Metabolic Activation and Cytotoxicity of Labetalol Hydrochloride Mediated by Sulfotransferases.

Labetalol hydrochloride (LHCl), an α- and ß-adrenoreceptor blocker, is widely used for the treatment of hypertension as well as angina pectoris. Previous reports have demonstrated the adverse events during clinical application of LHCl, such as liver injury and acute renal failure. The present study aimed to investigate metabolic activation of LHCl to initiate the elucidation of the mechanisms of its liver toxicity. One glutathione (GSH) conjugate was detected in rat and human primary hepatocytes as well as bile of rats after exposure to LHCl. The GSH conjugate was chemically synthesized and characterized by Q-TOF and 1H NMR. Pretreatment of 2,6-dichloro-4-nitrophenol (DCNP), a broad-spectrum sulfotransferase (SULT) inhibitor, significantly attenuated the formation of the GSH conjugate in LHCl-treated hepatocytes and animals, indicating the participation of SULTs in metabolic activation of LHCl. Moreover, pretreatment with DCNP displayed significant protection against the observed cytotoxicity in rat primary hepatocytes, which suggests a correlation of the bioactivation of LHCl mediated by SULTs with LHCl-induced hepatotoxicity.

Rational targeting of Wzb phosphatase and Wzc kinase interaction inhibits extracellular polysaccharides synthesis and biofilm formation in Acinetobacter baumannii.

Acinetobacter baumannii is an opportunistic nosocomial pathogen, and responsible for high mortality and morbidity. Biofilm formation is one of the resistance determinants, where extracellular polysaccharide (EPS) is an essential component. EPS synthesis and its export is regulated by the bacterial Wza-Wzb-Wzc system. Wzc exhibits auto-phosphorylation protein tyrosine kinase activity, while Wzb is a protein tyrosine phosphatase. Wzb mediates dephosphorylation of Wzc. Dephosphorylated Wzc is required for the export of the EPS through porin Wza-Wzc complex. It shows that the interaction of Wzb with Wzc is critical for the export of EPS. Therefore, if the Wzb-Wzc interaction is inhibited, then it might hinder the EPS transport and diminish the biofilm formation. In this study, we have modelled the Wzb, and Wzc proteins and further validated using PSVS, ProSA, RAMPAGE, and PDBsum. The modelled proteins were used for protein-protein docking. The docked protein-protein complex was minimized by Schrodinger software using OPLS_2005 force field. The binding site of the minimized Wzb-Wzc complex was identified by Sitemap. The high throughput virtual screening identified Labetalol hydrochloride and 4-{1-hydroxy-2-[(1-methyl-3-phenylpropyl) amino] propyl} phenol from FDA-approved drug library based on their interaction at the interface of Wzb-Wzc complex. The inhibitor-protein complex was further undergone molecular mechanics analysis using Generalized Born model and Solvent Accessibility (MMGBSA) to estimate the binding free energies. The lead was also used to generate the pharmacophore model and screening the molecule with antimicrobial scaffold. The identified lead was experimentally validated for its effect on EPS quantity and biofilm formation by A. baumannii. Wzb-Wzc interaction is essential for biofilm and EPS export; hence, the identified lead might be useful to regulate the biofilm formation by A. baumannii.

Development and validation of a bio-analytical method for simultaneous quantification of nebivolol and labetalol in aqueous humor and plasma using LC-MS/MS and its application to ocular pharmacokinetic studies.

Beta blockers is the class of choice of drugs in treatment of open angle Glaucoma. However, many of these drugs suffer from systemic side effects due to their absorption into systemic circulation via nasolachrymal duct. To evaluate the safety and efficacy of nebivolol and labetalol for the treatment of open angle glaucoma, it is important to have a bioanalytical method for measuring the drug concentrations both in aqueous humor and plasma. A simple, sensitive and high throughput liquid chromatography-tandem mass spectrometry (LC-MS/MS) method with protein precipitation technique was developed for simultaneous quantification of nebivolol and labetalol using nebivolol-d4 and metoprolol, respectively, as internal standards in aqueous humor and plasma. Nebivolol and labetalol were monitored in electrospray positive ionization (ESI) mode at transition 406.2/151.1 and 329.2/162.0, respectively. Mobile phase comprised of mixture of aqueous buffer (solvent A) and organic phase (solvent B) (mixture of A:B in the ratio of 30:70, v/v). The aqueous buffer was 5 mM ammonium acetate buffer adjusted to pH 3.5 ±â€¯0.05 with formic acid while the organic phase was a mixture of methanol and acetonitrile in the ratio of 25:75, v/v. Chromatographic separation was achieved using reverse phase Zorbax SB-C18 column (4.6 × 100 mm, 3.5 µm). Method was linear in both the matrices in the concentration range of 0.43-750 ng/mL for nebivolol and 0.39-668 ng/mL for labetalol with r2 > 0.99. Accuracy values, expressed in terms of bias (%), for nebivolol in aqueous humor and plasma were ≤9.6% and ≤11.4% and for labetalol were ≤8.6% and ≤5.9%, respectively. Inter-day and intra-day precision values, expressed in terms of RSD (%), for both the drugs were within 11.4%. No interference was obtained due to matrix components. Mean recovery (%) values in aqueous humor and plasma were 72.4% and 73.0% for nebivolol and 56.7% and 54.4% for labetalol, respectively. No significant degradation was observed in both the drugs in both the matrices when stored at -20 °C for 1 month. Aqueous humor and plasma samples of nebivolol and labetalol on bench top were stable for 18 h and 8 h, respectively. The developed method was applied for determining pharmacokinetic parameters of both drugs in aqueous humor following single dose ocular administration in rabbits.

Calculating Kinetic Rates and Membrane Permeability from Biased Simulations.

We present a simple approach to calculate the kinetic properties of lipid membrane crossing processes from biased molecular dynamics simulations. We demonstrate that by using biased simulations, one can obtain highly accurate kinetic information with significantly reduced computational time with respect to unbiased simulations. We describe how to conveniently calculate the transition rates to enter, cross, and exit the membrane in terms of the mean first passage times. To obtain free energy barriers and relaxation times from biased simulations only, we constructed Markov models using the dynamic histogram analysis method (DHAM). The permeability coefficients that are calculated from the relaxation times are found to correlate highly with experimentally evaluated values. We show that more generally, certain calculated kinetic properties linked to the crossing of the membrane layer (e.g., barrier height and barrier crossing rates) are good indicators of ordering drugs by permeability. Extending the analysis to a 2D Markov model provides a physical description of the membrane crossing mechanism.

α1-and ß-adrenergic antagonist labetalol induces morphological changes in human erythrocytes.

Labetalol is one of the most used drugs for the treatment of hypertension. This molecule is able to bind to both alpha-1 (α1) and beta (ß) adrenergic receptors present in vascular smooth muscle among other tissues. It has been determined that human erythrocytes possess both alpha receptors and beta-adrenergic receptors expressed on their surface. The objective of this work was to study the effect of labetalol on the morphology of human erythrocytes. To accomplish this goal, human erythrocytes and model membranes built of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE) were used. These lipid species are present in the outer and inner monolayers of the red blood cell membrane, respectively. Our findings obtained by X-ray diffraction and differential scanning calorimetry (DSC) indicate that labetalol interacted with both lipids in a process dependent on concentration. In fact, at low concentrations labetalol preferentially interacted with DMPE. On the other hand, results obtained by scanning electron microscopy (SEM) showed that labetalol alters the normal biconcave form of erythrocytes to stomatocytes and knizocytes (cells with one or more cavities, respectively). According to the bilayers couple hypothesis, this result implied that the drug inserted in the inner monolayer of the human erythrocyte membrane.

Derivatization of labetalol hydrochloride for its spectrofluorimetric and spectrophotometric determination inhuman plasma: Application to stability study.

Two simple, selective and accurate methods were developed for the determination of Labetalol hydrochloride in pure form and pharmaceutical tablets. Both methods are based on derivatization of the studied drug with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole (NBDCl) in alkaline medium (pH7.5).The reaction product was measured spectrofluorimetrically at 540nm after excitation at 476nm (method I) or spectrophotometrically at 480nm (method II). The calibration graphs were rectilinear over the concentration ranges of 0.10-2.0 and 1.0-11.0µgmL-1 for methods I and II, respectively. The proposed methods were successfully applied to the analysis of commercial tablets without interference from common excipients. Furthermore, the spectrofluorimetric method was utilized for the in vitro determination of labetalol in spiked human plasma, with a percent mean recovery (n=3) of 97.80±1.29%. Moreover, the spectrofluorimetric method was extended to examine the stability study of LBT under different stress conditions such as alkaline, acidic, oxidative, photolytic and a thermal degradation.

Graphene Facilitated Removal of Labetalol in Laccase-ABTS System: Reaction Efficiency, Pathways and Mechanism.

The widespread occurrence of the beta-blocker labetalol causes environmental health concern. Enzymatic reactions are highly efficient and specific offering biochemical transformation of trace contaminants with short reaction time and little to none energy consumption. Our experiments indicate that labetalol can be effectively transformed by laccase-catalyzed reaction using 2, 2-Azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) as a mediator, while no significant removal of labetalol can be achieved in the absence of ABTS. A total of three products were identified. It is interesting that the presence of graphene greatly increased the reaction rate while not changed the products. In the presence of 100 µg/L graphene, the pseudo-first-order reaction rate constant was increased ~50 times. We found that the enhancement of graphene is probably attributed to the formation and releasing of ABTS(2+) which has a much greater reactivity towards labetalol when graphene is present. This study provides fundamental information for laccase-ABTS mediated labetalol reactions and the effect of graphene, which could eventually lead to development of novel methods to control beta-blocker contamination.

The low/high BCS permeability class boundary: physicochemical comparison of metoprolol and labetalol.

Although recognized as overly conservative, metoprolol is currently the common low/high BCS permeability class boundary reference compound, while labetalol was suggested as a potential alternative. The purpose of this study was to identify the various characteristics that the optimal marker should exhibit, and to investigate the suitability of labetalol as the permeability class reference drug. Labetalol's BCS solubility class was determined, and its physicochemical properties and intestinal permeability were thoroughly investigated, both in vitro and in vivo in rats, considering the complexity of the whole of the small intestine. Labetalol was found to be unequivocally a high-solubility compound. In the pH range throughout the small intestine (6.5-7.5), labetalol exhibited pH-dependent permeability, with higher permeability at higher pH values. While in vitro octanol-buffer partitioning (Log D) values of labetalol were significantly higher than those of metoprolol, the opposite was evident in the in vitro PAMPA permeability assay. The results of the in vivo perfusion studies in rats lay between the two contradictory in vitro studies; metoprolol was shown to have moderately higher rat intestinal permeability than labetalol. Theoretical distribution of the ionic species of the drugs was in corroboration with the experimental in vitro and the in vivo data. We propose three characteristics that the optimal permeability class reference drug should exhibit: (1) fraction dose absorbed in the range of 90%; (2) the optimal marker drug should be absorbed largely via passive transcellular permeability, with no/negligible carrier-mediated active intestinal transport (influx or efflux); and (3) the optimal marker drug should preferably be nonionizable. The data presented in this paper demonstrate that neither metoprolol nor labetalol can be regarded as optimal low/high-permeability class boundary standard. While metoprolol is too conservative due to its complete absorption, labetalol has been shown to be a substrate for P-gp-mediated efflux transport, and both drugs exhibit significant segmental-dependent permeability along the gastrointestinal tract. Nevertheless, the use of metoprolol as the marker compound does not carry a risk of bioinequivalence: Peff value similar to or higher than metoprolol safely indicates high-permeability classification. On the other hand, a more careful data analysis is needed if labetalol is used as the reference compound.

Encapsulation of labetalol, pseudoephedrine in ß-cyclodextrin cavity: spectral and molecular modeling studies.

The absorption and fluorescence spectra of labetalol and pseudoephedrine have been studied in different polarities of solvents and ß-cyclodextrin (ß-CD). The inclusion complexation with ß-CD is investigated by UV-visible, steady state and time resolved fluorescence spectra and PM3 method. In protic solvents, the normal emission originates from a locally excited state and the longer wavelength emission is due to intramolecular charge transfer (TICT). Labetalol forms a 1:2 complex and pseudoephedrine forms 1:1 complex with ß-CD. Nanosecond time-resolved studies indicated that both molecules show triexponential decay. Thermodynamic parameters (ΔG, ΔH, ΔS) and HOMO, LUMO orbital investigations confirm the stability of the inclusion complex. The geometry of the most stable complex shows that the aromatic ring is deeply self included inside the ß-CD cavity and intermolecular hydrogen bonds were established between host and guest molecules. This suggests that hydrophobic effect and hydrogen bond play an important role in the inclusion process.

Kinetic capillary electrophoresis with mass-spectrometry detection (KCE-MS) facilitates label-free solution-based kinetic analysis of protein-small molecule binding.

Tandem tracker: Here we introduce a method for studying the kinetics of protein-small-molecule interactions based on kinetic capillary electrophoresis (KCE) separation and MS detection. Due to the variety of KCE methods and MS modes available, the KCE-MS tandem is a highly versatile platform for label-free, solution-based kinetic studies of affinity interactions.

Microcalorimetric and zeta potential study on binding of drugs on liposomes.

In this work, isothermal titration calorimetry (ITC) combined with zeta potential measurements was used to study the binding and partitioning of three beta-blockers, alprenolol, labetalol and propranolol, and the local anaesthetic tetracaine into liposomes. The thermodynamic parameters of enthalpy, entropy, the Gibbs energy and the binding constant were determined using the one site model. Furthermore, the binding constants corrected for the electrostatic contribution were used to assess the partition coefficients for the drugs. Also, the effect of the concentration, ionic strength, temperature and membrane curvature on the interaction was included in the evaluation.

Formulation and evaluation of a gastroretentive dosage form of labetalol hydrochloride.

Labetalol hydrochloride (LBT), 2-hydroxy-5-[1-hydroxy-2-[(1-methyl-3-phenylpropyl) amino] ethyl]-benzamide, a non-selective alpha, beta-adrenoceptor antagonist is used in the treatment of hypertension. It shows variable bioavailability ranging from 10-80% which may be attributed to its minimum solubility in pH range 6 to 10, the pH conditions prevailing at the major site of absorption i.e. small intestine. Also due to its half life of 3 to 6 hrs it is administered twice daily. In the present work non-effervescent sustained release gastroretentive floating tablets of labetalol hydrochloride have been developed using various grades of HPMC and Poloxamer M127 as wetting agent. The tablets were evaluated for in vitro drug release, floating time, floating lag time, swelling studies etc. The tablets formulated with HPMC K4M CR and HPMC K15M CR along with Poloxamer showed negligible floating lag time with a total floating time over 12 hrs with complete release. Formulation was optimized using Stat-Ease Design Expert 7.1 software. Optimized batch was evaluated for the effect of change of osmolarity and pH on drug release, floating and swelling behaviour.

In vitro and in vivo assessment of matrix type transdermal therapeutic system of labetalol hydrochloride.

OBJECTIVE: The aim of the investigation was to develop and evaluate matrix type transdermal therapeutic systems containing new polymeric combinations (Eudragit E PO/Eudragit RL 100 & Plasdone S 630) as polymers and Labetalol Hydrochloride (LBHCl) as a model drug. EXPERIMENTAL: The matrix type TTS of LBHCl were prepared by film casting technique. The patches were characterized for physical, in vitro release studies & ex-vivo permeation studies (human cadaver skin). On the basis of in vitro drug release and skin permeation performance, formulation A1 was found to be better than the other formulations and it was selected as the optimized formulation. The optimized patch was assessed for its pharmacokinetic, pharmacodynamic, skin irritation potential, and stability studies. RESULTS: The maximum percentage drug release & Permeation in 48 hrs were 92.43 % and 76.24 % respectively for optimized patch. The Korsmeyer peppas release exponent value of 0.604 suggested release mechanism towards first order release in the optimized formulation. The results obtained from the in vivo characterization of the optimized patch showed sustained action of the developed formulation. The interaction studies analysis indicated no chemical interaction between the drug and polymers. The optimized patch was seemingly free of potentially hazardous skin irritation as suggested by skin irritation score of 0.915<2.00 (under Draize score test). The optimized formulation was found to be stable at ambient storage conditions. CONCLUSION: The above TTS holds promise for improved bioavailability and better management of hypertension on long term basis.

Stereoselective analysis of labetalol in human plasma by LC-MS/MS: application to pharmacokinetics.

Labetalol is clinically available as a mixture of two racemates (four stereoisomers). The stereoisomer (R,R) has as main activity the beta1-antagonism and the stereoisomer (S,R) is highly selective for the alpha1 adrenoceptor and is responsible for most of the alpha-blocker activity. In the present investigation, a method for the analysis of labetalol stereoisomers in human plasma was developed and applied to pharmacokinetic studies. Plasma samples (0.5 ml) were extracted with methyl tert-butyl ether at pH 9.5. The four labetalol stereoisomers were analyzed by LC-MS/MS on a Chirobiotic V column using a mobile phase consisting of methanol, acetic acid, and diethylamine, with a recovery of more than 90% for all four. The quantitation limit was 0.5 ng/ml and linearity was observed at 250 ng/ml plasma for each stereoisomer. Studies of precision and accuracy presented coefficients of variation and percentage inaccuracy of less than 15%, indicating that the method is precise and accurate. The method was applied to the study of the kinetic disposition of labetalol over a period of 12 h after oral administration of a single 100 mg dose to a hypertensive pregnant woman. The clinical study revealed stereoselectivity in the pharmacokinetics of labetalol, with a lower plasma proportion for the active stereoisomers (R,R)-labetalol and (S,R)-labetalol. The stereoselectivity observed after oral administration is due to the hepatic metabolism and the first pass effect, with an AUC(R,R)/AUC(S,S) ratio of 0.5.

Miniaturized rotating disk intrinsic dissolution rate measurement: effects of buffer capacity in comparisons to traditional wood's apparatus.

PURPOSE: The objective was to investigate the feasibility of using a miniaturized disk intrinsic dissolution rate (IDR) apparatus to determine the Biopharmaceutics Classification System (BCS) solubility class, and to develop an approach where IDR measurements performed in media of different buffer capacity could be compared. METHODS: The disk IDR values of 14 model drugs were determined at 37 degrees C in US Pharmacopeia buffers at pH 1.2, 4.5, and 6.8. As little as 5 mg of drug were compressed in a die, with surface area of 0.071 cm(2), with the die assembly rotated at 100 rpm in 10 mL media. Drug concentration was measured by an in situ fiber optic ultraviolet method. The solubilities and pK(a)s were determined, and used to simulate dissolution profiles with a convective-diffusion-with-chemical-reaction model. RESULTS: The disk IDR values spanned six orders of magnitude (0.00014 to 114 mg min(-1) cm(-2)). The comparison of the miniaturized disk IDR values to published results using traditional dissolution bath apparatus indicated r (2) = 0.99. CONCLUSIONS: The results demonstrate that using 100-fold less drug does not sacrifice the quality of the measurement, and lends support to an earlier study Yu et al. (Int. J. Pharm. 270:221-227, 2004) that the disk IDR measurement may possibly serve as a surrogate for the BCS solubility classification.

Micellar enhanced spectrofluorometric determination of labetalol through complexation with aluminium(III): application to dosage forms and biological fluids.

Two simple, sensitive, and specific spectrofluorometric procedures have been developed for the determination of labetalol (LBT) in pharmaceuticals and biological fluids. LBT was found to react with Al3+, both in acetate buffer of pH 4.5 (Procedure I) and borate buffer of pH 8.0 (Procedure II), to produce highly fluorescent stable complexes. The fluorescence intensity could be enhanced by the addition of sodium dodecyl sulfate, resulting in 3.5- and 2.7-fold increases in the fluorescence intensity for Procedures I and II, respectively. In both procedures, the fluorescence intensity was measured at 408 nm after excitation at 320 nm. The different experimental parameters affecting the development and stability of the fluorescent products were carefully studied and optimized. The fluorescence intensity-concentration plots were rectilinear over the range of 0.02-0.1 and 0.01-0.05 microg/mL with a detection limit of 0.003 and 0.001 microg/mL for Procedures I and II, respectively. The proposed method was successfully applied to commercial tablets containing LBT. The results were in good agreement with those obtained using a reference spectrofluorometric method. Furthermore, the method was applied for the determination of LBT in spiked human plasma, and the recovery (n = 4) was 93.30 +/- 2.62%. A proposal of the reaction pathway was postulated for Procedures I and II, respectively.

Characterization of basic drug-human serum protein interactions by capillary electrophoresis.

Drug-protein interactions are determining factors in the therapeutic, pharmacodynamic and toxicological drug properties. The affinity of drugs towards plasmatic proteins is apparently well established in bibliography. Albumin (HSA) especially binds neutral and negatively charged compounds; alpha(1)-acid glycoprotein (AGP) binds many cationic drugs, lipoproteins bind to nonionic and lipophilic drugs and some anionic drugs while globulins interact inappreciably with the majority of drugs. In this paper, the characterization of the interaction between cationic drugs, beta-blockers and phenotiazines towards HSA, AGP, and both HSA + AGP mixtures of proteins under physiological conditions by CE-frontal analysis is presented. Furthermore, the binding of these drugs to all plasmatic proteins is evaluated by using ultrafiltration and CE. The results indicate that the hydrophobic character of compounds seems to be the key factor on the interaction between cationic drugs towards proteins. In fact, hydrophobic basic drugs bind in great extension to HSA, while hydrophilic basic drugs present low interactions with proteins and bind especially to AGP.

Transdermal drug delivery of labetolol hydrochloride: system development, in vitro; ex vivo and in vivo characterization.

OBJECTIVE: The aim of the present work was to develop and evaluate matrix type transdermal drug delivery systems (TDDS) of labetolol hydrochloride (L-HCL) effective for 48 hours. EXPERIMENTAL: The TDDS were prepared by solvent evaporation technique. Six formulations (carrying Eudragit RL100:Eudragit RS 100 in 7.5:4.5, 5.0:5.0, 3.5:8.5 in formulations X-1, X-2, X-3 and Eudragit RL100:PVP K-30 in 9.0:2.0, 5.0:5.0, 4.0:7.0 in formulations Y-1, Y-2, Y-3, respectively) were prepared. All formulations carried 36% w/w of L-HCL, 10-12% w/w of enhancer dimethyl sulfoxide and 2.5-7.5% w/w of plasticizer PEG 400 in methanol-acetone solvent system. The TDDS were evaluated by in vitro drug release, ex vivo skin permeation, stability and in vivo pharmacodynamic studies. RESULTS: The maximum drug release for X-series was 90.26% in 48 hours (X-1) and for Y-series, it was 83.24% (Y-1). Again formulations X-1 (Kp = 0.221x10(-2) cm hr(-1)) and Y-1 (Kp = 0.210x10(-2) cm hr(-1)) exhibited the best skin permeation potential in the respective series. This might be due to higher permeability characteristics of Eudragit RL100. A shelf life of 2.38 years was predicted for the TDDS. Mean systolic BP of the experimental hypertensive rats was significantly reduced (p<0.01) on TDDS treatment. CONCLUSION: The TDDS holds promise for clinical trials.

Polymeric alkenoxy amino acid surfactants: II. Chiral separations of beta-blockers with multiple stereogenic centers.

Two amino acid-based (leucine and isoleucine) alkenoxy micelle polymers were employed in this study for the separation of multichiral center-bearing beta-blockers, nadolol and labetalol. These polymers include polysodium N-undecenoxy carbonyl-L-leucinate (poly-L-SUCL) and polysodium N-undecenoxy carbonyl-L-isoleucinate (poly-L-SUCIL). Detailed synthesis and characterization were reported in our previous paper [26]. It was found that poly-L-SUCIL gives better chiral separation than poly-L-SUCL for both nadolol and labetalol isomers. The use of 50-100 mM poly-L-SUCIL as a single chiral selector provided separation of four and three isomers of labetalol and nadolol, respectively. Further optimization in separation of both enantiomeric pairs of nadolol and labetalol was achieved by evaluation of type and concentration of organic solvents, capillary temperature as well type and concentration of cyclodextrins. A synergistic approach, using a combination of poly-L-SUCIL and sulfated beta-CD (S-beta-CD) was evaluated and it showed dramatic separation for enantiomeric pairs of nadolol. On the other hand for labetalol enantiomers, separation was slightly decreased or remain unaffected using the dual chiral selector system. Finally, simultaneous separation of both nadolol and labetalol enantiomers was achieved in a single run using 25 mM poly-L-SUCIL and 5% w/v of S-beta-CD in less then 35 min highlighting the importance of high-throughput chiral analysis.

Chiral separation of labetalol stereoisomers in human plasma by capillary electrophoresis.

A newly derivatized cyclodextrin [octakis-(2,3-diacetyl-6-sulfato)-gamma-cyclodextrin] was investigated as a chiral selector in capillary zone electrophoresis in a study of the chiral separation of labetalol stereoisomers. Heptakis(2,3-diacetyl-6-sulfato)-beta-cyclodextrin (HDAS-beta-CD) and octakis(2,3-diacetyl-6-sulfato)-gamma-cyclodextrin (ODAS-gamma-CD) were shown to be effective in separating labetalol stereoisomers. Optimal separating conditions of the four stereoisomers of labetalol were achieved with 10 mM HDAS-beta-CD and 10 mM ODAS-gamma-CD in an acidic pH buffer of low molarity. Data illustrating the effects of capillary length and cyclodextrin concentration on the separation are presented. The longer capillary length and high voltage enabled the baseline separation of all isomers in less than 15 min. The optimized method was applied to the analysis of human control plasma containing labetalol utilizing solid-phase extraction (SPE) in the 96-well format.