Search results for "substitut"
showing 10 items of 1337 documents
Synthesis and cytotoxicity of 6,11-Dihydro-pyrido- and 6,11-Dihydro-benzo[2,3-b]phenazine-6,11-dione derivatives
2003
6,11-Dihydro-pyrido[2,3-b]phenazine-6,11-diones and 6,11-dihydro-benzo[2,3-b]phenazine-6,11-diones were synthesized from 6,7-dichloro-5,8-quinolinedione and 2,3-dichloro-1,4-naphthoquinone. The study on the cytotoxicity on these products revealed that the pyridophenazinediones, tetracyclic heteroquinone analogues with three nitrogen atoms exhibited a high cytotoxicity on several human tumor cell lines. Compound 9c and 9e showed in vitro antitumor activity comparable or superior to doxorubicin against the human ovarian tumor cells (SK-OV-3) and the human CNS cells (XF 498). The IC(50) value for compound 9e was 0.06 microM against the human CNS cells (XF 498), which was 2.6 times higher than …
Electrochemical and DFT studies of the oxidative decomposition of the trihydride complexes Cp*M(dppe)H3 (M = Mo, W) in acetonitrile
2006
International audience; A detailed electrochemical study of the oxidative decomposition of the trihydride complexes Cp*M(dppe)H3 (M = Mo, W) in acetonitrile is presented. For the Mo complex, the decomposition occurs by four different pathways involving classical and non-classical tautomers, whereas only the classical form is accessible for the W derivative. Each of the decomposition pathways has been quantitatively assessed by analyses of the linear sweep voltammograms. In addition to the previously established (B. Pleune, D. Morales, R. Meunier-Prest, P. Richard, E. Collange, J. C. Fettinger and R. Poli, J. Am. Chem. Soc., 1999, 121, 2209–2225) deprotonation, disproportionation, and H2 red…
Unique regioselectivity in the C(sp3)-H α-alkylation of amines: the benzoxazole moiety as a removable directing group.
2014
The benzoxazol-2-yl- substituent was found to act as a removable activating and directing group in the Ir-catalyzed alkylation of C(sp(3))-H bonds adjacent to nitrogen in secondary amines. It can be easily introduced by oxidative coupling or by an SNAr reaction, and it can be removed by hydroxide or by hydride reduction. For 1,2,3,4-tetrahydroisoquinolines, activation exclusively takes place in the 3-position. A variety of activated as well as unactivated terminal olefins are suitable reaction partners.
Herbizide, VI [1] kernfluorierte 2,4-dianilino-6-(dihexylamino)-1,3,5-triazine
1985
Zusammenfassung Auf dem Wege der nucleophilen Substitution der Chloratome in 2,4-Dichlor- 6-(dihexylamino)-1,3,5-triazin durch Anilin werden das 2,4-Dianilino-6-(dihexylamino)-1,3,5-triazin und durch fluorierte Amine die (Dihexylamino)- 1,3,5-triazine mit den folgenden Resten zuganglich: (2-Fluoranilino)-, (3-Fluoranilino)-, (4-Fluoranilino)-, (2,4-Difluoranilino)-, (2,5-Difluoranilino)- und (2,6-Difluoranilino)-. Zur Charakterisierung der neuen Verbindungen sind die IR-, 1 H-NMR- und Massenspektroskopie herangezogen worden. 2,4-Bis-(2,4-difluoranilino)-6-(dihexylamino)-1,3,5-triazin vermag insbesondere herbizide und antidiabetische Wirkungen auszuuben.
Hydrolysis of Phosphotriesters: A Theoretical Analysis of the Enzymatic and Solution Mechanisms
2012
A theoretical study on the alkaline hydrolysis of paraoxon, one of the most popular organophosphorus pesticides, in aqueous solution and in the active site of Pseudomonas diminuta phosphotriesterase (PTE) is presented. Simulations by means of hybrid quantum mechanics/molecular mechanics (QM/MM) potentials show that the hydrolysis of paraoxon takes place through an A(N)D(N) or associative mechanism both in solution and in the active site of PTE. The results correctly reproduce the magnitude of the activation free energies and can be used to rationalize the observed kinetic isotope effects (KIEs) for the hydrolysis of paraoxon in both media. Enzymatic hydrolysis of O,O-diethyl p-chlorophenyl …
Dual Substituent Parameter Modeling of Theoretical, NMR and IR Spectral Data of 5-Substituted Indole-2,3-diones
2002
Correlations of AM1 and PM3 theoretical data, 13C-NMR substituent chemical shifts (13C-SCS) and IR carbonyl group wave numbers [ν(C3â•ÂO)] were studied using dual substituent parameter (DSP) models for 5-substituted indole-2,3-diones. For the C7 atom a reverse substituent effect attributed to extended À-polarization was observed. On the other hand, the DSP approaches for the C3 atom showed normal substituent effects with some contribution of reverse effect supported strongly by 13C-SCS correlations. In the ν(C3â•ÂO) and p(C3â•ÂO) DSP correlations the field effect contribution predominates over the resonance effect, which justifies the using of earlier suggested vibrational cou…
Chemical model systems for cellular nitros(yl)ation reactions.
2009
S-nitros(yl)ation belongs to the redox-based posttranslational modifications of proteins but the underlying chemistry is controversial. In contrast to current concepts involving the autoxidation of nitric oxide ( • NO, nitrogen monoxide), we and others have proposed the formation of peroxynitrite (oxoperoxonitrate (1-)) as an essential intermediate. This requires low cellular fluxes of 'NO and superoxide ( • O 2 - ), for which model systems have been introduced. We here propose two new systems for nitros(yl)ation that avoid the shortcomings of previous models. Based on the thermal decomposition of 3-morpholinosydnonimine, equal fluxes of • NO and • O 2 - were generated and modulated by the …
Structural Basis and Enzymatic Mechanism of the Biosynthesis of C9- from C10-Monoterpenoid Indole Alkaloids
2009
Cutting carbons: The three-dimensional structure of polyneuridine aldehyde esterase (PNAE) gives insight into the enzymatic mechanism of the biosynthesis of C(9)- from C(10)-monoterpenoid indole alkaloids (see scheme). PNAE is a very substrate-specific serine esterase. It harbors the catalytic triad S87-D216-H244, and is a new member of the alpha/beta-fold hydrolase superfamily. Its novel function leads to the diversification of alkaloid structures.
Mo-W-containing tetragonal tungsten bronzes through isomorphic substitution of molybdenum by tungsten
2010
Mixed metal oxides based in Mo(W)–Nb–V–Te with tetragonal tungsten bronze (TTB) structure have been synthesized by a hydrothermal method from aqueous solutions of the corresponding Keggin-type heteropolyacids and further heat-treatment in N2 at 700 ◦ C. The materials have been characterized by several physico-chemical techniques, i.e. XRD, Raman, FTIR, SEM-EDS, and TEM. This procedure allows controlling the chemical species to be distributed in the different interstices of the TTB skeleton, which is a key factor to regulate the catalytic properties of the final solid. In this sense, the isomorphic replacement of Mo by W results in lattice parameter and crystal morphology variation, although…
Barriers to rotation in ortho-substituted tertiary aromatic amides: Effect of chloro-substitution on resonance and distortion
2018
Planarity of the amide bond represents one of the most widely recognized properties of amides. Herein, we report a combined structural and computational study on the effect of ortho-substitution on resonance and barriers to rotation in tertiary aromatic amides. We demonstrate that ortho-chloro substitution in a class of benzamides that are important from the reactivity and medicinal chemistry perspective results in increased barriers to rotation around both the N-C(O) and C-C(O) axes. The effect of steric hindrance on structures, resonance energies, barriers to rotation, and proton affinities is discussed. The present study strongly supports the use of ortho-substitution in common benzamide…