Structural identification of mouse urinary metabolites of pterostilbene using liquid chromatography/tandem mass spectrometry

Pterostilbene, the dimethoxy derivative of resveratrol, has drawn much attention recently due to its potential beneficial health effects. The metabolic fate of pterostilbene, however, is not well understood. In the present study, we identified nine novel mouse urinary pterostilbene metabolites, pterostilbene glucuronide, pterostilbene sulfate, mono‐demethylated pterostilbene glucuronide, mono‐demethylated pterostilbene sulfate, mono‐hydroxylated pterostilbene, mono‐hydroxylated pterostilbene glucuronide, mono‐hydroxylated pterostilbene sulfate, and mono‐hydroxylated pterostilbene glucuronide sulfate, using liquid chromatography/atmospheric pressure chemical ionization and electrospray ionization tandem mass spectrometry. The structures of these metabolites were confirmed by analyzing the MSⁿ (n = 1–3) spectra. To our knowledge, this is the first report of the identification of urinary metabolites of pterostilbene in mice. Copyright © 2010 John Wiley & Sons, Ltd.     

Simultaneous determination of fimasartan,a novel antihypertensive agent,and its active metabolite in rat plasma by liquid chromatography–tandem mass spectrometry

Fimasartan, 2‐butyl‐5‐dimethylaminothiocarbonylmethyl‐6‐methyl‐3‐[[2'‐(1H tetrazol ‐5‐yl)biphenyl‐4‐yl]methyl]pyrimidin‐4(3H)‐one (BR‐A‐657), is a novel angiotensin II receptor blocker exhibiting potent and selective AT₁ receptor blocking activity. This study reports the liquid chromatography–tandem mass spectrometry assay for the simultaneous determination of fimasartan and its active metabolite, BR‐A‐557, in rat plasma. The assay was validated to demonstrate the specificity, linearity, recovery, lower limit of quantification, accuracy, precision and stability. The multiple reaction monitoring was based on the transition of m/z 502.1 → 207.1 for fimasartan, 486.2 → 207.1 for BR‐A‐557 and 526.1 → 207.1 for BR‐A‐563 (internal standard). The assay utilized a simple precipitation procedure with acetonitrile and isocratic elution. The LLOQ was 0.2 ng/mL for fimasartan and BR‐A‐557 using 50 μL plasma samples. The assay was linear over a concentration range from 0.2 to 500 ng/mL for fimasartan and BR‐A‐557, with correlation coefficients >0.9995. The intra‐ and inter‐day assay accuracies were 93.6–108.0 and 90.8–101.4% for fimasartan and 102.2–107.1 and 99.6–103.3% for BR‐A‐557, respectively. The intra‐ and inter‐day precision were 2.4–4.4 and 3.0–13.4% for fimasartan and 3.1–5.2 and 2.8–9.8% for BR‐A‐557, respectively. The developed assay may be used to study the metabolism and mechanistic pharmacokinetics of fimasartan in future studies. Copyright © 2011 John Wiley & Sons, Ltd.     

Groups of continuous characters and brauer groups

We study some relations between groups of continuous characters and subgroups of Brauer groups.Explicit determination of some subgroups of Brauer groups arising from this connection are done for some cases in the local fields.     

N‐Heterocyclic Carbene Organocatalysis: Activation Modes and Typical Reactive Intermediates

N‐Heterocyclic carbene (NHC) organocatalysis has been developed as an important approach in modern organic synthesis. Versatile activation modes within NHC organocatalysis have been established with countless transformations being realized in both efficient and selective fashion. We would like to provide an overview on the key progresses achieved within this field in the past two decades. Since numerous excellent reviews have been documented within this area, we will mainly focus on the scientific development of this research field based on the basic reaction modes and typical reaction intermediates.