1193-00-6Relevant articles and documents
Tyrosinase-like reactivity in a CuIII2(??-O) 2 species
Company, Anna,Palavicini, Sara,Garcia-Bosch, Isaac,Mas-Ballesteì?, Ruben,Que Jr., Lawrence,Rybak-Akimova, Elena V.,Casella, Luigi,Ribas, Xavi,Costas, Miquel
, p. 3535 - 3538 (2008)
A study was conducted to demonstrate a bis(??-oxo)dicopper(III) species that binds and ortho-hydroxylates phenolates for reactivity of tyrosinase. The study characterized a metastable species from the low-temperature reaction of sodium p-chloro-phenolate (p-Cl-C6H4ONa) with a bis(??-oxo)dicopper(III) species. The study found that the addition of 10 equivalents of the sodium salt of p-chlorophenol at -90?°C can cause bleaching of the spectral features. High performance liquid chromatography (HPLC) analysis showed that 4-chlorocatechol was formed in 76% yield. The study used UV/UVis monitoring for reaction in acetone to determine the initial features to the bis(??-oxo) species and found that these features disappear after phenolate addition. The study observed that the activation parameters for the monophenolase reaction catalyzed by tyrosinase.
Non-Innocent Role of the Ceria Support in Pd-Catalyzed Halophenol Hydrodehalogenation
An, Yeongseo,Freppon, Daniel,Masching, Hayley,Naik, Pranjali J.,Sedinkin, Sergey L.,Slowing, Igor I.,Smith, Emily A.,Venditti, Vincenzo
, p. 10553 - 10564 (2021/09/04)
The hydrodehalogenation (HDH) of halophenols is efficiently catalyzed by palladium supported on high-surface ceria (Pd/CeO2) under mild conditions (35 °C, 1 atm H2). A combination of NMR, diffuse reflectance infrared Fourier transform spectroscopy, Raman spectroscopy, and XPS studies and HDH kinetics of substituted halobenzenes suggests that the reaction proceeds mainly via a sequence of dissociative adsorption of phenolic hydroxyl onto the support, oxidative addition of the C-halogen bond to Pd, and reductive elimination to give phenol and hydrogen halide. The dissociative adsorption of the -OH group onto oxygen vacancies of the ceria support results in an electron-rich intermediate that facilitates the turnover-limiting reductive elimination step. In contrast, the direct pathway catalyzed by Pd without dissociative adsorption of the reactants on the support takes place at a slower rate. The mechanistic insights gained in this study were used to modify the reaction conditions for enabling HDH of recalcitrant halides such as fluorides and iodides.
Synthetic method for 2,5-dichloro-4-(4-chlorophenoxyl)-acetophenone
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Paragraph 0005; 0008, (2017/02/09)
The invention discloses a synthetic method for 2,5-dichloro-4-(4-chlorophenoxyl)-acetophenone, which belongs to the field of chemical synthesis. The synthetic method comprises the following steps: adding sodium hydroxide into p-chlorophenol so as to obtain sodium p-chlorophenolate; then adding 1,3,5-trichlorobenzene, 1-methyl-2-pyrrolidone and a catalyst cuprous oxide so as to obtain a faint yellow viscous liquid; adding dichloroethane, an aluminum chloride catalyst and acetic anhydride into a bottle and slowing adding hydrochloric acid into the bottle in ice water with a temperature of 0 DEG C; and successively carrying out crystal precipitation, pumping filtration, cleaning, drying and recrystallization so as to obtain a 2,5-dichloro-4-(4-chlorophenoxyl)-acetophenone solid.
TREATMENT OF AMYOTROPHIC LATERAL SCLEROSIS
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Page/Page column 113, (2010/07/10)
The present invention relates to the identification of compounds and pharmaceutical compositions thereof for treating subjects with amyotrophic lateral sclerosis (ALS) and other neurodegenerative diseases. The invention also provides methods of preparing the provided compounds.
Mechanistic study of Protein Phosphatase-1 (PP1), a catalytically promiscuous enzyme
McWhirter, Claire,Lund, Elizabeth A.,Tanifum, Eric A.,Feng, Guoqiang,Sheikh, Qaiser I.,Hengge, Alvan C.,Williams, Nicholas H.
scheme or table, p. 13673 - 13682 (2009/02/06)
The reaction catalyzed by the protein phosphatase-1 (PP1) has been examined by linear free energy relationships and kinetic isotope effects. With the substrate 4-nitrophenyl phosphate (4NPP), the reaction exhibits a bell-shaped pH-rate profile for kcat/KM indicative of catalysis by both acidic and basic residues, with kinetic pKa values of 6.0 and 7.2. The enzymatic hydrolysis of a series of aryl monoester substrates yields a Bronsted βlg of -0.32, considerably less negative than that of the uncatalyzed hydrolysis of monoester dianions (-1.23). Kinetic isotope effects in the leaving group with the substrate 4NPP are 18(V/K)bridge = 1.0170 and 15(V/K) = 1.0010, which, compared against other enzymatic KIEs with and without general acid catalysis, are consistent with a loose transition state with partial neutralization of the leaving group. PP1 also efficiently catalyzes the hydrolysis of 4-nitrophenyl methylphosphonate (4NPMP). The enzymatic hydrolysis of a series of aryl methylphosphonate substrates yields a Bronsted βlg of -0.30, smaller than the alkaline hydrolysis (-0.69) and similar to the βlg measured for monoester substrates, indicative of similar transition states. The KIEs and the βlg data point to a transition state for the alkaline hydrolysis of 4NPMP that is similar to that of diesters with the same leaving group. For the enzymatic reaction of 4NPMP, the KIEs are indicative of a transition state that is somewhat looser than the alkaline hydrolysis reaction and similar to the PP1-catalyzed monoester reaction. The data cumulatively point to enzymatic transition states for aryl phosphate monoester and aryl methylphosphonate hydrolysis reactions that are much more similar to one another than the nonenzymatic hydrolysis reactions of the two substrates.
Do electrostatic interactions with positively charged active site groups tighten the transition state for enzymatic phosphoryl transfer?
Nikolic-Hughes, Ivana,Rees, Douglas C.,Herschlag, Daniel
, p. 11814 - 11819 (2007/10/03)
The effect of electrostatic interactions on the transition-state character for enzymatic phosphoryl transfer has been a subject of much debate. In this work, we investigate the transition state for alkaline phosphatase (AP) using linear free-energy relationships (LFERs). We determined fcat/K M for a series of aryl sulfate ester monoanions to obtain the Bronsted coefficient, βIg, and compared the value to that obtained previously for a series of aryl phosphorothioate ester dianion substrates. Despite the difference in substrate charge, the observed Bronsted coefficients for AP-catalyzed aryl sulfate and aryl phosphorothioate hydrolysis (-0.76 ± 0.14 and -0.77 ± 0.10, respectively) are strikingly similar, with steric effects being responsible for the uncertainties in these values. Aryl sulfates and aryl phosphates react via similar loose transition states in solution. These observations suggest an apparent equivalency of the transition states for phosphorothioate and sulfate hydrolysis reactions at the AP active site and, thus, negligible effects of active site electrostatic interactions on charge distribution in the transition state.
UV-Vis Spectrophotometric Determination of the Dissociation Constants for Monochlorophenols in Aqueous Solution at Elevated Temperatures
Uchida, Miho,Okuwaki, Akitsugu
, p. 19 - 39 (2007/10/03)
The dissociation constants of monochlorophenols (2-, 3-, 4-chlorophenols) were examined using direct UV-vis spectroscopy at temperatures from 25 to 175°C and at saturated vapor pressures in a high-temperature, high-pressure cell. The dissociation constant, Ka increased under experimental temperatures in the order: 2-chlorophenol, 3-chlorophenol, and 4-chlorophenol. The dissociation constant of 4-chlorophenol increased with increasing temperature under experimental conditions, while those of 2-and 3-chlorophenol reached maximum values at around 125°C, and then decreased with further increases in temperature. The slope of ?(log K)/? (1/T) was nonconstant and positive, that is, endothermic, below 150°C. The data on dissociation constants were analyzed by simultaneous regression to yield a five-term equation that described the Van't Hoff isobar. The magnitude of enthalpy ΔH increased at 25°C in the order: 3-chlorophenol, 4-chlorophenol, and 2-chlorophenol. The decrease in enthalpy at the absolute temperature was larger for 3-chlorophenol than for either 2- or 4-chlorophenol. Considering the equilibrium constant Kb for the isocoulombic reaction of monochlorophenol with OH-, the nearly linear relationship of log Kb vs. 1/T for temperatures between 25 and 175°C indicates that the ΔCp values for this isocoulombic reaction are low.
Kinetics and mechanism of alkaline hydrolysis of aryl carbazates
Vlasak, Petr,Mindl, Jaromir
, p. 1401 - 1404 (2007/10/03)
Hydrlysis of aryl carbazates (H2NNHCO2Ar with Ar=phenyl, 3- or 4-chlorophenyl, 3- or 4-nitrophenyl, 4-methylphenyl and 4-methoxyphenyl) and/or their 2- or 3-methyl derivatives in aqueous buffers or sodium hydroxide solutions gives phenolate and sodium carbazate. the kinetics and acidity constants and thermodynamic parameters are given.By analysing the pH profiles, the activation entropy, and effects of the substituent on the aromatic ring it was found that aryl carbazates containing a methyl group in the 2 position are hydrolysed by a BAc2 mechanism and the others by an E2cB mechanism.The pH profiles of nitrophenyl carbazates show a maximum.The rate of decarboxylation of carbazic acid decreases with increasing pH value.
Mechanisms of Nucleophilic Attack at Carbon-Nitrogen Double Bonds. The Reaction of Aryl N-Arylbenzimidates with Methoxide Ion
Rowe, Jeffrey E.
, p. 1259 - 1262 (2007/10/02)
Rate data for the reaction of three series of aryl N-arylbenzimidates with methoxide ion at 303 K are presented.Linear Hammett plots were obtained for each series.Solvent isotope effects have also been measured.The results are interpreted in terms of rate-determining formation of a tetrahedral intermediate, irrespective of the nature of the substituent.
Nouvelles syntheses de phenyl-4 allophanates
Al Sabbagh, Mohamed Mowafak,Calmon, Michelle,Calmon, Jean-Pierre
, p. 73 - 77 (2007/10/02)
The synthesis of eighteen alkyl or phenyl 4-phenylallophanates is described.The classical methods used for the preparation of allophanates - namely, condensation between an isocyanate and a carbamate, reaction between a urea and a carbonate, desulphurization of 3-thioallophanic acid esters - proved to be unsuitable for the synthesis of 4-phenylallophanic acid phenyl esters.Variously substituted 4-phenylallophanates can be obtained by reacting a chloroformate with a phenylurea in the presence of pyridine, which promotes the transfer of the carboxylate group.The occurence of electrondonating substituents, such as CH3, at the nitrogen atom receiving the carboxylate group promotes the reaction.The low yields observed for aliphatic esters can be accounted for by the instability of the alkyl chloroformate-pyridine complex.The structures of the derivatives synthesized was corroborated by the analysis of their n.m.r. and u.v. spectra. Non-commercial phenyl chloroformates were prepared by reacting phosgene with a sodium phenolate in the presence of anhydrous benzene.
