Development and validation of a nonaqueous capillary electrophoretic method for the enantiomeric purity determination of a synthetic intermediate of new 3,4-dihydro-2,2-dimethyl-2H-1-benzopyrans using a single-isomer anionic cyclodextrin derivative and an ionic liquid

The enantiomeric purity determination of a synthetic intermediate of new 3,4-dihydro-2,2-dimethyl-2H-1-benzopyrans, i.e. 4-amino-2,2-dimethyl-6-ethoxycarbonylamino-3,4-dihydro-2H-1-benzopyran, was successfully carried out using an anionic cyclodextrin (CD) derivative combined with a chiral ionic liquid (IL). In order to obtain high resolution and efficiency values, the addition of a chiral IL, i.e. ethylcholine bis(trifluoromethylsulfonyl)imide (EtChol NTf₂), to the background electrolyte containing heptakis(2,3-di-O-methyl-6-O-sulfo)-β-CD (HDMS-β-CD) was found to be essential. A simultaneous increase in separation selectivity and enantioresolution seems to indicate a synergistic effect of HDMS-β-CD and EtChol NTf₂. The best enantioseparation of the key intermediate was achieved using a methanolic solution of 0.75 M formic acid, 10 mM ammonium formate, 1.5 mM HDMS-β-CD and 5 mM EtChol NTf₂. Levamisole was selected as internal standard. The optimized conditions allowed the determination of 0.1% of each enantiomer in the presence of its stereoisomer using the method of standard additions. The NACE method was then fully validated with respect to selectivity, response function, trueness, precision, accuracy, linearity and limits of detection and quantification.     

Enantioseparation of solriamfetol and its major impurity phenylalaninol by capillary electrophoresis using sulfated gamma cyclodextrin

R-solriamfetol is a recently approved drug used for the treatment of excessive sleepiness associated with narcolepsy and sleep apnea. Herein, a capillary electrophoretic method was developed, enabling the simultaneous analysis of the API and its S-enantiomer in addition to the enantiomers of its major impurity phenylalaninol. Twenty-nine different cyclodextrins (CDs), including native, neutral, and charged ones were screened as potential chiral selectors, and the best results were obtained with sulfated CDs. Randomly sulfated-β-CD exhibited outstanding enantioresolution, the peaks of phenylalaninol enantiomers inserted between the two peaks of solriamfetol enantiomers, while sulfated-γ-CD (S-γ-CD) showed remarkable resolution values in a much shorter analysis time with the optimal enantiomer migration order. Among the single isomer sulfated CD derivatives, substituent dependent enantiomer migration order reversal could also be observed in the case of heptakis(6-O-sulfo)-β-CD (HS-β-CD) or heptakis(2,3-O-dimethyl-6-O-sulfo)-β-CD (HDMS-β-CD) with R-,S-solriamfetol, and heptakis(2,3-O-diacetyl-6-O-sulfo)-β-CD (HDAS-β-CD) resulting S-,R-solriamfetol migration order. The sulfated-γ-CD system was chosen for method optimization applying orthogonal experimental design. The optimized method (45 mM Tris-acetate buffer, pH 4.5, 4 mM S-γ-CD, 21°C, +19.5 kV) was capable for the baseline separation of solriamfetol and phenylalaninol enantiomers within 7 min. The optimized method was validated according to the ICH guidelines and successfully applied for the analysis of pharmaceutical preparation (Sunosi^® 75 mg tablet), thus it may serve as a routine procedure for the laboratories of regulatory authorities as well as in Pharmacopoeias.     

Enantioselective determination of modafinil in pharmaceutical formulations by capillary electrophoresis, and computational calculation of their inclusion complexes

A fast capillary electrophoretic method is described for the separation and determination of the enantiomers of the novel wake-promoting agent, modafinil. Several parameters affecting the separation were studied, including the type and concentration of chiral selector, buffer pH, buffer concentration, voltage and temperature. Good chiral separation of the racemic mixture was achieved in less than 5 min with resolution factor Rs?=?2.51, using a bare fused-silica capillary and a background electrolyte (BGE) of 25 mM H₃PO₄?1 M tris solution; pH 8.0; containing 30 mg mL^?1 of sulfated-β-cyclodextrin (S-β-CD). The separation was carried out in normal polarity mode at 25 ^?C, 18 kV and using hydrostatic injection. Acceptable validation criteria for selectivity, linearity, precision, and accuracy were included. The developed method was successfully applied to the assay of enantiomers of modafinil in pharmaceutical formulations. The computational calculations for the enantiomeric inclusion complexes rationalized the reasons for the different migration times between the modafinil enantiomers.     

Analysis of repaglinide enantiomers in pharmaceutical formulations by capillary electrophoresis using 2,6-di-o-methyl-β-cyclodextrin as a chiral selector

This study used the general applicability of 2,6-didi-o-methyl-β-cyclodextrin (DM-β-CD) as the chiral selector in capillary electrophoresis for fast and efficient chiral separation of repaglinide enantiomers. A systematic study of the parameters affecting separation was performed with UV detection at 243 nm. The optimum conditions were determined to be 1.25% (w/v) DM-β-CD in 20 mM sodium phosphate (pH 2.5) as the running buffer and separation voltage at 20 kV. DM-β-CD had the best enantiomer resolution properties under the tested conditions, whereas other β-cyclodextrins showed inferior performances or no performance. The proposed method had a linear calibration curve in the concentration range of 12.5-400 μg/mL. The limit of detection was 100 ng/mL. The intra-day and inter-day precisions were 2.8 and 3.2%, respectively. Recoveries of 97.9-100.9% were obtained. The proposed method was fast and convenient, and was determined to be efficient for separating enantiomers and applicable for analyzing repaglinide enantiomers in quality control of pharmaceutical production.     

Enantiomeric analysis of rivastigmine in pharmaceuticals by cyclodextrin-modified capillary zone electrophoresis

Chiral separation method development is usually very time-consuming due to the diversity in chemical structures of pharmaceutical drug substances as well as the suitable separation conditions and the problem to choose the appropriate chiral selector. This paper shows capillary zone electrophoresis (CZE) which was developed for chiral separation of a basic compound - rivastigmine (RIV) using 30 cm × 50 μm i.d. polyacrylamide (PAA)-coated fused-silica capillary (effective length 20 cm), amine-modified phosphate buffer of pH 2.5 and sulfated-β-CD (S-β-CD) as chiral selector. Other selected native or derivatized cyclodextrins (CDs) were also tested: β-CD (5, 30 mM), carboxymethyl-β-CD (5, 30 mM), dimethyl-β-CD (15 mM), hydroxypropyl-β-CD (5, 30 mM), hydroxypropyl-α-CD (5, 30 mM) and hydroxypropyl-γ-CD (5, 30 mM). Complete enantiomeric separation of RIV was achieved at 20 kV, 18 °C and detection at 200 nm within 8 min with R.S.D. for the absolute migration time reproducibility of less than 2.1%. Rectilinear calibration range was 5.0-500.0 μM of each enantiomer (r = 0.9994-0.9995). The CZE method proposed was used for the control of chiral purity of pharmaceutically active S-RIV and for the analysis of Exelon caps preparation.     

Determination of aminoglutethimide enantiomers in pharmaceutical formulations by capillary electrophoresis using methylated-β-cyclodextrin as a chiral selector and computational calculation for their respective inclusion complexes

A capillary electrophoretic method for the separation of the aminoglutethimide (AGT) enantiomers using methylated-β-cyclodextrin (M-β-CD) as chiral selector is described. Several parameters affecting the separation were studied, including the type and concentration of chiral selector, buffer pH, voltage and temperature. Good chiral separation of the racemic mixture was achieved in less than 9 min with resolution factor Rs = 2.1, using a fused-silica capillary and a background electrolyte (BGE) of tris-phosphate buffer solution (50 mmol L⁻¹, pH 3.0) containing 30 mg mL⁻¹ of M-β-CD. The separation was carried out in normal polarity mode at 25 °C, 16 kV and using hydrostatic injection. Acceptable validation criteria for selectivity, linearity, precision, and accuracy/recovery were included. The proposed method was successfully applied to the assay of AGT enantiomers in pharmaceutical formulations. The computational calculations for the inclusion complexes of the R- and S-AGT-M-β-CD rationalized the reasons for the different migration times between the AGT enantiomers.     

Simultaneous Chiral Separation of Geometry Isomers and Enantiomers of Nateglinide by Capillary Electrophoresis with Mixture of CD Derivations as Chiral Selector

Abstract

A capillary electrophoresis (CE) method for the simultaneous separation of geometry isomers and enantiomers of nateglinide was built. Several different dyclodextrin (CD) derivatives were tested for the chiral separation of nateglinide, and it was proved that ionic CDs [i.e., carboxymethy-β-CD (CM-β-CD) and sulphonic-β-CD (S-β-CD)] could show better chiral selectivity for both geometry isomers and enantiomers than the neutral CDs. The separation of geometry of both isomers and enantiomers of nateglinide was obtained by CE in a 75-µm i.d. × 60 cm (effective length 45 cm) fused-silica capillary at 11 kV voltage, while 30 mM phosphate (pH = 8.38) acted as running buffer and a mixture of 40 mM S-β-CD + 21 mM CM-β-CD served as chiral selector. The detective wavelength was set at 254 nm.     

Optimization and Parameter Study for Chiral Separation by Capillary Electrophoresis

Orthogonal design and uniform design were used for the optimization of separation of enantiomers using 2,6-di-O-methyl-β-cyclodextrin (DM-β-CD) as a chiral selector by capillary zone electrophoresis. The concentration of DM-β-CD, buffer pH, running voltage, and capillary temperature were selected as variable parameters, their different effects on peak resolution were studied by the design methods. It was concluded that orthogonal design offers a rapid and efficient means for testing the importance of individual parameters and for determining the optimum operating conditions. However, for a large number of both factors and levels, uniform design is more efficient. The effect of addition of methanol and citric acid buffer on the separation of enantiomers was also examined.     

Separation of enantiomers of norephedrine by capillary electrophoresis using cyclodextrins as chiral selectors: comparative CE and NMR studies

In this study, the enantiomer migration order (EMO) of norephedrine (NEP) in the presence of various CDs was investigated by CE. NMR and CE techniques were used to analyze the mechanism of the chiral recognition between NEP enantiomers and four CDs, i.e., native α-CD, β-CD, heptakis(2,3-di-O-acetyl-6-O-sulfo)-β-CD (HDAS-β-CD), and heptakis(2,3-di-O-methyl-6-O-sulfo)-β-CD (HDMS-β-CD). EMO was reversed in the presence of α-CD and β-CD, although only minor differences in the structures of the complexes formed between NEP and these CDs could be derived from rotating frame nuclear Overhauser experiments (ROESY). The complexes between the enantiomers of NEP and the sulfated CDs, HDMS-β-CD, and HDAS-β-CD, were substantially different. However, EMO of NEP was identical in the presence of these CDs. HDAS-β-CD proved to be the most suitable chiral selector for the CE enantioseparation of NEP.     

A β-cyclodextrin covalent organic framework used as a chiral stationary phase for chiral separation in gas chromatography

Chiral covalent organic frameworks(CCOFs) featuring chirality, stability, and good porosity have attracted a considerable amount of attention due to their important applications, such as asymmetric catalysis, chiral separation, and chiral recognition. In this study, a β-cyclodextrin(β-CD) covalent organic framework(β-CD-COF) diluted with polysiloxane OV-1701 was explored as a novel chiral stationary phase(CSP) for gas chromatography(GC) separation of racemates. The β-CD-COF coated capillary colu...     

Chiral separation of anticholinergic drug enantiomers in nonaqueous capillary electrophoresis

Nonaqueous capillary electrophoretic (NACE) method for the separation of nine structurally similar chiral anticholinergic drugs was developed. The eight drug enantiomers were separated on baseline within 18 min using 20mM phosphoric acid and 10 mM NaOH, containing 10 mM heptakis(2,3-dimethyl-6-sulfato)-4beta-cyclodextrin (HDMS-beta-CD) in methanol. The results were compared with those obtained in the high performance liquid chromatography system.     

Method development and validation for the separation and determination of omeprazole enantiomers in pharmaceutical preparations by capillary electrophoresis

A new capillary zone electrophoresis (CZE) method for the separation of omeprazole enantiomers has been developed. Methyl-β-cyclodextrin (methyl-β-CD) was chosen as the chiral selector, and several parameters, such as cyclodextrin structure and concentration, buffer concentration, pH, and capillary temperature were investigated in order to optimize separation and run times. Analysis times, shorter than 8 min were found using a background electrolyte solution consisting of 40 mM phosphate buffer adjusted to pH 2.2, 30 mM β-cyclodextrin and 5 mM sodium disulphide, hydrodynamic injection, and 15 kV separation voltage. Detection limits were evaluated on the basis of baseline noise and were established 0.31 mg/l for the omeprazole enantiomers. The proposed method was applied to five pharmaceutical preparations with recoveries between 84 and 104% of the labeled contents.     

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。     

6-O-(2-hydroxybutyl)-β-CD as a chiral selector for nonaqueous capillary electrophoretic separation of chiral drugs

6-O-(2-hydroxybutyl)-β-CD, as a new β-cyclodextrin (β-CD) derivative, was successfully synthesized. It was used as a chiral selector to separate six chiral drugs, including propranolol, anisodamine, promethazine, ketoconazole, benzhexol, and fenfluramine in nonaqueous capillary electrophoresis (NACE). The effects of the organic solvent, the electrolytes, the concentrations of cyclodextrin derivatives, and the pH of the buffer on the chiral resolution (Rs) were investigated. The baseline separation of enantiomers, including propranolol (Rs = 2.26), anisodamine (Rs = 2.31), promethazine (Rs = 2.42), ketoconazole (Rs = 2.56), benzhexol (Rs = 3.38), and fenfluramine (Rs = 3.04), could be achieved using a buffer of 100 mmol · L^t−1 citric acid and 50 mmol · L^t−1 Tris (hydroxymethyl) aminomethane (Tris) at pH 4.6 containing 100 mmol · L^t−1 6-O-(2-hydroxybutyl)-β-CD in formamide (FA).     

α-萘基缩水甘油醚对映体的毛细管区带电泳手性拆分

建立了毛细管区带电泳手性拆分α-萘基缩水甘油醚对映体的方法.考察了不同手性拆分试剂对手性选择性的影响,实验结果表明,20 mmol/L H3PO4-三乙醇胺(pH 2.5)、2%(w/V)HS-β-CD、毛细管温度20 ℃、运行电压-18 kV为最佳分离条件,在该分离条件下α-萘基缩水甘油醚对映体实现基线分离.方法简便、准确,可用于α-萘基缩水甘油醚的手性拆分和对映体过量值(ee,%)测定.     

Enantioselective analysis of ofloxacin and ornidazole in pharmaceutical formulations by capillary electrophoresis using single chiral selector and computational calculation of their inclusion complexes

A capillary electrophoretic method for the separation of the enantiomers of both ofloxacin and ornidazole is described. Several parameters affecting the separation were studied, including the type and concentration of chiral selector, buffer pH, voltage and temperature. Good chiral separation of the racemic mixtures was achieved in less than 16 min with resolution factors Rs = 5.45 and 6.28 for ofloxacin and ornidazole enantiomers, respectively. Separation was conducted using a bare fused-silica capillary and a background electrolyte (BGE) of 50 mM H₃PO₄-1 M tris solution; pH 1.85; containing 30 mg mL⁻¹ of sulfated-β-cyclodextrin (S-β-CD). The separation was carried out in reversed polarity mode at 25 °C, 18 kV, detection wavelength at 230 nm and using hydrodynamic injection for 15 s. Acceptable validation criteria for selectivity, linearity, precision, and accuracy were studied. The limits of detection (LOD) and limits of quantitation (LOQ) of the enantiomers (ofloxacin enantiomer 1 (OF-E1), ofloxacin enantiomer 2 (OF-E2), ornidazole enantiomer 1 (OR-E1) and ornidazole enantiomer 2 (OR-E2)) were (0.52, 0.46, 0.54, 0.89) and (1.59, 1.40, 3.07, 2.70) μg mL⁻¹, respectively. The proposed method was successfully applied to the assay of enantiomers of both ofloxacin and ornidazole in pharmaceutical formulations. The computational calculations for the enantiomeric inclusion complexes rationalized the reasons for the different migration times between the ofloxacin and ornidazole enantiomers.     

Enantioselective resolution of chiral aromatic acids by biphasic recognition chiral extraction

This paper reports a new chiral separation technology—biphasic recognition chiral extraction for the separation of aromatic acid enantiomers such as α-cyclohexyl-mandelic acid (CHMA) and naproxen (NAP). The biphasic recognition chiral extraction system was established by adding hydrophobic d(l)-isobutyl tartrate in 1,2-dichloroethane organic phase and hydrophilic β-cyclodextrin (β-CD) derivative in aqueous phase, which preferentially recognize the (R)-enantiomer and (S)-enantiomer, respectively. These studies involve an enantioselective extraction in a biphasic system, where aromatic acid enantiomers form complexes with the β-cyclodextrin derivative in the aqueous phase and d(l)-isobutyl tartrate in the organic phase, respectively. Factors affecting the extraction mechanism are analyzed, namely the influence of the concentrations of the extractants and aromatic acid enantiomers, the types of the extractants, pH, and temperature. The experimental results show that the biphasic recognition chiral extraction is of much stronger chiral separation ability than the monophasic recognition chiral extraction, which utilizes the cooperations of the forces of the tartrate and the β-CD derivative. Hydroxypropyl-β-cyclodextrin (HP-β-CD), hydroxyethyl-β-cyclodextrin (HE-β-CD), and methyl-β-cyclodextrin (ME-β-CD) have stronger recognition abilities for the (S)-aromatic acid enantiomers than those for (R)-aromatic acid enantiomers, among which HP-β-CD has the strongest ability. d-Isobutyl tartrate preferentially recognizes (R)-CHMA and (S)-NAP, while l-isobutyl tartrate preferentially recognizes (S)-CHMA and (R)-NAP. The maximum enantioselectivities of CHMA and NAP are 2.49 and 1.65, under conditions at which the pH values of the aqueous phases are 2.7 and 2.5, at the ratio of 2:1 of [isobutyl tartrate] to [HP-β-CD].     

Enantiomeric separation of dansylamino acids by capillary zone electrophoresis with selectively methylated γ-cyclodextrin derivatives

The chiral separation ability of octakis2-, 3- and 6-mono-O-methyl, 2,3-, 2,6- and 3,6-di-O-methyl, and 2,3,6-tri-O-methyl)-γ-cyclodextrins as chiral selectors in capillary zone electrophoresis was investigated using twelve dansylamino acids. Unmodified and 6-monomethylated -γ-cyclodextrins (γ-CDs) exhibited similar high enantioselectivities. γ-CD still exhibited a chiral separation ability after 2-monomethylation or 2,6-dimethylation. 3-Monomethylated -γ-CD could only separate the enantiomers of two dansylamino acids, but further methylation of the hydroxyl groups at the 6-positions of 3-monomethylated γ-CD resulted in the highest chiral separation ability. γ-CD completely lost its high enantioselectivity after methylation of both the 2- and 3-positions, regardless of 6-methylation.     

Electrophoretic separation strategy for chiral pharmaceuticals using highly-sulfated and neutral cyclodextrins based dual selector systems

The enantiomeric separation of chiral pharmaceuticals was investigated using dual systems with mixtures of cyclodextrin derivatives. The dual cyclodextrin systems, consisting of one highly-sulfated (α-, β-, and γ-HSCD) and one neutral cyclodextrin, i.e. either heptakis (2,3,6-tri-O-methyl)-β-CD (TMCD), heptakis (2,6-di-O-methyl)-β-CD (DMCD) or hydroxypropyl-β-CD (HPCD), are tested on 25 pharmaceutical compounds with different acid-basic properties (16 basics, 8 acids and 1 neutral). The influence on the separation of the type and concentration of neutral CD in highly-sulfated cyclodextrins-based dual selector systems, is investigated. For 11 of 16 basic compounds, a better separation is obtained with the CD mixtures compared to the use of only a highly-sulfated CD. Mixtures with TMCD give better results than those with DMCD and HPCD. Results showed that dual CD systems are useful to achieve and to optimise chiral separations of compounds not (sufficiently) separated with HSCDs alone. For example, ibuprofen was not resolved with α-, β- or γ-HSCD, but could be separated with the mixture 25 mM TMCD and 5% HS-β-CD. Based on the obtained results, a dual CD systems based separation strategy is defined.     

Chiral Separation of Ibuprofen and Terbutaline by Nonaqueous Capillary Electrophoresis with Conductance Detection

IntroductionThe separation of chiral substances is a chal-lenge task to analytical chemistry and pharmaceuti-cal chemistry.HPLC[1] and GC[2 ] are the commonchiral separation techniques.Unfortunately,theyare time- consuming and strenuous.In addition,thechiral separation columns are expensive and thebaseline separation is hard to be obtained.Recently,the researches of chiral separationwith capillary electrophoresis have been active[3 ,4 ] .However,the instrument with an optical detectorcosts …