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Benzyl
Terms modified by Benzyl Selected AbstractsHydrogen bonding of modified bases involving Watson-Crick sites: Crystal structure and conformation of Benzyl 6-aminopurine-7-carboxylateCRYSTAL RESEARCH AND TECHNOLOGY, Issue 7 2006J. M. Ohrt Abstract Crystals of benzyl 6-aminopurine-7-carboxylate (C13H11N5O2) are monoclinic, space group C2/c, Z = 8, with a = 25.448 (9), b = 6.052 (1), c = 16.975 (6)Å, , = 112.05 (5)°, M = 269.27, Dm= 1.49, Dx= 1.48 g/cm3. The structure was determined from three-dimensional diffractometric data by the multisolution technique and refined to a final reliability factor of 0.068. The molecule is planar with an intramolecular hydrogen bond from one of the amino hydrogens, Ha(N6) to the keto oxygen O(10) of the acyl group. The molecules are hydrogen bonded across the center of inversion by a pair of intermolecular hydrogen bonds using the Watson-Crick sites. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Resolution of Racemic N -Benzyl ,-Amino Acids by Liquid-Liquid Extraction: A Practical Method Using a Lipophilic Chiral Cobalt(III) Salen Complex and Mechanistic StudiesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 7 2008Pawel Dzygiel Abstract The efficient resolution of racemic N -benzyl ,-amino acids (N -Bn-AA) has been achieved by a liquid-liquid extraction process using the lipophilic chiral salen,cobalt(III) complex [CoIII(3)(OAc)]. As a result of the resolution by extraction, one enantiomer (S) of the N -benzyl ,-amino acid predominated in the aqueous phase, while the other enantiomer (R) was driven into the organic phase by complexation to cobalt. The complexed amino acid (R) was then quantitatively released by a reductive (CoIII,,,CoII) counter-extraction with aqueous sodium dithionite or L -ascorbic acid in methanol. Thereductive cleavage allowed to recover the [CoII(3)] complex in good yield, which could be easily re-oxidized to[CoIII(3)(OAc)] with air/AcOH and reused with essentially no loss of reactivity and selectivity. Investigation on the nitrogen substitution indicates that the presence of a single benzyl group on the amino acid nitrogen is important to obtain high enantioselectivity in the extraction process. The kinetic vs. thermodynamic nature of the resolution process was also investigated with an enantiomeric exchange experiment, which shows that the liquid-liquid extraction with [CoIII(3)(OAc)] is an equilibrium process operating under thermodynamic control. In the absence of a suitable crystal structure of the [CoIII(3)(N -Bn-AA)] complexes, computational and spectroscopic studies were used to investigate how the N -benzyl ,-amino acids are accommodated in the "binding pocket" of the chiral cobalt complex. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Effect of benzyl isothiocyanate on tomato fruit infection development by Alternaria alternataJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 9 2005R Troncoso-Rojas Abstract Benzyl isothiocyanate (BITC) is known to be a strong antifungal compound in vitro against different fungi. The effectiveness of benzyl isothiocyanate to control Alternaria alternata growth in vitro and in vivo was tested. BITC in vitro activity was evaluated in A alternata growing on potato dextrose agar and exposed to 0.025, 0.05, 0.1, 0.2 or 0.4 mg ml,1. In vivo activity was evaluated by exposing A alternata -inoculated tomato fruits for either 18 or 36 h to 0.28 or 0.56 mg ml,1 BITC packed on low-density polyethylene film (LDPF) bags. Additionally, the effect of BITC on post-harvest physiology and tomato quality throughout storage at 20 °C was evaluated daily by monitoring respiration rate and ethylene production, whereas total soluble solids, pH, titratable acidity and fresh weight loss were measured every 3 days. Results showed that the minimal inhibitory concentration of BITC in vitro was 0.1 mg ml,1. A combined use of 0.56 mg ml,1 BITC with LDPF for 18 h was the optimum treatment to control Alternaria rot in packed tomato fruit. No effect of BITC on respiration rate, ethylene production, total soluble solids, pH, weight loss and titratable acidity was observed. Results suggest that BITC can be used as a post-harvest treatment to control Alternaria rot in tomato fruit without detrimental effects on the tomato post-harvest quality. Copyright © 2005 Society of Chemical Industry [source] Calcium-katalysierte Friedel-Crafts-Alkylierung bei RaumtemperaturANGEWANDTE CHEMIE, Issue 21 2010Meike Niggemann Prof. Ein neuartiger Calcium-Katalysator ermöglichte die Funktionalisierung elektronenreicher Arene mit sekundären und tertiären Benzyl-, Propargyl- und Allylalkoholen unter sehr milden Bedingungen. Die Anwendungsbreite der bislang bis auf wenige Ausnahmen auf sekundäre Benzylalkoholderivate beschränkten Reaktion wurde mit dem neuen Katalysatorsystem beträchtlich erweitert. [source] Asymmetric Tandem Wittig Rearrangement/Mannich Reactions,ANGEWANDTE CHEMIE, Issue 16 2010Natalie Man hat die Wahl: Eine hoch stereoselektive Synthese von ,-Alkyl-,-hydroxy-,-aminoestern gelingt in einer Tandemreaktionssequenz aus Wittig-Umlagerung und Mannich-Reaktion. N -Benzyl- und N -Boc-Imine werden mit hoher Selektivität in die syn -Aminoalkohole überführt (siehe Beispiel), während N -Boc-2-(phenylsulfonyl)amine anti -Aminoalkohole liefern. Nach Abspaltung des Auxiliars (Umesterung oder Reduktion) werden die Produkte mit bis zu 96,%,ee erhalten. [source] ChemInform Abstract: A Mild and Efficient Approach for the Selective Deprotection of Benzyl and Phenyl Trimethylsilyl Ethers in 1-Butyl-3-methylimidazolium Chloride.CHEMINFORM, Issue 12 2009Ahmad Shaabani Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Synthesis and Antiprotozoal Evaluation of New N4 -(Benzyl)spermidyl-Linked Bis(1,3,5-thiadiazinane-2-thiones).CHEMINFORM, Issue 9 2009Julieta Coro Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] One-Pot Synthesis of 1,2,3-Triazoles from Benzyl and Alkyl Halides, Sodium Azide and Alkynes and Water under Transition-Metal-Catalyst Free Reaction Conditions.CHEMINFORM, Issue 31 2007Pinhua Li Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Palladium Catalyzed Heck Reaction of Arenediazonium Tetrafluoroborate Salts with Baylis,Hillman Adducts: Production of ,-Benzyl-,-keto Esters.CHEMINFORM, Issue 22 2006Rolando Perez Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Synthesis and Antimicrobial Activity of 5-(R1 -Benzyl)-2-(R-benzylidenehydrazono)-3- (2-furylmethyl)thiazolidin-4-ones.CHEMINFORM, Issue 41 2005V. M. Tsyalkovskii Abstract For Abstract see ChemInform Abstract in Full Text. [source] Selecting Against S1P3 Enhances the Acute Cardiovascular Tolerability of 3-(N-Benzyl)aminopropylphosphonic Acid S1P Receptor Agonists.CHEMINFORM, Issue 43 2004Jeffrey J. Hale No abstract is available for this article. [source] Novel N1 -(Benzyl)cinnamamidine Derived NR2B Subtype-Selective NMDA Receptor Antagonists.CHEMINFORM, Issue 25 2003Neil R. Curtis Abstract For Abstract see ChemInform Abstract in Full Text. [source] Deprotection of Benzyl and p-Methoxybenzyl Ethers by Chlorosulfonyl Isocyanate,Sodium Hydroxide.CHEMINFORM, Issue 18 2003Ji Duck Kim Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: Reactions of Alkyl, Benzyl, and Stannyl Halides with Lewis Acid Complexed ,-Lithiated Tertiary Amines.CHEMINFORM, Issue 28 2001Satinder V. Kessar Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] The energetic cost of activation in mouse fast-twitch muscle is the same whether measured using reduced filament overlap or N -benzyl- p -toluenesulphonamideACTA PHYSIOLOGICA, Issue 4 2008C. J. Barclay Abstract Aim:, Force generation and transmembrane ion pumping account for the majority of energy expended by contracting skeletal muscles. Energy turnover for ion pumping, activation energy turnover (EA), can be determined by measuring the energy turnover when force generation has been inhibited. Most measurements show that activation accounts for 25,40% of isometric energy turnover. It was recently reported that when force generation in mouse fast-twitch muscle was inhibited using N -benzyl- p -toluenesulphonamide (BTS), activation accounted for as much as 80% of total energy turnover during submaximal contractions. The purpose of this study was to compare EA measured by inhibiting force generation by: (1) the conventional method of reducing contractile filament overlap; and (2) pharmacological inhibition using BTS. Methods:, Experiments were performed in vitro using bundles of fibres from mouse fast-twitch extensor digitorum longus (EDL) muscle. Energy turnover was quantified by measuring the heat produced during 1-s maximal and submaximal tetanic contractions at 20 and 30 °C. Results:,EA measured using reduced filament overlap was 0.36 ± 0.04 (n = 8) at 20 °C and 0.31 ± 0.05 (n = 6) at 30 °C. The corresponding values measured using BTS in maximal contractions were 0.46 ± 0.06 and 0.38 ± 0.06 (n = 6 in both cases). There were no significant differences among these values. EA was also no different when measured using BTS in submaximal contractions. Conclusion:, Activation energy turnover is the same whether measured using BTS or reduced filament overlap and accounts for slightly more than one-third of isometric energy turnover in mouse EDL muscle. [source] Hydrogen bonding of modified bases involving Watson-Crick sites: Crystal structure and conformation of Benzyl 6-aminopurine-7-carboxylateCRYSTAL RESEARCH AND TECHNOLOGY, Issue 7 2006J. M. Ohrt Abstract Crystals of benzyl 6-aminopurine-7-carboxylate (C13H11N5O2) are monoclinic, space group C2/c, Z = 8, with a = 25.448 (9), b = 6.052 (1), c = 16.975 (6)Å, , = 112.05 (5)°, M = 269.27, Dm= 1.49, Dx= 1.48 g/cm3. The structure was determined from three-dimensional diffractometric data by the multisolution technique and refined to a final reliability factor of 0.068. The molecule is planar with an intramolecular hydrogen bond from one of the amino hydrogens, Ha(N6) to the keto oxygen O(10) of the acyl group. The molecules are hydrogen bonded across the center of inversion by a pair of intermolecular hydrogen bonds using the Watson-Crick sites. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Crystal structure of ,-phenoxo bridged dicopper complex: {N-[(2-hydroxylato-5-methyl)benzyl-(2,-hydroxylato-3,,5,-dimethylbenzyl)]ethyl amine dicopper(II)}CRYSTAL RESEARCH AND TECHNOLOGY, Issue 12 2002S. M. Malathy Sony Abstract The title compound crystallizes in monoclinic space group C2/c with cell parameters a = 21.404(2), b = 13.962(1), c = 17.917(1)Å, , = 124.394(2)°, V = 4418.3(6)Å3, Z = 8, Dcal = 1.193Mg/m3 and T = 293 K. The structure was solved by Patterson method and refined by full-matrix least-squares procedures to final R = 0.0882 using 5253 observed reflections. The tetra coordinated copper atom have a slight distorted square planar geometry with the Cu-Cu distance of 2.987(1)Å. The two six membered rings containing copper atom assume distorted sofa conformation. C-H,, and C-H,O type of intermolecular interactions play a role in stabilizing the crystal packing in addition to van der Waals forces. [source] Novel DNA repair alkyltransferase from Caenorhabditis elegansENVIRONMENTAL AND MOLECULAR MUTAGENESIS, Issue 2-3 2001Sreenivas Kanugula Abstract O6 -Alkylguanine DNA-alkyltransferase (AGT) is a widely distributed DNA repair protein that protects living organisms from endogenous and exogenous alkylation damage to DNA at the O6 -position of guanine. The search of the C. elegans genome database for an AGT protein revealed the presence of a protein (cAGT-2) with some similarity to known AGTs in addition to the easily recognized cAGT-1 protein. The predicted protein sequence of cAGT-2 contains the amino acid sequence ,ProCysHisPro, at the presumed active site of the protein, whereas all other known AGTs have ,ProCysHisArg,. A truncated version of the cAGT-2 protein was expressed in E. coli. This purified recombinant protein was able to repair O6 -methylguanine and O4 -methylthymine adducts in DNA in vitro and also reacted with the bulky benzyl adduct in O6 -benzylguanine. This fragment of cAGT-2 (104 amino acids) is the smallest protein possessing AGT activity yet described. The full-length cAGT-2 protein (274 amino acids) totally lacks the N-terminal domain present in all other known AGTs but has a long C-terminal extension that has significant homology to histone 1C. Expression of cAGT-2 in an E. coli strain lacking endogenous AGT activity provided modest but statistically significant resistance to the toxicity of N -methyl- N,-nitro- N -nitrosoguanidine, confirming that cAGT-2 is an alkyltransferase. Environ. Mol. Mutagen. 38:235,243, 2001. © 2001 Wiley-Liss, Inc. [source] Synthesis, Structure, Conductivity, and Calculated Nonlinear Optical Properties of Two Novel Bis(triphenylphosphane)copper(I) Dithiocarbamates,EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2009Abhinav Kumar Abstract A centrosymmetric binuclear [{Cu(PPh3)2}2(piperzdtc)] (1) [piperzdtc2, = piperazinebis(dithiocarbamate)] and another mononuclear [{Cu(PPh3)2}(BzMedtc)] (2) (BzMedtc, = N -benzyl- N -methyldithiocarbamate) complex have been synthesized and characterized by elemental analyses, IR, 1H, 13C, and 31P NMR spectroscopy and by X-ray crystallography. The nonlinear optical properties of 2 have been investigated by density functional theory and its electronic absorption bands have been assigned by time-dependent density functional theory (TD-DFT). Both complexes are weakly conducting (,rt , 10,8 S,cm,1) because of the absence of M···S/S···S intermolecular stacking and exhibit semiconductivity with band gaps of 0.94 and 1.24 eV, respectively.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Guest-Inclusion Behavior of Double-Strand 1D Coordination Polymers Based on N,N, -Type Schiff Base LigandsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 10 2008Qing Wang Abstract Four double-strand one-dimensional (1D) coordinationpolymers, namely, {[Ni(N3Py)2(NO3)2]·(C6H6)x·C2H5OH}n (1), [Cd(ImBNN)2(CH3C6H4SO3)2]n (2), {[Co(N3OPy)2(H2O)2](ClO4)2·C6H6·H2O}n (3), and {[Co(N3OPy)2(H2O)2](ClO4)2·(C8H10)x}n (4) were obtained from the assembly of three N,N, -type Schiff base ligands, 1,4-bis(3-pyridyl)-2,3-diaza-1,3-butadiene (N3Py), 2,5-bis(4,-(imidazol-1-yl)benzyl)-3,4-diaza-2,4-hexadiene (ImBNN), and bis[4-(3-pyridylmethylenemino)phenoxy]methane (N3OPy), with transition-metal ions. All complexes were characterized by single-crystal X-ray diffraction, X-ray powder diffraction, and FTIR measurements. The guest-inclusion behavior of these complexes were investigated by thermogravimetric and X-ray powder diffraction analyses. The structural relationship between the ligands and the cavity sizes and packing fashions have been discussed to elucidate the distinctive guest-inclusion behavior of these complexes.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Synthesis, Coordination and Catalytic Utility of Novel Phosphanyl,ferrocenecarboxylic Ligands Combining Planar and Central ChiralityEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 16 2007Martin Lama Abstract The chiral ferrocene derivative (R,Rp)-2-[1-(diphenylphosphanyl)ethyl]ferrocenecarboxylic acid (1) is prepared together with selected derivatives resulting from modification at the phosphane moiety [P -oxide (5) and P -sulfide (4)] and the carboxyl group {amides bearing benzyl (6) and (R)- or (S)-1-phenylethyl substituents [(R)- 7 and (S)- 7] at the amide nitrogen atom}. Acid 1 and amide 6 are studied as ligands in rhodium and palladium complexes. Bridge cleavage of the dimer [{Rh(,-Cl)Cl(,5 -C5Me5)}2] with 1 gives [RhCl2(,5 -C5Me5)(1 -,P)] (9) containing P-monodentate 1, which undergoes smooth conversion to the (phosphanylalkyl)ferrocenecarboxylato complex [RhCl(,5 -C5Me5){Fe(,5 -C5H5)(,5 -C5H3 -1-CH(Me)PPh2 -2-COO-,2O,P}] (10) upon treatment with silica gel or alumina. Yet another O,P -chelate complex,[Rh{Fe(,5 -C5H5)(,5 -C5H3 -1-CH(Me)PPh2 -2-COO-,2O,P}(CO)(PCy3)] (11; Cy = cyclohexyl) is obtained directly by an acid-base reaction between the acetylacetonato complex [Rh(acac)(CO)(PCy3)] and 1. Amide 6 reacts with [{Pd(,-Cl)(,3 -C3H5)}2] to give the expected phosphane complex [PdCl(,3 -C3H5)(6 -,P)] (12), while the replacement of the cyclooctadiene (cod) ligand in [PdCl(Me)(cod)] affords the chelate complex [PdCl(Me)(6 -,2O,P)] (13). All compounds are characterised by spectroscopic methods and the solid-state structures of 5, 9, 11, 13, (R,Sp)-2-[1-(diphenylphosphoryl)ethyl]-1-[N -(R)-(1-phenylethyl)carbamoyl]ferrocene [(R)- 8; phosphane oxide from (R)- 7], and the synthetic precursors (R,Sp)-1-bromo-2-[1-(diphenylphosphanyl)ethyl]ferrocene (2) and (R,Sp)-1-bromo-2-[1-(diphenylthiophosphoryl)ethyl]ferrocene (3) determined by single-crystal X-ray diffraction. The catalytic properties of 1 and the amides are probed in enanatioselective rhodium-catalysed hydrogenation and palladium-catalysed asymmetric allylic alkylation. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Electronic Control of the Rotational Barrier in ,2 -Alkyne-1-thio ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 7 2007Wolfram W. Seidel Abstract A family of thio-alkyne complexes [Tp,Mo(CO)(L)(BnSC2S)] {Bn = benzyl, Tp, = hydrotris(3,5-dimethylpyrazolyl)borate, L = carbonyl (2), 2,6-dimethylphenyl isocyanide (7), tert -butyl isocyanide (8), 4-(dimethylamino)pyridine (9)} was prepared by reductive removal of a benzyl group in the corresponding bis(benzylthio)acetylene complexes [Tp,Mo(CO)(L)(BnSC2SBn)](PF6) (1 -PF6, 4 -PF6, 5 -PF6 and 6 -PF6). All complexes were characterized by IR, 1H, 13C spectroscopy and cyclic voltammetry. X-ray diffraction studies of 5 -PF6, 8 and 9 were carried out. The alkyne ligand is bound symmetrically to molybdenum in 5 -PF6 and unsymmetrically in 8 and 9. The trend in the ,-acidity of ligand L is reflected in the spectroscopic and electrochemical data as well as in the molecular structures. Variable temperature 1H NMR investigations with 7, 8 and 9 disclosed that the barrier of the alkyne rotation at molybdenum decreases in the order of rising electron density at the metal center while the steric demand increases. Therefore, electronic control of the barrier by the specific character of the ligand L is evident.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Synthesis, Structure and Magnetic Properties of a Tetranuclear Copper(II) Complex on the Basis of a 2-Substituted Glucopyranoside Schiff Base Ligand,EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 17 2006Anja Burkhardt Abstract Condensation of a derivatized 2-aminoglucose fragment with salicylaldehyde affords the new sugar-based Schiff base ligand benzyl 4,6- O -benzylidene-2-deoxy-2-salicylideneamino-,- D -glucopyranoside (H2L). The reaction of the dibasic ligand H2L with [Cu(CH3COO)2]·H2O leads to the formation of the tetranuclear copper(II) complex [{Cu(L)}4] (3) by a self-assembly process. The X-ray structural analysis of complex 3 which crystallizes together with two molecules of chloroform and one molecule of ethanol in the space group P212121 revealed for all copper atoms a NO3 coordination environment with a square-planar geometry. The tetranuclear molecule 3 consists of four chiral building blocks {Cu(L)} with the rare 2,3-coordination of the trans -configured donor atoms of the sugar backbone. The observed coordination mode of the building blocks exemplifies how chitosan-derived polysaccharide ligands can act as a chiral support for transition-metal complexes. The C-3 alcoholate oxygen atoms of the carbohydrate unit is bridging adjacent {Cu(L)} moieties resulting in an eight-membered Cu4O4 ring with a boat-like conformation. Temperature-dependent magnetic measurements of 3 indicate moderate antiferromagnetic interactions between the four copper(II) ions with a coupling constant of J = ,130 cm,1.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Kinetic and Thermodynamic Studies of the Disproportionation of Hydrogen Peroxide by Dimanganese(ii,ii) and -(ii,iii) Complexes of a Bridging Phenolate LigandEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2005Lionel Dubois Abstract The dimanganese(ii,ii) complexes [Mn2(L)(OAc)2(CH3OH)]-(ClO4) (1a) and [Mn2(L)(OBz)2(H2O)](ClO4) (1b) as well as the dimanganese(ii,iii) complex [Mn2(L)(OAc)2(CH3OH)]-(ClO4)2 (2a), where HL is the asymmetric phenol ligand2-[bis(2-pyridylmethyl)aminomethyl]-6-{[(benzyl)(2-pyridyl-methyl)amino]methyl}-4-methylphenol, react with hydrogen peroxide in acetonitrile solution. The initial reaction rates and their temperature and acid/base dependencies were investigated by monitoring the dioxygen evolution. These studies revealed a first-order dependence on both the catalyst and H2O2 and a strong influence of the carboxylate. Electrospray ionisation mass spectrometry as well as EPR and UV/Vis spectroscopy were used to monitor the reaction catalysed by 2a. The same bis(,-oxo)dimanganese(III,IV) and (,-oxo)dimanganese(ii,iii) active species as found for 1a were detected in the catalytic medium. The EPR spectra recorded during the catalase-like reaction revealed the accumulation of the magnetically uncoupled dimanganese(ii,iii) precursor of the active bis(,-oxo)dimanganese(III,IV) species which dominates the spectra in the case of 1a. This difference can be attributed to the different pH conditions generated by the reaction and reflects differences in the initiation phases for the two catalysts. Overall, the kinetic and thermodynamic studies of H2O2 disproportionation by these dimanganese complexes are fully consistent with the mechanism deduced from our previous extensive spectroscopic studies. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Regiospecific Cyclometalation of Diphenyl(2-substituted phenyl)phosphane with Methyltetrakis(trimethylphosphane)cobalt(I)EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 5 2003Hans-Friedrich Klein Abstract The pre-chelate molecules 2-(diphenylphosphanyl)- N,N -dimethylaniline, [2-(diphenylphosphanyl)benzyl]dimethylamine, 1-(diphenylphosphanyl)-2-ethylbenzene, 1-(diphenylphosphanyl)-2-isopropylbenzene, and 2-(diphenylphosphanyl)benzonitrile, in a reaction with [CoMe(PMe3)4], eliminate methane to afford the selectively 6- ortho -metalated complexes 1,5 that contain four-membered metallacycles. The molecular structure of 3 shows a tbp-coordinated cobalt atom, with axial C and PMe3 donor groups. Metalation in the aliphatic side-chain occurs with 2-(diphenylphosphanyl)toluene, giving complex 6 that contains a five-membered metallacycle. Benzyldiphenylphosphane is selectively ortho -metalated in the benzyl group, affording 7. As shown by the molecular structures, complex 7 is a true ligand isomer of 6. Substitution of a trimethylphosphane group in compounds 4 and 6 by ethene gives the pentacoordinate complexes 8 and 9, respectively. The ethene ligand is ,-coordinated in the equatorial plane of a trigonal bipyramid. Under 1 bar of CO, complex 6 forms monocarbonyl complex 10. Carbonylation of complexes 3 and 4 proceeds by insertion of CO into the Co,C bond under ring expansion, affording the aroylcobalt complexes 11 and 12, respectively. Complex 6 reacts with iodomethane in an oxidative substitution reaction yielding a structurally characterized octahedral complex mer - 13, which eliminates a methyl group in THF at 20 °C to form a pentacoordinate cobalt(II) complex 14. Complex 3 oxidatively adds iodomethane in a stereoselective cis addition to give the cobalt(III) complex mer - 15, which retains its four-membered metallacycle and the CoCH3 group. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Synthesis of Enantiomerically Pure Highly Functionalized Furanoid Glycal and 2,5-Dihydrofuran Building Blocks,,§EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 13 2009Pinki Pal Abstract Differently protected enantiomerically pure furanoid glycals (5a,d) and highly functionalized 2,5-dihydrofurans (6a,b) were synthesized from their respective 2,3,4-trisubstituted tetrahydrofurans. These furanoid glycals were identified as1,4-anhydro-2-deoxy-5,6- O -isopropylidene-3- O -benzyl- L -arabino-hex-1-enitol, 1,4-anhydro-2-deoxy-5,6- O -isopropylidene-3- O -benzyl- L -ribo-hex-1-enitol, 1,4-anhydro-2-deoxy-5,6- O -isopropylidene-3- O -benzyl- D -ribo-hex-1-enitol and 1,4-anhydro-2-deoxy-5,6- O -isopropylidene-3- O -benzyl- D -arabino-hex-1-enitol, respectively. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Screening the Structural Space of Bicyclo-DNA: Synthesis and Thermal Melting Properties of bc4,3 -DNAEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 8 2009Andrea Stauffiger Abstract In attempts to screen the structural and functional properties of bicyclo-DNA, in which the ribose C(3,) and C(5,) centers are integrated into an additional five-membered carbocyclic ring ([3.3.0]-series) we have now synthesized and investigated a ring enlarged analogue in which C(5,) and C(3,) are spanned by a six-membered carbocyclic ring ([4.3.0]-series). The synthesis of the corresponding bc4,3 -T nucleoside 13 was performed in 12 steps by starting from known allyl furanose 1. X-ray analysis of its benzyl protected precursor 12 showed the cyclohexane ring to adopt a chair conformation with the O(5,) substituent in an axial position. The furanose part shows clearly S-type sugar pucker. This nucleoside was converted into the corresponding phosphoramidite building block 15 and incorporated into oligodeoxynucleotides by standard phosphoramidite chemistry. The thermal stabilities of oligonucleotides with single or double incorporations of bc4,3 -T residues, paired to complementary DNA or RNA, were found to be similar to those of unmodified oligonucleotides (,2.3 to +0.7 °C per modification) and to those with the known bc-T modifications. We also found that mismatch discrimination in the bc4,3 -T series was similar to that of the natural series but less discriminative in comparison to the known bc-T series.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Resolution of Racemic N -Benzyl ,-Amino Acids by Liquid-Liquid Extraction: A Practical Method Using a Lipophilic Chiral Cobalt(III) Salen Complex and Mechanistic StudiesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 7 2008Pawel Dzygiel Abstract The efficient resolution of racemic N -benzyl ,-amino acids (N -Bn-AA) has been achieved by a liquid-liquid extraction process using the lipophilic chiral salen,cobalt(III) complex [CoIII(3)(OAc)]. As a result of the resolution by extraction, one enantiomer (S) of the N -benzyl ,-amino acid predominated in the aqueous phase, while the other enantiomer (R) was driven into the organic phase by complexation to cobalt. The complexed amino acid (R) was then quantitatively released by a reductive (CoIII,,,CoII) counter-extraction with aqueous sodium dithionite or L -ascorbic acid in methanol. Thereductive cleavage allowed to recover the [CoII(3)] complex in good yield, which could be easily re-oxidized to[CoIII(3)(OAc)] with air/AcOH and reused with essentially no loss of reactivity and selectivity. Investigation on the nitrogen substitution indicates that the presence of a single benzyl group on the amino acid nitrogen is important to obtain high enantioselectivity in the extraction process. The kinetic vs. thermodynamic nature of the resolution process was also investigated with an enantiomeric exchange experiment, which shows that the liquid-liquid extraction with [CoIII(3)(OAc)] is an equilibrium process operating under thermodynamic control. In the absence of a suitable crystal structure of the [CoIII(3)(N -Bn-AA)] complexes, computational and spectroscopic studies were used to investigate how the N -benzyl ,-amino acids are accommodated in the "binding pocket" of the chiral cobalt complex. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Regiospecific Synthesis of 4-Deoxy- D - threo -hex-3-enopyranosides by Simultaneous Activation,Elimination of the Talopyranoside Axial 4-OH with the NaH/Im2SO2 System: Manifestation of the Stereoelectronic EffectEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 23 2006Emanuele Attolino Abstract A new and high-yielding method for the regioselective preparation of 4-deoxy- and 2,4-dideoxy-2-acetamido-,- D - threo -hex-3-enopyranosides has been developed. The process involves a simultaneous activation,elimination of the OH-4 group of ,- D -talopyranosides and 2-acetamido-2-deoxy-,- D -talopyranosides, mediated by the NaH/N,N,-sulfuryldiimidazole system at ,30 °C. The same reaction applied on the analogous ,- D -galactopyranosides takes place without any regioselectivity, affording mixtures of hex-3- and hex-4-enopyranosides. In the case of the methyl 2,3,6-tri- O -benzyl-,- D -talo- and ,- D -galactopyranosides, the corresponding 4- O -imidazylates can be isolated by quenching the reactions at ,30 °C. Upon warming these crude products to room temperature, the ,- talo -4- O -imidazylate gives the corresponding hex-3-eno derivative in very high yield, but its ,- galacto analogue gives the hex-4-enopyranoside enol ether in poor yield. The different regiochemical outcome between the talo and the galacto series has been attributed to the stereoelectronic effect exerted, exclusively in talo -configured compounds, by the axially disposed C-2 electronegative substituent, which selectively accelerates the breaking of the antiperiplanar C(3),H bond. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Synthesis of C-Nucleosidic ATP Mimics as Potential FGFR3 InhibitorsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 10 2006Patricia Busca Abstract Receptor tyrosine kinases (RTKs) play an important role in signal transduction pathways, and in particular, FGFR3 is one of the four RTKs related to the fibroblast growth factor family. This paper describes the synthesis of C-nucleosidic ATP mimics, as potential FGFR3 inhibitors, by nucleophilic epoxide ring-opening followed by in situ O -heterocyclization of 1,2:5,6-dianhydro-3,4-di- O -benzyl- D -mannitol or L -iditol. Cesium carbonate [Cs2CO3] was found to be the best catalyst for the reaction of purine derivatives with these bis-epoxides. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] | |||||||||||||||||||||||||||||||||||||