Chiral Assay Research Articles

Stereoselective distribution of tiaprofenic acid in synovium and cartilage in osteoarthritic patients.

In order to document the stereoselective distribution in joints of a chiral nonsteroidal anti-inflammatory drug, the relative affinities of the enantiomers of tiaprofenic acid in synovium and for cartilage were compared. The distribution of tiaprofenic acid in synovium and in cartilage was studied 25 h after administering the racemic drug for 2 days (600 mg of a sustained-release preparation, once daily), in 12 inpatients with osteoarthritis of the hip requiring arthroplasty. Enantiomers were quantified in plasma and freeze-ground tissues by a chiral HPLC assay. Plasma concentrations of the dextrorotatory (R) enantiomer (0.40 microgram/ml) were higher than those of its antipode. The concentration of racemate in synovium (in dried and fresh tissues, 150% and 40%, respectively, of the concentration in plasma) was much higher than that in cartilage (in dried tissues 32% of the plasma concentration). The ratio of the active, dextrorotatory (R) enantiomer to its antipode was higher in synovial tissue than in plasma. Tiaprofenic acid is distributed stereoselectively in plasma and synovium, which contain a higher concentration of the active, dextrorotatory (R) enantiomer. In cartilage, it reaches only a very low concentration.

Pharmacokinetics of ibutilide and its enantiomers in dogs.

Ibutilide fumarate, a new drug for the treatment of cardiac arrhythmias, contains a stereogenic center bearing a secondary alcohol group. Several single dose and multiple dose studies of racemic ibutilide or its enantiomers were performed by the oral and intravenous routes in dogs. A chiral assay was used to examine racemization and the individual enantiomer pharmacokinetics. Following low oral or intravenous doses (approximately 0.3 mg/kg), the pharmacokinetics of the enantiomers were nearly identical, with no substantial chiral conversion. Both enantiomers exhibited high clearance rates, large volumes of distribution, and low oral bioavailability. As the dose increased, pharmacokinetic differences between the enantiomers were observed. The greatest differences (3-fold) were seen after oral administration at 4 mg/kg, indicating that first-pass metabolism of ibutilide was highly enantioselective at high doses. The clearances of the enantiomers differed by up to 34% at 5 mg/kg followed intravenous administration of the racemate. At high doses, other non-linear pharmacokinetic behavior was also apparent. The intravenous clearance of ibutilide declined from 5.3 L/h/kg at 0.3 mg/kg to 3.7 L/h/kg at a dose of 5 mg/kg. The absolute oral bioavailability of the racemate increased from 2% at 0.3 mg/kg to as much as 84% at 5 mg/kg.

Chiral assay methods for lifibrol and metabolites in plasma and the observation of unidirectional chiral inversion following administration of the enantiomers to dogs

Lifibrol, a new drug for the treatment of hypercholesterolemia, contains a stereogenic center bearing a secondary alcohol group. A normal-phase achiral-chiral HPLC separation of the enantiomers of lifibrol and two of its metabolites was developed and validated for quantitation in dog plasma. A silica and a Chiralcel OD-H column were operated in series and all six enantiomeric components and internal standard were directly separated. An initial solid-phase extraction (phenyl) clean-up step and a column-switching step to eliminate late-eluting compounds were also utilized. The solid-phase extraction step was automated using a robotic system. Assay development, validation, and application of the method to a bioavailability study of the racemate and enantiomers of lifibrol in dogs are described. The lower limit of quantitation was 0.0125 microgram/ml for each enantiomer of lifibrol using 200 microliters of dog plasma with UV detection (255 nm). In dog plasma following oral or intravenous administration of the racemate, the (R)/(S) ratio of the enantiomers of lifibrol was greater than one and increased with time. Following administration of the individual enantiomers, chiral inversion of the (S)-enantiomer but not the (R)-enantiomer was observed.

Stereoselective disposition: enantioselective quantitation of 3,4-(methylenedioxy) methamphetamine and three of its metabolites by gas chromatography/electron capture negative ion chemical ionization mass spectrometry.

A new chiral assay for 3,4-(methylenedioxy)methamphetamine (MDMA) and three of its metabolites in biological specimens is based on direct aqueous derivatization with N-heptafluorobutyryl-S-prolyl chloride, followed by capillary chromatographic separation of the diastereomeric derivatives and detection by a mass spectrometer operated in the electron capture negative ion chemical ionization mode. The assay is linear from 5 to 1000 ng ml-1 for each enantiomer and allows simultaneous quantitation of MDMA and three of its metabolites in biological specimens. Investigation of the disposition of racemic MDMA in rats and mice revealed quantitative differences in the disposition of the enantiomers of MDMA in these species; the most noteworthy result was a two-fold greater urinary excretion of the neurotoxic S-(+)-MDMA by mice. Only MDMA and 3,4-(methylenedioxy)amphetamine (MDA) enantiomers were detected at measurable concentrations in the frontal cortices and hippocampis from rats dosed with 10 mg kg-1 of racemic MDMA; in this species the enantiomeric profiles of these two compounds were similar in brain and urine.

Retrospective analysis of some L-methamphetamine/L-amphetamine urine data.

A limited analysis is presented of data accumulated over about three years for specimens containing either nonracemic L-methamphetamine/L-amphetamine or racemic mixtures of the D and L stereoisomers. 55 data points for both nonracemic L-methamphetamine and racemic mixtures show that it is possible to report a specimen containing L-methamphetamine positive for illegal D-methamphetamine based on current guidelines unless chiral assays are performed on selected methamphetamine positives. Generation of only 45 racemic specimens from chiral analysis of about 5,000 urine methamphetamine positives demonstrates the overwhelming prevalence of nonracemic illegal D-methamphetamine in Southern California.

Recent Progress of HPLC Analysis for Drugs of Abuse.

Recent progress of high performance liquid chromatography (HPLC) for drugs of abuse was reviewed on over 100 papers. First, papers concerning screening analyses for drugs of abuse using HPLC were reviewed and discussed about their usefulness. Secondly, the progress of new analytical methods for high-sensitive detection of amphetamines, morphine, codeine, 6-acetylmorphine, cannabinoids, cocaine and others were reviewed by dividing into 1. fluorometric, 2. electrochemical, and 3. chemiluminescence detections. Thirdly, new studies on the chiral assay for amphetamines using chiral derivatization or chiral column were reviewed. Furthermore, the application to discrimination between use of over-the-counter drugs and illegal amphetamines was exemplified. Fourthly, the utility of a photodiode array detector and a mass detector for the confirmation of drugs was shown by citing several papers. Moreover, it was discussed about automation of the HPLC analysis using the column switching method, capillary electrophoresis and supercritical fluid chromatography applied for the analysis of drugs of abuse.