Kinetics of One-Electron Oxidation of Thiols and Hydrogen Abstraction by Thiyl Radicals from .alpha.-Amino C-H Bonds

Zhao, Rong; Lind, Johan; Merényi, Gábor; Eriksen, Trygve E.

doi:10.1021/ja00105a048

Cited by 136 publications

(129 citation statements)

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“…In synthetic contexts, thiyl radicals are known to engage in a number of useful reactions [191][192][193][194][195][196][197][198], including C-H bond abstraction [197,[199][200][201][202][203]. Recently, MacMillan has demonstrated the capacity of catalytically generated thiyl radicals to cleave the C-H bond of benzylic ethers for radical coupling reactions ( Figure 27) to form diaryl methanols (a) [204] or β-amino ethers (b) [205].…”

Section: Thiolsmentioning

confidence: 99%

Proton-Coupled Electron Transfer in Organic Synthesis: Fundamentals, Applications, and Opportunities

Miller

Tarantino

Knowles

2016

Topics in Current Chemistry Collections

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Proton-coupled electron transfers (PCETs) are unconventional redox processes in which both protons and electrons are exchanged, often in a concerted elementary step. While PCET is now recognized to play a central a role in biological redox catalysis and inorganic energy conversion technologies, its applications in organic synthesis are only beginning to be explored. In this chapter we aim to highlight the origins, development and evolution of PCET processes most relevant to applications in organic synthesis. Particular emphasis is given to the ability of PCET to serve as a non-classical mechanism for homolytic bond activation that is complimentary to more traditional hydrogen atom transfer processes, enabling the direct generation of valuable organic radical intermediates directly from their native functional group precursors under comparatively mild catalytic conditions. The synthetically advantageous features of PCET reactivity are described in detail, along with examples from the literature describing the PCET activation of common organic functional groups.

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Section: Thiolsmentioning

confidence: 99%

Proton-Coupled Electron Transfer in Organic Synthesis: Fundamentals, Applications, and Opportunities

Miller

Tarantino

Knowles

2016

Topics in Current Chemistry Collections

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“…13). Intramolecular H transfer from a-C-H groups to sulfur has now also been reported in homocysteine and cysteine (14) and 2-mercaptoethanol (15). Also Zhao et al have shown (14) that S-centered radicals are able to abstract a-C-H hydrogen atoms from the anions of glycine and alanine, and have estimated a value of 356 kJ mol-' for the tertiary a-C-H bond dissociation energy of H2NC(CH3)HC02-.…”

mentioning

confidence: 89%

Oxidative damage to the glycyl α-carbon site in proteins: an ab initio study of the C—H bond dissociation energy and the reduction potential of the C-centered radical

Armstrong¹,

Yu²,

Rauk³

1996

Can. J. Chem.

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The C—H bond dissociation energies (DC—H) of a series of model glycyl proteins were derived from selected isodesmic reactions based on high level ab initio calculations. At 298 K, the recommended values of DC—H, in kJ mol−1 are: NH2CH2CHO, 308; NH2CH2C(O)NH2, 336; HC(O)NHCH2CHO, 331; HC(O)NHCH2C(O)NH2, 350; CH3C(O)NHCH2C(O)NH2, 347; HC(O)NHCH2C(O)NHCH3, 349; and CH3C(O)NHCH2C(O)NHCH3, 346. The average of the last four values, 348 kJ mol−1, is the predicted bond dissociation energy of the α-C—H bond of a glycyl protein. The reduction potential in aqueous medium at 298 K and pH 7 for the process, R• + H+ + e− = RH, where R• = XNHCH•C(O)Y and X and Y represent extension of the protein chain, is E0′ 0.8 V. This result suggests that the α-C—H bond of a glycyl protein is susceptible to attack by RS•, ROO•, tyrosyl, and OH• radicals, whose reduction potentials for the analogous process are higher. The present study has established that the molecule HC(O)NHCHRC(O)NH2 (R = an amino acid side chain) serves as an accurate model for the α-C environment of an amino acid residue in a protein, and that a reliable DC—H value for the α-C—H bond may be obtained from calculations on this model at the B3LYP/6-31G(D) level of theory in conjunction with an isodesmic reaction using neutral glycine as reference. Key words: glycine, peptide, amino acid, bond energy, radicals, ab initio, computation.

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“…31 It was later described that the α-amino alkyl radical of GSH could be formed intramolecularly via the thiyl radical (as in eq 2). 32,33 Zhao et al reported in 1994 that intramolecular formation of captodatively stabilized α-amino alkyl radical in Hcy should be particularly favorable. 33a This was attributed to an intramolecular hydrogen abstraction mechanism, which involves a favored 5-membered ring transition state (Scheme 3).…”

Section: The Redox Chemistry Of Biological Thiols and Selective Hcy Dmentioning

confidence: 99%

“…34 The dication methyl viologen (10) was used by Zhao et al during thorough investigations of the equilibrium kinetics of the reducing disulfide (eq 1) and the reducing α-amino carboncentered radicals (eq 2) derived from the Hcy, Cys, and GSH thiyl radicals. 33 The formation of reducing radicals was monitored via changes in the UV -vis absorbance spectra, indicating the production of the methyl viologen radical cation. 33a Under the basic conditions used (pH 10.5), no colorimetric selectivity among GSH, Cys, and Hcy was observed.…”

Section: The Redox Chemistry Of Biological Thiols and Selective Hcy Dmentioning

confidence: 99%

“…22b It has been reported that α-amino acid alkyl radicals form NH 3 and several other radical termination and disproportionation products under ionizing radiation and relatively harsh oxidizing conditions. 33,35 Several byproducts of Hcy alkyl radical reactions are identified under our assay conditions at room temperature by using MALDI-TOF MS (Table 2). Scheme 5 shows a proposed mechanism of formation of these products.…”

Section: The Fate Of the α-Amino Carbon-centered Radical Of Hcymentioning

confidence: 99%

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Detection of Homocysteine and Cysteine

et al. 2005

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At elevated levels, homocysteine (Hcy, 1) is a risk factor for cardiovascular diseases, Alzheimer's disease, neural tube defects, and osteoporosis. Both 1 and cysteine (Cys, 3) are linked to neurotoxicity. The biochemical mechanisms by which 1 and 3 are involved in disease states are relatively unclear. Herein, we describe simple methods for detecting either Hcy or Cys in the visible spectral region with the highest selectivity reported to date without using biochemical techniques or preparative separations. Simple methods and readily available reagents allow for the detection of Cys and Hcy in the range of their physiologically relevant levels. New HPLC postcolumn detection methods for biological thiols are reported. The potential biomedical relevance of the chemical mechanisms involved in the detection of 1 is described.

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Kinetics of One-Electron Oxidation of Thiols and Hydrogen Abstraction by Thiyl Radicals from .alpha.-Amino C-H Bonds

Cited by 136 publications

References 1 publication

Proton-Coupled Electron Transfer in Organic Synthesis: Fundamentals, Applications, and Opportunities

Proton-Coupled Electron Transfer in Organic Synthesis: Fundamentals, Applications, and Opportunities

Oxidative damage to the glycyl α-carbon site in proteins: an ab initio study of the C—H bond dissociation energy and the reduction potential of the C-centered radical

Detection of Homocysteine and Cysteine

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