Ultrasensitive determination of 10 phenothiazine derivatives and their enantiomers in biological fluids by capillary electrophoresis with contactless conductivity detection

In this study, a simple, rapid, and ultrasensitive technique was developed to identify five pairs of phenothiazine drugs by using ultrasound-enhanced and surfactant-assisted dispersive liquid-liquid microextraction (UESA-DLLME), field-amplified sample injection with capillary electrophoresis (FASI-CE), and capacitively coupled capacitively coupled contactless conductivity detection (C4D). During the CE separation process, UESA-DLLME was used for sample clean-up and offline concentration, and FASI-CE was used for the online concentration of phenothiazine enantiomers. At baseline, the five pairs of phenothiazine enantiomer drugs required 18 min for separation. UESA-DLLME was then used to extract 0.01 mM Tween 80 at pH 10 from a sample solution (extraction solvent, 100 mL of dichloromethane). Subsequently, FASI was used to stack the sample solution (buffer, 30 mM 2-(N-morpholino)ethanesulfonic acid/aspartic acid, additive 4 mM hydroxypropyl-γ-cyclodextrin, pH 2.5), and C4D was used for signal detection (amplitude, 2 Vpp; frequency, 400 kHz). The results indicated that the linear range for quantifying all analyte enantiomers was 1.0-150 nM, with a coefficient of determination exceeding 0.99. In addition, the relative standard deviations in the migration time and peak areas for the 10 analytes were less than 3.2% and 7.2%, respectively. The proposed system has a limit of detection (LOD) for the 10 analytes at a signal-to-noise ratio of 3, ranging from 0.24 to 0.28 nM. The sensitivity enhancement, which compares the LOD0 (limit of detection in the normal method) to LOD1 (limit of detection achieved using the proposed UESA-DLLME-FASI-CE-C4D method), varies between approximately 1200 and 2000 for the 10 analytes. Analysis of the 10 separated analytes spiked in urine and serum samples revealed recovery rates of 88%-106% and 89%-105%, respectively. Therefore, this highly sensitive advanced technique was successfully used to analyze phenothiazine enantiomers in urine and serum samples.

Negatively charged cyclodextrins: Synthesis and applications in chiral analysis-A review

The negatively charged cyclodextrins (CDs) play an important role in chiral analysis due to the additional electrostatic effect beyond the host-guest inclusion, especially in enantioanalysis of positively charged and electrically neutral analytes. This review presents recent advances in application of anionic CDs for enantioanalysis during the past five years. Firstly, the synthesis approaches of random substitution and single isomers of anionic CDs are briefly discussed. The main part focuses on the chiral analysis using anionic CDs in various analytical techniques, including capillary electrophoresis, high-performance liquid chromatography, capillary electrochromatography, counter current chromatography, nuclear magnetic resonance, etc. Particular attention is given to the capillary electrophoresis application since charged CDs could be used as a carrier of enantiomers by virtue of their self-mobility and offer an easy adjustment of the enantiomer migration order. Finally, future opportunities are also discussed in the conclusion of this review.

Single isomer cyclodextrins as chiral selectors in capillary electrophoresis

Since decades, cyclodextrins are one of the most powerful selectors in chiral capillary electrophoresis for the enantioseparation of diverse organic compounds. This review concerns papers published over the last decade (from 2009 until nowadays), dealing with the capillary electrophoretic application of single isomer cyclodextrin derivatives in chiral separations. Following a brief overview of their synthetic approaches, the inventory of the neutral, negatively and positively charged (including both permanently ionic and pH-tunable ionizable substituents) and zwitterionic CD derivatives is presented, with insights to underlying structural aspects by NMR spectroscopy and molecular modeling. CE represents an ideal tool to study the weak, non-covalent supramolecular interactions. The published methods are reviewed in the light of enantioselectivity, enantiomer migration order and the fine-tuning of enantiodiscrimination by the substitution pattern of the single entity selector molecules, which is hardly possible for their randomly substituted counterparts. All the reviewed publications herein support that cyclodextrin-based chiral capillary electrophoresis seems to remain a popular choice in pharmaceutical and biomedical analysis.

Chiral separation of four phenothiazines by nonaqueous capillary electrophoresis and quality by design-based method development for quantification of dextromepromazine as chiral impurity of levomepromazine

The separation of the enantiomers of mepromazine, promethazine, thioridazine and alimemazine was studied by nonaqueous capillary electrophoresis in the presence of cyclodextrins using 1 M acetic acid and 50 mM ammonium acetate in methanol as background electrolyte. Heptakis(2,3-di-O-acetyl-6-O-sulfo)-β-cyclodextrin, heptakis(2,3-di-O-methyl-6-O-sulfo)-β-cyclodextrin (HDMS-β-CD) and octakis(2,3-di-O-methyl-6-O-sulfo)-γ-cyclodextrin were the most effective chiral selectors for mepromazine, promethazine and alimemazine. Subsequently, a method for the determination of dextromepromazine as chiral impurity of levomepromazine was developed employing quality by design principles. Using HDMS-β-CD as selector, a fractional factorial resolution V+ design was employed for evaluating the knowledge space, while a central composite face centered design provided further method optimization and the basis for the computation of the design space by Monte Carlo simulations. The final experimental conditions included a 30/40.2 cm fused-silica capillary with 75 µm inner diameter and a background electrolyte composed of 0.75 M acetic acid and 55 mM ammonium acetate in methanol containing 27.5 mg/mL HDMS-β-CD. The applied voltage was 22 kV and the capillary temperature was 15°C. Following method robustness testing via a Plackett-Burman design, the method was validated for dextromepromazine in the range of 0.01 to 3.0 % relative to a concentration of 0.74 mg/mL levomepromazine and applied to the analysis of reference standards of the European Pharmacopoeia and commercial tablets. The assay also allowed the detection of levomepromazine sulfoxide although the quantitation of the compound was hampered by the poor peak shape of the late migrating diastereomer.

Some thoughts about enantioseparations in capillary electrophoresis

In this overview the goal of the authors was to analyze from the historical perspective the reasons of success and failure of chiral capillary electrophoresis. In addition, the current trends are analyzed, unique advantages of capillary electrophoresis are highlighted and some future directions are discussed.

Combination of capillary electrophoresis and molecular modeling to study the enantiomer affinity pattern between β-blockers and anionic cyclodextrin derivatives in a methanolic and water background electrolyte

In order to have deep insights into the mechanisms of enantiomer affinity pattern in both aqueous and non-aqueous systems, an approach combining capillary electrophoresis and molecular modeling was undertaken. A chiral β-blocker; acebutolol, was enantioseparated in aqueous capillary electrophoresis and non-aqueous capillary electrophoresis using two anionic β-cyclodextrin derivatives. The enantiomer affinity pattern of acebutolol was found to be opposite when an aqueous background electrolyte was replaced with non-aqueous background electrolyte in the presence of heptakis(2,3-di-O-acetyl-6-sulfo)-β-cyclodextrin but remained the same in the presence of heptakis(2,3-di-O-methyl-6-sulfo)-β-cyclodextrin. Molecular docking of acebutolol into two β-cyclodextrin derivatives indicated two distinct binding modes called 'up' and 'down' conformations. After structure optimization by molecular dynamics and energy minimization, both enantiomers of acebutolol were preferred to the 'up' conformation with heptakis(2,3-di-O-methyl-6-sulfo)-β-cyclodextrin while 'down' conformation with heptakis(2,3-di-O-acetyl-6-sulfo)-β-cyclodextrin. The further calculation of the complex energy with solvent effect indicated that heptakis(2,3-di-O-acetyl-6-sulfo)-β-cyclodextrin had higher affinity to S-acebutolol than R-acebutolol in non-aqueous capillary electrophoresis while it showed better binding to R-acebutolol in aqueous capillary electrophoresis. However, the heptakis(2,3-di-O-methyl-6-sulfo)-β-cyclodextrin bound better to R-acebutolol in both aqueous and non-aqueous capillary electrophoresis, implying that the binding mode played more important role in chiral separation of heptakis(2,3-di-O-methyl-6-sulfo)-β-cyclodextrin while the solvent effect had prevailing impact on heptakis(2,3-di-O-acetyl-6-sulfo)-β-cyclodextrin.

Chiral Separation by NACE Using Polyol Derivative-Boric Acid Complexes

Nonaqueous capillary electrophoresis (NACE) is an effective method for chiral separation. Many polyol derivatives (e.g., D-(+)-xylose, lactobionic acid, diacetone-D-mannitol, L-sorbose, and D-gluconic acid δ-lactone) can react with boric acid in methanol to produce polyol derivative-boric acid complexes which can be utilized as chiral selectors of enantioseparations. The enantiomers of more than a dozen basic analytes can be resolved under the optimized NACE using these chiral selectors.

Contemporary theory of enantioseparations in capillary electrophoresis

The first separation of enantiomers in capillary electrophoresis (CE) counts slightly longer than three decades. Fast development of the practice and theory of chiral CE occurred in the past 30 years and today one can consider this technology to have a solid and mature theoretical background. The goal of the present review is not only to summarize the history and contemporary theory of enantioseparations by using CE but also to present the authors personal view where shall we head to with this attractive technology not only from the viewpoint of separation of enantiomers but also for better understanding the mechanisms of non-covalent (enantioselective) interactions in chemistry, biology, medicine and related disciplines.

Chiral separation of terbutaline and non-steroidal anti-inflammatory drugs by using a new lysine-bridged hemispherodextrin in capillary electrophoresis

A method for the separation of a mixture of terbutaline and non-steroidal anti-inflammatory drugs was developed using capillary electrophoresis with a new hemispherodextrin, ad hoc designed, the lysine - bridged hemispherodextrin (THLYSH). The use of lysine residues to bridge the trehalose capping unit moiety to the cyclodextrin cavity gives rise to a receptor with two long chains with amine nitrogen atoms, whose charge can be easily tuned as a function of the solution pH. The new hemispherodextrin was accurately characterised by ESI-MS and NMR spectroscopy, also highlighting its protonation behaviour. Circular dichroism and ESR spectroscopy measurements were also carried out to test its inclusion ability towards anthraquinone-3-sulfonate and its metal coordination ability towards copper(II) ion, respectively. Analogously to the other hemispherodextrins, the main skill of this new derivative lies in its chiral selector properties, as shown by the separation of the enantiomeric pairs of terbutaline and ibuprofen, flurbiprofen, suprofen and tiaprofenic acid by capillary electrophoresis. The focused use of the solution equilibria involved in the separations made it possible to understand the phenomena occurring in solution, and to finely tune the charge status of the receptor. In this way the chiral separation of the racemic mixture was successfully obtained, even if the receptor was individually used, differently by the other hemispherodextrins previously studied whose chiral separation capabilities are present only if used as binary mixtures.