Analysis of antibiotics by CE and their use as chiral selectors: An update

Fundamentals of chirality, resolution, and enantiopure molecule synthesis methods

The chirality of molecules is a concept that explains the interactions in nature. We may observe the same formula but different organizations revolving around the chiral center. Since Pasteur's meticulous observation of sodium ammonium tartrate crystals' structure, scientists have discovered many features of chiral molecules. The number of newly approved single enantiomeric drugs increases every year and takes place in the market. Thus, separation or resolution methods of racemic mixtures are of continued importance in the efficacy of drugs, installation of affordable production processes, and convenient synthetic chemistry practice. This article presents the asymmetric synthesis approaches and the classification of direct resolution methods of chiral molecules.

Investigation on improvement of enantioseparation in capillary electrophoresis based on maltodextrin by chiral ionic liquids

Taking advantage of chiral ionic liquids, this study deals with the improvement of the enantioseparation performance of a traditional chiral selector (maltodextrin) in capillary electrophoresis. Herein, two polyhydroxy compound-based chiral ionic liquids, namely tetramethylammonium-D-gluconic acid and tetramethylammonium-shikimic acid were designed and utilized as additives for chiral separation for the first time. The synergistic systems provided much better enantioseparations of twelve model drugs compared to the single maltodextrin system. These model analytes contained analgesics, antidepressants, antiallergic drugs, antifungal drugs, antihypertensive drugs, and antiparkinsonian drugs. After optimizing the separation conditions, the chiral recognition mechanism was probed by means of ultraviolet spectroscopy, nuclear magnetic resonance, and molecular modeling. The results of spectroscopic and computational analyses were in good consistency with enantioseparation outcomes. Finally, the proposed method was successfully used for the determination of the enantiomeric purity of duloxetine hydrochloride.

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.

Synthesis of molecularly imprinted polymers for extraction of fluoroquinolones in environmental, food and biological samples

In recent years, fluoroquinolones have been found present in important water resources and food sources which compromises the food quality and availability, thereby, causing risks to the consumer. Despite the recent advancement in the development of analytical instrumentation for routine monitoring of fluoroquinolones in water, food, and biological samples, sample pre-treatment is still a major bottleneck of the analytical methods. Therefore, fast, selective, sensitive, and cost-effective sample preparation methods prior to instrumental analysis for fluoroquinolones residues in environmental, food and biological samples are increasingly important. Solid-phase extraction using different adsorbents is one of the most widely used pre-concentration/clean-up techniques for analysis of fluoroquinolones. Molecularly imprinted polymers (MIPs) serve as excellent effective adsorbent materials for selective extraction, separation, clean-up and preconcentration of various pollutants in different complex matrices. Therefore, synthesis of MIPs remains crucial for their applications in sample preparation as this offers much-needed selectivity in the extraction of compounds in complex samples. In this study, the progress made in the synthesis of MIPs for fluoroquinolones and their applications in water, food and biological samples were reviewed. The present review discusses the selection of all the elements of molecular imprinting for fluoroquinolones, polymerization processes and molecular recognition mechanisms. In conclusion, the related challenges and gaps are given to offer ideas for future research focussing on MIPs for fluoroquinolones.

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.

Low-cost and versatile analytical tool with purpose-made capillary electrophoresis coupled to contactless conductivity detection: Application to antibiotics quality control in Vietnam

In this study, the development of our purpose-made capacitively coupled contactless conductivity detection (C⁴ D) for CE is reported. These systems have been employed as a simple, versatile, and cost-effective analytical tool. CE-C⁴ D devices, whose principle is based on the control of the ion movements under an electrical field, can be constructed even with a modest financial budget and limited infrastructure. A featured application was developed for quality control of antimicrobial drugs using CE-C⁴ D, with most recent work on determination of aminoglycoside and glycopeptide antibiotics being communicated. For aminoglycosides, the development of CE-C⁴ D methods was adapted to two categories. The first one includes drugs (liquid or powder form) for intravenous injection, containing either amikacin, streptomycin, kanamycin A, or kanamycin B. The second one covers drugs for eye drops (liquid or ointment form), containing either neomycin, tobramycin, or polymyxin. The CE-C⁴ D method development was also made for determination of some popular glycopeptide antibiotics in Vietnam, including vancomycin and teicoplanin. The best detection limit achieved using the developed CE-C⁴ D methods was 0.5 mg/L. Good agreement between results from CE-C⁴ D and the confirmation method (HPLC- Photometric Diode Array ) was achieved, with their result deviations less than 8% and 13% for aminoglycoside and glycopeptide antibiotics, respectively.

Advances in Chiral Separations at Nano Level

Background::

Nano level chiral separation is necessary and demanding in the development of the drug, genomic, proteomic, and other chemical and the environmental sciences. Few drugs exist in human body cells for some days at nano level concentrations, that are out of the jurisdiction of the detection by standard separation techniques. Likewise, the separation and identification of xenobiotics and other environmental contaminants (at nano or low levels) are necessary for our healthiness.

Discussion:

Conclusion:

This article will be beneficial for chiral chromatographers, academicians, pharmaceutical industries, environmental researchers and Government regulation authorities.

Determination of carbapenem antibiotics using a purpose-made capillary electrophoresis instrument with contactless conductivity detection

In this study, the employment of a purpose-made capillary electrophoresis (CE) instrument with capacitively coupled contactless conductivity detection (C⁴D) as a simple and cost-effective approach for simultaneous determination of different carbapenem antibiotics is reported. The developed CE-C⁴D approach was for the first time applied for quality control of various pharmaceutical formulations in Vietnam, as well as for therapeutic monitoring of these antibiotics in plasma samples from patients under intensive care. Four of the most popular carbapenems in Vietnam, doripenem, meropenem, imipenem and ertapenem, were determined using an electrolyte composed of 10 mM Tris adjusted to pH 8.0 with acetic acid. The best detection limits achieved using the developed CE-C⁴D method were 0.36 mg/L and 0.45 mg/L for pharmaceutical and plasma samples, respectively. Good agreement between results from CE-C⁴D and the confirmation method (HPLC-PDA) was achieved, with a coefficient of determination (r²) for the two pairs of data of 0.9967.

Dual-channel Microchip Electrophoresis with Amperometric Detection System for Rapid Analysis of Cefoperazone and Sulbactam

A dual-channel microchip electrophoresis (ME) with in-channel amperometric detection was developed for cefoperazone and sulbactam determination simultaneously. In this study, a microelectrode detector was made of gold nanoparticles (GNPs) modified indium tin oxide (ITO)-coated poly-ethylene terephthalate (PET) film. The parameters including detection potential applied on working electrode, buffer concentration and pH value were optimized to improve the detection sensitivity and separation efficiency of cefoperazone and sulbactam. Under the optimal conditions, sensitive detection of cefoperazone and sulbactam was obtained with limits of detection (LODs) (S/N = 3) of 0.52 and 0.75 μg/mL, respectively. The plasma sample, which was from a patient with a brain injury taking Sulperazone, was successfully detected with a simple sample pretreatment process by dual-channel ME amperometric detection. This rapid and sensitive method possesses practical potential in clinical applications, and could provide a guidance for clinical rational drug use.

Recognition Mechanisms of Chiral Selectors: An Overview

Stereospecific recognition of chiral molecules plays an important role in nature as the basis of the interaction of chiral bioactive compounds with the chiral target structures. In separation sciences such as chromatographic and capillary electromigration techniques, interactions between chiral analytes and chiral selectors, i.e., the formation of transient diastereomeric complexes in thermodynamic equilibria, are the basis for chiral separations. Due to the large structural variety of chiral selectors, different structural features contribute to the overall chiral recognition process. This introductory chapter briefly summarizes the present understanding of the structural enantioselective recognition processes for various types of chiral selectors.

Analysis of antibiotics by CE and CEC and their use as chiral selectors: An update

Natural, synthetic or semisynthetic antibiotics are highly used to prevent or treat diseases in humans and animals, and to promote animal growth. This fact makes that antibiotics residues or their transformation products may be present in food or in the environment after human or animal excretion. For this reason, it is imperative to develop reliable and sensitive analytical methodologies for their analysis. The main aim of this work is to present and discuss the most recent applications of capillary electromigration methods for the analysis of antibiotics, including the developments and applications of their use as chiral selectors in CE. The literature published from June 2015 to June 2017 is included following the previous review by Domínguez-Vega et al. (Electrophoresis, 2016, 37, 189-211). Information about the use of different detection systems, off-line and on-line strategies to improve sensitivity, and microchip devices for the analysis of antibiotics is provided and properly discussed.

Investigation of maltodextrin-based synergistic system with amino acid chiral ionic liquid as additive for enantioseparation in capillary electrophoresis

The combined use of chiral ionic liquids (ILs) and chiral selectors in capillary electrophoresis (CE) to establish a synergistic system has proven to be an effective approach for enantioseparation. In this article, tetramethylammonium-L-arginine, a kind of amino acid chiral IL, was applied to investigate its potential synergistic effect with maltodextrin in CE enantioseparation. The established maltodextrin-based synergistic system showed markedly improved enantioseparations compared with the single maltodextrin system. Parameters such as the chiral IL concentration, maltodextrin concentration, buffer pH, applied voltage, and capillary temperature were optimized. Satisfactory enantioseparation of the five studied drugs, including nefopam, duloxetine, ketoconazole, cetirizine, and citalopram was achieved in 50 mM Tris-H₃ PO₄ buffer solution (pH 3.0) containing 7.0% (m/v) maltodextrin and 60 mM tetramethylammonium-L-arginine. In addition, the chiral configuration of tetramethylammonium-L-arginine was also investigated to demonstrate the existence of a synergistic effect between chiral ILs and maltodextrin.

Recent developments in capillary and microchip electroseparations of peptides (2015-mid 2017)

The review brings a comprehensive overview of recent developments and applications of high performance capillary and microchip electroseparation methods (zone electrophoresis, isotachophoresis, isoelectric focusing, affinity electrophoresis, electrokinetic chromatography, and electrochromatography) to analysis, microscale isolation, purification, and physicochemical and biochemical characterization of peptides in the years 2015, 2016, and ca. up to the middle of 2017. Advances in the investigation of electromigration properties of peptides and in the methodology of their analysis (sample preseparation, preconcentration and derivatization, adsorption suppression and EOF control, and detection) are described. New developments in particular CE and CEC methods are presented and several types of their applications to peptide analysis are reported: qualitative and quantitative analysis, determination in complex (bio)matrices, monitoring of chemical and enzymatical reactions and physical changes, amino acid, sequence and chiral analysis, and peptide mapping of proteins. Some micropreparative peptide separations are shown and capabilities of CE and CEC methods to provide important physicochemical characteristics of peptides are demonstrated.

Establishment and molecular modeling study of maltodextrin-based synergistic enantioseparation systems with two new hydroxy acid chiral ionic liquids as additives in capillary electrophoresis

Discovering more superior performance of ionic liquids for the separation science has triggered increasing interest. In this work, two new Hydroxy acid-based chiral ionic liquids (CILs) (tertramethylammonium-d-pantothenate (TMA-d-PAN), tertramethylammonium-d-quinate (TMA-d-QUI)) were designed and first used as additives to establish the maltodextrin-based synergistic systems for enantioseparation in capillary electrophoresis (CE). Compared to traditional single maltodextrin chiral separation system, significantly improved separations of all tested drugs in the CIL/Maltodextrin synergistic systems were obtained. Some parameters (CIL concentration, maltodextrin concentration, buffer pH, and applied voltage) in the TMA-d-PAN/Maltodextrin synergistic system have been examined and optimized for analytes. The molecular docking software AutoDock was applied to simulate the recognition process and surmise feasible resolution mechanism in the Maltodextrin/CILs synergistic systems, which has certain guiding value.

Recent progress of sample stacking in capillary electrophoresis (2014-2016)

The term "sample stacking" comprises a relatively broad spectrum of techniques that already form an almost inherent part of the methodology of CZE. Their principles are different but the effect is the same: concentration of a diluted analyte into a narrow zone and considerable increase of the method sensitivity. This review brings a survey of papers on electrophoretic sample stacking published approximately since the second quarter of 2014 till the first quarter of 2016. It is organized according to the principles of the stacking methods and includes chapters aimed at the concentration adjustment principle (Kohlrausch stacking), techniques based on pH changes, micellar methods, and other stacking techniques. Not reviewed are papers on transient ITP that are covered by another review in this issue.

Chiral recognition in separation science - an update

Stereospecific recognition of chiral molecules is an important issue in various aspects of life sciences and chemistry including analytical separation sciences. The basis of analytical enantioseparations is the formation of transient diastereomeric complexes driven by hydrogen bonds or ionic, ion-dipole, dipole-dipole, van der Waals as well as π-π interactions. Recently, halogen bonding was also described to contribute to selector-selectand complexation. Besides structure-separation relationships, spectroscopic techniques, especially NMR spectroscopy, as well as X-ray crystallography have contributed to the understanding of the structure of the diastereomeric complexes. Molecular modeling has provided the tool for the visualization of the structures. The present review highlights recent contributions to the understanding of the binding mechanism between chiral selectors and selectands in analytical enantioseparations dating between 2012 and early 2016 including polysaccharide derivatives, cyclodextrins, cyclofructans, macrocyclic glycopeptides, proteins, brush-type selectors, ion-exchangers, polymers, crown ethers, ligand-exchangers, molecular micelles, ionic liquids, metal-organic frameworks and nucleotide-derived selectors. A systematic compilation of all published literature on the various chiral selectors has not been attempted.