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

'Ab Ovo' Chiral Phases and Chiral Reagents for Liquid Chromatographic Separation and Isolation of Enantiomers

The de-novo approach of mixing chirally pure reagents or Cu(II)-L-amino acid complexes in the slurry of silica gel for preparing TLC plates was reported from author's laboratory and was successful for separation and isolation of enantiomers. Using high molar absorptivity molecules, e. g., 1,5-difluoro-2,4-dinitrobenzene and cyanuric chloride, more than 38 new chiral derivatizing reagents were synthesized in our laboratory by straightforward nucleophilic substitution with simple chiral auxiliaries. Besides, (S)-naproxen, (S)-ketoprofen, and (S)-levofloxacin were used as chiral platforms. A conceptual approach using both achiral phases in chromatography for enantioseparation was also adopted. ¹ H NMR and DFT based software were used to explain structures of non-covalent and covalent diastereomeric pairs and determination of configuration and separation mechanism. The methods can be easily used to determine and control enantiomeric purity with advantages over a variety of commercial chiral phases.

(+) or (-)-1-(9-fluorenyl)ethyl chloroformate as chiral derivatizing agent: A review

Over the last 30years, (±)-1-(9-fluorenyl)ethyl chloroformate ((±)-FLEC) was used as a chiral derivatizing agent in various analytical applications involving a wide range of endogenous, pharmaceutical and environmentally relevant molecules. This comprehensive review aims to present all the significant aspects related to the state of the art in FLEC labeling and subsequent chiral separation of the resulting diastereomers using LC, SFC and CE techniques.

(S)-Naproxen based novel chiral reagent for C–N bond formation: enantioseparation of some β-blockers, determination of absolute configuration and elution order of diastereomers

Symmetrical anhydride proved to be a good reagent for C–N bond formation instead of direct reaction of amino group of analyte with (S)-Npx.

Reversed-phase high-performance liquid chromatographic enantioresolution of six beta-blockers using dinitrophenyl-L-Pro-N-hydroxysuccinimide ester, N-succinimidyl-(S)-2-(6-methoxynaphth-2-yl) propionate and twelve variants of Sanger's reagent as chiral derivatizing reagents

Twelve chiral derivatizing reagents (CDRs) were synthesized by substituting one of the fluorine atoms in 1,5-difluoro-2,4-dinitrobenzene (DFDNB) with three optically pure amines [(R)-(-)-1-cyclohexylethylamine, (+)-dehydroabietylamine and (S)-(-)-alpha,4-dimethylbenzylamine], six amino acid amides [L-Ala-NH(2), L-Phe-NH(2), L-Val-NH(2), L-Leu-NH(2), L-Met-NH(2) and D-Phg-NH(2)] and three amino acids [L-Ala, L-Val and L-Leu]. In addition, dinitrophenyl-L-Pro-N-hydroxysuccinimide ester and N-succinimidyl-(S)-2-(6-methoxynaphth-2-yl) propionate were also synthesized and used as CDR. Keeping in view the presence of an amino group, diastereomers of six beta-blockers (atenolol, propranolol, bisoprolol, metoprolol, salbutamol, and carvedilol) were synthesized by reaction with these 14 CDRs. The diastereomers were separated by RP-HPLC. The method was validated for linearity, accuracy, limit of detection and limit of quantification.

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.

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.

A minisensor for the rapid screening of atenolol in pharmaceutical preparations based on surface-stabilized bilayer lipid membranes with incorporated DNA

This work describes an electrochemical technique that is suitable for the rapid and sensitive screening of atenolol based on surface-stabilized bilayer lipid membranes (s-BLMs) composed from egg phosphatidylcholine (PC). The interactions of atenolol with s-BLMs produced electrochemical ion current increases that reproducible appeared within a few seconds after the exposure of the membranes to the drug. The current signal increase was related to the concentration of atenolol in bulk solution in the micromolar range. The present lipid film-based sensor provided fast response (i.e. on the order of a few seconds) to alterations of atenolol concentration (20 to 200 micro M) in electrolyte solution. ssDNA incorporated into s-BLMs can interact with atenolol, and decreased the detection limit of this drug by one order of magnitude. The oligomers used were single stranded deoxyribonucleic acids: thymidylic acid icosanucleotide terminated with a C-16 alkyl chain to assist incorporation into s-BLMs (5'-hexadecyl-deoxythymidylic acid icosanucleotide, dT(20)-C(16)). The electrochemical transduction of the interactions of atenolol with s-BLMs was applied in the determination of these compounds in pharmaceutical preparations by using the present minisensor.

Development of a chiral assay for a novel, nonfluorinated quinolone, PGE-9509924, in dog plasma using high performance liquid chromatography with electrospray tandem mass spectrometry or fluorescence detection

PGE-9509924 is a nonfluorinated quinolone and is active against a variety of susceptible and drug resistant bacteria in vitro and in animal infection models. A method for determining both enantiomers of PGE-9509924 in dog plasma has been developed. The enantiomers are derivatized with a chiral derivatizing agent, (-)-1-(9-fluorenyl)ethyl chloroformate (FLEC) and the resulting diastereomers are separated by reverse phase chromatography. Plasma samples are prepared via solid phase extraction (SPE) in a 96-well format prior to being derivatized. Samples are then analyzed by electrospray-LC/MS/MS with multiple reaction monitoring or by HPLC with fluorescence detection. Results of a side-by-side validation of the method with LC/MS/MS and HPLC/Fl detection are presented. Over the range selected for validation (0.025-10 micro g/ml), both methods give similar results with identical limits of quantitation. Due to the selectivity of LC/MS/MS and the use of a stable-isotopically labeled internal standard, significantly shorter chromatographic runtimes are achieved with LC/MS/MS, making it the method of choice for sample analysis.

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.

Improved enantioselective method for the determination of the enantiomers of reboxetine in plasma by solid-phase extraction, chiral derivatization, and column-switching high-performance liquid chromatography with fluorescence detection

A rapid enantioselective method is described for the quantitation of the reboxetine (R,R)- and (S,S)-enantiomers in plasma utilizing solid-phase extraction, derivatization, normal-phase high-performance liquid chromatography, and fluorescence detection. Plasma samples (0.1 ml) with added internal standard were applied to activated solid-phase extraction discs containing a nonpolar/strong cation mixed-phase, washed, eluted, evaporated to dryness, and derivatized for 5 min with (+)-1-(9-fluorenyl)ethyl chloroformate. After termination of the derivatization reaction, the samples were analyzed by isocratic normal-phase HPLC using a silica column and ethanol-heptane (1:124, v/v) as mobile phase. The derivatized reboxetine peak was column-switched onto cyano and Chiralcel OD-H columns in series using ethanol-heptane (1:49, v/v) as mobile phase to resolve the diastereomeric derivatives of the enantiomers and separate interferences. The column effluent was monitored with fluorescence detection at 260/315 nm. The range of quantitation of each enantiomer was 2-2000 ng/ml. One sample was injected every 18 min.

Enantioseparation of beta-blockers labelled with a chiral fluorescent reagent, R (-)-DBD-PyNCS, by reversed-phase liquid chromatography

A fluorescent chiral tagging reagent, 4-(3-isothiocyanatopyrrolidin-1-yl)-7-(N,N-dimethylaminosulfony l)-2,1, 3-benzoxadiazole [R(-)-DBD-PyNCS], has been used for the liquid chromatographic resolution of racemic pairs of beta-blockers. The reagents reacts with beta-blockers at 65 degrees C for 90 min in aqueous acetonitrile containing 0.05% triethylamine to produce the corresponding pair of diastereomers. No racemization occurs during the tagging reaction under these conditions. From results of the time-course study of oxprenolol the reactivities of the enantiomers of beta-blockers with R(-)-DBD-PyNCS are comparable. The optimum excitation and emission wavelengths of the resulting derivatives were ca. 460 and 550 nm, respectively. The derivatives of beta-blockers were efficiently resolved by a reversed-phase column with water-acetonitrile containing 0.1% trifluoroacetic acid as the eluent. The resolution (Rs) values of the diastereomers derived from 10 beta-blockers were in the range of 1.54-4.80. The Rs value for timolol was 0.643. The detection limits (signal-to-noise ratio of 2) were one or two orders of magnitude lower with beta-blockers having the iso-propylamino structure (15-300 fmol) than with those having the tert-butylamino structure (1.25-8.00 pmol). The proposed procedure was applied to the determination of R(+)- and S(-)-propranolol in rat plasma and saliva after oral administration of R(+)-propranolol hydrochloride or S(-)-propranolol hydrochloride.

4-(6-methoxy-2-naphthyl)-2-butyl chloroformate enantiomers: new reagents for the enantiospecific analysis of amino compounds in biogenic matrices

(+)- and (-)-4-(6-methoxy-2-naphthyl)-2-butyl chloroformate (NAB-C) were prepared from the prochiral non-steroidal anti-inflammatory agent nabumetone with the aim of developing easily detectable chloroformate reagents for the enantiospecific HPLC analysis of amino compounds in biogenic matrices on achiral stationary phases. The new reagents were tested in the derivatization of beta-adrenoceptor antagonists and anti-arrhythmic agents and allowed derivatization in the presence of water. (+)- and (-)-NAB-C were compared with other reagents with a 6-methoxy-2-naphthyl moiety as a chromophore. The reagents were suitable for the analysis of nanogram amounts of, for example, metoprolol enantiomers in plasma, a prerequisite for application in pharmaco- or toxicokinetic studies.

Recent progress in liquid chromatographic enantioseparation based upon diastereomer formation with fluorescent chiral derivatization reagents

Techniques for the resolution by liquid chromatography of racemic compounds based upon diastereomer formation with a fluorescent chiral reagent are outlined in this review. The tagging reagents for various functional groups, i.e. amine, carboxyl, hydroxyl and thiol, are evaluated in terms of optical purity, handling, flexibility, stability, sensitivity and selectivity. The applicabilities of the reagents to drugs and biologically important substances are included in the text. This review is limited to reagents with fluorophores and reagents that exhibit fluorescence.

Sensitive fluorimetric determination of gentamicin sulfate in biological matrices using solid-phase extraction, pre-column derivatization with 9-fluorenylmethyl chloroformate and reversed-phase high-performance liquid chromatography

A high-performance liquid chromatographic method is described for the determination of gentamicin in bacterial culture medium or plasma with increased sensitivity and improved separation of the C1 component. Gentamicin was extracted from the biological matrix with high efficiency using carboxypropyl (CBA)-bonded silica. Derivatization with 9-fluorenylmethyl chloroformate (FMOC-Cl) followed by C18 reversed-phase chromatography allowed the fluorimetric detection of gentamicins C1, C1a and C2. A fourth component, considered to be gentamicin C2a, was partially resolved from the C2 peak. Optimal conditions for the extraction and derivatization of gentamicin are described. The detection limit was below 50 micrograms/l, the assay was linear to 5 mg/l and showed good reproducibility. It is concluded that pre-column derivatization with FMOC-Cl substantially improves the analysis of gentamicin compared with present methods based on reaction with o-phthaldialdehyde.

Enantiomeric derivatization for biomedical chromatography

Derivatization reactions aimed at creating the basis for the chromatographic resolution of biologically and pharmaceutically important enantiomers are reviewed, with emphasis on the literature published in the last 10 years. Three main aspects of chiral derivatization are discussed. (a) Enantiomers containing suitable functional groups (amino, carboxyl, hydroxyl, epoxy, etc.) are transformed into covalently bonded diastereomeric derivatives using homochiral derivatizing agents. The diastereomers formed (esters, amides, urethanes, urea and thiourea, etc., derivatives) can be separated on achiral stationary phases. The derivatization reactions often afford further advantages, such as the improvement of chromatographic properties and the detectability of the solutes using UV and fluorimetric detectors. (b) Covalent but achiral derivatization is often necessary even with the use of chiral stationary phases enabling in principle direct enantioseparations (Pirkle-type columns, cyclodextrin-bonded phases, glycoprotein column and functionalized cellulose columns). The main goals of these derivatization reactions (which are analogous to those discussed above), are to introduce functional groups into the molecule of the enantiomers that improve the possibilities for chiral interactions or block functional groups to avoid non-specific interactions. (c) In the broader sense, the dynamic formation of diastereomers using chiral mobile phase additives (cyclodextrins, various reagents to form diastereomeric ion pairs, adducts, mixed metal complexes) can also be considered to be chiral derivatization reactions and is therefore briefly discussed also.

Sensitive enantiomer-specific high-performance liquid chromatographic analysis of methamphetamine and amphetamine from serum using precolumn fluorescent derivatization

In order to study the stereoselective disposition of methamphetamine (MAP), a widely abused drug, we have developed a sensitive HPLC assay to separate and quantitate the enantiomers of MAP and amphetamine (AP) in rat serum. Serum samples to which was added aniline sulfate (internal standard) were alkalized with 0.02 M carbonate buffer (pH 10.6) and extracted with ethyl acetate. Following back extraction with hydrochloric acid, neutralization, and reconstitution, the sample was derivatized with (-)-fluorenylethyl chloroformate overnight at room temperature. The derivatized products were separated following injection onto a reversed-phase C18 column. The mobile phase consisted of 0.02 M acetate buffer-acetonitrile-tetrahydrofuran (46:39:15, v/v). The fluorescent intensity of the effluent was monitored at excitation and emission wavelengths of 265 and 330 nm, respectively. The derivatized aniline, R-, S-AP, R- and S-MAP had retention times of 21.0, 22.6, 23.6, 27.7 and 29.0 min, respectively. Linear standard curves were obtained over the concentration range of 5-250 ng/ml. The inter-day and intra-day coefficients of variation for the assay of all four compounds at 12.5, 50.0 and 250 ng/ml were in the range of 2.1-18.6%. The method was applied to quantitate the concentrations of MAP and AP enantiomers in rat serum following a short term intravenous infusion of racemic MAP (15 mg/kg). There were no differences in serum concentrations of MAP enantiomers but the concentrations of S-AP were consistently greater than those of R-AP. These data suggest a stereoselective disposition for the formation and/or elimination of amphetamine.

High-performance liquid chromatographic determination of (SR)- and (RS)-enantiomers of mefloquine in plasma and capillary blood sampled on paper after derivatization with (-)-1-(9-fluorenyl)ethyl chloroformate

A sensitive, stereoselective and rapid reversed-phase liquid chromatographic method for the determination of (SR)- and (RS)-mefloquine enantiomers in 100 microliters plasma and capillary blood collected on chromatographic paper is presented. The assay involves protein precipitation from plasma, liquid-liquid extraction of mefloquine from plasma, capillary blood with methyl tert.-butyl ether under alkaline conditions and derivatization of MQ with (-)-1-(9-fluorenyl)ethyl chloroformate. Liquid chromatographic separation of the diastereomers was performed using an C18 reversed-phase column with acetonitrile-water-acetic acid 82:18:0.07 (v/v/v) as the mobile phase, and a flow-rate of 1.0 ml/min. When using 100 microliters of plasma the limit of determination is 250 nmol/l with ultraviolet- and 10 nmol/l with fluorescence detection. The present method offers several advantages over those previously reported; very low limit of determination, small sample volume, sampling onto paper and use of an inexpensive standard achiral HPLC column. No racemization during the derivatization procedure or storage of the MQ enantiomers was found.

Determination of S 12024 enantiomers in human plasma by liquid chromatography after chiral pre-column derivatization

S 12024-2 is a new drug in phase II development that possesses cognitive enhancing properties. As its molecular structure has a chiral centre, a stereoselective method for the analysis of both enantiomers in human plasma has been developed. The method involves pre-column derivatization of the amine moiety with a homochiral reagent (+)-1-(9-fluorenyl)ethyl chloroformate (FLEC), and chromatographic separation of the two diastereoisomers on an achiral reversed-phase cyanopropyl column, with fluorimetric detection (lambda ex = 260 nm; lambda em = 310 nm). A liquid-liquid extraction procedure with diethyl ether-dichloromethane (70:30, v/v) was used for sample preparation. This technique provides a linear response for both enantiomers over a concentration range of 10-500 ng ml-1 and the quantitation limit was set at 5 ng ml-1 in human plasma. Within-day and between-day precision and accuracy are within 9% limits for all concentrations assessed. This procedure was therefore used for determining both enantiomers in human plasma following oral administration of racemic S 12024-2 to elderly healthy subjects.

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.

Determination of the R,R- and S,S-enantiomers of vamicamide in human serum and urine by high-performance liquid chromatography on a Chiral-AGP column

An enantioselective liquid chromatographic assay for the determinations of the R,R- and S,S-enantiomers of vamicamide, a potent anticholinergic drug, in human serum and urine is described. Racemic vamicamide and internal standard were purified from biological fluids using a two-step extraction procedure involving diethyl ether and 0.1% phosphoric acid. The overall recoveries of racemic vamicamide and internal standard were greater than 80%. The purified samples were measured by high-performance liquid chromatography on a Chiral-AGP column with ultraviolet absorbance detection at 260 nm. The standard curves for the analytes were linear from 10 to 200 ng/ml in serum and from 0.25 to 50 micrograms/ml in urine. The quantification limit of both enantiomers was 10 ng/ml for serum and 250 ng/ml for urine. Both intra-day and inter-day accuracy and precision data showed good reproducibility of the method. The assay has been applied for the analysis of vamicamide enantiomers in serum and urine samples from a healthy volunteer.

Screening of beta-blockers in human serum by ion-pair chromatography and their identification as methyl or acetyl derivatives by gas chromatography-mass spectrometry

A simultaneous screening method for atenolol, acebutolol, metoprolol, oxprenolol, alprenolol and propranolol by ion-pair chromatography with a column-switching technique was developed. The serum samples were purified using either liquid-liquid extraction or solid-phase extraction methods. The pretreatment of the samples consisted of hydrolysis and protein precipitation. The drug separation was on either octadecylsilica or polymer-based alkyl column material. Binary eluent mixtures containing methanol and a buffer solution with a quaternary ammonium salt as an ion-pair former were used. Detection of the compounds in liquid chromatographic analysis was based on ultraviolet spectra. The effects of methanol, two buffers and the ion-pair former on the retention of the compounds were studied. The determination limits ranged from nanograms to micrograms in the ion-pair chromatographic method, depending on the drug studied. Identification was based on the mass spectra or, if necessary, on selected-ion monitoring spectra of either the methylated or the acetylated compounds obtained by means of gas chromatography-electron impact or negative chemical ionization mass spectrometry. The detection limits for the identified compounds were in the picogram range. The matrix effect was strong, and this resulted in determination limits in the nanogram range with the scan method.

Stereoselective pharmacokinetics of atenolol in the rat: influence of aging and of renal failure

The pharmacokinetics of R- and S-atenolol after intravenous administration of racemic atenolol were studied in 3-, 12- and 24-month-old rats and in 3-month-old rats with renal failure induced by uranyl nitrate. In all age groups, the area under the plasma concentration-time curves is higher for R- than for S-atenolol; volume of distribution, total clearance and renal clearance are lower for R-atenolol than for S-atenolol, but the differences are small. In function of age there is for both enantiomers a significant increase in AUC, due, at least in part, to a decreased renal clearance; the effect of aging is not stereoselective. In rats with renal failure, the AUC of both enantiomers increases, due mainly to a decrease in renal clearance, but to a lesser degree also to a decrease in nonrenal clearance. For both enantiomers, the volume of distribution decreases and the half-life increases in the uraemic rats. The total amount of both enantiomers excreted in the urine is decreased in the rats with renal failure. There are no stereoselective effects of treatment of the rats with uranyl nitrate.

Stereoselective features of (R)- and (S)-atenolol: clinical pharmacological, pharmacokinetic, and radioligand binding studies

In a randomized, double-blind, cross-over study in 12 healthy volunteers, the effects of single oral doses of 100 mg rac-atenolol were compared during exercise to those of equal amounts of the optically pure enantiomers, i.e., 50 mg (R)- and 50 mg (S)-atenolol. The mean rate pressure product decreased with rac-atenolol (-37%; P < 0.01) and half-dosed (S)-atenolol (-35%; P < 0.01) to the same extent, whereas (R)-atenolol caused no effect. Radioligand binding studies in beta-adrenergic receptors of the guinea pig heart yielded a eudismic ratio of 46 for (S)- to (R)-atenolol. The mean AUCs, maximal plasma concentrations, and plasma half-lives of the enantiomers were similar regardless of whether they were administered as optically pure enantiomers or as racemic mixture. On the other hand, the AUC of (R)-atenolol was 1.08-fold greater (P < 0.01) than that of the (S)-enantiomer. The reason for this finding remains unclear. We conclude that only (S)-atenolol, but not (R)-atenolol, contributes to the beta-blocking effect of currently used rac-atenolol since the same effect can be elicited with the (S)-enantiomer alone.

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.