Search results for "SUBSTITUTION"
showing 10 items of 536 documents
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 …
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…
Synthesis and application of new iminopyridine ligands in the enantioselective palladium-catalyzed allylic alkylation
2014
A variety of iminopyridines were obtained by condensation of chiral amines with pyridine-2-carboxaldehyde and quinoline-8-carbaldehyde, or of aminoalkylpyridine derivatives with chiral ketones. These ligands were assessed in the enantioselective palladium catalyzed allylic substitution of 1,3-diphenylprop-2-enyl acetate with dimethyl malonate affording the product dimethyl 1,3-diphenylprop-2-enylmalonate in good yields and moderate enantioselectivities (up to 62% ee). Catalytic activity and enantioselectivity were found to be highly dependent upon the steric properties of the ligands. The best enantioselectivity (62% ee) was obtained by an iminopyridine based on a camphane skeleton. © 2014 …
On the reaction of 3-bromo-2-nitrobenzo[b]thiophene with some ortho-substituted anilines: an analysis of the products of reaction and of their NMR an…
2003
Abstract The title reaction, carried out in DMF in the presence of triethylamine or potassium carbonate, has furnished the ‘expected’ 3-amino-2-nitrobenzo[ b ]thiophenes 2 o together with the ‘unexpected’ 2-amino-3-nitrobenzo[ b ]thiophenes 3 o , thus recalling the situation observed with other weak nucleophiles in the presence of non-nucleophilic bases. The effects (electronic as well as steric) of the ortho -substituent (OH, NH 2 , OMe, Me, Et, F, Cl and Br) on the course of the reaction have been investigated, determining their influence on yields and product ratios ( 2 o / 3 o ). An analysis of 13 C NMR and MS spectra of 2 o and 3 o has been carried out. Ab initio computations on 2 o f …
Ligand Effects on the Chemoselectivity of Ortho-Metalated Rhodium(II) Catalyzed α-Diazo Ketone Transformations
1997
Rh2(OOCR)2(PC)2 complexes (PC = orthometalated phosphines, OOCR = carboxylates) with very polarizable ligands, such as aromatic rings directly joined to the rhodium atoms, control chemoselectivity in competitive metal carbene transformations of α-diazo ketones. These catalysts have a mixed set of ligands that allows choosing among a big selection of ligands to gradually affect the electronic and steric properties of the catalyst. Their selectivity depends on the electrophilicity of the ligands and the polarizability of the metalated aromatic rings. Thus, Rh2(OOCR)2(PC)2 compounds [PC = (C6H4)P(CH3)(C6H5), (p-CH3C6H3)P(p-CH3C6H4)2, (C6H4)P(C6H5)2; R = C3F7 or CF3] exhibit an exceptional sele…
Unveiling the regioselectivity in electrophilic aromatic substitution reactions of deactivated benzenes through molecular electron density theory
2021
The origin of the meta regioselectivity in electrophilic aromatic substitution (EAS) reactions of deactivated benzene derivatives is herein analysed through Molecular Electron Density Theory (MEDT). To this end, the EAS reaction of benzenesulfonic acid with the nitronium NO2+ ion in H2SO4 solution has been studied at the ωB97X-D/6-311G(d,p) level. This reaction takes place through a two-step polar mechanism involving the formation of an unstable cation intermediate. The activation Gibbs free energies associated with the three competitive regioisomeric reaction paths are found in the narrow range of 15.5–18.3 kcal mol−1. By using the Eyring–Polanyi equation a relationship of 18.7 (ortho) : 8…