Rafael E. Barrientos-Astigarraga

Ticlopidine quantification in human plasma by high‐performance liquid chromatography coupled to electrospray tandem mass spectrometry. Application to bioequivalence study

A rapid, sensitive and specific analytical method was developed and validated to quantify gabapentin in human plasma using acetaminophen as an internal standard. The method employs a single plasma protein precipitation. The analytes are chromatographed on a C4 reversed-phase chromatographic column and analyzed by mass spectrometry in the multiple reaction monitoring (MRM) mode. The method has a chromatographic run time of 4 min and a linear calibration curve over the range 50-10 000 ng x ml(-1) (r > 0.999). The between-run precision, based on the relative standard deviation for replicate quality controls, was < or = 4.8 % (200 ng x ml(-1)), 6.0% (1000 ng x ml(-1)) and 4.4% (5000 ng x ml(-1)). The between-run accuracy was +/-2.6, 4.4 and 0.5% for the above-mentioned concentrations, respectively. This method was employed in a bioequivalence study of two gabentin capsule formulations (Progresse from Biosintética, Brazil, as a test formulation, and Neurotin from Parke-Davis, as a reference formulation) in 24 healthy volunteers of both sexes who received a single 300 mg dose of each formulation. The study was conducted using an open, randomized, two-period crossover design with a 7-day washout interval. The 90% confidence interval (CI) of the individual ratio geometric mean for Progresse/Neurotin was 87.9-115.6% for AUC(0-36 h) and 88.6-111.7% for Cmax. Since both 90% CI for AUC(0-36 h) and Cmax were included in the 80-125% interval proposed by the US Food and Drug Administration, Progresse was considered bioequivalent to Neurotin according to both the rate and extent of absorption.

Lansoprazole quantification in human plasma by liquid chromatography-electrospray tandem mass spectrometry.

An analytical method based on liquid chromatography with positive ion electrospray ionization (ESI) coupled to tandem mass spectrometry detection was developed for the determination of lansoprazole in human plasma using omeprazole as the internal standard. The analyte and internal standard were extracted from the plasma samples by liquid-liquid extraction using diethyl-ether-dichloromethane (70:30; v/v) and chromatographed on a C(18) analytical column. The mobile phase consisted of acetonitrile-water (90:10; v/v)+10 mM formic acid. The method has a chromatographic total run time of 5 min and was linear within the range 2.5-2000 ng/ml. Detection was carried out on a Micromass triple quadrupole tandem mass spectrometer by Multiple Reaction Monitoring (MRM). The intra- and inter-run precision, calculated from quality control (QC) samples, was less than 3.4%. The accuracy as determined from QC samples was less than 9%. The method herein described was employed in a bioequivalence study of two capsule formulations of lansoprazole.

Addition of Z-Vinylic Higher Order Cyanocuprates to Enones Followed by O-Functionalization

Abstract Transmetalation reaction between Z-vinylic tellurides and higher order cyanocuprates generated the corresponding Z-vinylic cyanocuprates. Conjugate addition of these cuprates to enones followed by O-functionalization led to silyl enol ethers, vinyl phosphates and vinyl triflates. The vinyl triflates were transformed into highly unsaturated systems by coupling with alkynes or with Z-vinyl zinc chlorides under Pd (0) catalysis.

Carbon–carbon bond formation by means of organotellurium compounds

Z vinylic tellurides are prepared by hydrotelluration of alkynes under nonreducing conditions using n-BuLi–Te–H2O as the hydrotellurating system. The same system promotes the hydrotelluration of alkenes containing electron withdrawing groups. Lithium and magnesium organotellurolates effect vinylic substitutions on vinylic halides, phosphates, sulphonates and acetates leading to the Z vinylic telluride exclusively. Tellurides are transmetallated with easily available organometallic reagents to give valuable synthetic building blocks (e.g. organolithiums and organocuprates). Reaction of vinylic tellurides with alkynes under Pd catalysis or with organocuprates gives the coupling products with retention of the double bond geometry.

Highly unsaturated conjugated systems from vinylic tellurides

Abstract 1,4 addition of higher order Z vinyl cuprates to enones followed by triflate trapping results in the corresponding enol triflates, which can be coupled with terminal alkynes or with Z vinyl zinc chloride under Pd0 catalysis.

Quantification of methyldopa in human plasma by high-performance liquid chromatography–electrospray tandem mass spectrometry: Application to a bioequivalence study

A method based on LC-MS-MS is described for the determination of methyldopa in human plasma using dopa-phenyl-D3 as the internal standard. The method has a chromatographic run time of 5.5 min and was linear in the range of 20-5000 ng/ml. The limit of quantitation was 20 ng/ml, the intra-day precisions were 7.3, 5.4 and 4.3% and the intra-day accuracies were -8.0, -1.3 and -2.0% for 30, 600 and 3000 ng/ml, respectively. The inter-day precisions were 7.7, 0.5 and 0.7% and the inter-day accuracies were 0.2, -1.1 and -2.3%, respectively, for the above concentrations. This method was employed in a bioequivalence study of two tablet formulations of methyldopa.

ADDITION OF Z-VINYLIC HIGHER ORDER CYANOCUPRATES TO HINDERED ENONES. THE INFLUENCE OF THE REACTION CONDITIONS

Z-Vinylic higher order cyanocuprates, prepared from the corresponding Z-vinylic tellurides, react efficiently with hindered enones in THFBF3·Et2O or in diethyl ether. In neat THF the hindered enones fail to react with Z-vinyl cyanocuprates prepared in this way.

Synthesis of functionalized tri- and tetrasubstituted vinylic tellurides from enolphosphates through vinylic substitution by lithium butyltellurolate

Abstract Vinylic tellurides are precursors of important highly reactive vinylic organometallics (e.g. vinyl Li and Cu species). Herein we report that tri- and tetrasubstituted functionalized vinylic tellurides can be prepared from enolphosphates through a vinylic substitution by lithium butyltellurolate. Starting from mixtures of Z - and E -enolphosphates, only the Z -vinylic telluride is formed.

Terbinafine quantification in human plasma by high-performance liquid chromatography coupled to electrospray tandem mass spectrometry: application to a bioequivalence study.

A method based on liquid chromatography with positive ion electrospray ionization and tandem mass spectrometry is described for the determination of terbinafine in human plasma using naftifine as internal standard. The method has a chromatographic run time of 5 minutes and was linear in the range 1.0 to 2000 ng/mL. The limit of quantification was 1.0 ng/mL; the intraday precision was 3.6%, 3.8%, 3.5%, and 4.1%; and the intraday accuracy was −2.7%, 7.7%, 4.8%, and −2.7% for 5.0, 80.0, 250.0, and 1500.0 ng/mL, respectively. The interday precision was 4.9%, 1.7%, 2.4%, and 4.6% and the interday accuracy was 0.3%, 5.8%, 6.5%, and −1.4% for the same concentrations. This method was used in a bioequivalence study of two tablet formulations of terbinafine. Twenty-four healthy volunteers (both sexes) received a single oral dose of terbinafine (250 mg) in an open, randomized, two-period crossover study. The 90% CI of geometric mean ratios between (Terbinafina®; Medley S/A Indústria Farmacêutica, Campinas, Brazil) and Lamisil® (Novartis Biociências S/A, São Paulo, Brazil) were 90.5% to 110.0% for C max , 92.2% to 108.1% for AUC last , and 91.3% to 107.5% for AUC 0–inf . Because the 90% CI for the above-mentioned parameters were included in the 80% to 125% interval proposed by the US FDA, the two formulations were considered bioequivalent in terms of rate and extent of absorption.

A general method of synthesis of functionalized Z-vinylic tellurides starting from β-dicarbonyl compounds

Z-Vinylic tellurides are prepared by stereoselective vinylic substitution on Z/E mixtures of enolphosphates, acetates, tosylates and triflates by organotellurolates. The reaction is sensitive to the nature of the organotellurolate; the aromatic derivatives react slower than the aliphatic ones. The reaction time is not influenced by the nature of the leaving group.