The free radical chemistry of carboxylic esters of 2-selenopyridine-N-oxide: a convenient synthesis of (L)-vinylglycine

Optically pure (L)-vinylglycine has been synthesised by two different methods. The first of these involves protected (L)-glutamate esters of $\text{N}$-hydroxy-2-seleno-pyridine. Such esters are shown to undergo the same decarboxylotive rearrangement as their thio-analogues. Oxidative elimination of the selenopyridine residue with ozone, and with the aid of hex-1-ene as sacrificial olefin for the work-up, gave the desired (L)-vinylglycine derivatives. Similarly, the modified Hunsdiecker reaction on the terminal carboxyl of suitably protected (L)-glutamic derivatives gave the nor-bromide which readily afforded the corresponding phenylselenides on treatment with phenylselenide anion. The sequence was then as above. Using the methyl ester with corbobenzyloxy protection for the amino-function an overall yield of crystalline optically pure (L)-vinylglycine of about 45% was obtained by either route.     

Further improvements of the dibutyl tin oxide-catalyzed regioselective diol tosylation

In this Letter, we report that selective monotosylation of a 1,2-diol is possible using only 0.1 mol % of Bu₂SnO. More interestingly, we found that the corresponding tin acetal 3b gave faster conversions and more reproducible reaction times. Moreover, the loading of this catalyst could be as low as 0.05-0.005 mol %.     

Determination of polyunsaturated fatty acid monoepoxides by high performance liquid chromatography-mass spectrometry

Despite the implication of polyunsaturated fatty acid monoepoxides in a large panel of biological effects, few methods allowing their separation in a single run are available. We describe here a simple method based on reversed-phase ion-pair high-performance liquid chromatography (RP-HPLC) and developed to successfully separate the various monoepoxides of eicosatrienoic, arachidonic, eicosapentaenoic and docosahexaenoic acids. These compounds were easily identified by liquid chromatography-mass spectrometry (LC-MS) with atmospheric pressure chemical ionisation owing to the volatility of counter-ion species. Compared to established methods, this new protocol proved its ability to totally resolve, in a single run, all of the different regioisomeric epoxides. In the long run, this method will demonstrate its efficacy to give insights into the cytochrome P450-dependent metabolism of polyunsaturated fatty acids (PUFAs) and the generation of physiologically active epoxy-derivatives.     

Large Scale Preparation of Protected 4-Aminomethylbenzamidine. Application to The Synthesis of the Thrombin Inhibitor,Melagatran

To allow the preparation of melagatran on a multigram scale, we have investigated several approaches for the synthesis of the key intermediate 4-aminomethylbenzamidine. The only industrially suitable pathway relies on the preparation of an N-hydroxyimino intermediate.     

Distribution coefficient and redox behaviour of uranium in Authie Bay (northern France)

Some mechanistic aspects associated with uranium release/immobilization and sedimentation in Authie Bay are presented in the present work. For this purpose, U contents in estuarine oxic waters, porewaters and sediment solids are determined. These analytical data allow us to appraise the partitioning of this metal between the liquid phase and the particulate matter/sedimentary material by calculating its distribution coefficient. Our findings further reveal that the distribution coefficient varies significantly with depth probably in response to the microbial activities in these sediments. This is confirmed by our studies on the geochemical behaviour of Fe and Mn in Authie Bay sediments. Finally, studies on the thermodynamic characteristics of sedimentary U in Authie Bay are undertaken in order to select possible U water–mineral equilibria that could involve in this environment, and to help define conditions of sedimentary U bioreduction.     

Mechanism of the Nickel-Catalyzed Electrosynthesis of Ketones by Heterocoupling of Acyl and Benzyl Halides

Summary.  The mechanism of the nickel-catalyzed electrosynthesis of ketones by heterocoupling of phenacyl chloride and benzyl bromide has been investigated by fast scan rate cyclic voltammetry with [Ni(bpy)²⁺ ₃](BF₄ ⁻)₂ as the catalytic precursor (bpy = 2,2{−}{ bipyridine}). The key step is an oxidative addition of Ni⁰(bpy) (electrogenerated by reduction of the Ni(II) precursor) to PhCH₂Br whose rate constant is found to be 10 times higher than that of PhCH₂COCl. The complex PhCH₂Ni^IIBr(bpy) formed in the oxidative addition is reduced at the potential of the Ni^II/Ni⁰ reduction by a two-electron process which affords an anionic complex PhCH₂Ni⁰(bpy)⁻ able to react with PhCH₂COCl to generate eventually the homocoupling product PhCH₂COCH₂Ph. The formation of the homocoupling product PhCH₂COCOCH₂Ph is prevented because of the too slow oxidative addition of Ni⁰(bpy) to PhCH₂COCl compared to PhCH₂Br. The formation of the homocoupling product PhCH₂CH₂Ph is also prevented because PhCH₂Ni⁰(bpy)⁻ does not react with PhCH₂Br. This explains why the electrosynthesis of the ketone can be performed selectively in a one-pot procedure, starting from an equal mixture of PhCH₂COCl and PhCH₂Br and a nickel catalyst ligated by the bpy ligand. Received June 27, 2000. Accepted July 11, 2000     

Synthesis of cycloalkenyl geminal bisphosphonates by ring closing metathesis

Five‐ and six‐membered cycloalkenyl bisphosphonates were obtained by ring closing metathesis (RCM) reactions of diethyl bis(alkenyl)methylene bisphosphonates using ruthenium alkylidene catalysts. The substitution pattern on the double bonds involved in the reaction greatly influences the reaction rate. The synthesis of the starting materials was carried out by dialkylation of tetraethyl methylene bisphosphonate or through a Michael addition of Grignard reagents to tetraethyl vinylidene bisphosphonate followed by alkylation, depending on the structure of the required substrate. © 2010 Wiley Periodicals, Inc. Heteroatom Chem 21:332–338, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20622     

Functional neural network analysis in frontotemporal dementia and Alzheimer's disease using EEG and graph theory

Background  

Although a large body of knowledge about both brain structure and function has been gathered over the last decades, we still have a poor understanding of their exact relationship. Graph theory provides a method to study the relation between network structure and function, and its application to neuroscientific data is an emerging research field. We investigated topological changes in large-scale functional brain networks in patients with Alzheimer's disease (AD) and frontotemporal lobar degeneration (FTLD) by means of graph theoretical analysis of resting-state EEG recordings. EEGs of 20 patients with mild to moderate AD, 15 FTLD patients, and 23 non-demented individuals were recorded in an eyes-closed resting-state. The synchronization likelihood (SL), a measure of functional connectivity, was calculated for each sensor pair in 0.5–4 Hz, 4–8 Hz, 8–10 Hz, 10–13 Hz, 13–30 Hz and 30–45 Hz frequency bands. The resulting connectivity matrices were converted to unweighted graphs, whose structure was characterized with several measures: mean clustering coefficient (local connectivity), characteristic path length (global connectivity) and degree correlation (network 'assortativity'). All results were normalized for network size and compared with random control networks.     

Chemical analysis of polymers using transmission electron microscopy/electron energy-loss spectroscopy: The example of poly(ethylene terephthalate)

We have performed EELS analysis of poly (ethylene terephthalate) (PET) in the analytical TEM in order to evaluate the possibility to obtain chemical analysis of the polymer at sub-micrometer scale. Due to irradiation damage, it revealed necessary to work at the lowest possible electron dose, typically below 10³ C.m⁻², and with the specimen cooled to liquid nitrogen temperature. In the acquired spectra, we propose an identification of the different chemical bondings in agreement with XANES experiments.     

Wire Rope Isolators for Seismic Base Isolation

Tall and slender substation equipment is prone to failure under seismic excitations. The consequences of such failure can be devastating and lead to weeks or months of lost power.
The IEEE Std 693-2005 ensures that all substation equipment installed in high seismic areas are designed to withstand earthquakes of a severity related to that area.
There are numerous ways to increase the seismic strength of substation equipment and this paper will discuss doing so by base isolation, specifically using wire rope isolators (WRIs).
It is the purpose of this paper to present a case study in which the Socitec Group provided a WRI base isolation design for a high voltage surge arrester. The simulation results show that the moment at the base of the surge arrester was reduced by 55% when using the Socitec designed WRI base isolation system.