- Mechanistic Features of the Oxidation-Reductive Coupling of Alcohols Catalyzed by Oxo-Vanadium Complexes
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The oxo-vanadium-catalyzed redox disproportionation of activated alcohols (oxidation-reductive coupling, Ox-RC) produces carbonyl compounds and hydrocarbon dimers. A mechanistic study of this novel reaction is reported herein. Following our initial disclosure, new findings include the following: (1) The [(salimin)VO2]--catalyzed Ox-RC of Ph2CHOH in the presence of fluorene affords the products of H-atom abstraction and all possible hydrocarbon dimers. (2) Electronic substituent effects on the relative rates of Ox-RC with respect to 4-X-BnOH reactants and Bu4N[(Y-salimin)VO2] catalysts (1a-c) reveal (a) a correlation of the oxidation rate of X-BnOH reactants with the radical σ parameter and (b) correlation of the oxidation rate for (Y-salimin)VO2- with the standard Hammett σ parameter. (3) The ease of electrochemical reduction of 1a-c is Y = NO2 > OMe > H. (4) Ambient 1H NMR studies of the interaction of 1 with alcohols suggest only a weak equilibrium association. (5) Density functional theory computational modeling of the Ox-RC reaction supports a ping-pong-type catalytic pathway, beginning with alcohol oxidation by (salimin)VO2-, preferably by stepwise-H-atom transfer from the alcohol to 1, affording the carbonyl product and the reduced (salimin)V(III)(OH)2-. The reduction half-reaction likely begins with condensation of the latter species with R2CHOH to give the alkoxide complex (salimin)V(OR)OH- homolysis of the R···OV(III)(salimin) bond affords (salimin)V(IV)OH(O)- and the R-radical; the latter dimerizes and the former can disproportionate via H-transfer to reform catalyst (salimin)VO2- (1) and (salimin)V(OH)2-.
- Steffensmeier, Eric,Swann, Matthew T.,Nicholas, Kenneth M.
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p. 844 - 854
(2019/01/04)
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- Design, synthesis and biological evaluation of antimicrobial diarylimine and –amine compounds targeting the interaction between the bacterial NusB and NusE proteins
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Discovery of antimicrobial agents with a novel model of action is in urgent need for the clinical management of multidrug-resistant bacterial infections. Recently, we reported the identification of a first-in-class bacterial ribosomal RNA synthesis inhibitor, which interrupted the interaction between the bacterial transcription factor NusB and NusE. In this study, a series of diaryl derivatives were rationally designed and synthesized based on the previously established pharmacophore model. Inhibitory activity against the NusB-NusE binding, circular dichroism of compound treated NusB, antimicrobial activity, cytotoxicity, hemolytic property and cell permeability using Caco-2 cells were measured. Structure-activity relationship and quantitative structure–activity relationship were also concluded and discussed. Some of the derivatives demonstrated improved antimicrobial activity than the hit compound against a panel of clinically important pathogens, lowering the minimum inhibition concentration to 1–2 μg/mL against Staphylococcus aureus, including clinical strains of methicillin-resistant Staphylococcus aureus at a level comparable to some of the marketed antibiotics. Given the improved antimicrobial activity, specific inhibition of target protein-protein interaction and promising pharmacokinetic properties without significant cytotoxicity, this series of diaryl compounds have high potentials and deserve for further studies towards a new class of antimicrobial agents in the future.
- Qiu, Yangyi,Chan, Shu Ting,Lin, Lin,Shek, Tsun Lam,Tsang, Tsz Fung,Barua, Nilakshi,Zhang, Yufeng,Ip, Margaret,Chan, Paul Kay-sheung,Blanchard, Nicolas,Hanquet, Gilles,Zuo, Zhong,Yang, Xiao,Ma, Cong
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p. 214 - 231
(2019/06/14)
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- Hydrogen bonding in Schiff bases - NMR, structural and experimental charge density studies
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A series of sixteen Schiff bases (derivatives of salicylaldehydes and aryl amines) was studied to reveal the influence of substituents and the length of the linker on the properties of the H-bonding formed. In theory, two groups of compounds, derivatives of 2-(2-hydroxybenzylidenoamine)phenol) and 2-hydroxy-N-(2-hydroxybenzylideno)benzylamine, can form different types of H-bonds using one or two hydroxyl groups present in the molecules. Two other groups of compounds, derivatives of 4-(2-hydroxybenzylidenoamine)phenol and N-(2-hydroxybenzyideno)benzylamine, can form only one type of H-bond. It was confirmed by 15N and 13C NMR experiments, that in all cases only traditional, H-bonded six-membered chelate rings were formed. The positions of the hydrogen atom in the rings depend on the substituent and phase. Generally, the OH H-bond form dominates in solution, with exception of the nitro derivatives, where the NH tautomer is present. In the solid state the tautomeric equilibrium is strongly shifted to the NH form. Only for the 5-Br derivative of one compound was the reverse relationship found. According to the results of experimental charge density investigations, two intramolecular H-bonds in the 5-methoxy derivative of 2-hydroxy-N-(2′-hydroxybenzylideno) benzylamine) differ significantly in terms of charge density properties. The intra- and intermolecular H-bonds formed by the deprotonated oxygen atom from 2-OH group are strong, with significant charge density concentration at the bond critical point and a straight, well-defined bond path, whereas the second intramolecular H-bond formed by the oxygen atom from the 2′-OH group is quite weak, with ca. five times smaller charge density concentration than in the previous case and a bent bond path. In terms of energy densities, the latter H-bond appears to be a non-bonding interaction, with total energy density being slightly positive. In terms of source contributions to the density at the H-bond critical point from the atoms involved, the intermolecular, linear H-bond is very strong and charge-assisted in the source function classification, the N(1)-H(1N)...O(1) H-bond is medium-strength, while the third H-bond is extremely weak.
- Makal, Anna,Schilf, Wojciech,Kamienski, Bohdan,Szady-Chelmieniecka, Anna,Grech, Eugeniusz,Wozniak, Krzysztof
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supporting information; experimental part
p. 421 - 430
(2011/02/23)
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