High-performance liquid chromatographic determination of the enantiomers of beta-adrenoceptor blocking agents in biological fluids. II. Studies with atenolol

Different approaches of impregnation for resolution of enantiomers of atenolol, propranolol and salbutamol using Cu(II)-L-amino acid complexes for ligand exchange on commercial thin layer chromatographic plates

Atenolol and propranolol (the beta-blocking agents) and salbutamol (broncho- and vasodilator) were resolved into their enantiomers by adopting different modes of loading/impregnating the Cu(II) complexes of L-proline (L-Pro), L-phenylalanine (L-Phe), L-histidine (L-His), N,N-dimethyl-L-phenylalanine (N,N-Me(2)-L-Phe), and L-tryptophan (L-Trp) on commercial precoated normal phase plates. The three different approaches were (A) using the Cu(II)-L-amino acid complex as chiral mobile phase additive, (B) ascending development of plain commercial plates in the solutions of Cu complex, and (C) using a solution of Cu(II) acetate as mobile phase additive for the commercial TLC plates impregnated with ascending development of plates in the solutions of amino acid. Spots were located using iodine vapour. The results obtained for the three methods have been compared for their efficiency and the issue of involvement of the Cu(II) cation for the best performance of the three methods has been discussed with respect to the same mobile phase. The detection limit is 0.18 microg for each enantiomer.

Chiral cardiovascular drugs: an overview

Stereochemistry in drug molecules is rapidly becoming an important aspect in drug research, design, and development. Recently, individual stereoisomers of drug molecules with asymmetric centers such as fexofenadine, cetirizine, verapamil, fluoxetine, levalbutarol, and amphetamine, for example, have been separated and developed as individual drugs. These stereoisomers have different therapeutic activity, and each isomer has contributed differently with respect to its formulation's pharmacologic activity, side effects, and toxicity. The present overview discusses chirality among a select group of cardiovascular drugs, their stereochemical synthesis/preparation, isolation techniques using chiral chromatography, methods for confirmation of their enantiomeric purity, pharmacodynamics, and pharmacokinetics. Chirality has been visualized as an important factor in cardiovascular research. It is also becoming evident in other areas of therapeutics.

Comparison of methods for measurement of organic compounds at ultra-trace level: analytical criteria and application to analysis of amino acids in extraterrestrial samples

The need for criteria to compare different analytical methods for measuring extraterrestrial organic matter at ultra-trace levels in relatively small and unique samples (e.g., fragments of meteorites, micrometeorites, planetary samples) is discussed. We emphasize the need to standardize the description of future analyses, and take the first step toward a proposed international laboratory network for performance testing.

Resolution of chiral drugs by liquid chromatography based upon diastereomer formation with chiral derivatization reagents

Chiral derivatization reagents for resolution of biologically important compounds, such as chiral drugs by high-performance liquid chromatography (HPLC), based upon pre-column derivatization and diastereomer formation, are reviewed. The derivatization reagents for various functional groups, i.e., amine, carboxyl, carbonyl, hydroxyl and thiol, are evaluated in terms of reactivity, stability, wavelength, handling, versatility, sensitivity, and selectivity. The applicability of the reagents to the analyses of drugs and bioactive compounds are included in the text.

Chiral derivatization reagents for drug enantioseparation by high-performance liquid chromatography based upon pre-column derivatization and formation of diastereomers: enantioselectivity and related structure

Structures and related enantioselectivities of the respective chiral derivatization reagents (CDRs) for drug enantioseparation by high-performance chromatography based upon pre-column derivatization and diastereomeric formation are reviewed. The elution order of diastereomers caused reaction of some CDRs with enantiomeric amino acids and carboxylic acids. The development of new CDRs available for indirect HPLC methods is also discussed. (c) 2001 John Wiley & Sons, Ltd.

Reversed-phase high-performance liquid chromatographic analysis of atenolol enantiomers in rat hepatic microsome after chiral derivatizaton with 2,3,4,6,-tetra-O-acetyl-beta-D-glycopyranosyl isothiocyanate

A reversed-phase high-performance liquid chromatographic method for the determination of the enantiomers of atenolol in rat hepatic microsome has been developed. Racemic atenolol was extracted from alkalinized rat hepatic microsome by ethyl acetate. The organic layer was dried with anhydrous sodium sulfate and evaporated using a gentle stream of air. Atenolol racemic compound was derivatized with 2,3,4,6-tetra-O-acetyl-beta-D-glycopyranosyl isothiocyanate at 35 degrees C for 30 min to form diastereomers. After removal of excess solvent, the diastereomers were dissolved in phosphate buffer (pH 4.6)-acetonitrile (50:30). The diastereomers were separated on a Shimadzu CLC-C18 column (10 microm particle size, 10 cm x 0.46 cm I.D.) with a mobile phase of phosphate buffer-methanol-acetonitrile (50:20:30, v/v) at a flow-rate of 0.5 ml/min. A UV-VIS detector was operated at 254 nm. For each enantiomer, the limit of detection was 0.055 microg/ml (signal-to-noise ratio 3) and the limit of quantification (signal-to-noise ratio 10) was 0.145 microg/ml (RSD <10%). In the range 0.145-20 microg/ml, intra-day coefficients of variation were 1.0-7.0% and inter-day coefficients of variation were 0.4-16.5% for each enantiomer. The assay was applied to determine the concentrations of atenolol enantiomers in rat hepatic microsome as a function of time after incubation of racemic atenolol.

New method for the resolution of the enantiomers of 5,6-dihydroxy-2-methyl-aminotetralin by selective derivatization and HPLC analysis: application to biological fluids

A new chiral derivatization procedure for the HPLC resolution of chiral catecholamines and structurally related compounds is described. The homochiral reagent, (+)-(R)-1-phenylethyl isocyanate (RPEIC), was added to separate and quantitate the enantiomers of rac-5,6-dihydroxy-2-methyl-aminotetralin, the main metabolite of rac-5, 6-diisobutyryl-2-methyl-aminotetralin, a potent dopamine agonist, by reversed-phase HPLC analysis. To avoid catecholamine degradation in the basic reaction medium and to obtain the selective and quantitative derivatization of the amino group of the compound, the reversible complex formation between diphenylborinic acid (DPBA) and the catechol group, in alkaline medium, was performed before homochiral isocyanate addition. The RPEIC derivatization was completed in 30 min and then the DPBA complex was dissociated by adding dilute acid. The structure of intermediates and urea derivatives was confirmed by mass spectometry. The use of an electrochemical detector, operating in redox mode, allowed HPLC quantitation of enantiomers at the nanogram level in plasma and urine. The derivatization procedure is also suitable for other catecholamine-related compounds.

Enantioselective bioanalysis of beta-blocking agents: focus on atenolol, betaxolol, carvedilol, metoprolol, pindolol, propranolol and sotalol

The recent developments in enantioselective HPLC-separation techniques are impressive and are driven by industrial and academic interests; thus there is for instance a high demand for developing stereoselective assays for chiral drugs in biological fluids. The beta-blocking agents, which possess an amino-propanol- or -ethanol side chain with at least one chiral centre, represent one of the most intensively investigated groups of more than 40 drugs introduced world wide. Seven of the most popular beta-blockers were chosen as representatives: atenolol; betaxolol; carvedilol; metoprolol; pindolol; propranolol; and sotalol, these span the whole range of lipophilicity to hydrophilicity (polarity). Enantioselective HPLC bioassays for these beta-blockers published so far, including techniques based on chiral derivatizing agents (CDAs), chiral stationary phases (CSPs) and chiral mobile phase additives (CMPAs) have been reviewed and documented in the light of general aspects together with pharmacokinetic and pharmacodynamic considerations.

Selective method for plasma quantitation of the stereoisomers of a new aminotetralin by high-performance liquid chromatography with electrochemical detection

A high-performance liquid chromatographic method is described for the quantitation in plasma of the four stereoisomers of a new aminotetralin, (SRR, RSS)(SRS, RSR)-5,6-dimethoxy-2-[3'-(p-hydroxyphenyl)-3'-hydroxy-2'- propyl]aminotetralin (CHF 1255, internal code). After liquid-liquid extraction of the drug, separation was obtained after chiral derivatization with R-(+)-alpha-methylbenzyl isocyanate. The selective derivatization of the amino group was obtained by controlling the pH of the reaction medium at 7.5. The reaction was quantitative after a period of 16 h. The structures of the urea derivatives were confirmed by proton nuclear magnetic resonance spectroscopy and high-performance liquid chromatography with mass spectrometric detection. The use of an electrochemical detector, operating in the oxidative mode, allows the quantitation in plasma of all four urea derivatives at the nanogram level. The method was demonstrated to be precise, reproducible and applicable to pharmacokinetics studies after administration of the two epimeric racemates.

Stereoselective HPLC bioanalysis of atenolol enantiomers in plasma: application to a comparative human pharmacokinetic study

An enantioselective HPLC bioassay has been developed relying on extraction of (R)- and (S)-atenolol from alkalinized plasma or serum (pH > 12) into dichloromethane containing 5% (v/v) 1-butanol followed by an achiral derivatization of the drug with phosgene leading to (R)- and (S)-oxazolidine-2-one derivatives. Under these conditions there was quantitative conversion of the acetamido group to the corresponding nitrile. These stable derivatives were separated on a (R,R)-diaminocyclohexane-dinitrobenzoyl chiral stationary phase [(R,R)-DACH-DNB] using dichloromethane/methanol 98/2 as mobile phase. Determination limits of 0.5 ng for (R)- and 0.6 ng for (S)-atenolol could be achieved using fluorimetric detection. The assay was applied to a human pharmacokinetic study which was performed in a randomized cross-over, double-blind fashion in 12 healthy volunteers, administering single oral doses of 100 mg (R,S)-, 50 mg (R)-, and 50 mg (S)-atenolol. AUC0-24 and Cmax values of (R)-atenolol were slightly but significant higher than those of (S)-atenolol. The R/S ratios were 1.09 for AUC(R)/AUC(S) and 1.03 for Cmax (R)/Cmax(S) (P < 0.01) respectively after administration of the racemic drug. However, there were no difference between AUC, Cmax, and t1/2 values of each enantiomer, whether they were administered as single enantiomers or in the form of its racemic mixture.

Chiral separation by high performance liquid chromatography. I. Review on indirect separation of enantiomers as diastereomeric derivatives using ultraviolet, fluorescence and electrochemical detection

The increased attention on the therapeutic implications of stereoisomerism has provided an impetus for the development of analytical methods for enantiomeric separation. The indirect method of separation of enantiomers as diastereomers using high performance liquid chromatography (HPLC) has emerged as an efficient and versatile approach. This is due mainly to the availability of numerous chiral derivatization reagents (CDRs). This article reviews CDRs useful for the development of an indirect HPLC method using ultraviolet, fluorescence and electrochemical detection. In addition, factors crucial for the development of the indirect method are discussed.

The chiral chromatographic separation of β-adrenoceptor blocking drugs

Over 100 chromatographic procedures for the separation of beta-blocker enantiomers are reviewed including a large number for the analysis of biological samples. All the principal chiral chromatographic procedures have found use, namely Chiral Mobile Phase Additives (CMPA), Chiral Derivatization Agents (CDA) and Chiral Stationary Phases (CSP). Chiral Mobile Phase Additives are less frequently employed than the other two procedures and many of the earlier methods were based on the use of CDAs. However, the recent development of sophisticated custom-made CSPs has allowed the separation of native (underivatized) analytes and this approach appears to be gaining in popularity. The beta-blockers are an extensive group of drugs and stereoselective separations have been reported for 40 different structures.

Reversed-phase high-performance liquid chromatographic analysis of atenolol enantiomers in plasma after chiral derivatization with (+)-1-(9-fluorenyl)ethyl chloroformate

A sensitive high-performance liquid chromatographic method for the determination of the enantiomers of atenolol in rat plasma has been developed. Racemic atenolol and practolol (internal standard) were extracted from alkalinized plasma (pH 12) into dichloromethane containing 3% (v/v) heptafluoro-1-butanol, and the organic layer was evaporated. The samples were derivatized with (+)-1-(9-fluorenyl)ethyl chloroformate at pH 8.5 for 30 min. After removal of excess reagent, the diastereomers were extracted into dichloromethane. The diastereomers were separated on a Microspher C18 column (3 microns) with a mobile phase of acetonitrile-sodium acetate buffer (0.01 M, pH 7) (50:50, v/v) at a flow-rate of 0.8 ml/min. Fluorescence detection (lambda ex = 227 nm, lambda em = 310 nm) was used. When 100 microliters of plasma were used, the quantitation limit was 10 ng/ml for the atenolol enantiomers. The assay was applied to measure concentrations of atenolol enantiomers in plasma after intravenous administration of racemic atenolol to rats.

Chromatography of beta-adrenergic blocking agents

The determination of beta-blockers has posed pharmaceutical analysts with a variety of problems arising from the essential characteristics of these compounds as bases and the variability of physicochemical properties of individual drugs. Liquid chromatography has become the favoured method of analysis and to a certain extent there is a standardised approach to analysis based on either solvent or solid-phase extraction and reversed-phase high-performance liquid chromatography coupled to fluorescence detection. The analyst must be aware of interactions occurring during extraction stages. All manipulations should be fully evaluated for individual drugs and metabolites prior to use. Other analytical options are chosen for specific or more demanding applications. The use of unmodified silicas for the liquid chromatography of beta-blockers (and other basic drugs) is an example of a potential alternative mode of chromatography. The stereoselectivity of the pharmacology of beta-blockers has spawned a great deal of literature describing the resolution of enantiomers by chromatographic methods. It is envisaged that this area will achieve greater prominence in the future as drug development pursues optical purity. The demand for the availability of enantiomerically pure pharmaceutical preparations will certainly see developments for preparative-scale separations as well as analytical methods and will surely promote developments in new and established methods of chromatography.