Fast enantiomeric separation of propranolol by affinity capillary electrophoresis using human serum albumin as chiral selector: application to quality control of pharmaceuticals

Chiral separation of propranolol by electrokinetic chromatography using nanodiamonds and human serum albumin as a pseudo-stationary phase in river water

Propranolol is currently considered as an emerging contaminant in water bodies. In this study, R- and S-propranolol were determined in river samples by electrokinetic chromatography (EKC) using nanodiamonds (NDs) and human serum albumin (HSA) as a pseudo-stationary phase in order to achieve enantioseparation. Previously, river samples were preconcentrated using a column filled with Amberlite® IR-120 and Dowex® 50WX8 resins. The setting up of influential factors such as temperature, voltage, pH, and HSA and NDs concentration is accurately described along this manuscript. A multivariate study and optimization was carried out to obtain the enantioseparation of propranolol (Rs = 2.91), which was reached under the following experimental conditions: voltage of 16 kV, temperature of 16°C, phosphate buffer pH 9.5, NDs of 0.20%, and HSA of 15 μmol l-1 . The recoveries of analytes under optimal conditions were higher than 98%. The limits of detection were 0.85 μg l-1 for R- and S-propranolol. The method was applied to real samples, and the obtained results in three different water sources studied were 1.02, 0.59, and 0.30 μg l-1 for the R-enantiomer and 0.99, 0.54, and 0.28 μg l-1 for the S-enantiomer. The accuracy of the proposed methodology (including bias and precision) has allowed us to propose it as a successful tool for the control of water quality.

Enantioresolution and Binding Affinity Studies on Human Serum Albumin: Recent Applications and Trends

The interaction between proteins and drugs or other bioactive compounds has been widely explored over the past years. Several methods for analysis of this phenomenon have been developed and improved. Nowadays, increasing attention is paid to innovative methods, such as high performance affinity liquid chromatography (HPALC) and affinity capillary electrophoresis (ACE), taking into account various advantages. Moreover, the development of separation methods for the analysis and resolution of chiral drugs has been an area of ongoing interest in analytical and medicinal chemistry research. In addition to bioaffinity binding studies, both HPALC and ACE al-low one to perform other type of analyses, namely, displacement studies and enantioseparation of racemic or enantiomeric mixtures. Actually, proteins used as chiral selectors in chromatographic and electrophoretic methods have unique enantioselective properties demonstrating suitability for the enantioseparation of a large variety of chiral drugs or other bioactive compounds. This review is mainly focused in chromatographic and electrophoretic methods using human serum albumin (HSA), the most abundant plasma protein, as chiral selector for binding affinity analysis and enantioresolution of drugs. For both analytical purposes, updated examples are presented to highlight recent applications and current trends.

Two dimensional chromatography mass spectrometry: Quantitation of chiral shifts in metabolism of propranolol in bioanalysis

In this study a heart-cutting 2D-LC method was successfully developed and optimized in order to discriminate and quantitate (S)-propranolol, (R)-propranolol, and its hydroxy metabolites, namely the isomeric (S)-4'‑hydroxy propranolol, (R)-4'‑hydroxy propranolol, (S)-5'‑hydroxy propranolol, (R)-5'‑hydroxy propranolol, (S)-7'-hydroxy propranolol, and (R)-7'‑hydroxy propranolol in one chromatographic run. Thereby, experiments investigating chiral discrimination in ring hydroxylation of propranolol were made feasible. Analysis of human urine samples after administration of a single oral dose of 40 mg of propranolol clearly revealed considerable chiral shifts in propranolol and its 4'-, 5'-, and 7'-hydroxy metabolites. Furthermore, the excretion rates of the individual (S)- and (R)-enantiomers were continuously monitored over 24 h post administration. Studies were performed utilizing a 2D-LC system hyphenated to a triple quadrupole mass spectrometer. The chromatographic system was endued with a reversed phase column (phenyl-hexyl) in first dimension and a teicoplanin based chiral column in second dimension. The method was basically validated and successfully evaluated as robust. Calibration was performed achieving accuracy between 80% and 120%. Maximal excretion rates of (S)-propranolol, (R)-propranolol, (S)-4'‑hydroxy propranolol, (R)-4'‑hydroxy propranolol, (S)-5'‑hydroxy propranolol, (R)-5'‑hydroxy propranolol, and (R)-7'‑hydroxy propranolol were 237 ng/min, 281 ng/min, 4 ng/min, 4 ng/min, 1 ng/min, 9 ng/min, and 3 ng/min, respectively.

Magnetic multi-walled carbon nanotube poly(styrene-co-divinylbenzene) for propranolol extraction and separation by capillary electrophoresis

AIM

The preparation of magnetic multi-walled carbon nanotube poly(styrene-co-divinylbenzene) for propranolol magnetic solid-phase extraction is described.

MATERIALS & METHODS

A study comparing propranolol adsorption and desorption was performed with only magnetic multi-walled carbon nanotubes, and different poly(styrene-co-divinylbenzene) with and without magnetic multi-walled carbon nanotubes. Enantiomeric separation of propranolol took place by cyclodextrin-modified capillary electrophoresis and the method was validated in spiked human urine samples.

RESULTS

Recovery values raised when styrene/divinylbenzene millimoles ratio was 19.57:15.80. Enrichment factors increased up to approximately 100, detection limits were 13.8 and 10.5 ng ml^-1 for R- and S-propranolol respectively, quantitation limits were 46.0 and 34.8 ng ml^-1 for R- and S-propranolol respectively, recoveries from spiked samples ranged from 90.9 to 109.0%, and relative standard deviations were <6.3%.

CONCLUSION

This methodology was proven to be more effective than classical solid-phase extraction strategies and may be applied to other kind of biological samples.

Propranolol

Propranolol is a noncardioselective β-blocker. It is reported to have membrane-stabilizing properties, but it does not own intrinsic sympathomimetic activity. Propranolol hydrochloride is used to control hypertension, pheochromocytoma, myocardial infarction, cardiac arrhythmias, angina pectoris, and hypertrophic cardiomyopathy. It is also used to control symptoms of sympathetic overactivity in the management of hyperthyroidism, anxiety disorders, and tremor. Other indications cover the prophylaxis of migraine and of upper gastrointestinal bleeding in patients with portal hypertension. This study provides a detailed, comprehensive profile of propranolol, including formulas, elemental analysis, and the appearance of the drug. In addition, the synthesis of the drug is described. The chapter covers the physicochemical properties, including X-ray powder diffraction, pK, solubility, melting point, and procedures of analysis (spectroscopic, electrochemical, and chromatographic). In-depth pharmacology is also presented (pharmacological actions, therapeutic dosing, uses, Interactions, and adverse effects and precautions). More than 60 references are given as a proof of the abovementioned studies.

Qualitative analysis of chiral alanine by UV-visible-shortwave near infrared diffuse reflectance spectroscopy combined with chemometrics

UV-vis-SWNIR DRS is firstly and successfully used to discriminate the chirality of compounds in powder with a good accuracy.

Recent advances in affinity capillary electrophoresis for binding studies

The present review covers recent advances and important applications of affinity capillary electrophoresis (ACE). It provides an overview about various ACE types, including ACE-MS, the multiple injection mode, the use of microchips and field-amplified sample injection-ACE. The most common scenarios of the studied affinity interactions are protein-drug, protein-metal ion, protein-protein, protein-DNA, protein-carbohydrate, carbohydrate-drug, peptide-peptide, DNA-drug and antigen-antibody. Approaches for the improvements of ACE in term of precision, rinsing protocols and sensitivity are discussed. The combined use of computer simulation programs to support data evaluation is presented. In conclusion, the performance of ACE is compared with other techniques such as equilibrium dialysis, parallel artificial membrane permeability assay, high-performance affinity chromatography as well as surface plasmon resonance, ultraviolet, circular dichroism, nuclear magnetic resonance, Fourier transform infrared, fluorescence, MS and isothermal titration calorimetry.

Advances in the enantioseparation of β-blocker drugs by capillary electromigration techniques

β-Blocker drugs or β-adrenergic blocking agents are an important class of drugs, prescribed with great frequency. They are used for various diseases, particularly for the treatment of cardiac arrhythmias, cardioprotection after myocardial infarction (heart attack), and hypertension. Almost all β-blocker drugs possess one or more stereogenic centers; however; only some of them are administered as single enantiomers. Since both enantiomers can differ in their pharmacological and toxicological properties, enantioselective analytical methods are required not only for pharmacodynamic and pharmacokinetic studies but also for quality control of pharmaceutical preparations with the determination of enantiomeric purity. In addition to the chromatographic tools, in recent years, capillary electromigration techniques (CE, CEC, and MEKC) have been widely used for enantioselective purposes employing a variety of chiral selectors, e.g. CDs, polysaccharides, macrocyclic antibiotics, proteins, chiral ion-paring agents, etc. The high separation efficiency, rapid analysi,s and low consumption of reagents of electromigration methods make them a very attractive alternative to the conventional chromatographic methods. In this review, the development and applications of electrodriven methods for the enantioseparation of β-blocker drugs are reported. The papers concerning this topic, published from January 2000 until December 2010, are summarised here. Particular attention is given to the coupling of chiral CE and CEC methods to MS, as this detector provides high sensitivity and selectivity.

Role of chemical structure in stereoselective recognition of beta-blockers by cyclodextrins in capillary zone electrophoresis

Most of the beta-blocking drugs for treating diseases of the cardiovascular system are chiral aryloxy-propanolamine derivatives. Tipically, the S(-) enantiomers are more active than the R(+) enantiomers. Only some of them (for example timolol) are used as single enantiomers, the others are employed as racemates. For the determination of the enantiomeric purity of timolol European Pharmacopoeia prescribes an HPLC method using chiral stationary phase. However, the use of chiral capillary zone electrophoresis for the determination of the enantiomeric purity is of pharmaceutical interest. This study describes the application of various cyclodextrin derivatives, hydroxypropyl-beta-cyclodextrin, randomly methylated beta-cyclodextrin, sulphated beta-cyclodextrin and sulphated alpha-cyclodextrin for the stereoselective analyses of beta-blockers. Baseline separation was obtained for bopindolol, carvedilol, mepindolol, pindolol and alprenolol, while only partial separation was observed for sotalol, propranolol, oxprenolol, atenolol, bisoprolol, bupranolol, and metoprolol. The uneven molecular recognition of the enantiomers of the beta-blockers, especially of the optical isomers of labetalol and nadolol, showed the importance of the chemical nature of the separators and the analytes.

Determination of association constants between steroid compounds and albumins by partial-filling ACE

ACE is a popular technique for evaluating association constants between drugs and proteins. However, ACE has not previously been applied to study the association between electrically neutral biomolecules and plasma proteins. We studied the affinity between human and bovine serum albumins (HSA and BSA, respectively) and three neutral endogenous steroid hormones (testosterone, epitestosterone and androstenedione) and two synthetic analogues (methyltestosterone and fluoxymesterone) by applying the partial-filling technique in ACE (PF-ACE). From the endocrinological point of view, the distribution of endogenous steroids among plasma components is of great interest. Strong interactions with albumins suppress the biological activity of steroids. Notable differences in the association constants were observed. In the case of the endogenous steroids, the interactions between testosterone and the albumins were strongest, and those between androstenedione and the albumins were substantially weaker. The association constants, K(b), for testosterone, epitestosterone and androstenedione and HSA at 37 degrees C were 32 100 +/- 3600, 21 600 +/- 1500 and 13 300 +/- 1300 M(-1), respectively, while the corresponding values for the steroids and BSA were 18 800 +/- 1500, 14 000 +/- 400 and 7800 +/- 900 M(-1). Methyltestosterone was bound even more strongly than testosterone, while fluoxymesterone was only weakly bound by the albumins. Finally, the steroids were separated by PF-ACE with HSA and BSA used as resolving components.

Evaluation of enantioselective binding of antihistamines to human serum albumin by ACE

The drug binding to plasma and tissue proteins is a fundamental factor in determining the overall pharmacological activity of a drug. HSA, together with alpha(1)-acid glycoprotein, are the most important plasma proteins, which act as drug carriers, with implications on the pharmacokinetic of drugs. Among plasma proteins, HSA possesses the highest enantioselectivity. In this paper, a new methodology for the study of enantiodifferentiation of chiral drugs with HSA is developed and applied to evaluate the possible enantioselective binding of four antihistamines: brompheniramine, chlorpheniramine, hydroxyzine and orphenadrine to HSA. This study includes the determination of affinity constants of drug enantiomers to HSA and the evaluation of the binding sites of antihistamines on the HSA molecule. The developed methodology includes the ultrafiltration of samples containing HSA and racemic antihistaminic drugs and the analysis of the free or bound drug fraction using the affinity EKC-partial filling technique and HSA as chiral selector. The results shown in this paper represent the first evidence of the enantioselective binding of antihistamines to HSA, the major plasmatic protein.

Enantiomeric quality control of antihistamines in pharmaceuticals by affinity electrokinetic chromatography with human serum albumin as chiral selector

The present paper deals with the enantiomeric separation of six antihistaminic enantiomers by affinity electrokinetic chromatography (AEKC)-partial filling technique using human serum albumin (HSA) as chiral selector. A multivariate optimization approach of the most critical experimental variables in enantioresolution, running pH, HSA concentration and HSA plug length (SPL) was carried out since there are interactions between variables that could not be considered in an univariate optimization. The estimated and experimental resolution values obtained for antihistaminic enantiomers varied from 1.13 (for orphenadrine) to 2.15 (for brompheniramine). The optimum experimental conditions for enantioresolution of each compound were: brompheniramine, pH 8.5, [HSA] 180 microM, SPL 180 s; chlorcyclizine, pH 6.5, [HSA] 180 microM, SPL 150 s; chlorpheniramine, pH 8.25, [HSA] 160 microM, SPL 150 s; hydroxyzine, pH 7.0, [HSA] 180 microM, SPL 150 s; and orphenadrine, pH 7.8, [HSA] 160 microM, SPL 150 s. pH and the quadratic term of pH seem to be the most critical factors that determine enantioresolution of antihistamines. The validity of the developed methodologies to enantiomeric quality control of antihistamines in pharmaceutical formulations is demonstrated analyzing the content of brompheniramine, chlorpheniramine and hyroxyzine enantiomers in commercially available pharmaceutical formulations containing racemic mixtures of compounds. Resolution, accuracy, reproducibility, cost and sample throughput of the proposed methodologies make them suitable for quality control of the enantiomeric composition of antihistamines in pharmaceutical preparations.

Potential of human serum albumin as chiral selector of basic drugs in affinity electrokinetic chromatography-partial filling technique

The enantiomeric resolution of compounds using HSA by means of affinity EKC (AEKC)-partial filling technique is the result of a delicate balance between different experimental variables such as protein concentration, running pH (background electrophoretic buffer (BGE), protein, and compound solutions), and plug length. In this paper, the possibility of using HSA as chiral selector for enantioseparation of 28 basic drugs using this methodology is studied. The effect of the physicochemical parameters, the structural properties of compounds, and compound-HSA protein binding percentages over their chiral resolution with HSA is outlined. Based on the results obtained, a decision tree is proposed for the "a priori" prediction of the capability of HSA for enantioseparation of basic drugs in AEKC. The results obtained indicated that enantioresolution of basic compounds with HSA depends on the hydrophobicity, polarity, and molar volume of compounds.

Enantioseparation of phenotiazines by affinity electrokinetic chromatography using human serum albumin as chiral selector: application to enantiomeric quality control in pharmaceutical formulations

Nowadays, there is a special interest within the pharmaceutical laboratories to develop single enantiomer formulations and consequently a need for analytical methods to determine the enantiomeric purity of drugs. The present paper deals with the enantiomeric separation of promethazine and trimeprazine enantiomers by affinity electrokinetic chromatography (AEKC)-partial filling technique using human serum albumin (HSA) as chiral selector. A multivariate optimization of the most critical experimental variables in enantioresolution, running pH, HSA concentration and plug length, is carried out to obtain enantioresolution of promethazine and trimeprazine. The estimated maximum and optimum resolution of trimeprazine and prometazine enantiomers (Rs=1.74 and 2.01, respectively) corresponded to the following experimental conditions: pH 7.5; [HSA] 170 microM and plug length 190 s and pH 7.6; [HSA] 170 microM and plug length 170 s, for trimeprazine and prometazine, respectively. The developed methodologies were applied for the enantiomeric quality control of promethazine and trimeprazine enantiomers in commercially available pharmaceutical formulations. Resolution, accuracy, reproducibility, cost and sample throughput of the proposed methodologies make it suitable for quality control of the enantiomeric composition of promethazine and trimeprazine in pharmaceutical preparations.

Chiral separations by capillary electrophoresis: Recent developments and applications

This paper provides an overview of the different classes of chiral selectors that are used in CE. The main properties of every class are described, together with the mechanism of enantioseparation. Newly introduced selectors are also discussed. Pharmaceutical and biomedical applications published from January 2004 till March 2005 are summarized.

Capillary electrophoresis for the analysis of small-molecule pharmaceuticals

This paper reviews the application of CE to the analysis of small-molecule pharmaceuticals. The areas of pharmaceutical analysis covered are enantiomer separation, the analysis of small molecules such as amino acids or drug counter-ions, pharmaceutical assay, determination of related substances and physicochemical measurements such as log P and pK(a) of compounds. The different electrophoretic modes available and their advantages for pharmaceutical analysis are described. Recent applications of CE for each subject area are tabulated with electrolyte details.

Role of chemical structure in stereoselective recognition of beta-blockers and H1-antihistamines by human serum transferrin in capillary zone electrophoresis

Studies on chiral resolution of beta-blocker and H1-antihistamine drugs by CZE using human serum transferrin are described. The drugs with different structures passed a pseudostationary protein zone in a coated capillary applying the partial filling method for the chiral separation. In this study we screened 15 compounds; most of them showed longer migration time, indicating an interaction with transferrin. Stereoselective interaction was observed only for five beta-blockers (celiprolol, talinolol, mepindolol, bopindolol, and oxprenolol) and for one H1-antihistamine (brompheniramine). The most important finding was that very small differences in the chemical structure of the drug resulted in significant changes in the stereoselective recognition. Resolution of mepindolol enantiomers was observed showing the essential role of one methyl group compared to pindolol, which is not resolved by transferrin. Bopindolol, also a derivative of pindolol having bigger difference in the structure, showed more experienced separation. The very slight difference between alprenolol and oxprenolol was also revealed with these methods, since only oxprenolol enantiomers, having an extra oxygen in the structure, are resolved. Determining the migration order of the eutomers and distomers (chlorpheniramine, brompheniramine) we can deduct conclusions about the role of serum proteins in the delivery of drugs within the body.

Recent advances in pharmaceutical applications of chiral capillary electrophoresis

This review article summarizes developments and applications of chiral capillary electrophoresis (CE) in the pharmaceutical field published from January 2004 to June 2005. Due to the tremendous number of publications, this article is aimed to focus on major developments in chiral separations and some selected applications rather than to provide a descriptive overview of all published papers. Valuable information is also collected from several excellent reviews published during this period. Developments are classified according to CE modes, namely capillary zone electrophoresis (CZE), micellar electrokinetic capillary chromatography (MEKC), microemulsion electrokinetic chromatography (MEEKC). In the CZE section, different types of chiral selectors including cyclodextrins, oligo- and polysaccharides, crown ethers, macrocyclic antibiotics, ligand exchange systems and proteins are described. Nonaqueous capillary electrophoresis is also included in this section. Coupling CE to MS is discussed in a separate part, followed by a summary of selected pharmaceutical applications of enantioselective CE. Finally, some conclusions are drawn and prospects of CE in chiral analysis are also drafted.

N-Menthoxycarbonylation combined with trimethylsilylation for enantioseparation of β-blockers by achiral dual-column gas chromatography

Solvent extractive two-phase menthoxycarbonyl (MnOC) derivatization was combined with trimethylsilyl (TMS) reaction for enantioseparation of beta-blockers by gas chromatography employing achiral DB-5 and DB-17 dual-columns of different polarity. beta-Blockers in alkaline solution were vortex-mixed with menthyl chloroformate present in dichloromethane to be extracted as diastereomeric N-MnOC derivatives. The subsequent O(N)-TMS reaction allowed complete enantioseparations of two beta-blockers and partial separations of five as N-MnOC/O(N)-TMS derivatives in a single analysis. The temperature-programmed retention index sets were characteristic of each derivative, facilitating chiral discrimination of each enantiomer.

Multivariate optimization approach for chiral resolution of drugs using human serum albumin in affinity electrokinetic chromatography-partial filling technique

The enantiomeric resolution of chiral compounds using HSA by means of affinity EKC (AEKC)-partial filling technique is the result of a delicate balance between different experimental variables such as protein concentration, running pH (background electrophoretic buffer, protein and compound solutions) and protein solution plug length. In this paper multivariate optimization approaches for chiral separation of four basic drugs (alprenolol, oxprenolol, promethazine and propranolol) using HSA as chiral selector in AEKC-partial filling technique are studied. The experimental conditions to achieve maximum resolution are optimized using the Box-Behnken experimental design. Partial least squares and pareto charts are used to analyse the main effects on the resolution. The experimental resolutions observed for all compounds studied in optimum conditions agree with the estimated values based on response surface models. The results obtained show that the range of experimental conditions that provided enantioresolution narrows as hydrophobicity of analytes decreases. This fact can be explained by assuming that hydrophobicity controls the interaction of basic compounds with HSA.

Chiral separation of oxprenolol by affinity electrokinetic chromatography-partial filling technique using human serum albumin as chiral selector

The intrinsic characteristics of capillary electrophoresis have made this technique a powerful tool in the chiral separation field. The present paper deals with the enantiomeric separation of oxprenolol enantiomers by affinity electrokinetic chromatography-partial filling technique using human serum albumin (HSA) as chiral selector. Several experimental conditions and variables affecting the separation such as pH, HSA concentration and plug length, background electrolyte concentration, temperature and voltage were studied. Baseline separation of oxprenolol enantiomers was obtained in less than 8 min under the following selected conditions: electrophoretic buffer composed of 50 mM Tris-(hydroximethyl)-aminomethane (Tris) at pH 8.5; 190 microM HSA solution applied at 50 mbar for 225 s as chiral selector; oxprenolol samples contained 190 microM HSA solution injected hydrodynamically at 30 mbar for 2s and the electrophoretic runs performed at 30 degrees C applying 15 kV voltage. The proposed methodology was applied for the analysis of two pharmaceutical preparations. Resolution, accuracy, reproducibility, speed and cost of the proposed method make it suitable for quality control of the enantiomeric composition of oxprenolol in drugs. The results show that a different affinity between oxprenolol enantiomers and HSA exists and can contribute to the pharmacokinetic differentiation of these enantiomers.

Probing affinity via capillary electrophoresis: advances in 2003–2004

This review addresses recent advances in capillary electrophoresis of biological-based molecular interaction from a broader perspective, based on applications reported during the period 2003-2004. These capillary electrophoresis-based studies of molecular interactions include affinity capillary electrophoresis, electrokinetic chromatography, and free zone electrophoresis. The review is written as a general synopsis of applications and does not cover the theory or protocol involved in the implementation of the analyses.