2078-12-8Relevant articles and documents
Identification of an acyl-enzyme intermediate in a meta-cleavage product hydrolase reveals the versatility of the catalytic triad
Ruzzini, Antonio C.,Ghosh, Subhangi,Horsman, Geoff P.,Foster, Leonard J.,Bolin, Jeffrey T.,Eltis, Lindsay D.
, p. 4615 - 4624 (2012)
Meta-cleavage product (MCP) hydrolases are members of the α/β-hydrolase superfamily that utilize a Ser-His-Asp triad to catalyze the hydrolysis of a C-C bond. BphD, the MCP hydrolase from the biphenyl degradation pathway, hydrolyzes 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoic acid (HOPDA) to 2-hydroxypenta-2,4-dienoic acid (HPD) and benzoate. A 1.6 A resolution crystal structure of BphD H265Q incubated with HOPDA revealed that the enzyme's catalytic serine was benzoylated. The acyl-enzyme is stabilized by hydrogen bonding from the amide backbone of 'oxyanion hole' residues, consistent with formation of a tetrahedral oxyanion during nucleophilic attack by Ser112. Chemical quench and mass spectrometry studies substantiated the formation and decay of a Ser112-benzoyl species in wild-type BphD on a time scale consistent with turnover and incorporation of a single equivalent of 18O into the benzoate produced during hydrolysis in H218O. Rapid-scanning kinetic studies indicated that the catalytic histidine contributes to the rate of acylation by only an order of magnitude, but affects the rate of deacylation by over 5 orders of magnitude. The orange-colored catalytic intermediate, ESred, previously detected in the wild-type enzyme and proposed herein to be a carbanion, was not observed during hydrolysis by H265Q. In the newly proposed mechanism, the carbanion abstracts a proton from Ser112, thereby completing tautomerization and generating a serinate for nucleophilic attack on the C6-carbonyl. Finally, quantification of an observed pre-steady-state kinetic burst suggests that BphD is a half-site reactive enzyme. While the updated catalytic mechanism shares features with the serine proteases, MCP hydrolase-specific chemistry highlights the versatility of the Ser-His-Asp triad.
Production of acyloxysilane
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Paragraph 0059-0064, (2021/10/30)
[A] a method for producing functional chemicals useful as efficient acyloxysilane. The silanol Si-to-OH bond [a], in the presence of a catalyst, comprising the step of reacting a carboxylic acid anhydride, Si-to-OCO bond (OCO is, oxycarbonyl groups (=O) O-a C shown. ) Having an acyloxysilane manufacturing method, wherein the catalyst, or (2) (1) production of acid catalyst selected from the next acyloxysilane. (1) 3 - 15 Of the periodic table of the first group the first group element selected from the perchlorate salt, trifluoromethanesulfonic acid salt, a bis (trifluoromethanesulfonyl imide) salt, lithium hexafluorophosphate salt, chloride, or bromide; inorganic acids; or an organic acid. (2) Inorganic or organic solid acid compounds[Drawing] no
Copper-Catalyzed Enantioselective Radical 1,4-Difunctionalization of 1,3-Enynes
Zeng, Yuehua,Chiou, Mong-Feng,Zhu, Xiaotao,Cao, Jie,Lv, Daqi,Jian, Wujun,Li, Yajun,Zhang, Xinhao,Bao, Hongli
supporting information, p. 18014 - 18021 (2020/11/02)
Chiral allenes are important structural motifs frequently found in natural products, pharmaceuticals, and other organic compounds. Asymmetric 1,4-difunctionalization of 1,3-enynes is a promising strategy to construct axial chirality and produce substituted chiral allenes from achiral substrates. However, the previous state of the art in 1,4-difunctionalization of 1,3-enynes focused on the allenyl anion pathway. Because of this, only electrophiles can be introduced into the allene backbones in the second functionalization step, consequently limiting the reaction and allene product types. The development of asymmetric 1,4-difunctionalization of 1,3-enynes via a radical pathway would complement previous methods and support expansion of the toolbox for the synthesis of asymmetric allenes. Herein, we report the first radical enantioselective allene formation via a group transfer pathway in the context of copper-catalyzed radical 1,4-difunctionalization of 1,3-enynes. This method addresses a longstanding unsolved problem in asymmetric radical chemistry, provides an important strategy for stereocontrol with free allenyl radicals, and offers a novel approach to the valuable, but previously inaccessible, chiral allenes. This work should shed light on asymmetric radical reactions and may lead to other enantioselective group transfer reactions.
A simple and efficient room temperature silylation of diverse functional groups with hexamethyldisilazane using CeO2 nanoparticles as solid catalysts
Anbu, Nagaraj,Vijayan, Chellappa,Dhakshinamoorthy, Amarajothi
, (2019/06/08)
In this study, a mild and efficient method is developed for the silylation of diverse functional groups using CeO2 nanoparticles (n-CeO2) as solid catalysts with hexamethyldisilazane (HMDS) as silylating agent at room temperature. Alcohols, phenols and acids are silylated to their respective silyl derivatives with faster reaction rate while amines and thiols required relatively longer reaction time. Moreover, the solid catalyst is easily be separated from the reaction mixture and recycled more than five times without any obvious decay in its activity. Powder X-ray diffraction (XRD), transmission electron microscope (TEM), UV–vis diffuse reflectance spectra (UV-DRS) and Raman analyses revealed identical structural integrity, particle size, absorption edge and valence state for the reused solid compared to the fresh solid catalyst.
