A comparison of chiral resolution of antifungal agents on different polysaccharide chiral columns under various mobile phase modes: Application in the biological samples

Molecular structure and selective theophylline complexation by conformational change of diethyl N,N'-(1,3-phenylene)dicarbamate

The receptor ability of diethyl N,N'-(1,3-phenylene)dicarbamate (1) to form host-guest complexes with theophylline (TEO) and caffeine (CAF) by mechanochemistry was evaluated. The formation of the 1-TEO complex (C12H16N2O4·C7H8N4O2) was preferred and involves the conformational change of one of the ethyl carbamate groups of 1 from the endo conformation to the exo conformation to allow the formation of intermolecular interactions. The formation of an N-H...O=C hydrogen bond between 1 and TEO triggers the conformational change of 1. CAF molecules are unable to form an N-H...O=C hydrogen bond with 1, making the conformational change and, therefore, the formation of the complex impossible. Conformational change and selective binding were monitored by IR spectroscopy, solid-state 13C nuclear magnetic resonance and single-crystal X-ray diffraction. The 1-TEO complex was characterized by IR spectroscopy, solid-state 13C nuclear magnetic resonance, powder X-ray diffraction and single-crystal X-ray diffraction.

Enantiomeric separation of thiourea derivatives of naringenin on amylose and cellulose polymeric chromatographic chiral columns

Due to a great demand for amylose and cellulose polymeric chromatographic chiral columns, the enantiomeric separation of thiourea derivatives of naringenin was achieved on the different amylose (Chiralpak-IB) and cellulose chiral (Chiralcel-OJ and Chiralcel-OD-3R) columns with varied chromatographic conditions. The isocratic mobile phases used were ethanol and methanol, where ethanol/hexane and methanol/hexane were used as gradient mode and were prepared in volume/volume relation. The separation and resolution factors for all the enantiomers were in the range of 1.25 to 3.47 and 0.48 to 1.75, respectively. The enantiomeric resolution was obtained within 12 min making fast separation. The docking studies confirmed the chiral recognition mechanisms with binding affinities in the range of -4.7 to -5.7 kcal/mol. The reported compounds have good anticoagulant activities and may be used as anticoagulants in the future. Besides, chiral separation is fast and is useful for enantiomeric separation in any laboratory in the world.

Microbiological and spectrophotometric methods for the determination of tioconazole: A comparative thermodynamic study

Two sensitive microbiological and charge transfer spectrophotometric methods have been developed for the quantitative determination of the antifungal drug, tioconazole, in its pure form and pharmaceutical preparations. The microbiological assay was based on the agar disk diffusion method by measuring the diameter of the inhibition zones related to different concentrations of tioconazole. The spectrophotometric method relied on charge transfer complex formation between tioconazole as an n-donor and chloranilic acid as a π-acceptor at room temperature. The formed complex was measured at λ_max = 530 nm. The molar absorptivity and the formation constant of the formed complex were determined using different models, including the Benesi-Hildebrand, Foster-Hammick-Wardley, Scott, Pushkin-Varshney-Kamoonpuri, and Scatchard equations. Different thermodynamic parameters associated with the complex formation, including the free energy change (ΔG°), the standard enthalpy (ΔH°), and the standard entropy change (ΔS°), were evaluated. The two methods were validated in conformity with ICH-recommended guidelines and employed successfully for the quantification of tioconazole in both pure form and pharmaceutical formulations.

Rapid chiral separation of potential antibiotics using supercritical fluid chromatography

WHO is searching most active antibiotics due to the bacterial resistance problem. The activities of the racemic antibiotics may be augment by preparing optically active antibiotics by the chiral separation. Chiral separation of potential antibiotics such as cefotaxime and ofloxacin was studied using amylose-based packing chiral stationary phases (CSPs) such as Chiralpak IA and Chiralpak IG. Supercritical fluid chromatography (SFC) was employed to carry out this study. Both immobilized CSPs such as Chiralpak IA and IG have sown remarkable selectivity for the reported drugs by using SFC. The values of retention factor (k) for ofloxacin enantiomers were 9.63 and 11.81, followed by 2.94 and 5.96 for cefotaxime enantiomers. The values of separation factor (α) for both the reported drugs were 1.22 and 2.03, respectively Similarly, the values of resolution factor (Rs) for both the enantio-selective drugs were 1.49 and 2.06, separately and respectively. The chiral recognition mechanism was developed and it was observed that the π-π interactions are playing a major role. The developed method is effective, reproducible, eco-friendly, and may be used to discriminate the enantiomers of the reported drugs in any sample.

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.