Mn(III)-mediated formal [3+3]-annulation of vinyl azides and cyclopropanols: a divergent synthesis of azaheterocycles

Mn(III)-mediated formal [3+3]-annulation has been developed using readily available vinyl azides and cyclopropanols with a wide range of substituents. Vinyl azides were successfully applied as a three-atom unit including one nitrogen to prepare pyridines and δ-lactams by the reactions with monocyclic cyclopropanols as well as to construct 2-azabicyclo[3.3.1] and 2-azabicyclo[4.3.1] frameworks with bicyclic cyclopropanols, bicyclo[3.1.0]hexan-1-ols, and bicyclo[4.1.0]heptan-1-ols. These reactions were initiated by a radical addition of β-carbonyl radicals, generated by the one-electron oxidation of cyclopropanols with Mn(III), to vinyl azides to give iminyl radicals, which cyclized with the intramolecular carbonyl groups. In addition, application of the present methodology to a synthesis of the quaternary indole alkaloid, melinonine-E, was accomplished.     

Quantification of L‐ergothioneine in human plasma and erythrocytes by liquid chromatography‐tandem mass spectrometry

A sensitive analytical method has been developed and validated for the quantification of L‐ergothioneine in human plasma and erythrocytes by liquid chromatography‐tandem mass spectrometry. A commercially available isotope‐labeled L‐ergothioneine‐d₉ is used as the internal standard. A simple protein precipitation with acetonitrile is utilized for bio‐sample preparation prior to analysis. Chromatographic separation of L‐ergothioneine is conducted using gradient elution on Alltime C18 (150 mm × 2.1 mm, 5 µ). The run time is 6 min at a constant flow rate of 0.45 ml/min. The mass spectrometer is operated under a positive electrospray ionization condition with multiple reaction monitoring mode. The mass transitions of L‐ergothioneine and L‐ergothioneine‐d₉ are m/z 230 > 127 and m/z 239 > 127, respectively. Excellent linearity [coefficient of determination (r²) ≥ 0.9998] can be achieved for L‐ergothioneine quantification at the ranges of 10 to 10 000 ng/ml, with the intra‐day and inter‐day precisions at 0.9–3.9% and 1.3–5.7%, respectively, and the accuracies for all quality control samples between 94.5 and 101.0%. This validated analytical method is suitable for pharmacokinetic monitoring of L‐ergothioneine in human and erythrocytes. Based on the determination of bio‐samples from five healthy subjects, the mean concentrations of L‐ergothioneine in plasma and erythrocytes are 107.4 ± 20.5 ng/ml and 1285.0 ± 1363.0 ng/ml, respectively. Copyright © 2013 John Wiley & Sons, Ltd.     

New Indole Alkaloids from Kopsia. Alkaloid Variation in Kopsia singapurensis

Five new indole alkaloids, viz., kopsiloscine G ( 2 ), kopsidarine ( 4 ), kopsimaline F ( 6 ), kopsidine C N‐oxide ( 7 ), and aspidophylline B ( 9 ), in addition to 17 other known alkaloids, were obtained from the leaf and stem‐bark extract of the Malaysian Kopsia singapurensis. The structures were determined by using NMR and MS analysis. The results are compared with the alkaloidal composition of another sample of K. singapurensis, collected from the same location but at a different time of the year, as well as with other samples of K. singapurensis collected from different locations.     

Mn(III)-catalyzed synthesis of pyrroles from vinyl azides and 1,3-dicarbonyl compounds

Polysubstituted N-H pyrroles with a wide variety of substituents were prepared from vinyl azides and 1,3-dicarbonyl compounds by using Mn(III) complexes as catalysts.     

Bioavailability of metallic impurities in carbon nanotubes is greatly enhanced by ultrasonication

Metallic impurities within carbon nanotubes (CNTs) are considered as the main cause of their toxicity. Ultrasonication is a common procedure used to purify and obtain homogeneous dispersions of CNTs as well as to mix them with other components for further processing into composites. Herein, the influence of ultrasonication upon the bioavailability of metallic impurities in CNTs was investigated. We showed that even ultrasonication times as short as 5?min significantly enhanced the bioavailability of metallic impurities, which can therefore interact more actively with biologically important molecules. These findings will have profound impact on the processing of CNTs as well as on nanotoxicity studies.     

Copper-catalyzed aerobic intramolecular carbo- and amino-oxygenation of alkynes for synthesis of azaheterocycles

A synthetic method of highly substituted quinolines has been developed from N-(2-alkynylaryl)enamine carboxylates under Cu-catalyzed aerobic conditions via intramolecular carbo-oxygenation of alkynes. This strategy was further applied for N-alkynylamidines for amino-oxygenation of alkynes, leading to imidazole and quinazoline derivatives.     

Recent advances in analytical chemistry--a material approach

Advancements of materials research have profound direct impacts on developments in analytical chemistry and may hold the key to improvement of existing or new techniques at present times and near future. Applications of materials in analytical chemistry are reviewed, with focus on sensors, separations and extraction techniques. This review aims to survey examples of interesting works carried out in the last five years over a broad spectrum of materials classified as hybrids, nanomaterials and biomolecular materials.     

Quintic and septic Eisenstein series

Using results that were well-known to Ramanujan, we give proofs of some results for Eisenstein series in the lost notebook. Our proofs have the additional advantage that it is not necessary to know the results in advance; that is, the proofs are derivations as opposed to verifications.