown that a synergistic effect on the resolution of chiral amines is observed when the chiral crown ether and cyclodextrins are simultaneously used in the same buffer system. This approach opens interesting perspectives for further method optimization.     

Enantiomeric separation of chiral peptide nucleic acid monomers by capillary electrophoresis with charged cyclodextrins

Direct chiral separation of chiral peptide nucleic acid (PNA) monomers has been achieved for the first time by capillary electrophoresis (CE) with charged cyclodextrins as chiral selectors added to the electrophoretic buffer. Selectively modified 6-deoxy-6-N-histamino-beta-cyclodextrin and sulfobutyl ether-beta-CD were successfully used as chiral selectors for the enantiomeric separation of chiral monomers based on different aminoethylamino acids bearing thymine or adenine as nucleobases. Chiral separations were obtained at low selector concentrations (1-3 mM) with good enantioselectivity and resolution factors. Separations were optimized as a function of pH in order to exploit the effect of the electrostatic interactions between the oppositely charged selector and selectand. The method has been applied to the analysis of the enantiomeric excess of chiral monomers used for the solid phase synthesis of chiral PNA oligomers. CE chiral analysis showed that a very high enantiomeric purity was generally achieved in the synthesis of all monomers, except for histidine and aspartic acid based monomers in which ca. 10% of the "wrong" enantiomer was always present.     

Enantiomeric separation of some common controlled stimulants by capillary electrophoresis with contactless conductivity detection

CE methods with capacitively coupled contactless conductivity detection (C⁴D) were developed for the enantiomeric separation of the following stimulants: amphetamine (AP), methamphetamine (MA), ephedrine (EP), pseudoephedrine (PE), norephedrine (NE) and norpseudoephedrine (NPE). Acetic acid (pH 2.5 and 2.8) was found to be the optimal background electrolyte for the CE‐C⁴D system. The chiral selectors, carboxymethyl‐β‐cyclodextrin (CMBCD), heptakis(2,6‐di‐O‐methyl)‐β‐cyclodextrin (DMBCD) and chiral crown ether (+)‐(18‐crown‐6)‐2,3,11,12‐tetracarboxylic acid (18C6H₄), were investigated for their enantioseparation properties in the BGE. The use of either a single or a combination of two chiral selectors was chosen to obtain optimal condition of enantiomeric selectivity. Enantiomeric separation of AP and MA was achieved using the single chiral selector CMBCD and (hydroxypropyl)methyl cellulose (HPMC) as the modifier. A combination of the two chiral selectors, CMBCD and DMBCD and HPMC as the modifier, was required for enantiomeric separation of EP and PE. In addition, a combination of DMBCD and 18C6H₄ was successfully applied for the enantiomeric separation of NE and NPE. The detection limits of the enantiomers were found to be in the range of 2.3–5.7 μmol/L. Good precisions of migration time and peak area were obtained. The developed CE‐C⁴D method was successfully applied to urine samples of athletes for the identification of enantiomers of the detected stimulants.     

Enantiomeric separation of dansylamino acids by capillary zone electrophoresis based on complexation with cyclodextrins

Summary The enantiomeric separation ability of unmodified and methylated cyclodextrins (CDs) during capillary zone electrophoresis (CZE) was investigated using twelve dansylamino acids. Unmodified - and -CDs exhibited high enantioselectivities. -CD could scarcely separate the enantiomers before and after dimethylation, but obtained enantioselectivity after trimethylation. On the other hand, dimethylation of -CD removed much of its high enantioselectivity. Moreover, the chemical modifications produced a reverse in the migration order of the enantiomers. The inclusion of dansyl-DL-phenylalanine with CDs was evaluated using 600 MHz ¹H NMR spectroscopy.     

Enantiomeric separation of D- and L-carnitine by integrating on-line derivatization with capillary zone electrophoresis.

A new capillary zone electrophoretic method has been developed for the enantiomeric separation and quantification of enantiomers of carnitine, D- and L-carnitine were derivatized with 9-fluorenylmethyl chloroformate in a flow system, working on-line with the capillary electrophoretic equipment. The separation was performed using a selective chiral buffer containing 2,6-dimethyl-beta-cyclodextrin (heptakis). Triethanolamine was used as electroosmotic modifier and the separation was carried out in a uncoated capillary. Under the optimal conditions the resolution between D- and L-carnitine was 1.2 and the limits of detection for both isomers were about 5.0 microM. The proposed method was applied to the determination of D-carnitine in excess of L-carnitine in synthetic samples, and the results demonstrated that the maximal D-:L-carnitine ratio determined was approximately 1:100.     

Enantiomeric separation of alanyl and leucyl dipeptides by capillary electrophoresis with cyclodextrins as chiral selectors

Eight neutral cyclodextrins were tested for the enantiomeric separation of alanyl and leucyl dipeptides by capillary electrophoresis at pH 3, and seven out of the eight cyclodextrins proved suitable for the separation of one or more of the dipeptide enantiomer pairs. The best results were obtained with heptakis(2,6-di-O-methyl)-beta-cyclodextrin. The dipeptides that were separated were mainly the aromatic and the more lipophilic aliphatic dipeptides. Mobility difference plots at pH 3.0 with malonic acid-triethanolamine as background electrolyte showed that the aromatic dipeptides had higher affinities for the cyclodextrin than the nonpolar, aliphatic dipeptides. The results suggested that, under the conditions applied, the C-terminal amino acid rather than the N-terminal one is involved in the chiral discrimination.