Development of a high-performance liquid chromatography method for the simultaneous determination of chiral impurities and assay of (S )-clopidogrel using a cellulose-based chiral stationary phase in methanol/water mode

Effect of mobile-phase modifiers on the enantioselective retention behavior of methyl mandelate with an amylose 3,5-dimethylphenylcarbamate chiral stationary phase under reversed-phase conditions

In this study, methanol, ethanol, n-propyl alcohol, isopropyl alcohol, acetone, and tert-butanol were used as organic modifiers in reversed-phase mode chiral liquid-chromatography to systematically investigate the effects of mobile phase components on the enantioselective retention behavior of methyl mandelate with immobilized amylose 3,5-dimethylphenylcarbamate-based sorbent called Chiralpak IA. A two-site enantioselective model was used to obtain information on the recognition mechanisms by observing the dependence of the enantioselectivity and retention factor difference on the modifier content. Similar enantioselective retention behaviors were observed for all modifiers, and characteristic modifier concentration points (P_L , P_M , and P_H ) were identified. At modifier concentrations up to P_M , the weakened hydrophobic environment resulted in polymer structural relaxation, which changed the recognition mechanisms. By contrast, at concentrations beyond P_H , considerably different enantioselectivity behaviors were observed, indicating that the existence of dipole-dipole interaction, which was stronger at higher modifier concentrations, contributed to the retention mechanisms. The concentrations at which these characteristic points occurred were dependent on the carbon number of the modifier molecule. Modifiers with more carbon numbers facilitated the transition in the enantioselective behaviors. These results demonstrated that the proposed method can provide a physically consistent quantitative description of enantioselective retention behavior in reversed-phase mode.

Enantioselective HPLC analysis of Escitalopram oxalate and its impurities using a cellulose-based chiral stationary phase under normal- and green reversed-phase conditions

Normal-phase and reversed-phase high-performance liquid chromatography methods for the separation of the active pharmaceutical ingredient Escitalopram from its (R)-enantiomer impurity have been developed on the cellulose-based Chiralcel OJ-H chiral stationary phase. Both methods share two features: they use ethanol as a cosolvent and are able to give a complete enantioseparation without interference from other associated chiral impurities. With the green eluent mixture ethanol-water-diethylammine 70:30:0.1 (v/v/v) the resolution between escitalopram and (R)-enantiomer was 2.09 at 30°C. The limits of quantification for the (S) and (R) enantiomers were 4.5 μg mL^-1 and 3.8 μg mL^-1 , respectively. This article is protected by copyright. All rights reserved.

Simultaneous enantio- and diastereo-selective high-performance liquid chromatography separation of paroxetine on an immobilized amylose-based chiral stationary phase under green reversed-phase conditions

A simple and green high-performance liquid chromatography method for the separation of paroxetine from its enantiomeric and diastereomeric impurities has been developed. The simultaneous chromatographic resolution was carried out on the amylose-based Chiralpak IA-3 chiral stationary phase using the mixture ethanol-water-diethylamine 80:20:0.1 (v/v/v) as a mobile phase. The effects of substitution of ethanol with methanol or acetonitrile and changes in column temperature on selectivity have been carefully investigated. The optimized single-run HPLC protocol allows the baseline separation of the enantiomers of paroxetine without suffering from interference from five other chiral and achiral impurities reported in the monograph of the European Pharmacopoeia.

Computer-assisted UHPLC method development and optimization for the determination of albendazole and its related substances

Computer-aided ultrahigh performance liquid chromatographic (UHPLC) method development and optimization was undertaken in order to replace an underperforming European Pharmacopoeia method for the determination of albendazole and its related substances. In the preliminary screening, a temperature-gradient time bidimensional model was chosen to aid selection of the proper stationary phase. Hereinafter temperature-gradient time-ternary composition and temperature-gradient time-pH tridimensional models were applied for the optimization of critical method parameters. The simulation and in silico robustness testing were realized using DryLab modeling software. The final method was validated for quantification of impurities and assay of the active substance according to the current ICH guidance. The validated methods were tested on a real, commercial tablet formulation. The experimental design-based and software-assisted method development proved to be a fast and reliable way of replacing a method with inadequate selectivity and long runtime with a robust UHPLC-based method, which offers baseline separation for all monitored impurities in 10 min. Results confirm that software-based chromatographic modelling can not only speed up the analytical method development process, but also improve the reliability of the developed method.

Effect of 2-propanol content on solute retention mechanisms determined using amylose tris(3,5-dimethylphenylcarbamate) chiral stationary phase under normal- and reversed-phase conditions

The electrostatic interactions between chiral solutes and polysaccharide (PS)-based chiral selectors are the key to achieving chiral recognition; however, PS-based sorbents, derivatized of phenyl moieties, can exhibit considerably non-polar characteristics, and they are also useful for the separation of enantiomers in the reversed-phase mode. In this study, an immobilized amylose 3,5-dimethylphenylcarbamate-based sorbent was used to investigate the balance between electrostatic interactions and solvophobic interactions, with complementary effects on solute retention behavior when the isopropanol (IPA) concentration was altered. It was proposed that in both normal- and reversed-phase modes, information on the retention mechanisms could be obtained by observing the curvature of the logarithm of the retention factor versus the logarithm of the IPA concentration, and the slope values of the curves were related to the number of displaced IPA molecules upon solute adsorption. Using the proposed model and the two-site adsorption model, the retention behaviors of pantolactone (PL) enantiomers in both normal- and reversed-phase modes were investigated. The PL-sorbent interactions were classified into four types: electrostatic/enantioselective, electrostatic/nonselective, solvophobic/enantioselective, and solvophobic/nonselective. At IPA concentrations below 50 vol.% in n-hexane, the retention behaviors of PL were dominated by electrostatic/enantioselective sites, whereas at IPA concentrations beyond 50 vol.%, the solvophobic interactions of PL-sorbent were strengthened and mostly nonselective. By contrast, in the reversed-phase mode, a reverse in the enantiomeric elution order of PL was observed at 10 vol.% IPA, and considerably different enantioselectivity behaviors were found below and above 20 vol.%, indicating an abrupt change in the sorbent molecular environment. At IPA concentrations beyond 40 vol.%, the presence of PL-sorbent electrostatic interactions enhanced chiral recognition.

Development and validation of a LC-MS/MS method for the enantioseparation and determination of clopidogrel bisulfate in beagle plasma and its application to a stereoselective pharmacokinetic study

A rapid and sensitive chiral liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the enantioseparation and determination of clopidogrel bisulfate enantiomers in beagle plasma was established and successfully applied to a stereoselective pharmacokinetic study. The chromatographic separation was achieved on an Ultron ES-OVM column (150 × 2.0 mm, 5 μm) with acetonitrile-ammonium acetate (10 mM, pH 4.5) (22:78, v/v) at a flow rate of 0.3 mL/min. The mass detection was conducted using multiple reaction monitoring mode with the transition of the m/z 322.00→212.00 for clopidogrel and m/z 285.00→193.00 for diazepam (IS), respectively. The calibration curve was linear at the range of 1-800 ng/mL (r²>0.997) for each enantiomer. The intra- and inter-day precision (CV%) was within 10.9 % and the accuracy was at the range of 88.5 %-101.3 % for both enantiomers. The extraction recovery was >90.2 % and no obvious matrix effect was observed. The pharmacokinetic results showed that the R-CB have higher Cmax and AUC than that of S-CB. It is first time to find the chiral inversion between S-CB and R-CB in beagle.

Single-run reversed-phase HPLC method for determining sertraline content, enantiomeric purity, and related substances in drug substance and finished product

A direct enantio-, diastereo-, and chemo-selective high-performance liquid chromatographic method was developed for determining the content, enantiomeric purity, and related substances of the chiral antidepressant drug sertraline HCl in a single chromatographic run. The separation was achieved on a chiral stationary phase based on amylose tris(3-chloro-5-methylphenylcarbamate) under reversed-phase conditions. The method was optimized by evaluating the influence of the temperature and mobile phase composition on the retention and selectivity. The application of the single-run approach allowed to baseline resolve all investigated species in less than 15 min, without using buffers or tandem-coupled columns. The chromatographic method was validated according to the guidelines of the Official Medicines Control Laboratory and applied to control the content of sertraline HCl and related chiral substances in a generic antidepressant formulation.

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Sertraline displays two stereogenic centers but only the (1S,4S) form is clinically useful.

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A direct method was developed for evaluating assay and impurities in a single HPLC run.

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The single-run RP method allowed resolving all species within 15 min, without using buffers.

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Amylose tris(3-chloro-5-methylphenylcarbamate)-based CSP was used as a chiral support.

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The method is selective, precise and accurate and it meets the requirements of the EP guidelines.

Analysis of Aspirin, Prasugrel and Clopidogrel in Counterfeit Pharmaceutical and Herbal Products: Plackett–Burman Screening and Box–Behnken Optimization

An isocratic reversed-phase high-performance liquid chromatographic method has been developed and validated for the simultaneous determination of aspirin, prasugrel HCl and clopidogrel bisulfate in the presence of clopidogrel-related compound (impurity-A) in focus on counterfeit. This method was used to determine counterfeited antiplatelet drugs in two substandard Indian pharmaceutical products sold on the market in Yemen and two traditional herbal medicines sold on the market in China. Thin layer chromatography and mass spectrometry of counterfeit herbal medicines have additionally been carried out to verify the identification of adulterants. Chromatographic separation was performed on Inertsil ® ODS-3 C18 (4.6 × 250 mm, 5 μm) with isocratic mobile phase elution containing a mixture of acetonitrile: (25 mM) potassium dihydrogen phosphate buffer, pH 2.7 adjusted with 0.1 M o-phosphoric acid (79: 21, v/v), at a flow rate of 1 mL/min and UV detection at 220 nm. Designs of experiment methodology, Plackett–Burman and Box–Behnken designs were used for the screening and optimization of the mobile phase composition. The method validation was also performed in accordance with the International Council on Harmonization (ICH) guidelines. The method developed for routine analysis was found to be sensitive, simple, accurate and highly robust. The results were statistically compared to reference methods using Student’s t-test and variance ratio F-test at P < 0.05.

Stationary phase based on cellulose dodecanoate physically immobilized on silica particles for high-performance liquid chromatography

The chemical agent free preparation of a stationary phase using a natural macromolecule was the focus of this paper. Thermal immobilization of cellulose dodecanoate on silica particles was used for the preparation of a stationary phase without the use of chemical reagents. Cellulose modification was performed to produce a hydrophobic macromolecule with solubility in common organic solvents. The new stationary phase was characterized morphologically and physico-chemically, presenting as spherical particles immobilized with a thin cellulose dodecanoate layer. The degree of substitution of cellulose dodecanoate was 1.7, which resulted in a separation mechanism in reversed phase mode, but with lower hydrophobicity and higher steric selectivity, which are properties from cellulose. These characteristics resulted in a stationary phase with intrinsic selectivity that was able to separate mixtures of polar drugs, homologs of an anionic surfactant and omeprazole isomers, which are not well resolved in typical C₁₈ phases. Considering that cellulose is a natural polymer and the preparation method of stationary phase involves only physical processes of silica modification, the final material presents as a stationary phase with specific retention properties coming from both dodecanoate and cellulose.

The molecularly imprinted polymer essentials: curation of anticancer, ophthalmic, and projected gene therapy drug delivery systems

The development of polymeric materials as drug delivery systems has advanced from systems that rely on classical passive targeting to carriers that can sustain the precisely controlled release of payloads upon physicochemical triggers in desired microenvironment. Molecularly imprinted polymers (MIP), materials designed to capture specific molecules based on their molecular shape and charge distribution, are attractive candidates for fulfilling these purposes. In particular, drug-imprinted polymers coupled with active targeting mechanisms have been explored as potential drug delivery systems. In this review, we have curated important recent efforts in the development of drug-imprinted polymers in a variety of clinical applications, especially oncology and ophthalmology. MIP possesses properties that may complement the traditional delivery systems of these two disciplines, such as passive enhanced permeability and retention effect (EPR) in cancer tumors, and passive drug diffusion in delivering ophthalmic therapeutics. Furthermore, the prospects of MIP integration with the emerging gene therapies will be discussed.

The determination of enantiomer composition of 1-((3-chlorophenyl)-(phenyl)methyl) amine and 1-((3-chlorophenyl)(phenyl)-methyl) urea (Galodif) by NMR spectroscopy, chiral HPLC, and polarimetry

For the first time, a method for enantiomer resolution of the anticonvulsant Galodif (1-((3-chlorophenyl)(phenyl)methyl) urea) by chiral HPLC was developed, whereas the enantiomeric composition of 1-((3-chlorophenyl)(phenyl)methyl) amine-precursor in Galodif synthesis-cannot be resolved by this method. However, starting 1-((3-chlorophenyl)(phenyl)methyl) amine quantitatively forms diastereomeric N-((3-chlorophenyl)(phenyl)methyl)-1-camphorsulfonamides in reaction with chiral (1R)-(+)- or (1S)-(-)-camphor-10-sulfonyl chlorides. The diastereomeric ratio of obtained camphorsulfonamides can be easily determined by NMR ¹ H and ¹³ C spectroscopy. The DFT calculations of specific rotation of Galodif enantiomers showed good agreement with experimental data. The absolute configuration of enantiomers was proposed for the first time.