Chiral counter-current chromatography of gemifloxacin guided by capillary electrophoresis using (+)-(18-crown-6)-tetracarboxylic acid as a chiral selector

Open tubular capillary column immobilized with sulfobutylether-β-cyclodextrin for chiral separation in capillary electrochromatography

A novel chiral open tubular capillary column was fabricated with sulfobutylether-β-cyclodextrin and glycidyl methacrylate for enantioseparation in capillary electrochromatography. First, the pretreated silica-fused capillary was treated with 3-trimethoxysilyl propyl methacrylate to attach double bond ligand onto the surface. A copolymer layer was formed on the surface of capillary using glycidyl methacrylate and ethylene dimethacrylate by in situ one-pot polymerization. Sulfobutylether-β-cyclodextrin was encapsulated inside the copolymerized layer. The morphology of the developed column was characterized by field emission scanning electron microscopy. The effect of organic percentage and pH value of the mobile phase on electroosmotic flow and resolution was also investigated. The performance of the fabricated column was validated by separation of amlodipine besilate, 2,3-diphenylpropionic acid, tropic acid, and pantoprazole enantiomers with good resolutions of 3.67, 4.82, 3.34, and 2.61, respectively. The repeatabilities of column-to-column and day-to-day through relative standard deviation were found better than 4%, exhibiting satisfactory repeatability of the developed column. The results reveal that open tubular capillary columns modified with β-cyclodextrin show a great prospect for enantioseparation of chiral drugs in capillary electrochromatography.

Dual 2-Hydroxypropyl-β-Cyclodextrin and 5,10,15,20-Tetrakis (4-Hydroxyphenyl) Porphyrin System as a Novel Chiral-Achiral Selector Complex for Enantioseparation of Aminoalkanol Derivatives with Anticancer Activity in Capillary Electrophoresis

In this study, a complex consisting of 2-hydroxypropyl-β-cyclodextrin and 5,10,15,20-tetrakis (4-hydroxyphenyl) porphyrin, (named dual chiral-achiral selector complex) was used for the determination of two novel potential anticancer agents of (I) and (II) aminoalkanol derivatives. This work aimed at developing an effective method that can be utilized for the determination of I (S), I (R), and II (S) and II (R) enantiomers of (I) and (II) compounds through the use of a dual chiral-achiral selector complex consisting of hydroxypropyl-β-cyclodextrin and 5,10,15,20-tetrakis (4-hydroxyphenyl) porphyrin system by applying capillary electrophoresis. This combination proved to be beneficial in achieving high separation selectivity due to the combined effects of different modes of chiral discrimination. The enantiomers of (I) and (II) compounds were separated within a very short time of 3.6–7.2 min, in pH 2.5 phosphate buffer containing 2-hydroxypropyl-β-cyclodextrin and 5,10,15,20-tetrakis (4-hydroxyphenyl) porphyrin system at a concentration of 5 and 10 mM, respectively, at 25 °C and +10 kV. The detection wavelength of the detector was set at 200 nm. The LOD for I (S), I (R), II (S), and II (R) was 65.2, 65.6, 65.1, and 65.7 ng/mL, respectively. LOQ for I (S), I (R), II (S), and II (R) was 216.5, 217.8, 217.1, and 218.1 ng/mL, respectively. Recovery was 94.9–99.9%. The repeatability and reproducibility of the method based on the values of the migration time, and the area under the peak was 0.3–2.9% RSD. The stability of the method was determined at 0.1–4.9% RSD. The developed method was used in the pilot studies for determining the enantiomers I (S), I (R), II (S), and II (R) in the blood serum.

Enantioseparation of three constitutional isomeric 2-(methylphenyl)propanoic acids by countercurrent chromatography

2-(3-Methylphenyl)propanic acid and 2-(4-methylphenyl)propanoic acid were successfully enantioseparated by countercurrent chromatography using hydroxypropyl-β-cyclodextrin (HP-β-CD) as a chiral selector. 2-(2-Methylphenyl)propanoic acid was also studied to compare the enantioseparation ability of three isomeric 2-(methylphenyl)propanoic acids. Totally 20 mg of 2-(3-methylphenyl)propanic acid and 20mg of 2-(4-methylphenyl)propanic acid were enantioseparated individually by countercurrent chromatography. Recovery for the (±)-2-(3-methylphenyl)propanic acid enantiomer was in the range of 85%-90% with 98.0%-98.8% purity and recovery for the (±)-2-(4-methylphenyl)propanic acid enantiomer was in the range of 80%-83% with 97.0%-98.0% purity. The enantioseparation factor in countercurrent chromatography for 2-(4-methylphenyl)propanic acid and 2-(3-methylphenyl)propanic acid were 1.31 and 1.26, and the peak resolution in HPLC reached 2.2 and 1.4. However, no enantioseparation could be found for 2-(2-methylphenyl)propanic acid. In addition, the inclusion complexes were investigated by UV spectrophotometer. The inclusion formation constant of inclusion complex between 2-(4-methylphenyl)propanic acid, 2-(3-methylphenyl)propanic acid, 2-(2-methylphenyl)propanic acid and HP-β-CD were determined as 121.73 mol/L, 78.12 mol/L and 53.18 mol/L, respectively. The present results showed that enantiorecognition was greatly affected by substituted positions of methyl group on the benzene ring. Combined with our previous results, the steric hindrance had a significant effect on inclusion interaction between HP-β-CD and racemic 2-(substitutedphenyl)propanoic acids. No enantiorecognition could be achieved for 2-(substitutedphenyl)propanoic acids with ortho-substituent group on benzene, while the influence of meta- and para- group on enantiorecognition varies with different substituent groups on benzene ring.

Hydroxypropyl-β-cyclodextrin encapsulated stationary phase based on silica monolith particles for enantioseparation in liquid chromatography

Hydroxypropyl-β-cyclodextrin-encapsulated stationary phase incorporated on silica monolith particles was prepared by physical embedding, providing a new method for the development of chiral stationary phase for enantioseparation in liquid chromatography. Ground silica monolith particles of about 2.0 μm were prepared via sol-gel reaction followed by differential sedimentation. Initially, the silica monolith particles were pretreated with 3-trimethoxysilyl propyl methacrylate to attach double-bonded ligands onto the surface, then a network structure was formed onto the surface of the particle using N-isopropyl acrylamide as functional monomer. Hydroxypropyl-β-cyclodextrin was encapsulated inside N-isopropyl acrylamide copolymerized layer on the surface of silica monolith particles. The effect of the amount of chiral selector on the chromatographic efficiency of the chiral stationary phase was examined. The glass lined stainless steel columns (1 mm internal diameter, 300 mm length) were packed with the stationary phase for estimation of the efficiency by separation of phenylsuccinic acid, oxybutynin, equol, and naproxen enantiomers in high-performance liquid chromatography, with the resolutions of 1.54, 1.72, 2.54, and 2.31, respectively. The column to column repeatabilities through relative standard deviation were found better than 3%. The experimental results indicate that the sol-gel ground silica particles modified with β-cyclodextrin provide a promising way for the separation of chiral enantiomers.

Chiral counter-current chromatography: A survey of its instrument, mechanism, procedure, and applications

The chiral separation by counter-current chromatography has made great progress in the past three decades. It has become increasingly popular in the field of chiral separation, and many applications have been introduced during the last years. This review mainly focuses on the current topics, applications, and trends in chiral separation by counter-current chromatography. It contains the development of modern counter-current chromatography apparatus, theory of counter-current chromatography, overview of applications of chiral counter-current chromatography enantioseparation, its current situation, and challenges. At last, some conclusions and perspectives also have been discussed in this review.

An overview of recent progress in solvent systems, additives and modifiers of counter current chromatography

Solvent systems are critical to counter current chromatography (CCC). Appropriate additives and modifiers can be used to improve the separation efficiency of CCC.

Chiral separation of quinolones by liquid chromatography and capillary electrophoresis

The quinolones are derivatives of oxoquinolines and mostly known for their antibacterial and antiviral activities. Many quinolones are chiral compounds having asymmetric centers and important due to their enantioselective biological activities. In order to study the biological activities of quinolone enantiomers, to control the manufacturing of homochiral drugs and to prepare necessary quantities of pure enantiomers for preclinical or clinical trials, respective chiral separation methods are urgently needed. In this context, the present review discusses chromatographic and electrophoretic methods for the enantioseparation of chiral quinolones and provides some useful information on their physical and pharmaceutical properties. The drawbacks of currently used techniques are revealed and ways to overcome them are outlined. Moreover, recommendations for an optimal choice of a separation protocol are given.

Supramolecular interaction of gemifloxacin and hydroxyl propyl β-cyclodextrin spectroscopic characterization, molecular modeling and analytical application

The solid inclusion complex of gemifloxacin (GFX) and hydroxyl propyl β-cyclodextrin (HPβ-CD) was prepared and examined by UV-visible, FTIR, NMR, electrospray ionization mass spectrometry (ESI-MS) and fluorescence spectroscopy. The formation of inclusion complex has been confirmed on the basis of changes of spectroscopic properties. Further the interaction between GFX and HPβ-CD was studied using molecular modeling approaches. The results showed that HPβCD reacted with GFX to form a 1:1 host-guest inclusion complex. Based on the enhancement of the fluorescence intensity of GFX produced through complex formation, a simple, accurate, rapid and highly sensitive spectrofluorometric method for the determination of GFX in pharmaceutical formulation was developed. The linear relationships between the intensity and GFX concentration was obtained in the concentration range of 20-140 ng/mL with good correlation coefficients (0.9997). The limit of detection (LOD) was found to be 4 ng/mL. The proposed method was successfully applied to the analysis of GFX in pharmaceutical preparation.

Chiral High-Speed Counter-Current Chromatography: Future Strategies for Chiral Selector Development

In conventional high-performance liquid chromatography, chiral separations are performed by chiral column with a chiral selector (CS) chemically boned to the solid support. In contrast, high-speed counter-current chromatography (HSCCC) performs chiral separations by dissolving CS in the liquid stationary phase. During the past two decades, several CSs were developed to successfully carry out chiral HSCCC which include N-dodecanoyl-L-proline-3,5-dimethylanilide, β-cyclodextrin derivatives, vancomycin, cinchona alkaloid derivatives, cellulose and amylose derivatives, tartaric acid derivatives, etc. Compared to HPLC which uses over hundred different kinds of CSs, the number of CSs effectively used in HSCCC is limited to several compounds. This may be due to the violent molecular movement of CS dissolved in the liquid stationary phase which reduces chiral selectivity based on steric affinity. Future development strategy of CS for HSCC proposed here is to suppress the molecular movement of the CS in the liquid stationary phase by the following three ways: 1) using viscous stationary phase such as aqueous-aqueous polymer phase system; 2) attaching a long hydrophobic chain to the asymmetric carbon, or 3) chemically bonding CS onto hydrophobic small particles such as carbon nanotubes, gold colloidal particles, and submicron silica particles.

Spectrophotometric determination of gemifloxacin mesylate, moxifloxacin hydrochloride, and enrofloxacin in pharmaceutical formulations using Acid dyes

SIMPLE, RAPID, AND EXTRACTIVE SPECTROPHOTOMETRIC METHODS WERE DEVELOPED FOR THE DETERMINATION OF SOME FLUOROQUINOLONES ANTIBIOTICS: gemifloxacin mesylate (GMF), moxifloxacin hydrochloride (MXF), and enrofloxacin (ENF) in pure forms and pharmaceutical formulations. These methods are based on the formation of ion-pair complexes between the basic drugs and acid dyes, namely, bromocresol green (BCG), bromocresol purple (BCP), bromophenol blue (BPB), bromothymol blue (BTB), and methyl orange (MO) in acidic buffer solutions. The formed complexes were extracted with chloroform and measured at 420, 408, 416, 415, and 422 nm for BCG, BCP, BPB, BTB, and MO, respectively, for GMF; at 410, 415, 416, and 420 nm for BCP, BTB, BPB, and MO, respectively, for MXF; and at 419 and 414 nm for BCG and BTB, respectively, in case of ENF. The analytical parameters and their effects are investigated. Beer's law was obeyed in the ranges 1.0-30, 1.0-20, and 2.0-24  μ g mL(-1) for GMF, MXF, and ENF, respectively. The proposed methods have been applied successfully for the analysis of the studied drugs in pure forms and pharmaceutical formulations. Statistical comparison of the results with the reference methods showed excellent agreement and indicated no significant difference in accuracy and precision.

Anodic Voltammetric determination of gemifloxacin using screen-printed carbon electrode

The electrochemical oxidation behavior and voltammetric assay of gemifloxacin were investigated using differential-pulse and cyclic voltammetry on a screen-printed carbon electrode. The effects of pH, scan rates, and concentration of the drug on the anodic peak current were studied. Voltammograms of gemifloxacin in Tris–HCl buffer (pH 7.0) exhibited a well-defined single oxidation peak. A differential-pulse voltammetric procedure for the quantitation of gemifloxacin has been developed and suitably validated with respect to linearity, limits of detection and quantification, accuracy, precision, specificity, and robustness. The calibration was linear from 0.5 to 10.0 μM, and the limits of detection and quantification were 0.15 and 5.0 μM. Recoveries ranging from 96.26% to 103.64% were obtained. The method was successfully applied to the determination of gemifloxacin in pharmaceutical tablets without any pre-treatment. Excipients present in the tablets did not interfere in the assay.

Validated Method for the Simultaneous Determination of Gemifloxacin and H2‐receptor Antagonists in Bulk, Pharmaceutical Formulations and Human Serum by RP‐HPLC; In‐vitro Applications

Simple, isocratic and rapid RP‐HPLC method has been developed for the simultaneous analysis of gemifloxacin and H2‐receptor antagonists i.e. Cimetidine, Famotidine and Ranitidine, in bulk, pharmaceutical formulation and human serum. Separation was achieved on the RP‐Mediterranea column [C18 (250 × 4.6 mm, 5 μ)] at ambient temperature using mobile phase consisting of acetonitrile: methanol: water (20:28:52 v/v/v pH 2.8 adjusted by phosphoric acid). Flow rate was 1.0 mL/min with an average operating pressure of 180 kg/cm2. Gatifloxacin (GATI) was used as an internal standard (IS). Quantitation was achieved with UV detection at 221, 256 and 267 nm, respectively. Linear calibration curves, at concentration ranges of 0.05‐37.5 μgmL‐L with a correlation coefficient of ±0.9994. The detection and quantification limits were in the ranges of 0.023‐0.250 μgmL‐L and 0.071‐0.756 μgmL‐L, respectively. Friedman's and Student's t‐test were applied to correlate these results. Method was validated in terms of selectivity, linearity, precision, robustness, recovery, limits of detection and quantitation and is applicable to the routine analysis of GFX and H2‐receptor antagonists, alone or in combination.

Development and validation of a RP-HPLC method for stability-indicating assay of gemifloxacin mesylate including identification of related substances by LC-ESI-MS/MS, 1H and 13C NMR spectroscopy

A validated stability indicating RP-HPLC assay of gemifloxacin mesylate was developed by separating its related substances on an Inertsil-ODS3V-C18 (4.6 × 250 mm; 5 μm) column using 0.1% trifluoroaceticacid (pH 2.5) and methanol as a mobile phase in a gradient elution mode at a flow rate of 1.0 mL/min at 27°C. The column effluents were monitored by a photodiode array detector set at 287 nm. The method was validated in terms of accuracy, precision and linearity as per ICH guidelines. Forced degradation of gemifloxacin (GFX) was carried out under acidic, basic, thermal, photolysis and peroxide conditions and the degradation products were separated and characterized by ESI-MS/MS, (1) H and (13) C NMR spectroscopy. The method was successfully applied to the analysis of bulk drugs and the recoveries of gemifloxacin and impurities were in the range of 97.60-102.90 and 96.99-102.10%, respectively. No previous reports were found in the literature on identification of degradation products of gemifloxacin.

Separation of alpha-cyclohexylmandelic acid enantiomers using biphasic chiral recognition high-speed counter-current chromatography

This work concentrates on a chiral separation technology named biphasic recognition applied to resolution of alpha-cyclohexylmandelic acid enantiomers by high-speed counter-current chromatography (HSCCC). The biphasic chiral recognition HSCCC was performed by adding lipophilic (-)-2-ethylhexyl tartrate in the organic stationary phase and hydrophilic hydroxypropyl-beta-cyclodextrin in the aqueous mobile phase, which preferentially recognized the (-)-enantiomer and (+)-enantiomer, respectively. The two-phase solvent system composed of n-hexane-methyl tert-butyl ether-water (9:1:10, v/v/v) with the above chiral selectors was selected according to the partition coefficient and separation factor of the target enantiomers. Important parameters involved in the chiral separation were investigated, namely the types of the chiral selectors (CS); the concentration of each chiral selector; pH of the mobile phase and the separation temperature. The mechanism involved in this biphasic recognition chiral separation by HSCCC was discussed. Langmuirian isotherm was employed to estimate the loading limits for a given value of chiral selectors. Under optimum separation conditions, 3.5-22.0 mg of alpha-cyclohexylmandelic acid racemate were separated using the analytical apparatus and 440 mg of racemate was separated using the preparative one. The purities of both of the fractions including (+)-enantiomer and (-)-enantiomer from the preparative CCC separation were over 99.5% determined by HPLC and enantiomeric excess reached 100% for the (+/-)-enantiomers. Recovery for the target compounds from the CCC fractions reached 85-88% yielding 186 mg of (+)-enantiomer and 190 mg of (-)-enantiomer. The overall experimental results show that the HSCCC separation of enantiomer based on biphasic recognition, in which only if the CSs involved will show affinity for opposite enantiomers of the analyte, is much more efficient than the traditional monophasic recognition chiral separation, since it utilizes the cooperation of both of lipophilic and hydrophilic chiral selectors.

Countercurrent chromatography: people and applications

The scientific literature was scanned for the published research articles dealing with countercurrent chromatography (CCC) over the time period 1980-May 2008. The search returned 1638 articles that were analyzed focussing on people and applications. Concerning the people, it was found that the geographical location of the CCC authors was relatively well balanced between USA, Asia with mainly China and Japan and Europe. Yoichiro Ito, the inventor of the technique, is by far the most productive author in the field with 331 articles or more than one over five CCC articles published in the time period. Without surprise, English is the dominant language with more than 82% of the articles. A significant 8% amount of CCC articles were published in Chinese in Chinese journals. Chromatography journals are the logical tribune for half of the published CCC articles. Concerning the applications, the separation and purification of natural compounds is the dominant theme in CCC making the subject of more than one article over two. Starting from the plant extract, CCC in few steps can produce significant amounts of more than 95% pure compounds used for identification and/or property studies. Other applications are found in the pharmaceutical and chemical field. The separation of enantiomers on the preparative scale is a field of growing importance.