Equilenin-2'-deoxynucleoside adducts: analysis with nano-liquid chromatography coupled to nano-electrospray tandem mass spectrometry

The interaction of 4-hydroxy metabolites of estrogens with DNA leads to the formation of DNA adducts. These adducts are believed to play an important role in the incidence of breast and endometrial cancer. In order to be able to analyze these adducts in in vivo samples a method based upon the coupling of miniaturized liquid chromatography (LC) to electrospray tandem mass spectrometry (ES-MS/MS) was developed for the analysis of the adducts formed with 4-hydroxyequilenin. In vitro synthesized adducts obtained by the reaction of 4-hydroxyequilenin with the main 2'-deoxynucleosides were separated on a Hypersyl C(18) BDS nano-HPLC column (15 cm x 75 microm i.d.) at a flow-rate of 300 nl min(-1) using gradient elution with CH(3)OH--0.2% CH(3)COOH in H(2)O. The column was coupled, in combination with a column switching system, to a nano-electrospray interface. Analysis of the low- and high-resolution low-energy collision-activated dissociation product ion spectra of normal and deuterated adducts supported earlier data demonstrating equilenin to form different isomeric adducts, except with thymidine, for which no adducts were found. The nano-HPLC column-switching ES-MS system was tested for its sensitivity on a triple-quadrupole instrument, and detection limits down to 197 fg in the single reaction monitoring mode were obtained for semi-preparatively isolated equilenin--2'-deoxyguanosine adduct.     

Efficient synthesis of N-benzyl-3-aminopyrrolidine-2,5-dione and N-benzyl-3-aminopyrrolidin-2-one

Reaction of N-tert-butyloxycarbonylasparagine (Boc-Asn) with 2 equiv of benzyl bromide in presence of cesium carbonate led to N-benzyl-3-Boc-amino-pyrrolidin-2,5-dione 1a (N-benzyl-3-Boc-aminosuccinimide). Borane dimethylsulfide reduced 3-Boc-aminopyrrolidine-2,5-dione 1a into 3-Boc-aminopyrrolidin-2-one 2a. The same procedure could also be used to prepare derivatives 1 and 2 substituted on the aromatic ring.     

Scope and limitations of a new highly selective synthesis of unsymmetrical monomers for the synthesis of precursors toward poly(arylenevinylene)s

In our laboratory a precursor route to poly(p-phenylenevinylene) derivatives is developed in which unsymmetrically substituted p-xylene derivatives, possessing a benzylic sulfinylalkyl group, are used as monomers. Because of this unsymmetry, we were forced to investigate thoroughly the synthesis of these sulfoxides, as we start from symmetric and readily accessible molecules, namely, bis(halomethyl)-p-xylene derivatives. In a former publication, a new extremely effective route for the production of these unsymmetrically substituted sulfinyl monomers was presented. This paper expands upon these previously reported results. To examine the scope and limitations of this elegant route, this new method was applied to the synthesis of various derivatives not included in the initial work.     

Borane-catalyzed hydroboration of substituted alkenes by lithium borohydride or sodium borohydride

In the presence of a catalytic amount of BH₃·Me₂S, TiCl₄ or Me₃SiCl, LiBH₄ or NaBH₄ are capable of hydroborating alkenes by following the unusual order of decreasing reactivity: tetramethylethylene > 1-methylcyclohexene > cyclohexene; the key step of the catalytic cycle is the exchange reaction between LiBH₄ and the mono- or dialkylboranes resulting from hydroboration of the more substituted alkenes with BH₃.     

From anisole to 1,2,4,5‐tetramethoxybenzene: Theoretical study of the factors that determine the conformation of methoxy groups on a benzene ring

Unhindered ortho‐dimethoxy‐substituted phenyl rings often display a coplanar conformation. A theoretical study of a series of methoxybenzenes consisting of methoxybenzene (anisole), the three dimethoxybenzenes, and 1,2,4,5‐tetramethoxybenzene, at the DFT/B3LYP/6‐311++G** level of theory, allows us to identify the factors influencing the conformational preference and attribute the coplanarity of such methoxy groups to mesomeric effects. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Perhydroisoindoliniums et perhydroisoquinoliniums: Préparation et étude stéréochimique

By cyclization in aqueous media, 2-aminomethyl 1-alcynyl 1-cyclohexanols lead to perhydroisoindolinium or perhydroisoquinolinium salts. The stereochemistry of isolated diastereoisomers is elucidated. A stereoselectivity favouring trans junction of the rings is pointed out.     

Effect of pressure on free-radical copolymerization kinetics. I. A concept of additivity of partial molar volumes of activation

A short review of the effect of pressure on copolymerization kinetics shows the necessity of simple models for a better understanding of activation volumes. Therefore, a simple concept, possibly generally valid for free-radical polymerization, is proposed, based on the assumption that molar volumes of activation can be expressed as an addition of a characteristic radical and a monomer contribution, regardless of the combination involved. The scheme may facilitate the visualization of the transition state and contribute to the understanding of reaction mechanisms of radical polymerizations. Ethylene–vinyl acetate copolymerization at 62°C with tert-butyl alcohol as solvent agrees with the proposed scheme, appearing from the pressure independence of the product of reactivity ratios at the different levels (35,600, and 1200 kg/cm²). Implicitly it can be shown that an ethylene monomer contributes about 2 cm³/mole more to the activation volumes of the propagation reactions than does the vinyl acetate monomer, whereas for the radicals the difference of the respective contributions to the activation volumes is opposite in sign.     

Selenium in environmental waters: Determination, speciation and concentration levels

This article reviews the different methods used for the determination of selenium species in all types of environmental waters. Basic difficulties are discussed and the efficiency of the methods is explained in view of the sub-mug/1. concentration levels. Special attention is paid to preconcentration steps. Published data on speciation and concentration levels in various water samples are critically reviewed.     

Conversion of diaryliodonium salts to aryl fluorides

The preparation of aryl fluorides by the reaction of diaryliodonium salts with KF is discussed. Generally, best results were obtained when the salt Ar₂I⁺X^? was heated with KF in the absence of solvent. The counterion, X^?, must be non-nucleophilic.     

Preparation and properties of two indium antimony selenides

Crystals of antimony-doped In₂Se₃ were grown by the Bridgeman method. This compound, whose composition is In_1.8Sb_0.2Se₃, appears to be isostructural with In_1.9As_0.1Se₃. The refined unit cell parameters are a = 3.97(1), c = 18.87(1) Å. Orthorhombic crystals of InSbSe₃ were grown from an isothermal melt. The refined unit cell parameters are a = 9.43(1), b = 14.02(5), and c = 3.96(1) Å. These parameters agree with those determined for α-InSbSe₃ by other studies. The observed densities measured by a hydrostatic technique are 5.98(3) g/cm³ for In_1.8Sb_0.2Se₃ and 6.07(2) g/cm³ for InSbSe₃. The room temperature dc resistivity for In_1.8Sb_0.2Se₃ has been found to be 4.4 × 10⁴ Ω-cm, whereas that of InSbSe₃ has been found to be 15.2(1) Ω-cm. A resistivity versus temperature study has beenn carried out for InSbSe₃ between 230 and 400°K. Optical studies indicate that In_1.8Sb_0.2Se₃ is an n-type semiconductor with a band gap of 1.1 eV and InSbSe₃ is a p-type semiconductor with a band gap of 0.92 eV.