Simultaneous determination of losartan,EXP-3174 and hydrochlorothiazide in plasma via fully automated 96-well-format-based solid-phase extraction and liquid chromatography–negative electrospray tandem mass spectrometry

An automated, sensitive and high-throughput liquid chromatographic/electrospray tandem mass spectrometric (LC–MS/MS) assay was developed for the simultaneous determination of losartan (LOS), its major circulating metabolite EXP-3174 and hydrochlorothiazide (HCTZ) in human plasma. LOS and HCTZ coexist in the same drug formulation, and this is the first method that enables the simultaneous determination of both drugs along with the active metabolite of LOS. Since these drugs have different physicochemical properties, the employment of a liquid–liquid extraction (LLE) protocol was precluded. A fully automated solid-phase extraction (SPE) protocol, based on 96-well format plates, was used to isolate these compounds and furosemide (internal standard, IS) from plasma. Washing and elution steps were amended accordingly in order to minimize any matrix effect from components of the plasma without reducing the elution of the molecules of interest. The compounds were eluted from a C18 column and detected with an API 3000 triple-quadrupole mass spectrometer using negative electrospray ionization and multiple reaction monitoring (MRM). The assay was linear over the range 1.00–400 ng/mL for LOS and EXP-3174 and 0.500–200 ng/mL for HCTZ, respectively, when 200 μl of plasma was used in the extraction. The overall intra- and interassay variations were within acceptance limits. The analysis time for each sample was 4 min, and more than 300 samples could be analyzed in one day by running the system overnight. The assay was simple, highly sensitive, selective, precise, fast, and it enables the reliable determination of LOS, EXP-3174 and HCTZ in pharmacokinetic or bioequivalence studies after per os administration of a single tablet containing both drugs.     

Water‐Soluble Carbon Nanotubes by Redox Radical Polymerization

Water‐soluble single‐ and multi‐walled carbon nanotubes (CNTs) were prepared by grafting polyacrylamide chains from the graphitic surface via ceric ion‐induced redox radical polymerization. The reducing functionalities were covalently attached to the tubes by peroxide‐assisted radical reaction. The results showed that polymer chains were grafted onto CNTs by the redox process. The redox radical polymerization initiated by carbon nanotube‐bearing functionalities not only provides a powerful strategy for modifying the carbon nanostructures but also gives us the knowledge of their sidewall chemistry.

     

Beta-orcinol metabolites from the lichen Hypotrachyna revoluta

Four new beta-orcinol metabolites, hypotrachynic acid (1), deoxystictic acid (2), cryptostictinolide (3) and 8'-methylconstictic acid (4) along with the metabolites 8'-methylstictic acid (5), 8'-methylmenegazziaic acid (6), stictic acid (7), 8'-ethylstictic acid (8) and atranorin (9), that have been previously described, were isolated for the first time from the tissue extracts of the lichen Hypotrachyna revoluta (Fl?rke) Hale. The structures of the new metabolites were elucidated on the basis of extensive spectroscopic analyses. Radical scavenging activity (RSA) of the metabolites isolated in adequate amounts, was evaluated using luminol chemiluminescence and comparison with Trolox.     

Sequential injection affinity chromatography utilizing an albumin immobilized monolithic column to study drug-protein interactions

In this study, sequential injection affinity chromatography was used for drug-protein interactions studies. The analytical system used consisted of a sequential injection analysis (SIA) manifold directly connected with convective interaction media (CIM) monolithic epoxy disks modified by ligand-immobilization of protein. A non-steroidal, anti-inflammatory drug, naproxen (NAP) and bovine serum albumin (BSA) were selected as model drug and protein, respectively. The SIA system was used for sampling, introduction and propulsion of drug towards to the monolithic column. Association equilibrium constants, binding capacity at various temperatures and thermodynamic parameters (free energy DeltaG, enthalpy DeltaH) of the binding reaction of naproxen are calculated by using frontal analysis mathematics. The variation of incubation time and its effect in on-line binding mode was also studied. The results indicated that naproxen had an association equilibrium constant of 2.90 x 10(6)M(-1) at pH 7.4 and 39 degrees C for a single binding site. The associated change in enthalpy (DeltaH) was -27.36 kcal mol(-1) and the change in entropy (DeltaS) was -73 cal mol(-1)K(-1) for a single type of binding sites. The location of the binding region was examined by competitive binding experiments using a biphosphonate drug, alendronate (ALD), as a competitor agent. It was found that the two drugs occupy the same class of binding sites on BSA. All measurements were performed with fluorescence (lambda(ext)=230 nm, lambda(em)=350 nm) and spectrophotometric detection (lambda=280 nm).     

Initial example of a triangular single-molecule magnet from ligand-induced structural distortion of a [MnIII3O]7+ complex

The reaction of [Mn3O(O2CR)6(py)3](ClO4) (R = Me, Et) with methyl 2-pyridyl ketone oxime (mpkoH) in a 1:3 molar ratio in MeOH/MeCN leads to [Mn3O(O2CR)3(mpko)3](ClO4) in 80-90% isolated yield. Ferromagnetic exchange interactions between the three MnIII ions in the nonplanar [MnIII3O]7+ triangular core lead to a spin ground state of S = 6; single-crystal studies reveal the temperature and sweep rate dependent hysteresis loops expected for a single-molecule magnet.     

A new scalable synthesis of entecavir

A new synthesis of entecavir from d-glucose in an average total yield of 3.5% was achieved via an intramolecular nitrile oxide cycloaddition (INOC) reaction and a Peterson olefination as key-steps. The present process was designed for industrial application, using widely available raw materials, simple and cheap reagents and avoiding low reaction temperatures, which are very common in the synthetic approaches towards similarly complex structures.     

Development and validation of a method for the determination of buprenorphine and norbuprenorphine in breast milk by gas chromatography-mass spectrometry

Buprenorphine (BUP) is used for the maintenance of opioid‐addicted pregnant women. Because BUP and its main metabolite nor‐BUP are excreted into breast milk, a sensitive and specific GC/MS method has been developed, optimized and validated for their determination in breast milk. BUP‐d4 was used as internal standard. The sample preparation includes combination of protein precipitation with solid‐phase extraction and derivatization (acetylation). The absolute recovery for both analytes was found to be higher than 87.3%. The limits of detection and quantification were 0.07 and 0.20 µg/L, respectively. The calibration curves were linear within the dynamic range 0.20–20.0 µg/L, with a correlation coefficient higher than 0.996. Intra‐ and inter‐day accuracies were ranged from ?7.06 to 4.50 and from ?5.88 to 7.00%, respectively, while intra‐ and inter‐day precision were less than 5.7 and 6.1%. The analytes were found to be stable in breast milk at 4°C for one week, at ?20°C for one month, and after three freeze–thaw cycles. The method can be used for the determination of BUP and nor‐BUP in breast milk of BUP‐maintained mothers, in order to calculate the amount of drug that could pass to the newborn via breast milk and to avoid toxic consequences of breastfeeding. Copyright © 2011 John Wiley & Sons, Ltd.     

Development of a rapid method for the determination of glimepiride in human plasma using liquid-liquid extraction based on 96-well format micro-tubes and liquid chromatography/tandem mass spectrometry

A semi-automated liquid chromatography/tandem mass spectrometry (LC/MS/MS) method was developed for the determination of glimepiride in human plasma. The plasma samples were treated by liquid-liquid extraction (LLE) in 1.2 mL 96-well format micro-tubes. Glimepiride and the internal standard (IS) glibenclamide were extracted from human plasma by LLE, using a mixture of ethyl acetate/diethyl ether 50:50 (v/v) as the organic solvent. After vortexing, centrifugation and freezing, the supernatant organic solvent was evaporated. The analyte and IS were dissolved in a small volume of a reconstitution solution, an aliquot of which was analyzed by reversed-phase LC/MS/MS with positive ion electrospray ionization, using multiple reaction monitoring. The method proved to be sensitive and specific for both drugs, and statistical evaluation revealed excellent linearity for the range of concentrations 2.0-500.0 ng/mL with very good accuracy and inter- and intra-day precisions. The proposed method enabled the rapid and reliable determination of glimepiride in pharmacokinetic or bioequivalence studies after per os administration of a 3 or 4 mg tablet of glimepiride.