Simultaneous enantioseparation and purity determination of chiral switches of amlodipine and atenolol by liquid chromatography

Derivatization-free conventional and synchronous spectrofluorimetric estimation of atenolol and amlodipine

Fixed-dose combinations for treatment of hypertension are observed in many dosages in the global market because of their high efficacy compared to single component dosage forms. One of these effective combinations is atenolol/amlodipine which is usually administered to patients with hypertension. Hence, development of facile, accurate, and sensitive methods for simultaneous estimation of atenolol and amlodipine is of great importance for quality control testing and pharmacokinetic studies. In our study, we developed two spectrofluorimetric methods to estimate both compounds in different pharmaceuticals. The first method is based on the estimation of atenolol and amlodipine by double-scan conventional spectrofluorimetry where the fluorescence intensities of atenolol and amlodipine were measured at 299 and 434 nm after excitation at 274 and 358 nm, respectively. The second method depends on synchronous spectrofluorimetric measurements at Δλ = 70 nm, where atenolol is assayed at 266 nm and amlodipine is assayed at 363 nm. Methods' optimizations were carried out to select the optimum conditions that render high selectivity and sensitivity. Such optimizations included assessment of solvents, surfactants, buffer volumes and pHs. The conventional spectrofluorimetric method was rectilinear over concentration range of 30.0-300.0 ng mL-1 for atenolol and 0.25-7.00 µg mL-1 for amlodipine while the synchronous spectrofluorimetric method showed linearity over the ranges of 0.60-6.00 µg mL-1 for atenolol and 0.25-7.00 µg mL-1 for amlodipine with low detection limits (≤0.12 µg mL-1) for both compounds in the two methods. It is the first work that demonstrates estimation of atenolol and amlodipine in their combinations by conventional and synchronous spectrofluorimetry. Both methods were applied to estimate atenolol and amlodipine in different pharmaceuticals with high %recovery and low %RSD.

Quality by Design Assisted Optimization of a Chiral Capillary Electrokinetic Chromatographic Method for the Separation of Amlodipine Enantiomers Using Maltodextrin as Chiral Selector

Analytical-method development based on design of experiment has been applied for optimizing the enantioseparation of amlodipine by chiral capillary electrokinetic chromatography using maltodextrin as the chiral selector. The effect of different factors on the enantioresolution quality was screened. Three separation factors, namely maltodextrin concentration, pH of the background electrolyte and applied voltage were selected as independent variables. The number of experiments was reduced while maximizing the information content using design of experiment. Based on a full-quadratic design that included three variables on three levels, the total design space could be reduced to fifteen factor combinations using a D-optimal algorithm. The aim of the experiment was to find the optimal factor combinations with respect to resolution. The maltodextrin concentration (7.5–10% w/v) demonstrated the strongest effect on the resolution followed by pH (2–4) of the background electrolyte and the applied voltage (15–20 kV). An increase in the maltodextrin concentration was found to result in a greater stereoselectivity, represented by the higher resolution values (R_s ≥ 1.5). The separation conditions in the proposed method were feasible to be adjusted within the applied range with an acceptable resolution.

Bioanalytical Method Development of Atenolol Enantiomers: Stereoselective Behavior in Rabbit Plasma by RP-UFLC Method

Objective:

The objective of the method was to develop a new, simple and reliable enantioselective Reverse Phase- Ultra-Fast Liquid Chromatography (RP-UFLC) method for the separation of Atenolol enantiomers. A comprehensive study was performed by extending the work to pharmacokinetic studies using rabbit plasma.

Background:

Many methods were reported for enantioseparation of Atenolol enantiomers but no attempts were made for chiral separation of Atenolol using rabbit plasma. Moreover, pharmacokinetic data to prove the efficiency of particular enantiomers in rabbit plasma was not studied.

Methods:

In the present examination, the binary RP-UFLC technique was developed on Phenomenex® Lux cellulose i5 segment (150×4.6 mm, 5μ) using di-sodium hydrogen phosphate buffer (pH 6.8): acetonitrile (35:65 v/v) as the mobile phase.

Results:

The elution of Atenolol was observed at 225 nm with a stream rate of 1 mL.min-1. The described technique offered a linear relationship with a regression coefficient of r2 = 0.997 and 0.996 for (R) and (S)-enantiomer respectively, between the concentration range of 2-10 ng.mL-1. Atenolol enantiomers were detected at a retention time (tR) of 2.7 min and 3.10 min for R and S-enantiomer respectively. The rate of recovery of both Atenolol enantiomers was observed to be (R) 98.18% and (S) 100.45% individually. USFDA guidelines May 2018 were systematically followed for the development and validation of the bioanalytical method.

Conclusion:

The developed technique was applied for the separation of Atenolol enantiomers and for the pharmacokinetic determination of Atenolol enantiomers in rabbit plasma.

Recent advances in chiral analysis for biosamples in clinical research and forensic toxicology

This article covers current methods and applications in chiral analysis from 2010 to 2020 for biosamples in clinical research and forensic toxicology. Sample preparation for aqueous and solid biological samples prior to instrumental analysis were discussed in the article. GC, HPLC, capillary electrophoresis and sub/supercritical fluid chromatography provide the efficient tools for chiral drug analysis coupled to fluorescence, UV and MS detectors. The application of chiral analysis is discussed in the article, which involves differentiation between clinical use and drug abuse, pharmacokinetic studies, pharmacology/toxicology evaluations and chiral inversion. Typical chiral analytes, including amphetamines and their analogs, anesthetics, psychotropic drugs, β-blockers and some other chiral compounds, are also reviewed.

Dispersive solid-phase extraction of racemic drugs using chiral ionic liquid-metal-organic framework composite sorbent

Nowadays, enantioseparation of racemic pharmaceuticals in preparations is a prime concern by drug authorities across the globe. In the present work, it was attempted to develop novel enantioselective extraction method for five clinically used drugs (atenolol, propranolol, metoprolol, racecadotril, and raceanisodamine in their tablets) as racemates. The enantioselective solid-liquid extraction of these racemic drugs was carried out successfully by the use of chiral ionic liquid (CIL) in combination with a metal organic framework (MOF) for the first time. The composite CIL@MOF was synthesized from tropine based chiral ionic liquids with L-proline anion ([C_nTr][L-Pro], n=3-6) and HKUST-1 type MOF, which was comprehensively characterized before being used as sorbent for enantioselective dispersive solid-liquid extraction. Preliminary selection of appropriate CIL was carried out on thin layer chromatography (TLC); under the joint participation of copper ion in the developing reagent, [C₃Tr][L-Pro] ionic liquid showed better resolution performance with ΔR_f value of 0.35 between the enantiomers was obtained for racemic atenolol. Moreover, the effect of copper salt dosage, amount of CIL, soli-liquid ratio and extraction time were investigated. The optimal conditions were obtained after thorough investigations; i.e. sample solution: ethanol, elution solvent: methanol, solid-liquid ratio: 12.5 mg:50 mL, amount of copper salt: 8 mg L^-1, amount of impregnated CIL: 30% and extraction time of 30 min. As a result, enantiomeric excess values are 90.4%, 95%, 92%, 81.6% and 83.2% for atenolol, propranolol, metoprolol, racecadotril and raceanisodamine, respectively. The developed enantioselective method was validated following ICH guidelines and it was proved to be simple, effective and enantioselective way for separation of racemic pharmaceuticals with similar behaviors.

The Crystal Structure of N-(1-Arylethyl)-4-methyl- 2,2-dioxo-1H-2λ6,1-benzothiazine-3-carboxamides as the Factor Determining Biological Activity Thereof

In order to detect new structural and biological patterns in a series of hetaryl-3-carboxylic acid derivatives, the optically pure (S)- and (R)-enantiomers of N-(1-arylethyl)-4-methyl- 2,2-dioxo-1H-2λ6,1-benzothiazine-3-carboxamides, their true racemates, and mechanical racemic mixtures have been synthesized in independent ways. The particular features of the 1Н- and 13С-NMR spectra of all synthesized substances, liquid chromato-mass spectrometric behavior thereof under electrospray ionization conditions, and also the results of polarimetric and X-ray diffraction studies have been discussed. Pharmacological screening on a model of carrageenan inflammation has found a clear relationship between the spatial structure of the studied objects and biological activity thereof. Enantiomers with chiral centers having (S)-configuration showed weak inhibition of pain and inflammatory reactions, while their mirror (R)-isomers exhibited very powerful analgesic and antiphlogistic properties under the same conditions, with the level of specific activity exceeding that of Lornoxicam and Diclofenac. Taking obtained data into account, a noticeable decrease in the activity of mechanical racemic mixtures, consisting of one-half of the “wrong” (S)-enantiomers, is quite natural. The true racemate of N-(1-phenylethyl)-amide proved itself in a similar way, while 4-methoxy-substituted analog thereof stood out against this background with unexpectedly high analgesic and anti-inflammatory activities. A comparative analysis of X-ray diffraction data has found that crystalline and molecular structure of racemic N-[1-(4-methoxyphenyl)ethyl]-4-methyl-2,2-dioxo-1H-2λ6,1-benzothiazine-3-carboxamide is completely different from that of the original enantiomers and, moreover, very unusual for racemates. Obviously, it is the factor determining the unique character of the biological effects of the said substance.

Comparative Enantioseparation of Amlodipine by HPLC and Capillary Electrophoresis

Objective: The purpose of this study was to separate the enantiomers of amlodipine by High Performance Liquid Chromatography (HPLC) using ovomucoid (OVM) as chiral selector, respectively by Capillary Electrophoresis (CE) using cyclodextrines and to evaluate the analytical performance of the both proposed methods.

Material and methods: HPLC enantioseparation of amlodipine was performed on an HPLC Agilent Technologies 1100 series using as chiral stationary phase an Ultron ES OVM, 150x4.6 mm column with ovomucoid as chiral selector. The stereoselective CE analysis of amlodipine was achieved on Agilent Technologies 7100 CE using uncoated fused-silica capillaries 48 cm x 50 mm and different type of cyclodextrins as chiral selectors.

Results: A mobile phase consisting of 80% Na2HPO4 10 mM at a pH level of 5.0 and 20% ACN, isocratic elution at a flow of 1 ml/min turned to be the optimal experimental conditions for HPLC analysis (R=5.51; α=1.71) with retention times shorter than 10 minutes for the two isomers, tR (S-AML) = 4.63 (min); tR (R-AML) = 5.54 (min). The migration times for amlodipine enantiomers were tm (S-AML) = 8.15 (min) and tm (R-AML)= 8.45 (min) and the optimum CE conditions have proven to be a buffer solution containing 25 mM H3PO4 at pH 3.0 and 20 mM α-CD as chiral selector and a capillary temperature set at 15°C (R=1.51; α=1.03).

Conclusion: The analytical performances of the chromatographic method using OVM as chiral selector are superior to the electrophoretic analysis method but the CE method is more economical and may represent an alternative to the HPLC chromatographic separation.

Spectrofluorimetric determination of atenolol from human urine using high-affinity molecularly imprinted solid-phase extraction sorbent

This study presents a novel, sensitive and selective molecularly imprinted solid-phase extraction (MISPE)-spectrofluorimetric method for the removal and determination of atenolol from human urine. Molecularly imprinted and non-imprinted polymers were synthesized thermally using a radical chain polymerization technique and used as solid-phase extraction sorbents. Acrylic acid ethylene glycol dimethacrylate, dibenzoyl peroxide and dichloroethane were used as a functional monomer, cross-linker, initiator and porogen, respectively. The calibration curve was in the range of 0.10-2.0 μg/ml for the developed method. Limit of detection and limit of quantification values were 0.032 and 0.099 μg/ml, respectively. Owing to the selectivity of the MISPE technique and the sensitivity of spectrofluorimetry, trace levels of atenolol have been successfully determined from both organic and aqueous media. Relatively high imprinting factor (4.18) and recovery results (74.5-75.3%) were obtained. In addition, intra- and interday precision values were 0.38-1.03% and 0.47-2.05%, respectively, proving the precision of the proposed method. Thus, a selective, sensitive and simple MISPE-spectrofluorimetric method has been developed and applied to the direct determination of atenolol from human urine.

An overview of experimental designs in HPLC method development and validation

Chemometric approaches have been increasingly viewed as precious complements to high performance liquid chromatographic practices, since a large number of variables can be simultaneously controlled to achieve the desired separations. Moreover, their applications may efficiently identify and optimize the significant factors to accomplish competent results through limited experimental trials. The present manuscript discusses usefulness of various chemometric approaches in high and ultra performance liquid chromatography for (i) methods development from dissolution studies and sample preparation to detection, considering the progressive substitution of traditional detectors with tandem mass spectrometry instruments and the importance of stability indicating assays (ii) method validation through screening and optimization designs. Choice of appropriate types of experimental designs so as to either screen the most influential factors or optimize the selected factors' combination and the mathematical models in chemometry have been briefly recalled and the advantages of chemometric approaches have been emphasized. The evolution of the design of experiments to the Quality by Design paradigm for method development has been reviewed and the Six Sigma practice as a quality indicator in chromatography has been explained. Chemometric applications and various strategies in chromatographic separations have been described.

HPLC Enantioseparation of β-Blockers on Ovomucoid Stationary Phase†

The purpose of this study was to separate single and multiple pairs of six β-blockers enantiomers by high performance liquid chromatography on ovomucoid (OM) column in optimal conditions. The separation was performed isocratically or in gradient elution at 25°C, flow rate of 1 mL/min and 220 nm. The mobile phase consisted of phosphate buffer/acetonitrile or methanol. The effect of the organic modifier, the influence of pH and the percentage of the aqueous phase on resolution were investigated. The elution order of propranolol (PRP) enantiomers was established as well as the detection and quantification limits. The results show that OM was suitable for enantiomeric separation of the nonselective β-blockers carvedilol, PRP, pindolol and oxprenolol, and not for the two β-1 selective blockers, atenolol and metoprolol. A hypothesis regarding a possible correlation between structure-pharmacological activity-chromatographic behavior is proposed.