scholarly journals Selective Hydrogen Atom Abstraction from Dihydroflavonol by a Nonheme Iron Center Is the Key Step in the Enzymatic Flavonol Synthesis and Avoids Byproducts

2019 ◽  
Vol 141 (51) ◽  
pp. 20278-20292 ◽  
Author(s):  
Sidra Ghafoor ◽  
Asim Mansha ◽  
Sam P. de Visser
Keyword(s):  
Hydrogen Atom ◽  
Nonheme Iron ◽  
Hydrogen Atom Abstraction ◽  
Iron Center

Properties and reactivities of nonheme iron(iv)–oxo versus iron(v)–oxo: long-range electron transfer versus hydrogen atom abstraction

2014 ◽  
Vol 16 (41) ◽  
pp. 22611-22622 ◽  
Author(s):  
Baharan Karamzadeh ◽  
Devendra Singh ◽  
Wonwoo Nam ◽  
Devesh Kumar ◽  
Sam P. de Visser
Keyword(s):  
Electron Transfer ◽  
Hydrogen Atom ◽  
Long Range ◽  
Cation Radical ◽  
Nonheme Iron ◽  
Hydrogen Atom Abstraction ◽  
Computational Studies ◽  
Radical Species ◽  
Oxo Ligand

Computational studies show that the perceived nonheme iron(v)–oxo is actually an iron(iv)–oxo ligand cation radical species.

scholarly journals Density Functional Theory Study into the Reaction Mechanism of Isonitrile Biosynthesis by the Nonheme Iron Enzyme ScoE

2021 ◽  
Author(s):  
Hafiz Saqib Ali ◽  
Sidra Ghafoor ◽  
Sam P. de Visser
Keyword(s):  
Reaction Mechanism ◽  
Hydrogen Atom ◽  
Proton Transfer ◽  
Active Site ◽  
Density Functional ◽  
Active Species ◽  
Nonheme Iron ◽  
Catalytic Cycle ◽  
Hydrogen Atom Abstraction ◽  
Catalytic Cycles

AbstractThe nonheme iron enzyme ScoE catalyzes the biosynthesis of an isonitrile substituent in a peptide chain. To understand details of the reaction mechanism we created a large active site cluster model of 212 atoms that contains substrate, the active oxidant and the first- and second-coordination sphere of the protein and solvent. Several possible reaction mechanisms were tested and it is shown that isonitrile can only be formed through two consecutive catalytic cycles that both use one molecule of dioxygen and α-ketoglutarate. In both cycles the active species is an iron(IV)-oxo species that in the first reaction cycle reacts through two consecutive hydrogen atom abstraction steps: first from the N–H group and thereafter from the C–H group to desaturate the NH-CH2 bond. The alternative ordering of hydrogen atom abstraction steps was also tested but found to be higher in energy. Moreover, the electronic configurations along that pathway implicate an initial hydride transfer followed by proton transfer. We highlight an active site Lys residue that is shown to donate charge in the transition states and influences the relative barrier heights and bifurcation pathways. A second catalytic cycle of the reaction of iron(IV)-oxo with desaturated substrate starts with hydrogen atom abstraction followed by decarboxylation to give isonitrile directly. The catalytic cycle is completed with a proton transfer to iron(II)-hydroxo to generate the iron(II)-water resting state. The work is compared with experimental observation and previous computational studies on this system and put in a larger perspective of nonheme iron chemistry.

Mechanistic insight into the hydroxylation of alkanes by a nonheme iron(v)–oxo complex

2014 ◽  
Vol 50 (42) ◽  
pp. 5572-5575 ◽  
Author(s):  
Eunji Kwon ◽  
Kyung-Bin Cho ◽  
Seungwoo Hong ◽  
Wonwoo Nam
Keyword(s):  
Hydrogen Atom ◽  
Nonheme Iron ◽  
Hydrogen Atom Abstraction ◽  
Alkane Hydroxylation ◽  
Mechanistic Insight ◽  
Insight Into

The alkane hydroxylation by a mononuclear nonheme iron(v)–oxo complex occurs via a hydrogen-atom abstraction–oxygen non-rebound mechanism.

scholarly journals Axial ligand tuning of a nonheme iron(IV) oxo unit for hydrogen atom abstraction

2007 ◽  
Vol 104 (49) ◽  
pp. 19181-19186 ◽  
Author(s):  
C. V. Sastri ◽  
J. Lee ◽  
K. Oh ◽  
Y. J. Lee ◽  
J. Lee ◽  
...  
Keyword(s):  
Hydrogen Atom ◽  
Axial Ligand ◽  
Nonheme Iron ◽  
Hydrogen Atom Abstraction

2-Deoxyribose Radicals in the Gas Phase and Aqueous Solution. Transient Intermediates of Hydrogen Atom Abstraction from 2-Deoxyribofuranose

2005 ◽  
Vol 70 (11) ◽  
pp. 1769-1786 ◽  
Author(s):  
Luc A. Vannier ◽  
Chunxiang Yao ◽  
František Tureček
Keyword(s):  
Aqueous Solution ◽  
Hydrogen Atom ◽  
Gas Phase ◽  
Computational Study ◽  
Hydrogen Atom Abstraction ◽  
Oh Radical ◽  
Free Energies ◽  
Intramolecular Hydrogen ◽  
Solvation Free Energies ◽  
Transient Intermediates

A computational study at correlated levels of theory is reported to address the structures and energetics of transient radicals produced by hydrogen atom abstraction from C-1, C-2, C-3, C-4, C-5, O-1, O-3, and O-5 positions in 2-deoxyribofuranose in the gas phase and in aqueous solution. In general, the carbon-centered radicals are found to be thermodynamically and kinetically more stable than the oxygen-centered ones. The most stable gas-phase radical, 2-deoxyribofuranos-5-yl (5), is produced by H-atom abstraction from C-5 and stabilized by an intramolecular hydrogen bond between the O-5 hydroxy group and O-1. The order of radical stabilities is altered in aqueous solution due to different solvation free energies. These prefer conformers that lack intramolecular hydrogen bonds and expose O-H bonds to the solvent. Carbon-centered deoxyribose radicals can undergo competitive dissociations by loss of H atoms, OH radical, or by ring cleavages that all require threshold dissociation or transition state energies >100 kJ mol-1. This points to largely non-specific dissociations of 2-deoxyribose radicals when produced by exothermic hydrogen atom abstraction from the saccharide molecule. Oxygen-centered 2-deoxyribose radicals show only marginal thermodynamic and kinetic stability and are expected to readily fragment upon formation.

scholarly journals A cross-dehydrogenative C(sp3)−H heteroarylation via photo-induced catalytic chlorine radical generation

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Chia-Yu Huang ◽  
Jianbin Li ◽  
Chao-Jun Li
Keyword(s):  
Hydrogen Atom ◽  
Hydrogen Evolution ◽  
Alkyl Radical ◽  
Cobalt Catalyst ◽  
Alkylation Reaction ◽  
Hydrogen Atom Abstraction ◽  
Dehydrogenative Coupling ◽  
Radical Generation ◽  
Limited Scope

AbstractHydrogen atom abstraction (HAT) from C(sp3)–H bonds of naturally abundant alkanes for alkyl radical generation represents a promising yet underexplored strategy in the alkylation reaction designs since involving stoichiometric oxidants, excessive alkane loading, and limited scope are common drawbacks. Here we report a photo-induced and chemical oxidant-free cross-dehydrogenative coupling (CDC) between alkanes and heteroarenes using catalytic chloride and cobalt catalyst. Couplings of strong C(sp3)–H bond-containing substrates and complex heteroarenes, have been achieved with satisfactory yields. This dual catalytic platform features the in situ engendered chlorine radical for alkyl radical generation and exploits the cobaloxime catalyst to enable the hydrogen evolution for catalytic turnover. The practical value of this protocol was demonstrated by the gram-scale synthesis of alkylated heteroarene with merely 3 equiv. alkane loading.

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