2906-29-8Relevant academic research and scientific papers
A long-lived, substrate-hydroxylating peroxodiiron(III/III) intermediate in the amine oxygenase, AurF, from Streptomyces thioluteus
Korboukh, Victoria Korneeva,Li, Ning,Barr, Eric W.,Bollinger Jr., J. Martin,Krebs, Carsten
, p. 13608 - 13609 (2009)
(Chemical Equation Presented) The amine oxygenase AurF from Streptomyces thioluteus catalyzes the six-electron oxidation of p-aminobenzoate (pABA) to p-nitrobenzoate (pNBA). In this work, we have studied the reaction of its reduced Fe2(II/II) c
Kinetics and mechanism of the pyridinolysis of S-4-nitrophenyl 4-substituted thiobenzoates in aqueous ethanol
Castro, Enrique A.,Vivanco, Melissa,Aguayo, Raul,Santos, Jose G.
, p. 5399 - 5404 (2004)
The pyridinolysis of S-4-nitrophenyl 4-X-substituted thiobenzoates (X = H, Cl, and NO2; 1, 2, and 3, respectively) is studied kinetically in 44 wt % ethanol-water, at 25.0 °C and an ionic strength of 0.2 M (KCl). The reactions are measured spectrophotometrically (420-425 nm) by following the appearance of 4-nitrobenzenethiolate anion. Pseudo-first-order rate coefficients (kobsd) are obtained throughout, under excess of amine over the substrate. Plots of kobsd vs [free amine] at constant pH are linear with the slope (kN) independent of pH. The Bronsted-type plot (log kN vs pKa of the conjugate acids of the pyridines) for the reactions of thiolbenzoate 1 is curved with a slope at high pK a, β1 = 0.20, and slope at low pKa, β2 = 0.94. The pKa value for the center of the Bronsted curvature is pKa0 = 9.7. The pyridinolysis of thiolbenzoates 2 and 3 show linear Bronsted-type plots of slopes 0.94 and 1.0, respectively. These results and other evidence indicate that these reactions occur with the formation of a zwitterionic tetrahedral intermediate (T±). For the pyridinolysis of thiolbenzoate 1, breakdown of T± to products (k2 step) is rate-limiting for weakly basic pyridines and T± formation (k1 step) is rate-determining for very basic pyridines. The k2 step is rate-limiting for the reactions of thiolbenzoates 2 and 3. The smallest pK a0 value for the reaction of 1 is due to a the weakest electron withdrawal of H (relative to Cl and NO2) in the acyl group, which results in the smallest k-1/k2 ratio. The pK a0 values for the title reactions are smaller than those for the reactions of secondary alicyclic amines with thiolbenzoates 1-3. This is attributed to a lower leaving ability from the T± of pyridines than isobasic alicyclic amines. The lower pKa0 value found for the pyridinolysis of 2,4-dinitrophenyl benzoate (pK a0 = 9.5), compared with that for the pyridinolysis of 1, is explained by the greater nucleofugality from T± of 2,4-dinitrophenoxide than 4-nitrobenzenethiolate, which renders the k -1/k2 ratio smaller for the reactions of the benzoate relative to thiolbenzoate 1. The title reactions are also compared with the aminolysis of similar thiolbenzoates in other solvents to assess the solvent effect.
Four-electron oxidation of p-hydroxylaminobenzoate to p-nitrobenzoate by a peroxodiferric complex in AurF from Streptomyces thioluteus
Li, Ning,Korboukh, Victoria Korneeva,Krebs, Carsten,Bollinger Jr., J. Martin
, p. 15722 - 15727 (2010)
The nonheme di-iron oxygenase, AurF, converts p-aminobenzoate (Ar-NH2, where Ar = 4-carboxyphenyl) to p-nitrobenzoate (Ar-NO2) in the biosynthesis of the antibiotic, aureothin, by Streptomyces thioluteus. It has been reported that this net six-
Unexpected resistance to base-catalyzed hydrolysis of nitrogen pyramidal amides based on the 7-azabicyclic[2.2.1]heptane scaffold
De Velasco, Diego Antonio Ocampo Gutiérrez,Su, Aoze,Zhai, Luhan,Kinoshita, Satowa,Otani, Yuko,Ohwada, Tomohiko
, (2018/09/26)
Non-planar amides are usually transitional structures, that are involved in amide bond rotation and inversion of the nitrogen atom, but some ground-minimum non-planar amides have been reported. Non-planar amides are generally sensitive to water or other n
An unusual peroxo intermediate of the arylamine oxygenase of the chloramphenicol biosynthetic pathway
Makris, Thomas M.,Vu, Van V.,Meier, Katlyn K.,Komor, Anna J.,Rivard, Brent S.,Münck, Eckard,Que, Lawrence,Lipscomb, John D.
supporting information, p. 1608 - 1617 (2015/03/05)
Streptomyces venezuelae CmlI catalyzes the six-electron oxygenation of the arylamine precursor of chloramphenicol in a nonribosomal peptide synthetase (NRPS)-based pathway to yield the nitroaryl group of the antibiotic. Optical, EPR, and M?ssbauer studies show that the enzyme contains a nonheme dinuclear iron cluster. Addition of O2 to the diferrous state of the cluster results in an exceptionally long-lived intermediate (t1/2 = 3 h at 4 °C) that is assigned as a peroxodiferric species (CmlI-peroxo) based upon the observation of an 18O2-sensitive resonance Raman (rR) vibration. CmlI-peroxo is spectroscopically distinct from the well characterized and commonly observed cis-μ-1,2-peroxo (μ-η1:η1) intermediates of nonheme diiron enzymes. Specifically, it exhibits a blue-shifted broad absorption band around 500 nm and a rR spectrum with a β(O-O) that is at least 60 cm-1 lower in energy. M?ssbauer studies of the peroxo state reveal a diferric cluster having iron sites with small quadrupole splittings and distinct isomer shifts (0.54 and 0.62 mm/s). Taken together, the spectroscopic comparisons clearly indicate that CmlI-peroxo does not have a μ- η1:η1-peroxo ligand; we propose that a μ- η1:η2-peroxo ligand accounts for its distinct spectroscopic properties. CmlI-peroxo reacts with a range of arylamine substrates by an apparent second-order process, indicating that CmlI-peroxo is the reactive species of the catalytic cycle. Efficient production of chloramphenicol from the free arylamine precursor suggests that CmlI catalyzes the ultimate step in the biosynthetic pathway and that the precursor is not bound to the NRPS during this step.
On the dual role of N-heterocyclic carbenes as bases and nucleophiles in reactions with organic halides
Knappke, Christiane E. I.,Arduengo, Anthony J.,Jiao, Haijun,Neudoerfl, Joerg-Martin,Jacobivonwangelin, Axel
, p. 3784 - 3795 (2012/01/11)
The synthetic consequences of different basicities, nucleophilicities, and sterics of N-heterocyclic carbenes have been studied in reactions of imidazolin-2-ylidenes with organic halides. Highly nucleophilic and less basic carbenes cleanly gave alkyli-deneimidazolines, the deoxy analogues of Breslow-type intermediates. More basic NHCs engaged in unwanted deprotonation or dehydrohalogenation reactions. Georg Thieme Verlag Stuttgart. New York.
Competitive endo- and exo-cyclic C-N fission in the hydrolysis of N-aroyl β-lactams
Tsang, Wing Y.,Ahmed, Naveed,Hemming, Karl,Page, Michael I.
, p. 1432 - 1439 (2007/10/03)
The balance between endo- and exo-cyclic C-N fission in the hydrolysis of N-aroyl β-lactams shows that the difference in reactivity between strained β-lactams and their acyclic analogues is minimal. Attack of hydroxide ion occurs preferentially at the exocyclic acyl centre rather than that of the β-lactam during the hydrolysis of N-p-nitrobenzoyl β-lactam. In general, both endo- and exo-cyclic C-N bond fission occurs in the alkaline hydrolysis of N-aroyl β-lactams, the ratio of which varies with the aryl substituent. Hence, the Bronsted β-values differ for the two processes: -0.55 for the ring-opening reaction and -1.54 for the exocyclic C-N bond fission reaction. For the pH-independent and acid-catalysed hydrolysis of N-benzoyl β-lactam, less than 3% of products are derived from exocyclic C-N bond fission.
Elimination reactions of (Z)-thiophene- and (Z)-furan-2-carbaldehyde O- benzoyloximes. Effect of β-aryl group upon the nitrile-forming anti transition state
Cho, Bong Rae,Cho, Nam Soon,Song, Sang Hun,Lee, Sang Kook
, p. 8304 - 8309 (2007/10/03)
Elimination reactions of (Z)-thiophene- and (Z)-furan-2-carbaldehyde O- benzoyloximes 1 and 2 with DBU in MeCN have been investigated kinetically. The reactions are second order and exhibit substantial values of Hammett ρ and k(H)/k(D) values, and an E2 m
Nucleophilic displacement at the benzoyl centre: A study of the change in geometry at the carbonyl carbon atom
Colthurst, Matthew J.,Williams, Andrew
, p. 1493 - 1497 (2007/10/03)
The second-order rate constants for the reaction between hydroxide ion and phenoxide ion with 4-nitrophenyl esters of substituted benzoic acids in 10% acetonitrile-water (v/v) solution obey Hammett σ correlations. The values of the Hammett ρ of 1.67 (κArO) and 2.14 (κOH) are consistent with a large change in hybridization at the central carbon by comparison with the ρ value for a standard reaction where a full sp2 to sp3 change occurs. The transition state for the concerted reaction thus has a substantially tetrahedral geometry. The observation of the anti-Hammond effect whereby the ρ value for the hydroxide ion exceeds that of the less reactive phenoxide ion is consistent with a concerted, ANDN, mechanism for these reactions. A stepwise mechanism, AN + DN, is unlikely to yield a measurable break in the Hammett correlation for a change in the benzoyl substituent if the partitioning of the putative tetrahedral intermediate involves forward and reverse reactions with Hammett correlations possessing similar ρ values.
Intramolecular Catalysis of Thiol Ester Hydrolysis by a Tertiary Amine and a Carboxylate
Brown,Aman, Ahmed
, p. 4816 - 4820 (2007/10/03)
The syntheses of 4-nitro thiol benzoate esters of ethyl 2-mercaptoacetate, thioglycolic acid, 2-(dimethylamino)ethanethiol, and 2-(N,N,N-trimethylammono)ethanethiol iodide (10-13) have been carried out and their rates of hydrolysis at 50°C studied as a function of pH. Thiol esters 10 and 13 have linear pH-log kobs profiles indicative of an exclusive specific base attack of OH-. Thiol esters 11 and 12 exhibit a plateau in their pH/log kobs profiles due to the participation of pendant carboxylate and dimethylamino groups, respectively, most probably as intramolecular general bases. At higher pH, specific base catalysis becomes predominant for both 11 and 12. In the plateau region, the hydrolysis of 12 is subject to a solvent deuterium kinetic isotope effect of 2.2, consistent with the operation of a general base role for the pendant dimethylamino group. The hydrolysis of 12 in the presence of Ellman's reagent produces the Ellman's anion at a rate that is identical to that for disappearance of the thioester, consistent with a general base process where the thiolate anion product of hydrolysis is produced in the rate-limiting step.
