610-78-6Relevant articles and documents
A directing group-assisted ruthenium-catalyzed approach to access: Meta -nitrated phenols
Sasmal, Sheuli,Sinha, Soumya Kumar,Lahiri, Goutam Kumar,Maiti, Debabrata
supporting information, p. 7100 - 7103 (2020/07/14)
meta-Selective C-H nitration of phenol derivatives was developed using a Ru-catalyzed σ-activation strategy. Cu(NO3)2·3H2O was employed as the nitrating source, whereas Ru3(CO)12 was found to be the most suitable metal catalyst for the protocol. Mechanistic studies suggested involvement of an ortho-CAr-H metal intermediate, which promoted meta-electrophilic aromatic substitution and silver-assisted free-radical pathway.
Probing synergy between two catalytic strategies in the glycoside hydrolase O-GlcNAcase using multiple linear free energy relationships
Greig, Ian R.,Macauley, Matthew S.,Williams, Ian H.,Vocadlo, David J.
supporting information; experimental part, p. 13415 - 13422 (2010/01/16)
Human O-GlcNAcase plays an important role in regulating the post-translational modification of serine and threonine residues with β-O-linked N-acetylglucosamine monosaccharide unit (O-GlcNAc). The mechanism of O-GlcNAcase involves nucleophilic participation of the 2-acetamido group of the substrate to displace a glycosidically linked leaving group. The tolerance of this enzyme for variation in substrate structure has enabled us to characterize O-GlcNAcase transition states using several series of substrates to generate multiple simultaneous free-energy relationships. Patterns revealing changes in mechanism, transition state, and rate-determining step upon concomitant variation of both nucleophilic strength and leaving group abilities are observed. The observed changes in mechanism reflect the roles played by the enzymic general acid and the catalytic nucleophile. Significantly, these results illustrate how the enzyme synergistically harnesses both modes of catalysis; a feature that eludes many small molecule models of catalysis. These studies also suggest the kinetic significance of an oxocarbenium ion intermediate in the O-GlcNAcase-catalyzed hydrolysis of glucosaminides, probing the limits of what may be learned using nonatomistic investigations of enzymic transition-state structure and offering general insights into how the superfamily of retaining glycoside hydrolases act as efficient catalysts.
Kinetics and mechanism of base-catalysed degradations of substituted aryl-N-hydroxycarbamates, their N-methyl and N-phenyl analogues
Beier, Petr,Mindl, Jaromir,Sterba, Vojeslav,Hanusek, Jiri
, p. 562 - 569 (2007/10/03)
The kinetics and mechanism of the degradation reactions of substituted phenyl N-hydroxycarbamates and their N-methyl and N-phenyl analogues have been studied at pseudo-first-order reaction conditions in aqueous buffers and sodium hydroxide solutions at 20°C and 60°C and at I = 1 mol·1 -1. The dependence of log kobs on pH for phenyl N-hydroxycarbamates at pH 13 is linear with the unit slope; at pH 10-12 log kobs is pH independent. The Bronsted coefficient βlg is about -1 (pH 7-13) and -1.53 (pH > 13) indicating that the degradation reaction of phenyl N-hydroxycarbamates follows an ElcB mechanism giving the corresponding phenol/phenolate and HO-N=C=O. The latter species undergoes further decomposition to give carbonate, nitrogen and ammonia as final products. In contrast to the phenyl N-hydroxycarbamates the N-methyl derivatives at pH 7-9 undergo degradation to the corresponding phenol/phenolate, carbonate and methylamine via a concerted mechanism (βlg is about - 0.75). The only exception is 4-nitrophenyl N-hydroxy-N-methylcarbamate in which the predominant break down pathway proceeds via the Smiles rearrangement to give sodium N-methyl-(4-nitrophenoxy)carbamate. At pH > 9 the reaction of N-hydroxy-N-methylcarbamates is kinetically complex: the dependence of absorbance on time is not exponential and it proceeds as a consecutive two-step reaction. N-Hydroxy-N-phenylcarbamate under the same conditions undergoes degradation to phenol, carbonate, aniline and azoxybenzene.
