Analytical separation of four stereoisomers of luliconazole using supercritical fluid chromatography: Thermodynamic aspects and simulation study with chiral stationary phase

Update on chiral recognition mechanisms in separation science

The stereospecific analysis of chiral molecules is an important issue in many scientific fields. In separation sciences, this is achieved via the formation of transient diastereomeric complexes between a chiral selector and the selectand enantiomers driven by molecular interactions including electrostatic, ion-dipole, dipole-dipole, van der Waals or π-π interactions as well as hydrogen or halogen bonds depending on the nature of selector and selectand. Nuclear magnetic resonance spectroscopy and molecular modeling methods are currently the most frequently applied techniques to understand the selector-selectand interactions at a molecular level and to draw conclusions on the chiral separation mechanism. The present short review summarizes some of the recent achievements for the understanding of the chiral recognition of the most important chiral selectors combining separation techniques with molecular modeling and/or spectroscopic techniques dating between 2020 and early 2024. The selectors include polysaccharide derivatives, cyclodextrins, macrocyclic glycopeptides, proteins, donor-acceptor type selectors, ion-exchangers, crown ethers, and molecular micelles. The application of chiral ionic liquids and chiral deep eutectic solvents, as well as further selectors, are also briefly addressed. A compilation of all published literature on chiral selectors has not been attempted.

Recent advances in chiral liquid chromatography stationary phases for pharmaceutical analysis

Chirality is a common phenomenon in nature. Different enantiomers of chiral drug compounds have obvious differences in their effects on the human body. Therefore, the separation of chiral drugs plays an extremely important role in the safe utilization of drugs. High-performance liquid chromatography (HPLC) is an effective tool for the separation and analysis of compounds, in which the chromatographic packing plays a key role in the separation. Chiral pharmaceutical separation and analysis in HPLC rely on chiral stationary phases (CSPs). Thus, various CSPs are being developed to meet the needs of chiral drug separation and analysis. In this review, recent developments in CSPs, including saccharides (cyclodextrin, cellulose, amylose and chitosan), macrocycles (macrocyclic glycopeptides, pillar[n]arene and polyamide) and porous organic materials (metal-organic frameworks, covalent organic frameworks, and porous organic cages), for pharmaceutical analysis in HPLC were summarized, the advantages and disadvantages of various stationary phases were introduced, and their development prospects were discussed.

Circular dichroism assessment of an imidazole antifungal drug with plant based silver nanoparticles: Quantitative and DFT analysis

Circular dichroism (CD) methods have been developed for the analysis of luliconazole (LUC) using plant based silver nanoparticles (P-AgNPs). Cleaner and natural approach have found significant attention in recent times owing to their exceptional physicochemical characteristics. Utilizing FTIR, SEM, and XRD, the produced nanoparticles were analyzed. The produced P-AgNPs were then used to assay LUC in formulation drugs. Four CD methods are developed as zero order and second order derivative methods. Methods I and II are based on a normal CD scan (zero order) that produced calibration range from 2 - 16 μgmL^-1 at 232 nm (positive band) and 299 nm (negative band), respectively. Methods III and IV are the second order derivative methods that are developed at 232 nm (negative band) and at 251 nm (positive band). Density functional theory study was done to comprehend the feasibility of the developed methods and to optimize the structure and energy gap that validated the experimental procedure. The LUC assay methods using the proposed CD approach are simple, sensitive and precise with a limit of detection for methods I, II, III and IV of 0.527, 0.428, 0.250 and 0.30 μgmL^-1 and limit of quantification of 1.75, 1.42, 0.833 and 1.0 μgmL^-1, respectively. For intra- and inter-day precision, the recovery data ranged from 99.48 to 101% and 99.37 to 101%, respectively. The methods were used in dosage forms that produced a relative standard deviation of less than 2% and the true bias (θ_L and θ_U) within ±2%, demonstrating the potential use of the developed methods.

Evaluation of Chiral Fungicide Penflufen in Legume Vegetables: Enantioseparation and Its Mechanism, Enantioselective Behaviors, and Risk Assessment

Illustrating the enantioselective behaviors of the novel chiral fungicide penflufen was extremely important for ecological safety and human health. For penflufen enantiomers, an excellent separation method including a short analysis time (4 min), a high sensitivity (2 ng/g), and lesser consumption of an organic solvent was first established through supercritical fluid chromatography-tandem mass spectrometry. The enantioseparation mechanism was explained by computational chemistry, and the stronger binding ability of S-(+)-penflufen with cellulose tris-(3-chloro-4-methylphenylcarbamate) (the chiral stationary phase OZ-3 column) contributed to the posterior elution. In legume vegetables, penflufen dissipation was the fastest in Pisum sativum Linn plants (half-life, 1 day) and the slowest in Glycine max plants (half-lives, 11.3-12.9 days). After 30, 50, and 40 days, the rac-penflufen residues were lower than the maximum residue level value in the Electronic Code of Federal Regulations (10 ng/g) in G. max, P. sativum Linn, and Vigna unguiculata, respectively. Abundant S-(+)-penflufen was found in these plants with stereoisomeric excess (se) changes being >10% in the initial stage, so the risk assessment might be driven by S-(+)-penflufen. However, the se changes were <10% in V. unguiculata plants, and the risk assessment might be calculated based on rac-penflufen. Moreover, penflufen enantiomers could be transferred from legume vegetables to soils, and the concentrations increased with time. The high persistence and medium mobility of penflufen in soils might lead to potential groundwater contamination, which was noteworthy. These results could contribute to a more accurate risk assessment of penflufen in legume vegetables.

Advances and challenges in the pharmacokinetics and bioanalysis of chiral drugs

Enantioselective analytical approaches are essential for monitoring pharmacokinetics and acquiring accurate data to better understand the role of stereochemistry in pharmacokinetics. Enantioselectivity significantly impacts the pharmacokinetics of chiral drugs, especially in metabolic profile, leading to toxicity of enantiomer. Consequently, there is a need to study the pharmacokinetics of enantiomerically pure drugs and racemates as they differ in affinity with enzymes and proteins. Combining the best enantioseparation conditions with the specified biological matrix and the intended purpose of the analysis is a challenging task. This review discusses the importance of chirality in stereoselective pharmacokinetics with more relevant examples, various enantioselective analytical techniques, and stationary phases employed. Challenges such as lack of universal chiral columns, biological inversion of the isomers, and others have been discussed. Further presented the recent advances in the screening of chiral drugs and innovative improvements in the analytical approaches for chiral molecule analysis such as supercritical fluid chromatography, simulated moving bed chromatography, and other techniques are discussed.

Supercritical Fluid Chromatography for Chiral Analysis, Part 2: Applications

In the second part of this review article, the recent progress in supercritical fluid chromatography (SFC) for enantiomeric separations is evaluated. With the substantial developments carried out over the past years in instrumentation, columns, and detector hyphenation, the interest in chiral SFC has been steadily growing in various fields. In combination with novel developments in chiral stationary phase chemistries, the enantioselective analysis range has been significantly extended. Several applications reported on the enantioselective separation of drugs and pharmaceutical compounds using chiral SFC are discussed, including pharmaceutical applications, clinical research, forensic toxicology, and environmental sciences.

Development of a novel HPLC-ESI-MS/MS method to analyze the stereoselective pharmacokinetics and tissue distribution of isoconazole enantiomers in rats

Isoconazole with an asymmetrical carbon is a broad-spectrum antimicrobial imidazole, but there is still lack of relevant report about the potential enantioselectivity in biological samples. The object of this research was to develop and validate a sensitive and effective high performance liquid chromatography-electrospray ionization coupled with tandem mass spectrometry (HPLC-ESI-MS/MS) method for stereoselective separation and determination of isoconazole enantiomers in Sprague-Dawley (SD) rat plasma and tissues. The greater enantioseparation of isoconazole enantiomers was obtained on a Chiralpak IC column with a mobile phase consisted of acetonitrile-10 mM aqueous ammonium acetate (90:10, v/v) under the reversed-phase mode. Subsequently, the studied compounds and internal standard (IS) were detected on a multiple reaction monitoring (MRM) mode with positive electrospray ionization source. The experimental and theoretical Electronic Circular Dichroism (ECD) spectra were employed to confirm the absolute configuration of isoconazole enantiomers. Eventually, after full method validation, the newly developed method was successfully applied to the study of enantioselectivity in plasma and tissues in SD rats. Results illustrated that the enantioselective differences in plasma were observed for the evidence that the concentrations of S-(-)-isoconazole were always higher than R-(+)-isomer. In terms of tissue distribution, liver, kidney, lung, spleen, and small intestine were the mainly distributed tissues and then followed by heart and muscle. This is the first study to reveal the stereoselective behavior of isoconazole enantiomers in vivo, which also provides reliable and valuable reference for further elucidating the enantioselective metabolisms of isoconazole enantiomers.

Separation of chiral and achiral impurities in paroxetine hydrochloride in a single run using supercritical fluid chromatography with a polysaccharide stationary phase

Separating paroxetine hydrochloride and its impurities using conventional reversed-phase liquid chromatography (RPLC) is challenging due to their highly similar structures. In the present study, a rapid, simple, sensitive and environmentally friendly method was developed for the determination of chiral and achiral impurities in raw materials of paroxetine hydrochloride using chiral supercritical fluid chromatography (SFC). The impacts of chiral stationary phases (CSPs), mobile phases, column temperature and back pressure on the retention and separation of analytes were comprehensively evaluated. After method optimization, a satisfying result was obtained on a cellulose tris-(3-chloro-4-methylphenylcarbamate) stationary phase in 4.0 min using 70% CO₂ and 20 mM ammonium acetate in 30% methanol as the mobile phase. Molecular docking was further performed to understand the interactions between the analytes and CSP. The results suggested that hydrogen bonding and π-π interactions were the dominant interactions. The affinity given by the software was in good agreement with the elution order and free energy (△G) values obtained from van't Hoff equations. The results of molecular docking also provide insights into the different retentions of N-methylparoxetine at different temperatures. The results of method validation revealed that the method was sensitive with a limit of detection of approximately 0.05 μg·mL^-1 (corresponding to approximately 0.005% paroxetine hydrochloride in the sample solution). The relative standard deviations (RSDs) of precision and intra-assay precision were all less than 2.0%, and the recoveries of the method were 93.8~105.3% with RSDs less than 3.0%. The chiral and achiral RPLC methods included in the Chinese pharmacopoeia and the SFC method proposed in this study were simultaneously used to determine the impurity content in the raw materials of paroxetine hydrochloride. The results showed that impurities that cannot be detected by the reference method can be accurately quantified using the SFC method. In addition, the SFC method has advantages in terms of throughput, analysis cost and simplicity. This study can provide a reference for further research of impurities in paroxetine hydrochloride and promote the application of chiral SFC in the rapid separation of structurally similar compounds.

A Review of Characteristics, Properties, Application of Nanocarriers and Analytical Methods of Luliconazole

Luliconazole is an imidazole agent, used for the treatment of fungi infection, especially dermatophytes. The mechanism of action of the drug consisting in inhibits sterol 14α-demethylase which interferes with ergosterol biosynthesis. Due to low aqueous solubility and highly lipophilic, there is a need to develop drug delivery systems (nanocarriers) capable to increase the solubility, permeability, and skin retention of luliconazole, and promote a better therapeutic effect. In this context, this review presents characteristics, properties, nanocarriers, and analytical methods used for luliconazole. From the analyzed studies, the majority reports the use of RP-HPLC techniques for luliconazole determination, but also are cited spectrophotometric UV methods. The luliconazole has been qualitatively and quantitatively analyzed in different matrices, such as raw material and pharmaceutical formulations, however, in this review, only one study was found with the luliconazole quantification biological matrix, demonstrating the lack of studies related to the quantification of the drug in biological matrices. The drug quantification in different matrices by analytical methods is of great importance since they assist in the control of the quality, efficacy, and safety of the medicine.

Chiral separation and molecular simulation study of six antihistamine agents on a coated cellulose tri-(3,5-dimethylphenycarbamate) column (Chiralcel OD-RH) and its recognition mechanisms

Enantiomeric separation of six antihistamine agents was first systematically investigated on a cellulose-based chiral stationary phase (CSP), that is, cellulose tris-(3,5-dimethyl phenyl carbamate) (Chiralcel OD-RH), under the reversed-phase mode. Orphenadrine, meclizine, terfenadine, dioxopromethazine, and carbinoxamine enantiomers were completely separated under the optimized mobile phase conditions with resolutions of 5.02, 1.93, 1.68, 1.67, and 1.54, respectively. Mequitazine was partially separated with a resolution of 0.77. The influences of type and concentration of buffer salt, the pH of buffer solution, and the type and ratio of organic modifier on the chiral separation were evaluated and optimized. For a better insight into the enantiorecognition mechanisms, molecular docking was carried out via the Autodock software. The lowest binding energy and the optimal conformations of the analytes/CSP complexes were supplied, and the mechanisms of chiral recognition were determined. According to the results, the key interactions for the chiral recognition of these six analytes on CDMPC were π-π interactions, hydrophobic interactions, hydrogen bond interactions, and some special interactions.

Comparison of Coated and Immobilized Chiral Stationary Phases Based on Amylose tris-[(S)-α-Methylbenzylcarbamate] for the HPLC Enantiomer Separation of α-Lipoic Acid and Its Reduced Form

The couple of chiral sulfur compounds α-lipoic acid (ALA)/α-dihydrolipoic acid (DHALA) has attracted considerable attention in recent years owing to its remarkable anti-inflammatory and antioxidant properties. It is well known that the chirality of the C6 plays a key role in determining the biological activity of ALA. The natural occurring (R)-ALA enantiomer is an essential cofactor for key oxidative metabolism enzyme complexes and, after oral administration of the racemic mixture, it shows higher plasma concentration than (S)-ALA. Differently, the in vivo enantioselective action difference between the enantiomers of DHALA has not yet been studied. This lacking is perhaps due to the unavailability of analytical methods capable of determining the enantiomeric composition of biological samples during pharmacokinetic and pharmacodynamic events. In the present work, the direct and baseline enantioresolution of both chiral acids by HPLC on two amylose-derived chiral stationary phases is presented. The proposed chiral enantioselective protocol, therefore, does not require pre- or on-column derivatization. The performance of the coated Chiralpak AS-H CSP and the new immobilized Chiralpak IH-3 CSP, which have the same chiral selector amylose tris-[(S)-α-methylbenzylcarbamate], were compared using conventional normal-phase mobile phases containing ethanol or 2-propanol as alcoholic solvents and a fixed percentage of trifluoroacetic acid. Nonconventional eluents containing dichloromethane, ethyl acetate, and 2-methyltetrahydrofuran as organic cosolvents were applied in the separation of the enantiomers of two carboxylic acids on the immobilized Chiralpak IH-3 CSP. The effect of the column temperature was carefully evaluated in order to improve enantioselectivity. Adequate amounts of enantiomers were isolated by an analytical-size Chiralpak IH-3 column and submitted to chiroptical measurements. The absolute configuration assignment of the isolated enantiomers was determined by a multidisciplinary procedure based on the comparison of the experimental and calculated chiroptical properties.

An overview of chiral separations of pharmaceutically active substances by HPLC (2018-2020)

This review provides a brief survey of chiral separation of pharmaceutically active substances published over the last 3 years (2018-2020). Chiral separation of drugs is an important area of research. The control of enantiomeric purity and determination of individual enantiomeric drug molecules is a necessity especially for clinical, analytical, and regulatory purposes. Among chromatographic resolution methods, high-performance liquid chromatography based on chiral stationary phases remains the most popular and effective method used for chiral separation of various drugs. In this review, attention is paid to several classes of chiral stationary phases that have been the most frequently used for drug enantioseparation during this period.

GRAPHIC ABSTRACT

Application of chiral chromatography in radiopharmaceutical fields: A review

Chiral column chromatography (CCC) is a revolutionary analytical methodology for the enantioseparation of novel positron emission tomography (PET) tracers in the primary stages of drug development. Due to the different behaviors of tracer enantiomers (e.g. toxicity, metabolism and side effects) in administrated subjects, their separation and purification is a challenging endeavor. Over the last three decades, different commercial chiral columns have been applied for the enantioseparation of PET-radioligand (PET-RL) or radiotracers (PET-RT), using high-performance liquid chromatography (HPLC). The categorization and reviewing of them is a vital topic. This review presents a brief overview of advances, applications, and future prospectives of CCC in radiopharmaceutical approaches. In addition, the effective chromatographic parameters and degravitation trends to enhance enantioseparation resolution are addressed. Moreover, the application and potential of chiral super fluidical chromatography (CSFC) as an alternative for enantioseparation in the field of radiopharmaceutical is discussed. Finally, the crucial application challenges of CCC are explained and imminent tasks are suggested.