Phosphine-catalyzed [3 + 2] annulation of 2-aminoacrylates with allenoates and mechanistic studies

2020 ◽  
Vol 10 (12) ◽  
pp. 3959-3964 ◽  
Author(s):  
Xiao-Yun Wu ◽  
Hou-Ze Gui ◽  
Harish Jangra ◽  
Yin Wei ◽  
Hendrik Zipse ◽  
...  
Keyword(s):  
Catalytic Mechanism ◽  
Kinetic Studies ◽  
Mechanistic Studies ◽  
Stereogenic Center

A phosphine catalyzed formal [3 + 2] annulation was disclosed, affording 3-pyrrolines containing an amino quaternary stereogenic center in good to excellent yields. The catalytic mechanism was investigated by DFT and kinetic studies.

Role of Lys-226 in the Catalytic Mechanism ofBacillus StearothermophilusSerine HydroxymethyltransferaseCrystal Structure and Kinetic Studies†,‡

Biochemistry ◽  
2005 ◽  
Vol 44 (18) ◽  
pp. 6929-6937 ◽  
Author(s):  
Siddegowda Bhavani ◽  
V. Trivedi ◽  
V. R. Jala ◽  
H. S. Subramanya ◽  
Purnima Kaul ◽  
...  
Keyword(s):  
Catalytic Mechanism ◽  
Kinetic Studies

Facilitating the Transmetalation Step with Aryl-Zincates in Nickel-Catalyzed Enantioselective Arylation of Secondary Benzylic Halides

2019 ◽  
Author(s):  
Weichen Wan ◽  
Mei Hu ◽  
Xiaolong Wan ◽  
Qilong Shen
Keyword(s):  
Coupling Reaction ◽  
Cross Coupling ◽  
Mechanistic Studies ◽  
Cross Coupling Reaction ◽  
Stereogenic Center

<div> <div> <div> <p>A method for the highly enantioselective construction of fluoroalkyl-substituted stereogenic center by a nickel-catalyzed asymmetric Suzuki-Miyaura coupling of a-bromobenzyl trifluoro-/difluoro-/monofluoromethanes with a variety of lithium organoborate in the presence of 1.0 equivalent of ZnBr2 was described. Preliminary mechanistic studies disclosed that reaction of lithium organoborate with ZnBr2 generated a zincate [Ph2ZnBr]Li, which facilitates the transmetallation step of the nickel-catalyzed cross-coupling reaction to enable high enantioselectivity. <br></p> </div> </div> </div>

scholarly journals Aspartate or arginine? Validated redox state X-ray structures elucidate mechanistic subtleties of FeIV = O formation in bacterial dye-decolorizing peroxidases

2021 ◽  
Vol 26 (7) ◽  
pp. 743-761
Author(s):  
Marina Lučić ◽  
Michael T. Wilson ◽  
Dimitri A. Svistunenko ◽  
Robin L. Owen ◽  
Michael A. Hough ◽  
...  
Keyword(s):  
Redox State ◽  
Kinetic Studies ◽  
Site Directed Mutagenesis ◽  
X Rays ◽  
Mechanistic Studies ◽  
X Ray ◽  
X Ray Crystallography ◽  
Structural Framework ◽  
Solvent Isotope ◽  
Heme Peroxidases

AbstractStructure determination of proteins and enzymes by X-ray crystallography remains the most widely used approach to complement functional and mechanistic studies. Capturing the structures of intact redox states in metalloenzymes is critical for assigning the chemistry carried out by the metal in the catalytic cycle. Unfortunately, X-rays interact with protein crystals to generate solvated photoelectrons that can reduce redox active metals and hence change the coordination geometry and the coupled protein structure. Approaches to mitigate such site-specific radiation damage continue to be developed, but nevertheless application of such approaches to metalloenzymes in combination with mechanistic studies are often overlooked. In this review, we summarize our recent structural and kinetic studies on a set of three heme peroxidases found in the bacterium Streptomyces lividans that each belong to the dye decolourizing peroxidase (DyP) superfamily. Kinetically, each of these DyPs has a distinct reactivity with hydrogen peroxide. Through a combination of low dose synchrotron X-ray crystallography and zero dose serial femtosecond X-ray crystallography using an X-ray free electron laser (XFEL), high-resolution structures with unambiguous redox state assignment of the ferric and ferryl (FeIV = O) heme species have been obtained. Experiments using stopped-flow kinetics, solvent-isotope exchange and site-directed mutagenesis with this set of redox state validated DyP structures have provided the first comprehensive kinetic and structural framework for how DyPs can modulate their distal heme pocket Asp/Arg dyad to use either the Asp or the Arg to facilitate proton transfer and rate enhancement of peroxide heterolysis. Graphic abstract

Purification and characterization of purine nucleoside phosphorylase from developing embryos of Hyalomma dromedarii

1991 ◽  
Vol 69 (4) ◽  
pp. 223-231 ◽  
Author(s):  
Mamdouh Y. Kamel ◽  
Afaf S. Fahmy ◽  
Abdel H. Ghazy ◽  
Magda A. Mohamed
Keyword(s):  
Purine Nucleoside Phosphorylase ◽  
Catalytic Mechanism ◽  
Kinetic Studies ◽  
Purine Nucleoside ◽  
Hyalomma Dromedarii ◽  
Ph Optimum ◽  
Nucleoside Phosphorylase ◽  
Apparent Homogeneity ◽  
Camel Tick

Purine nucleoside phosphorylase from Hyalomma dromedarii, the camel tick, was purified to apparent homogeneity. A molecular weight of 56 000 – 58 000 was estimated for both the native and denatured enzyme, suggesting that the enzyme is monomeric. Unlike purine nucleoside phosphorylase preparations from other tissues, the H. dromedarii enzyme was unstable in the presence of β-mercaptoethanol. The enzyme had a sharp pH optimum at pH 6.5. It catalyzed the phosphorolysis and arsenolysis of ribo- and deoxyribo-nucleosides of hypoxanthine and guanine, but not of adenine or pyrimidine nucleosides. The Km values of the enzyme at the optimal pH for inosine, deoxyinosine, guanosine, and deoxyguanosine were 0.31, 0.67, 0.55, and 0.33 mM, respectively. Inactivation and kinetic studies suggested that histidine and cysteine residues were essential for activity. The pKa values determined for catalytic ionizable groups were 6–7 and 8–9. The enzyme was completely inactivated by thiol reagents and reactivated by excess β-mercaptoethanol. The enzyme was also susceptible to pH-dependent photooxidation in the presence of methylene blue, implicating histidine. Initial velocity studies showed an intersecting pattern of double-reciprocal plots of the data, consistent with a sequential mechanism.Key words: Acarina, Hyalomma dromedarii, purine nucleoside phosphorylase, kinetics, active site, catalytic mechanism.

scholarly journals The Structure and Function of Paraoxonase-1 and Its Comparison to Paraoxonase-2 and -3

Molecules ◽  
2020 ◽  
Vol 25 (24) ◽  
pp. 5980
Author(s):  
Ajda Taler-Verčič ◽  
Marko Goličnik ◽  
Aljoša Bavec
Keyword(s):  
Catalytic Mechanism ◽  
Kinetic Studies ◽  
Amino Acid Sequences ◽  
Site Directed Mutagenesis ◽  
Paraoxonase 1 ◽  
Homocysteine Thiolactone ◽  
Substrate Promiscuity ◽  
Serum Paraoxonase ◽  
And Function ◽  
Derivatives Of

Serum paraoxonase-1 (PON1) is the most studied member of the group of paraoxonases (PONs). This enzyme possesses three enzymatic activities: lactonase, arylesterase, and paraoxonase activity. PON1 and its isoforms play an important role in drug metabolism as well as in the prevention of cardiovascular and neurodegenerative diseases. Although all three members of the PON family have the same origin and very similar amino acid sequences, they have different functions and are found in different locations. PONs exhibit substrate promiscuity, and their true physiological substrates are still not known. However, possible substrates include homocysteine thiolactone, an analogue of natural quorum-sensing molecules, and the recently discovered derivatives of arachidonic acid—bioactive δ-lactones. Directed evolution, site-directed mutagenesis, and kinetic studies provide comprehensive insights into the active site and catalytic mechanism of PON1. However, there is still a whole world of mystery waiting to be discovered, which would elucidate the substrate promiscuity of a group of enzymes that are so similar in their evolution and sequence yet so distinct in their function.

Mechanistic Studies on Class I Polyhydroxybutyrate (PHB) Synthase fromRalstonia eutropha:  Class I and III Synthases Share a Similar Catalytic Mechanism†

Biochemistry ◽  
2001 ◽  
Vol 40 (4) ◽  
pp. 1011-1019 ◽  
Author(s):  
Yong Jia ◽  
Wei Yuan ◽  
Jola Wodzinska ◽  
Chung Park ◽  
Anthony J. Sinskey ◽  
...  
Keyword(s):  
Catalytic Mechanism ◽  
Class I ◽  
Mechanistic Studies ◽  
Phb Synthase
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