bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis of Hydroxylated and Methoxylated Polybrominated Diphenyl Ethers − Natural Products and Potential Polybrominated Diphenyl Ether Metabolites
Authors: Marsh Göran , Stenutz Roland , Bergman Åke 
Published: July 2003

AbstractHydroxylated and methoxylated polybrominated diphenyl ethers (OH‐PBDEs and MeO‐PBDEs) may be natural products or they may be formed as metabolites of polybrominated diphenyl ethers (PBDEs), frequently used as flame retardants. The aim of this work was to synthesize authentic OH‐ and MeO‐PBDE reference standards for analytical and toxicological studies. Brominated phenoxybenzaldehydes were prepared either by coupling of 2,4‐dibromophenol with various fluorobenzaldehydes or by coupling of brominated hydroxybenzaldehydes with 2,2′,4,4′‐tetrabromodiphenyliodonium chloride. OH‐PBDEs were synthesized via the brominated phenoxybenzaldehydes by Baeyer−Villiger oxidation and acid‐catalyzed hydrolysis. These OH‐PBDEs were ortho‐ and para‐brominated (relative to the hydroxy group) with benzyltrimethylammonium tribromide and/or ortho‐brominated with bromine/tert‐butylamine, and were also brominated with bromine in one case. MeO‐PBDEs were obtained by methylation of the prepared OH‐PBDEs. MeO‐PBDEs were also prepared through the coupling of brominated methoxyphenols with 2,2′,4,4′‐tetrabromodiphenyliodonium salts, the corresponding OH‐PBDEs being obtained after demethylation. A majority of the OH‐/MeO‐PBDEs prepared have the hydroxy/methoxy group in the ortho position relative to the diphenyl ether bond. All OH‐/MeO‐PBDEs prepared have 2,4‐dibromo substitution patterns (relative to the diphenyl ether bond) in the non‐hydroxy‐/non‐methoxy‐containing ring. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Diastereoselective Preparation of Silylated Pyrrolidones through Palladium‐Catalysed Cyclisations
Authors: Thorimbert Serge , Giambastiani Giuliano , Commandeur Claude , Vitale Maxime , Poli Giovanni , Malacria Max 
Published: July 2003

AbstractA new palladium‐catalysed allylic alkylation affording silylated 3‐vinylpyrrolidones has been developed. The method relies upon the interaction between a stabilized acetamide enolate anion and a silicon‐containing, nitrogen‐tethered η3‐allylpalladium moiety. Two variants have been studied, involving the location of the silicon atom on either olefinic carbon atom of the cyclisation precursor. In both cases 5‐exo ring closure was the only cyclisation process observed. The stereoselectivity of these processes is discussed. These results contrast with related β‐oxo ester cyclisations, in which competitive 7‐endo mode is observed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Synthesis of Non‐Natural Amino Acids from N‐(p‐Tolylsulfonyl)‐α,β‐didehydroamino Acid Derivatives
Authors: Ferreira Paula M. T. , Maia Hernâni L. S. , Monteiro Luís S. 
Published: July 2003

AbstractCarbon nucleophiles, amines, and oxygen nucleophiles were treated with the methyl ester of N‐(tert‐butoxycarbonyl)‐N‐(p‐tolylsulfonyl)‐α,β‐didehydroalanine, and also with the methyl esters of N‐(tert‐butoxycarbonyl)‐O‐(p‐tolylsulfinyl)‐α,β‐didehydroserine and N‐(tert‐butoxycarbonyl)‐β‐(1,2,4‐triazol‐1‐yl)‐α,β‐didehydroalanine, both of which were obtained from the former substrate. Carbon nucleophiles of the β‐dicarbonyl type gave furanic amino acids, which were converted into the corresponding pyrrole derivatives (dehydroprolines) in high yields, while use of amines allowed the synthesis of α,α‐diamino acids and β‐amino‐α,β‐didehydroamino acids. Different types of alkoxyamino acids were obtained by treatment of the above substrates with oxygen nucleophiles. The reactivities of the α,β‐didehydroaminobutyric and α,β‐didehydrophenylalanine analogues were also tested. Some of the methods developed were applied to the synthesis of cross‐linked amino acids, namely didehydrolanthionine and histidino‐α,β‐didehydroalanine derivatives. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Strained Aromatic Compounds: Are σ‐ and π‐Strains Additive? A Hybrid DFT Study of Dicyclobutano‐, Dicyclobutadieno‐ and Di(1,3‐methanocyclopentano)[2,2]paracyclophanes
Authors: Stanger Amnon , Ben‐Mergui Na'ama , Perl Sharon 
Published: July 2003

AbstractThe structures and energies of dicyclobutano[2,2]paracyclophane (1), dicyclobutadieno[2,2]paracyclophane (2) and di(1,3‐methanocyclopentano)[2,2]paracyclophane (3) were calculated at the B3LYP/6‐31G* theoretical level, in order to understand the behavior of systems that are π‐ and σ‐strained. It was found that the effect of the two types of strain on the geometry is approximately additive, and that the slight deviation found is due to specific interactions (electronic or steric) between the ethano bridges in the [2,2]paracyclophanes and the aromatic moieties or between a substituent and another aromatic moiety. It was found that 1 is ca. 3 kcal mol−1 less strained than [2,2]paracyclophane and cyclobutabenzene, 2 is ca. 6 kcal mol−1 less strained than [2,2]paracyclophane and benzocyclobutadiene, and 3 is ca. 6 kcal mol−1 more strained than [2,2]paracyclophane and 1,3‐methanoindane. These deviations from additivity are explained by the above‐mentioned interactions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Synthesis of Methoxy‐Substituted Exocyclic (E)‐ and (Z)‐Unsaturated Methyl Pyranosides and a Study of Their Reactivity towards Lewis Acids
Authors: Deleuze Aurélie , Sollogoub Matthieu , Blériot Yves , Marrot Jérôme , Sinaÿ Pierre 
Published: July 2003

AbstractThe first synthesis of methoxy‐substituted exocyclic (E)‐ and (Z)‐unsaturated methyl pyranosides is reported involving the syn elimination of a selenoxide derivative as a key step. The rearrangement of these exocyclic enol ethers in the presence of TIBAL and DIBAL‐H is also described. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Pyridinium‐Based Cationic Lipids as Gene‐Transfer Agents
Authors: Ilies Marc Antoniu , Seitz William A. , Caproiu Miron T. , Wentz Melissa , Garfield Robert E. , Balaban Alexandru T. 
Published: July 2003

AbstractCationic lipids are a promising alternative to viral vectors for gene therapy, allowing the delivery of larger plasmids without immunogenicity, despite their lower transfection efficiency. Among them, heterocyclic systems with imidazolium or pyridinium polar head groups have definite advantages such as the excellent transfection profiles and low cytotoxicity. Our approach for synthesizing heterocyclic cationic lipids differs from those previously described because we synthesize a pyridinium ring from simple starting materials. First a pyrylium salt is formed via diacylation of alkenes. The pyrylium salt is then converted by primary amines into pyridinium salts. Appropriate choice of the primary amine allows the attachment of two hydrophobic chains yielding compounds 21A and 25A (with various chain lengths derived from palmitic, stearic and oleic acids). The same strategy allowed the preparation of lipophilic derivatives 21B, 25B useful as strongly fluorescent markers for the study of the properties of biological membranes. Preliminary tests with some of the compounds 21A and 25A, on several cell lines, showed comparable transfection efficiencies and lower cytotoxicity than those obtained with standard commercial transfection agents. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
An Iterative Procedure for the Synthesis of Conjugated ψ‐Chlorotrienoic and ‐tetraenoic Esters and Related Derivatives
Authors: Mladenova Margarita , Tavlinova Maya , Momchev Momcho , Alami Mouâd , Ourévitch Michèle , Brion Jean Daniel 
Published: July 2003

AbstractAn iterative stereoselective procedure for the synthesis of isomers of conjugated ψ‐chlorotrienoic esters and ψ‐chlorotetraenoic esters as well as related conjugated ψ‐chloropolyenynoic esters is described, using readily available conjugated chlorodienol and chloroenynol derivatives as starting materials. The two‐step sequence studied is based on repetition of a one‐pot conjugated allylic alcohol oxidation/Wittig reaction followed by a reduction step. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
A Cyclopropyl‐Homoallyl Rearrangement Accompanying the Borane‐Mediated Reduction of Tosylhydrazones
Authors: Kragol Goran , Benko Iva , Muharemspahić Jasmina , Mlinarić‐Majerski Kata 
Published: July 2003

AbstractThe Wolff−Kishner reduction of strained cyclopropyl ketones 9‐oxo‐2,8‐didehydronoradamantane (1) and 5‐oxo‐2,4‐didehydrobrendane (5) proceeds without rearrangement, while the borane‐mediated reduction of the corresponding tosylhydrazones 1a and 5a affords the rearranged products tricyclo[4.2.1.03,8]non‐4‐ene (3) and 4‐brendene (7), respectively. Rearrangement also occurs during the reduction of the less‐strained tosylhydrazones 8a and 10a derived from cyclopropyl methyl ketone (8) and bicyclo[4.1.0]heptan‐2‐one (10). The results obtained in experiments with deuterated reagents support a concerted mechanism of diazene decomposition/cyclopropyl‐homoallyl rearrangement. This rearrangement offers a great possibility for the preparation of new polycyclic molecules and, moreover, is a convenient method for regiospecific isotopic labeling using deuterated reagents. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Palladium‐Catalyzed C−C Bond Formation: Synthesis of 1,1‐Dialkylbuta‐1,3‐dienes and β‐Phenylstyrenes via Organoboron Intermediates
Authors: Deagostino Annamaria , Prandi Cristina , Zavattaro Chiara , Venturello Paolo 
Published: July 2003

Abstractα,β‐Unsaturated and α‐phenyl acetals show different reactivity when treated with LIC‐KOR superbase and trialkylboranes, in the presence of the reagent system PdL4‐ArX (Suzuki−Miyaura cross‐coupling conditions). In particular, unsaturated acetals yield gem‐dialkylbutadienes via the formation of an intermediate π‐allyl complex that facilitates an anionotropic alkyl migration; in the case of α‐phenyl derivatives, the corresponding cross‐coupling products are recovered. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Rearrangement of Germacranolides. Synthesis and Absolute Configuration of Elemane and Heliangolane Derivatives from Cnicin
Authors: Rosselli Sergio , Maggio Antonella , Raccuglia Rosa Angela , Bruno Maurizio 
Published: July 2003

AbstractA study of the Cope rearrangement of 15‐oxo‐germacranolides to 15‐oxo‐elemanolides has been carried out. The synthesis of two natural elemanolides, isolated from Centaurea paui, and an efficent isomerization of the C‐4/C‐5 double bond of 15‐oxo‐germacranolides to form heliangolides are reported. The absolute configuration of all the compounds has been ascertained. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Highly Efficient Synthesis of Chloro‐ and Phenoxy‐Substituted Subphthalocyanines
Authors: Claessens Christian G. , González‐Rodríguez David , del Rey Belen , Torres Tomás , Mark Gertraud , Schuchmann Heinz‐Peter , von Sonntag Clemens , MacDonald J. Gavin , Nohr Ronald S. 
Published: July 2003

AbstractA highly efficient method for the synthesis of chloro‐substituted subphthalocyanines employing a 1 M boron trichloride solution in p‐xylene is described and compared to other previously described results. The substitution reaction of the axial chlorine atom by a phenoxy group has been optimized. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
A New N,P‐Ligand with Achiralgem‐Dimethyloxazoline for Palladium(II)‐Catalyzed Cyclization of 1,6‐Enynes: Transition State Probe for theN/C transMode in Mizoroki−Heck‐Type C−C Bond Formation
Authors: Hatano Manabu , Yamanaka Masahiro , Mikami Koichi 
Published: July 2003

AbstractA highly effectiveC1‐symmetricgem‐dimethyl N,P‐ligand has been developed for enantioselective palladium(II)‐catalyzed carbocyclization of 1,6‐enynes, in which theN/Ctransmode is established for the first time in the “Mizoroki−Heck‐type” transition state by virtue of theC1‐symmetric N,P‐ligand. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Dicyanocarbene and Its Isomers: A Matrix Spectroscopic Study
Authors: Maier Günther , Reisenauer Hans Peter , Ruppel Raimund 
Published: July 2003

AbstractIrradiation of matrix‐isolated dicyanodiazomethane (4) with 254 nm‐light leads to the dicyanocarbene 5, which, upon further photoexcitation, undergoes successive isomerizations until a photoequilibrium between the five C3N2 isomers dicyanocarbene (T‐5), cyanoisocyanocarbene (T‐6), 3‐cyano‐2H‐azirenylidene (S‐7), 3‐isocyano‐2H‐azirenylidene (S‐8), and diisocyanocarbene (S‐9) is reached. The preferential formation of a specific member of this group can be achieved by changing the wavelength of the irradiating light. The structural elucidation of the unknown compounds 6−9 is based on a comparison of their calculated and experimental IR spectra. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Cover Picture: Synthesis and Biological Evaluation of Imino Sugar−Oligoarabinofuranoside Hybrids, a New Class of Mycobacterial Arabinofuranosyltransferase Inhibitors (Eur. J. Org. Chem. 14/2003)
Authors: Marotte Karine , Ayad Tahar , Génisson Yves , Besra Gurdyal S. , Baltas Michel , Prandi Jacques 
Published: July 2003

AbstractThe cover picture shows a schematic view of the expected cooperative effect of linking a potential mycobacterial arabinosyltransferase inhibitor to an acceptor‐like ligand. Important enhancement of the in vitro inhibitory porperties of various hydroxylated and fluorinated pyrrolidines was obseved when they were covalently linked to a single arabinofuranosidic unit while a longer triarabinofuranoside was deleterious for the inhibition. Details are discussed in the article by M. Baltas and J. Prandi et al. on p. 2557 ff. Photo courtesy of P. Gournon, Institut Pasteur, Paris.
Electrochemical Behavior and Detection of Dopamine and Ascorbic Acid at an Iron(II)tetrasulfophthalocyanine Modified Carbon Paste Microelectrode
Authors: Oni Joshua , Westbroek Philippe , Nyokong Tebello 
Published: July 2003

AbstractIn this article the electrocatalytic behavior of an iron(II)tetrasulfophthalocyanine modified carbon paste microelectrode for the oxidation of dopamine (DA) and ascorbic acid (AA) is described. Although the oxidation potential of ascorbic acid is shifted by over 100 mV to more positive potentials, no peak separation could be obtained. This can be explained by the immediate homogeneous reduction of the oxidation product of dopamine by ascorbic acid in solution. However, this reaction induces a shift of the half‐wave potential as a function of ratio of concentration of dopamine to ascorbic acid (cDA/cAA). Therefore it was possible to determine the cAA and cDA from this potential shift and the experimental peak current. Detection limits of 4.5±0.2×10−7 and 7.5±0.5×10−7 mol L−1 were obtained respectively for dopamine and ascorbic acid for cDA/cAA>0.01.
An Electroanalytical Investigation on the Redox Properties of Calcium Antagonist Dihydropyridines
Authors: Toniolo Rosanna , Tubaro Franco , Ursini Fulvio , Bontempelli Gino 
Published: July 2003

AbstractThe antioxidant capacity of some calcium antagonists and one calcium agonist 1,4‐dihydropyridines (DHPs) was evaluated by a competitive kinetic procedure. With the exception of Amlodipine, all the calcium antagonist DHPs display an unambiguous antioxidant capacity, while for the calcium agonist DHP (Bay K 8644) no measurable reactivity towards peroxyl radicals could be detected. The finding was corroborated by an electroanalytical investigation of the redox properties of DHPs compounds to get an insight about both the thermodynamic constraints of their oxidation process and reaction pattern. The oxidation potentials decrease with both antioxidant capacity and increasing basic character, thus suggesting the relevance of the electron density on the DHP ring. For all the compounds investigated, the overall oxidation process takes place through a primary one‐electron step accompanied by a fast proton release and the formation of a neutral radical undergoing a second much easier one‐electron step. The protonated form of the parent pyridine derivative is thus generated as the final product. This pattern is relevant for the antioxidant effect, since the radical intermediate is much more prone to be oxidized than to be reduced, thus fully preventing the propagation of the oxidative chain reaction. In the case of calcium antagonist DHPs, the above release of protons complicates the overall oxidation process by introducing a parasitic side reaction where a coupling between protons and the starting species takes place. This DHP self‐protonation subtracts part of the original species from the electrode process because the parent cationic species is no longer electroactive. Conversely, the calcium agonist DHP, which is more difficult to be oxidized, turned out to be such a weak base as to be unable to undergo the self‐protonation reaction. The combined effect of oxidation potentials and proton binding capacity of DHPs is a key element for the redox transition, which could support their antioxidant effect and should be considered to some extent in accounting for the calcium antagonist vs calcium agonist effect.
Microchip Separation and Electrochemical Detection of Amino Acids and Peptides Following Precolumn Derivatization with Naphthalene‐2,3‐dicarboxyaldehyde
Authors: Wang Joseph , Chen Gang , Pumera Martin 
Published: July 2003

AbstractAn integrated microfluidic device is used to derivatize, separate, and amperometrically detect amino acids and peptides in the presence of naphthalene‐2,3‐dicarboxyaldehyde (NDA). The integrated system offers a rapid (4 min) simultaneous measurements of 5 amino acids (Arg, Lys, Gly, Cys, PhenA) down to the 3.2 μM level in connection to a precolumn reaction chamber, an electrophoretic separation channel, and an end‐column thick‐film carbon‐electrode detector. The effect of the separation voltage, detection potential, reagent concentration, and other variables on the response is examined. Calibration and precision experiments indicate a linear and reproducible response. Applicability for the separation and detection of small peptides is demonstrated. Such on‐chip generation of electroactive products offers great promise for detecting other nonelectroactive analytes.
Determination of Chlorides in Meat Products with Ion‐Selective Electrode Using the Batch Injection Technique
Authors: Šucman Emanuel , Bednář Jiří 
Published: July 2003

AbstractA procedure was developed for determination of salt in various meat products using a chloride ion‐selective electrode. The technique of batch injection analysis was used together with an ultrasound based sample extraction step. Various kinds of meat products were analyzed. The relative standard derivation lies between 0.9% and 2.7%. The accuracy of the method was proved by an independent reference method. Differences between the results of the batch injection analysis method and the reference method were found to be statistically non‐significant. Total analysis time was 7 minutes on average. The described batch injection analysis method is fast, accurate, reliable and suitable for routine analytical work.
Polymeric ISE for Hydrogen Sulfite Based on Bis‐Urea Calix[4]diquinones as Neutral Lipophilic Ionophores
Authors: Jeon Seungwon , Yeo Heekyoung , Jeong Haesang , Min Oh Jung , Chun Nam Kye 
Published: July 2003

AbstractA new PVC membrane electrode for HSO3− anion based on bis‐urea calix[4]diquinones I–VI as neutral ionophores is prepared. Of the various membranes prepared, the membrane based on calix[4]diquinone III exhibits a linear stable response over a wide concentration range (6.0×10−5−1.0×10−2) with a slope of −51.5 mV/decade and a detection limit of 2.2×10−6 M. With the exception of HSO3− anion, the remainder of the anions responds based on their hydrophobicity. The membrane revealed improved selectivity coefficients for HSO3− over a wide variety of other anions, and the comparable selectivity for the HSO3−selective membranes is iodide anion.
Some Electrochemical Characteristics of Boron‐ and Phosphorus‐Doped Glassy Carbon Electrodes
Authors: Abramović Biljana F. , Bjelica Luka J. , Gaál Ferenc F. , Guzsvány Valéria J. , Jovanovic Ljiljana S. 
Published: July 2003

AbstractThree glassy carbon (GC) samples: undoped and doped with boron or phosphorus, prepared at 1000 °C, were compared in respect to hydrodynamic current‐potential curves in acidic medium, cyclic voltammograms for Fe3+/2+ and Fe(CN)63−/4− and argentometric titrations of halides. Some experiments were also carried out using standard Tokai and Sigri GC and Ag electrode. It appeared that GC doped with boron and phosphorus exhibited significant increase in hydrogen evolution overpotential. As for the electrode kinetics (ΔEp criterion), no significant difference was observed between doped and undoped electrodes. In the potentiometric titrations the phosphorus‐doped electrode was advantageous over the other GC and Ag electrodes as it enabled more precise end‐point detection.
Electrochemical Reduction of a Conjugated Cinnamic Acid Diazonium Salt as an Immobilization Matrix for Glucose Biosensor
Authors: Yang Xinhao , Hall Simon B. , Ngin Tan Swee 
Published: July 2003

AbstractInitial results on the synthesis of a new conjugated diazonium salt of trans‐4‐cinnamic acid diazonium fluoroborate, which is used for the chemical modification of the glassy carbon (GC) electrode with trans‐4‐cinnamic acid groups through electrochemical reduction, and direct covalent immobilization of glucose oxidase (GOD) on the cinnamic acid groups are presented. The chemically modified GC electrode exhibits a good selectivity relative to the bare GC electrode for the various possible interfering compounds in glucose analysis: namely ascorbic acid and 4‐acetamidophenol. Covalent immobilization of GOD on the chemically modified GC electrode produces a biosensor which responds to glucose concentration changes in the presence of a soluble redox mediator (ferrocenemethanol). The chemical modification of GC by cinnamic acid groups is potentially useful for the attachment of other enzymes and biochemical reagents.
In Vivo Monitoring of the Thiols in Rat Striatum by Liquid Chromatography with Amperometric Detection at a Functionalized Multi‐Wall Carbon Nanotubes Modified Electrode
Authors: Cao Xu‐Ni , Lin Li , Xian Yue‐Zhong , Zhang Wen , Xie Yun‐Feng , Jin Li‐Tong 
Published: July 2003

AbstractA new chemically modified electrode (CME) was fabricated, which was based on the immobilization of multi‐wall carbon nanotubes fuctionalized with carboxylic group (MWNT‐COOH). The results indicated that the CME exhibited efficiently electrocatalytic oxidation for L‐cysteine and glutathione with relatively high sensitivity, stability and long‐life. Coupled with HPLC, the MWNT‐COOH CME was utilized for amperometric detection of the thiols. The peak currents of L‐cysteine and glutathione were linear to their concentrations ranging from 3.0×10−7 to 1.0×10−3 mol/L with the calculated detection limit (S/N=3) of 1.2×10−7, 2.2×10−7 mol/L, respectively. The method had been successfully applied to assess the contents of L‐cysteine and glutathione in rat striatal microdialysates.