Investigation of the Enantioseparation of Basic Drugs with Erythromycin Lactobionate as a Chiral Selector in CE

Recent advances in chiral selectors immobilization and chiral mobile phase additives in liquid chromatographic enantio-separations: A review

For decades now, the separation of chiral enantiomers of drugs has been gaining the interest and attention of researchers. In 1991, the first guidelines for development of chiral drugs were firstly released by the US-FDA. Since then, the development in chromatographic enantioseparation tools has been fast and variable, aiming at creating a suitable environment where the physically and chemically identical enantiomers can be separated. Among those tools, the immobilization of chiral selectors (CS) on different stationary phases and the chiral mobile phase additives (CMPA) which have been progressed and studied extensively. This review article highlights the major advances in immobilization of CS together with their different recognition mechanisms as well as CMPA as a cheaper and successful alternative for chiral stationary phases. Moreover, the role of molecular modeling tool as a pre-step in the choice of CS for evaluating possible interactions with different ligands has been pointed up. Illustrations of reported methods and updates for immobilized CS and CMPA have been included.

The Use of Antibiotics as Chiral Selectors in Capillary Electrophoresis: A Review

Chirality is becoming an essential issue in modern pharmaceutical research as regulatory agencies emphasize the safety and efficiency of enantiomers in drug development. The development of efficient and reliable chiral separation methods became a necessity in the last 30 years, and capillary electrophoresis (CE), due to its relatively low costs and “green” features, is attracting increased attention. Cyclodextrin (CD) and their derivatives are the most frequently used chiral selectors (CSs) in CE, however, the use of antibiotics as CSs represents an interesting alternative. Various classes of antibiotics (aminoglycosides, ansamycins, glycopeptides, lincosamides, macrolides, tetracyclines) have been used more or less successfully for the enantio-separation of pharmaceuticals. Antibiotics offer the possibility of a multitude of potential interactions (electrostatic, inclusion, hydrogen bonding, etc.) due to their chemical diversity, allowing the enantio-separation of analytes with a wide range of structural characteristics. This article aims to review the application of various classes of antibiotics in the CE enantio-separation of pharmaceuticals. Antibiotic physiochemical characteristics, variables impacting enantio-separation, advantages, and disadvantages when certain antibiotics are used as CSs in CE are also explored.

Enantioseparation of N-methyl duloxetine, duloxetine and fluoxetine by countercurrent chromatography using anionic β-cyclodextrin as chiral selector

Two anionic. This article is protected by copyright. All rights reserved.

Reversed-phase-HPLC enantioseparation and control of enantiomeric purity of duloxetine using a new chiral reagent and recovery of enantiomers

This study reports a rapid and low-cost LC method for control of enantiomeric purity of duloxetine. Though duloxetine, as marketed and administered, is expected to be a single (S)-enantiomer, the analysis of a few commercial branded samples by the method developed and presented here showed that they contain a relatively high percentage of (R)-enantiomer (e.g., 2.71-5.42%, which is undesirable in drug formulations). A new chiral derivatizing reagent [isatinyl-(S)-naproxen amide] was synthesized on (S)-naproxen platform. Diastereomeric derivatives were synthesized under microwave irradiation and were separated using reversed-phase-HPLC on a C₁₈ column. A combination of acetonitrile and triethylammonium phosphate buffer (9 mM, pH 4) as the mobile phase and detection at 273 nm were found successful. The diastereomeric derivatives at preparative scale were separated using open column chromatography, and the native enantiomers were obtained and characterized. The HPLC separation method was validated for detection limit, linearity, accuracy, and precision. The limits of detection of (S,R)-diastereomer and (S,S)-diastereomer were found to be 12 and 16 pg/mL, respectively, for the 20-μL injected volume. The method so developed has a practical significance and greater societal impact in establishing the control of enantiomeric purity and in ensuring the enantiomeric purity of the drug meant for human consumption.

Past, present, and future developments in enantioselective analysis using capillary electromigration techniques

Enantioseparation of chiral products has become increasingly important in a large diversity of academic and industrial applications. The separation of chiral compounds is inherently challenging and thus requires a suitable analytical technique that can achieve high resolution and sensitivity. In this context, CE has shown remarkable results so far. Chiral CE offers an orthogonal enantioselectivity and is typically considered less costly than chromatographic techniques, since only minute amounts of chiral selectors are needed. Several CE approaches have been developed for chiral analysis, including chiral EKC and chiral CEC. Enantioseparations by EKC benefit from the wide variety of possible pseudostationary phases that can be employed. Chiral CEC, on the other hand, combines chromatographic separation principles with the bulk fluid movement of CE, benefitting from reduced band broadening as compared to pressure-driven systems. Although UV detection is conventionally used for these approaches, MS can also be considered. CE-MS represents a promising alternative due to the increased sensitivity and selectivity, enabling the chiral analysis of complex samples. The potential contamination of the MS ion source in EKC-MS can be overcome using partial-filling and counter-migration techniques. However, chiral analysis using monolithic and open-tubular CEC-MS awaits additional method validation and a dedicated commercial interface. Further efforts in chiral CE are expected toward the improvement of existing techniques, the development of novel pseudostationary phases, and establishing the use of chiral ionic liquids, molecular imprinted polymers, and metal-organic frameworks. These developments will certainly foster the adoption of CE(-MS) as a well-established technique in routine chiral analysis.

Carbamoylated azithromycin incorporated zirconia hybrid monolith for enantioseparation of acidic chiral drugs using non-aqueous capillary electrochromatography

Carbamoylated derivatives of two antibiotics, namely, clindamycin phosphate (CLIP) and erythromycin (ERY) were successfully employed as co-precursors, in combination of zirconium tetrabutoxide as a precursor, to prepare chiral organic-zirconia hybrid monoliths (i.e., CLIP-ZHMs and ERY-ZHMs, respectively) via a single-step in-situ sol-gel approach in our previous works. Their superiority over chiral organic-zirconia/silica monoliths, prepared by post-modification approach, in terms of better enantioresolution and enhanced stability inspired us to prepare ZHMs based on an another antibiotic, azithromycin (i.e., AZI-ZHMs). Monolithic columns were employed for capillary electrochromatographic enantioseparation of acidic chiral drugs in mobile phases consisting of acetonitrile (ACN) and methanol (MeOH) as organic modifiers, and acetic acid (AcOH) and triethylamine (TEA) as electrolytes. The effects of composition of mobile phase and applied voltage on chiral separation were investigated by using ketoprofen as a representative analyte. Baseline resolutions were obtained for six acidic drugs in mobile phase consisting of 80/20 (v/v) ACN/MeOH with 300mM AcOH and 10mM TEA at a 10kV applied voltage and 25°C capillary temperature. The relative standard deviations for resolution values regarding column to column and batch to batch repeatability were less than 2.5% (for n=3) under optimized conditions, indicating satisfactory stability of the columns and reproducibility of the column preparation process.

Chiral separation by nonaqueous capillary electrophoresis using l-sorbose–boric acid complexes as chiral ion-pair selectors

A chiral nonaqueous capillary electrophoresis (NACE) method using l-sorbose–boric acid complexes as the chiral ion-pair selectors was developed for enantioseparation of nineteen chiral analytes.

Enantioseparation of basic chiral drugs on a carbamoylated erythromycin-zirconia hybrid monolith using capillary electrochromatography

An organic-inorganic hybrid monolithic column was prepared within the confines of a capillary via a single-step in situ sol-gel approach using zirconium tetrabutoxide as a precursor to compose the inorganic backbone and 3-triethoxysilylpropyl carbamoylated derivative of erythromycin (TEOSPC-ERY) as a co-precursor to introduce the organic chiral selector moiety in the zirconia backbone. The resulting carbamoylated ERY-zirconia hybrid monolith (ERY-ZHM) showed homogeneous morphology with well-defined through pores and was tightly connected with the inner wall of the capillary. The column was employed for capillary electrochromatographic enantioseparation of six basic chiral drugs in mobile phases (MPs) consisting of acetonitrile (ACN) and triethylammonium acetate (TEAA) buffer. The effects of composition of MP and applied voltage on chiral separation were investigated by using propranolol as a representative analyte. The highest resolution (Rs=3.33) was obtained with a MP consisting of 10/90 (v/v) ACN/TEAA buffer (10mM, pH 7), 10 kV applied voltage and 25°C capillary temperature. The relative standard deviations for resolution values regarding run to run, day to day, column to column and batch to batch repeatability were 0.41%, 0.89%, 1.80% and 2.26% (for n=3), respectively, indicating satisfactory stability of columns and reproducibility of column preparation process.

Clarithromycin as a chiral selector for enantioseparation of basic compounds in nonaqueous capillary electrophoresis

The first use of macrolide antibiotic clarithromycin (CLM) in nonaqueous media for enantioseparation (partial or baseline) of the following compounds: alprenolol, atenolol, metoprolol, clenbuterol, methoxyphenamine, pindolol, propranolol, sotalol, synephrine, labetalol, and fenoterol is reported. Each analysis took less than 15 min. To find optimal separation conditions, some properties of CLM (adsorption, solubility), as well as the effect of experimental parameters on the enantioseparation of analytes (background electrolyte composition, chiral selector concentration, temperature, and applied voltage) were studied. The best chiral resolution was achieved in methanolic solution of 100 mM citric acid, 10 mM NaOH, 240-300 mM H3 BO3 , and 60-75 mM CLM. Using the proposed procedure, adsorption of CLM on the capillary wall was negligible and the repeatability of the migration times (RSD) was as good as 1.6%. For the analysis of propranolol, the linearity was achieved in the concentration range 2.5 × 10(-2) - 3.0 × 10(-1) mg/mL with the LODs (3 × S/N) being equal 2.6 × 10(-3) mg/mL and 2.8 × 10(-3) mg/mL for the first and the second enantiomers, respectively. Linear range for metoprolol enantiomers was 1.0 × 10(-2) -1.6 × 10(-1) mg/mL. The LODs (3 × S/N) were determined as 2.8 × 10(-3) and 3.0 × 10(-3) mg/mL for the first and the second enantiomers, respectively.

Development of chiral methodologies by capillary electrophoresis with ultraviolet and mass spectrometry detection for duloxetine analysis in pharmaceutical formulations

Two chiral methodologies were developed by capillary electrophoresis (CE) with UV and mass spectrometry (MS) detection to ensure the quality control of the drug duloxetine, commercialized as a pure enantiomer. Both methods were optimized to achieve a high baseline enantioresolution (Rs>2) and an acceptable precision (RSD values <5% for instrumental repeatability and <10% for intermediate precision). In addition to allow the unequivocal identification of duloxetine enantiomers, the CE-MS method improved the sensitivity with respect to the use of CE-UV (LOD 200 ng/mL by CE-UV and 20 ng/mL by CE-MS) enabling to detect 0.02% of duloxetine enantiomeric impurity. This is the lowest LOD value ever reported for this drug, being this work the first one enabling to accomplish with the ICH guidelines requirements. The developed methods were validated and applied for the first time to the analysis of four pharmaceutical formulations. The content of R-duloxetine in all these samples was below the detection limit and the amount of S-duloxetine was in good agreement with the labeled content, obtaining results by the two methods that did not differ significantly (p-values >0.05).

Application of antibiotics as chiral selectors for capillary electrophoretic enantioseparation of pharmaceuticals: a review

Recent years have witnessed several new trends in chiral separation, for example, the enantiorecognition ability of several new antibiotics has been explored using capillary electrophoresis (CE) prior to HPLC; antibiotics have been employed as chiral selectors (CSs) in a nonaqueous CE (NACE) mode; and several new detection techniques (namely, capacitively coupled contactless conductivity detection) have been used in combination with CE for quantification of enantiomers. On account of these emerging trends, this article aims to review the application of various classes of antibiotics for CE enantioseparation of pharmaceuticals. A detailed account of the basic factors affecting enantioseparation, certain limitations of antibiotics as CSs and strategies to mitigate them, and advantages of NACE while using antibiotics as CSs has also been presented.

Chiral selectors in CE: recent developments and applications

This review article provides an overview of the recent advances in enantioanalysis by use of electrophoretic techniques. Due to the big number of publications in the subject mentioned above, this article is focused on chiral method developments and applications published from 2008 until 2011, and it demonstrates chiral selectors used in CE. Numerous chiral selectors have been used over the years, and these include the cyclic and the linear oligo- and polysaccharides, the branched polysaccharides, the polymeric and monomeric surfactants, the macrocyclic and other antibiotics, and the crown ethers. Different dual-selector systems are also presented in this article, and the results are compared with those obtained by use of a single chiral selector. Finally, several pharmaceutical and biomedical applications based on chiral recognition are summarized.

Recentchiral selectors for separation in HPLC and CE

Enantiomers (stereoisomers) can exhibit substantially different properties if present in chiral environments. Since chirality is a basic property of nature, the different behaviors of the individual enantiomers must be carefully studied and properly treated. Therefore, enantioselective separations are a very important part of separation science. To achieve the separation of enantiomers, an enantioselective environment must be created by the addition of a chiral selector to the separation system. Many chiral selectors have been designed and used in various fields, such as the analyses of drugs, food constituents and agrochemicals. The most popular have become the chiral selectors and/or chiral stationary phases that are of general use, i.e., are applicable in various separation systems and allow for chiral separation of structurally different compounds. This review covers the most important chiral selectors / chiral stationary phases described and applied in high performance liquid chromatography and capillary electrophoresis during the period of the last three years (2008–2011).