bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fat‐Derived Aziridines and Their N‐Substituted Derivatives: Biologically Active Compounds Based on Renewable Raw Materials
Authors: Fürmeier Sandra , Metzger Jürgen O. 
Published: February 2003

AbstractThe first successful preparation of the aziridines methyl (9Z,12S,13R)‐12,13‐epimino‐9‐octadecenoate (10), derived from vernolic acid, and methyl (9R,10S,12R)‐9,10‐epimino‐12‐hydroxyoctadecanoate (12a) and methyl (9S,10R,12R)‐9,10‐epimino‐12‐hydroxyoctadecanoate (12b), both derived from ricinoleic acid, is reported. These are the first examples of enantiomerically pure fat‐derived aziridines. Treatment of the corresponding epoxides with sodium azide and ammonium chloride in ethanol in the presence of water yielded the new azido hydroxy compounds, which could be treated in an improved way with polymer‐bound triphenylphosphane to afford the aziridines in good yields. The intermediate azido hydroxy compounds could easily be reduced and so offer access to a variety of interesting β‐amino alcohols 17−21. The synthesis of various N‐substituted aziridine derivatives 22−29 by treatment of methyl cis‐9,10‐epiminooctadecanoate (3) with phenyl isocyanate and isothiocyanate, acetyl chloride, alkyl and aryl chloroformates and acrylonitrile is described. Finally, the fat‐derived 2,5‐dialkyl‐substituted pyrrole methyl 9‐(5‐pentyl‐1H‐pyrrol‐2‐yl)nonanoate (9) was obtained. The previously reported bis(aziridine) methyl cis‐9,10;cis‐12,13‐diepiminooctadecanoate, derived from linoleic acid, and tris(aziridine) methyl cis‐9,10;cis‐12,13;cis‐15,16‐triepiminooctadecanoate, derived from linolenic acid,1 have been subjected to different biological tests and showed cytotoxic and antimicrobial activity as well as remarkable antitumour‐promoting and good neuroprotective effects. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Synthesis of Buta‐1,3‐diyne‐Bridged Macrocycles with (Z)‐1,4‐Diethynyl1,4‐dimethoxycyclohexa‐2,5‐diene as the Building Block
Authors: Srinivasan Manivannan , Sankararaman Sethuraman , Hopf Henning , Varghese Babu 
Published: February 2003

Abstract(Z)‐1,4‐Diethynyl‐1,4‐dimethoxycyclohexa‐2,5‐diene has been used as a building block for the synthesis of two novel macrocycles containing buta‐1,3‐diyne units as bridges. The tetrayne derivative 5c has been structurally characterized by single crystal X‐ray crystallographic data. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Semisynthesis of 7‐Deoxypaclitaxel Derivatives Devoid of an Oxetane D‐Ring, Starting from Taxine B
Authors: Beusker Patrick H. , Veldhuis Harald , Brinkhorst Johan , Hetterscheid Dennis G. H. , Feichter Nicolas , Bugaut Anthony , Scheeren Hans W. 
Published: February 2003

AbstractSix 7‐deoxypaclitaxel derivatives have been prepared from taxine B; they contribute to understanding of the effect of the oxetane D‐ring in paclitaxel on the cytotoxic activity of paclitaxel. Three of these analogues each contain a double bond instead of a D‐ring at the C‐4 position, while two others each contain a three‐membered ring in place of the oxetane ring. Both the C‐4 double bond and the small D‐ring in these paclitaxel derivatives were intended to act as substitutes for the paclitaxel oxetane D‐ring and were expected to impose on the taxane skeleton and the pendant groups a kind of rigidity and conformation similar to that produced by the oxetane ring in paclitaxel. All the derivatives demonstrated considerably reduced in vitro cytotoxic activity − relative to paclitaxel − against a panel of seven well‐characterized human tumor cell lines. The general picture coming out of the structure‐activity relationships of the paclitaxel derivatives reported here is that the presence of an oxygen atom at a spatial position resembling that of the oxygen atom in the oxetane ring of paclitaxel is important if a paclitaxel derivative is to retain considerable cytotoxic activity. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
On the Mechanism of Carbohydroxypalladation of Enynes. Additional Insights on the Cyclization of Enynes with Electrophilic Metal Complexes
Authors: Nevado Cristina , Charruault Lise , Michelet Véronique , Nieto‐Oberhuber Cristina , Muñoz M. Paz , Méndez María , Rager Marie‐Noëlle , Genêt Jean‐Pierre , Echavarren Antonio M. 
Published: February 2003

AbstractDifferent mechanisms have been proposed for the cyclization of enynes catalyzed by electrophilic metal halides or complexes. We present evidence to indicate that the previously reported “carbohydroxypalladation” and the “hydroxycyclization catalyzed by PtII” are closely related reactions. Thus, palladium complexes formed in situ from PdCl2 and trisulfonated phosphane TPPTS or cyclic phosphite P(OCH2)3CEt as the ligands catalyze the methoxy‐ or hydroxycyclization of enynes with selectivities similar to those observed with PtII complexes. Deuteration studies indicate that activation of the alkyne by PdII promotes an anti‐addition of the alkene. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Synthesis and SAR Studies of 3‐Substituted 1′‐Benzylspiro[[2]benzoxepine1,4′‐piperidines]
Authors: Maier Christoph A. , Wünsch Bernhard 
Published: February 2003

AbstractThe preparation of the hitherto unknown spiro[[2]benzoxepine‐1,4′‐piperidine] ring system is described. The synthesis consists of a Wittig reaction of 2‐bromobenzaldehyde (4) and (1,3‐dioxolan‐2‐ylmethyl)triphenylphosphonium bromide (5) to yield an α,β‐unsaturated acetal. The double bond of 6 was subsequently hydrogenated. The resulting brominated acetal 7 was treated with n‐butyllithium and then with 1‐benzylpiperidin‐4‐one (9) to yield the hydroxy acetal 10. Acid‐catalyzed cyclization of 10 with p‐toluenesulfonic acid or aqueous HCl resulted in the formation of the 1′‐benzylspiro[[2]benzoxepine‐1,4′‐piperidines] 11 and 12, respectively. The substituents in the 3‐position of the spiro compounds 11 and 12 were further modified by reaction with trimethylsilyl cyanide or (cyanomethylene)triphenylphosphorane in order to introduce residues with one or two carbon atoms, respectively. The synthesized compounds were evaluated for σ1‐ and σ2‐receptor affinity in vitro. The most potent σ1‐ligand was the methoxy derivative 11 (Ki = 2.56 nM), whereas the cyanomethyl derivative 20 turned out to be the most σ1‐selective compound (σ1/σ2 selectivity 768). ((© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Three New 2,3‐Dihydroxy Fatty Acid Glycosphingolipids from the Mediterranean Tunicate Microcosmus sulcatus
Authors: Aiello Anna , Fattorusso Ernesto , Mangoni Alfonso , Menna Marialuisa 
Published: February 2003

AbstractThree new glycosphingolipids (2a−4a) were isolated as their peracetates (2b−4b) from the marine ascidian Microcosmus sulcatus, and their structures were elucidated by spectroscopic and chemical analysis. Compounds 2a−4a are the first natural glycosphingolipids whose ceramide contains a 2,3‐dihydroxy acid. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Iron‐Mediated Synthesis of Carbazomycin G and Carbazomycin H, the First Carbazole‐1,4‐quinol Alkaloids from Streptoverticillium ehimense
Authors: Knölker Hans‐Joachim , Fröhner Wolfgang , Reddy Kethiri R. 
Published: February 2003

AbstractThe total synthesis of the carbazole‐1,4‐quinol alkaloids carbazomycin G (7) and carbazomycin H (8) was achieved by a highly convergent iron‐mediated construction of the carbazole framework. Electrophilic substitution of the arylamine 15 using the iron complex salts 13 and 14, followed by oxidative iron‐mediated arylamine cyclization, afforded the carbazole derivatives 11 and 12, respectively. These carbazoles were transformed to the corresponding carbazole‐1,4quinones 9 and 10 by oxidation with cerium(IV) ammonium nitrate. Finally, regioselective addition of methyllithium at C−1 provided carbazomycin G (7) and carbazomycin H (8). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
New Bis(chalcones) and Their Transformation into Bis(pyrazoline) and Bis(pyrazole) Derivatives
Authors: Pinto Diana C. G. A. , Silva Artur M. S. , Cavaleiro José A. S. , Elguero José 
Published: February 2003

AbstractThe reaction of bis(chalcones) 1a−d and bis(chalcone) tetrabromo derivatives 3a−d with hydrazine hydrate gave bis(pyrazolines) 4a−d and bis(pyrazoles) 5a−d, respectively. Bis(pyrazoles) 5e,f bearing hydroxyphenyl substituents have been prepared from the reaction of bis(chromones) 6c,d with hydrazine hydrate, because their synthesis from the corresponding benzyloxy‐substituted 5c,d gave very poor yields. The structures of all new compounds have been established by extensive NMR spectroscopic studies. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Unusual Rearrangements of cis‐4,7‐Disubstituted 4,7‐Dihydro4,7‐dihydroxy[2.2]paracyclophanes on Dehydration: Stereoselective Formation of Planar Chiral Cyclohexadienones
Authors: Vorontsova Natalia , Rozenberg Valeria , Vorontsov Evgenii , Antonov Dmitrii , Starikova Zoya 
Published: February 2003

AbstractUnder acid conditions, cis‐4,7‐disubstituted 4,7‐dihydro‐4,7‐dihydroxy[2.2]paracyclophanes undergo dehydration accompanied by rearrangement, affording cyclohexadienone derivatives as major products and with polysubstituted phenols being formed as minor products. The formation of either an ortho or a para semiquinoid system, as well as the configuration of the newly formed asymmetric center, depended strictly on the nature of the substituent (alkyl, allyl, or phenyl). The structures of 3,4‐dihydro‐3,7‐dimethyl[2.2]paracyclophane‐4‐one (10), 3,7‐diallyl‐3,4‐dihydro[2.2]paracyclophane‐4‐one (12), and 4,7‐dihydro‐7,8‐diphenyl[2.2]paracyclophane‐4‐one (22) were determined by X‐ray structural analysis. [2.2]Paracyclophane‐4,7‐quinone (1) was obtained in optically active form. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Voltammetric Study of Nitro Radical Anion Generated from Some Nitrofuran Compounds of Pharmacological Significance
Authors: Bollo S. , Núñez‐Vergara L. J. , Martinez C. , Chauviere G. , Périé J. , Squella J. A. 
Published: February 2003

AbstractThe electrochemical behavior of 2‐(5‐amino‐ 1,3,4‐oxadiazolyl)‐5‐nitrofuran (NF359) and its comparison with well‐known drugs such as nifurtimox (NFX) and nitrofurazone (NFZ) in protic, mixed and aprotic media by cyclic voltammetry, tast and differential pulse polarography was studied. All the compounds were electrochemically reducible in all media being the reduction of the nitrofuran group the main voltammetric signal. The one‐electron reduction couple due to the nitro radical anion formation was visualized in mixed (for NF359 and NFZ) and aprotic media (for all compounds). By applying a cyclic voltammetric methodology we have calculated the decay constants (k2) of the corresponding nitro radical anions in mixed and aprotic media. In mixed medium data fit well with a disproportionation reaction of the nitro radical anion but in aprotic medium fit better with a dimerization reaction. Also, considering cyclic voltammetric measurements in aprotic media we have estimated the reduction potential of the RNO2/RNO2.− couple in aqueous medium, pH 7 (E17 values) finding very good correlation with E17 values obtained by pulse radiolysis. Furthermore we have calculated the equilibrium constants from the electron transfer from nitro radical anion to oxygen (kO2) finding that nitro radical anion from NF359 is thermodynamically favored to react with oxygen in respect to both NFZ and NFX.
Characterization of the Surface Redox Process of Adsorbed Cercosporin (CER) at Glassy Carbon Electrodes by Anodic Stripping Square‐Wave Voltammetry
Authors: Marchiando Nancy Cristina , Zón María Alicia , Fernández Héctor 
Published: February 2003

AbstractThe adsorptive accumulation of cercosporin (CER) at glassy carbon electrodes is studied by square‐wave voltammetry (SWV). The Freundlich adsorption isotherm resulted in being the best one to describe the specific interaction of CER with glassy carbon electrodes by using a fitting procedure of experimental fractional surface coverage vs. the CER bulk concentration (c*CER). SWV was also used to generate Q vs. c*CER and Ip, n. vs. c*CER calibration plots from pure commercial reagent solutions. Theoretical detection limits of 1.8×10−7 and 9.7×10−8 M were calculated from Q. vs. c*CER and Ip, n vs. c*CER plots, respectively. The lowest concentration value measured experimentally from calibration plots performed at a f =40 Hz for a signal to noise ratio of 2 : 1 was 3.7×10−8 M, being this value two orders of magnitude smaller than that obtained previously by us from the diffusion controlled CER reduction peak. Ip, n./f vs. f plots from SW voltammograms performed at different c*CER as well as different accumulation times showed the so‐called “quasi‐reversible maxima”. A splitting of the voltammetric peak was also observed by increasing the SW amplitude at a given frequency. A value of (−0.260±0.011) V was determined for the formal potential of the adsorbed redox couple from the split voltammetric peak. A full characterization of the surface redox process was obtained by applying the methods of the “quasi‐reversible maximum” and the “split SW peak”. In 1 M HClO4 aqueous solution, the formal rate constant and the anodic transfer coefficient were (3.5±0.5)×102 s−1 and (0.50±0.03), respectively. Besides, the number of electrons exchanged during the redox reaction was calculated as n≈1.
Electrochemical Nitric Oxide Sensors for Biological Samples – Principle, Selected Examples and Applications
Authors: Bedioui Fethi , Villeneuve Nicole 
Published: February 2003

AbstractThe discoveries made in the 1980s that NO could be synthesized by mammalian cells and could act as physiological messenger and cytotoxic agent had elevated the importance of its detection. The numerous properties of NO, that enable it to carry out its diverse functions, also present considerable problems when attempting its detection and quantification in biological systems. Indeed, its total free concentration in physiological conditions has been established to be in nanomolar range. Thus, detection of nitric oxide remains a challenge, pointing out the difficult dual requirements for specificity and sensitivity. Exception made for the electrochemical techniques, most of the approaches (namely UV‐visible spectroscopy, fluorescence, electron paramagnetic resonance spectroscopy) use indirect methods for estimating endogenous NO, relying on measurements of secondary species such as nitrite and nitrate or NO‐adducts. They also suffer from allowing only ex situ measurements. So, the only strategies that allow a direct and in vivo detection of NO are those based on the use of ultramicroelectrodes. The reality is that surface electrode modification is needed to make the ultramicroelectrode material selective for NO. Therefore, the design of modified electrode surfaces using organized layers is very attractive and provides the ideal strategy. This review addresses a global description of the various approaches that have involved chemically modified microelectrodes specially designed for the electrochemical detection of NO in biological media. Selected significant examples of applications in biological tissues are also reported in order to highlight the importance of this approach in having new insights into the modulatory role of NO in physiology and pathophysiology.
Background and operating parameters in microemulsion electrokinetic chromatography
Authors: Altria Kevin D. , Mahuzier Pierre‐Etienne , Clark Brian J. 
Published: February 2003

AbstractMicroemulsion electrokinetic chromatography (MEEKC) is an electrodriven separation technique. Separations are generally achieved using microemulsions consisting of surfactant‐coated nanometer‐sized oil droplets suspended in aqueous buffer. A cosurfactant such as a short‐chain alcohol is generally used to stabilize the microemulsion. This review summarizes the various microemulsion types and compositions that have been used in MEEKC. The effects of key‐operating variables such as surfactant type and concentration, cosurfactant type and concentration, buffer pH and type, oil type and concentration, use of organic solvent and cyclodextrin additions, and temperature are described. Specific examples of water‐in‐oil microemulsions and chirally selective separations are also covered.
Analysis of selected withanolides in plant extract by capillary electrochromatography and microemulsion electrokinetic chromatography
Authors: Cherkaoui Samir , Cahours Xavier , Veuthey Jean‐Luc 
Published: February 2003

AbstractMicroemulsion electrokinetic chromatography (MEEKC) coupled with a diode‐array detector was developed for the simultaneous analysis of natural steroidal compounds, withanolides including withaferin A, withacnistin and iochromolide. Optimal resolution was obtained with a microemulsion consisting of 70 mM octane, 800 mM 1‐butanol, 100 mM sodium dodecyl sulfate (SDS), and 10 mM phosphate‐borate buffer (pH 7) using a fused‐silica capillary at 25 kV and 40°C. Since this technique is not compatible with mass spectrometry detection, a capillary electrochromatographic method was developed to separate the investigated withanolides. The effects of mobile phase composition and pH were systematically investigated. Complete separation was obtained with a capillary electrochromatography (CEC) Hypersil C18 bonded silica column (packed length, 25 cm×100 μm ID and 375 μm OD), packed with 3 μm particles. The mobile phase consisted of formic acid‐ammonia, pH 8 / acetonitrile (40/60 v/v); the voltage was set at 25 kV and the temperature at 20°C. Under these conditions, resolution of these closely related compounds, including the critical pair withacnistin and iochromolide, was achieved in less than 5 min. The separations by MEEKC and CEC were compared with that obtained by reversed‐phase liquid chromatography and showed similar retention order, indicating the analogy of the retention mechanism of these techniques. To further improve specificity and sensitivity, the developed CEC method was interfaced with electrospray ionization mass spectrometry using a Teflon connection between the CEC column and a void fused‐silica capillary. Finally, the described methods were applied to the qualitative analysis of withanolides in Iochroma gesnerioides plant extract.
Influence of methanol as a buffer additive on the mobilities of organic cations in capillary electrophoresis
Authors: Roy Kimberly I. , Lucy Charles A. 
Published: February 2003

AbstractThe mobilities of a series of aromatic ammonium ions, ranging in charge from +1 to + 3, were investigated by capillary electrophoresis using buffers consisting of 0–75% v/v methanol. This is an extension of our previous studies involving anion mobility in methanol‐water media [1]. Absolute mobilities were determined by extrapolation of the effective mobilities to zero ionic strength according to the Pitts' equation. For all of the buffer compositions studied, the ionic strength effect increased with increasing cation charge, and varied as a function of solvent 1/ηε1/2 as predicted by the electrophoretic term within the Pitts' equation. In the presence of methanol, the ionic strength effects became more dramatic. The absolute mobilities of the cations were altered by the addition of methanol to the electrophoretic media. For example, at 75% MeOH, a migration order reversal was observed between the + 2 and + 3 ammonium ions. These solvent‐induced selectivity changes are attributed to dielectric friction. As predicted by the Hubbard‐Onsager dielectric friction model, dielectric friction increased with increasing methanol content and with increasing analyte charge. Further, the changes in cation mobility correlated to the changes in solvent relaxation time (τ), ε and η. Although not predicted by the Hubbard‐Onsager theory, the + 3 ammonium ion experienced more dielectric friction than the − 3 sulfonate and − 3 carboxylate investigated previously [1]. This apparent failure of the Hubbard‐Onsager model results from its continuum nature, whereby ion‐solvent interactions are not taken into account.
Control of electroosmotic flow in nonaqueous capillary electrophoresis by polymer capillary coatings
Authors: Steiner Frank , Hassel Marc 
Published: February 2003

AbstractIn aqueous capillary electrophoresis the electroosmotic flow (EOF) can be strongly suppressed or eliminated by coating the capillary surface silanols either by buffer additive adsorption or chemical modification. Hydrophilic coatings, e.g., polyvinyl alcohol (PVA) proved to be most efficient for EOF control in applications like DNA analysis. In nonaqueous capillary electrophoresis (NACE), however, the EOF cannot be totally suppressed with these capillaries and coating efficiency turned out to be solvent‐depending. In this paper, fused‐silica capillaries with monomeric and polymeric coatings differing in hydrophobicity and chemical properties (vinyl, vinyl acetate, vinyl alcohol and acrylates with different alkyl chain length) were investigated. Besides studying the EOF characteristics with different organic solvents and water, gas chromatography (GC) measurements were carried out to probe the silanol reduction via ether retention and the surface hydrophobicity by retention of nonane. Good correlations between GC results and EOF magnitude could be found. It could be demonstrated that the polymeric coating has to be solvatized by the buffer solvent to reduce the EOF. The PVA coating was optimal for aqueous systems but not effective for some nonaqueous buffers. On the other hand, polyvinyl acetate and polyethyl acrylate as polymeric coatings proved to be optimal to reduce the EOF in NACE.
Anomalously fast migration of triplet‐repeat DNA in capillary electrophoresis with linear polymer solution
Authors: Kiba Yuriko , Zhang Lihua , Baba Yoshinobu 
Published: February 2003

AbstractWe investigated the capillary electrophoretic behavior of single‐stranded DNA fragments in methylcellulose solution, and found that triplet‐repeat DNA showed anomalously faster mobilities than DNA markers with random sequence. Through the further study on the electrophoretic data, reptation model is proven appropriate to describe the migration of DNA under our experimental conditions. Accordingly, with the equations based on reptation theory, we could obtain the persistence length of DNA fragments and find that these values of triplet‐repeat DNAs are larger than that of DNA markers with random sequence, which means the former DNAs are less flexible than the latter ones when they migrate in the electric field. This phenomenon is supposed to result from the characteristic higher‐order structure formed by GC base pairs within triplet‐repeat DNA, which is further proven by the resumed migration order in accordance with DNA size when the denaturant is added into the sieving matrix.
Stacking phenomena in electromigration: From basic principles to practical procedures
Authors: Urbánek Marek , Křivánková Ludmila , Boček Petr 
Published: February 2003

AbstractThe review describes principles of procedures and techniques used in capillary zone electrophoresis for enhancement of sensitivity that are based on increasing analyte mass in its zone during the electromigration process, for which the term stacking is generally used. Attention is paid to intrinsic stacking in samples with low conductivity, transient isotachophoretic stacking applied in samples with high conductivity, and sweeping in micellar electrokinetic chromatography. Principles of these stacking schemes are explained, new procedures and instrumental arrangements are discussed, and all contributions involving stacking principles that have been published since the year 2000 are surveyed.