Iron-catalysed reductive radical

Iron-catalysed reductive radical formation reactions have shown success toward olefin hydrofunctionalisation. Typically, procedures are general and operationally simple, allowing for rapid substrate derivatisation, both in simple and eomplex frameworks. 

NADH, which enters the Krebs cycle. However, during cerebral ischaemia, metabolism becomes anaerobic, which results in a precipitous decrease in tissue pH to below 6.2 (Smith etal., 1986 Vonhanweh etal., 1986). Tissue acidosis can now promote iron-catalysed free-radical reactions via the decompartmentalization of protein-bound iron (Rehncrona etal., 1989). Superoxide anion radical also has the ability to increase the low molecular weight iron pool by releasing iron from ferritin reductively (Thomas etal., 1985). Low molecular weight iron species have been detected in the brain in response to cardiac arrest. The increase in iron coincided with an increase in malondialdehyde (MDA) and conjugated dienes during the recirculation period (Krause et al., 1985 Nayini et al., 1985). 

Indeed, when present in concentrations sufficient to overwhelm normal antioxidant defences, ROS may be the principal mediators of lung injury (Said and Foda, 1989). These species, arising from the sequential one-electron reductions of oxygen, include the superoxide anion radical, hydrogen peroxide, hypochlorous ions and the hydroxyl radical. The latter species is thought to be formed either from superoxide in the ptesence of iron ions (Haber-Weiss reaction Junod, 1986) or from hydrogen peroxide, also catalysed by ferric ions (Fenton catalysis Kennedy et al., 1989). 

Iron and copper catalyse the formation of oxyradicals. Three reactions are relevant in this context (1) Autoxidation of metal complexes may yield the superoxide radical which by itself is not very reactive, but is a precursor of more reactive radical species. (2) The one-electron reduction of hydrogen peroxide -the Fenton reaction - results in hydroxyl radicals via a higher oxidation state of iron [2]. (3) A similar reaction with organic peroxides leads to alkoxyl radicals, although a recent report alleges that hydroxyl radicals are also formed [3]. There is a fourth radical, the formation of which does not require mediation by a metal complex. This is the alkyldioxyl radical, ROO , which is formed at a... 

This review is concerned with the quantitative aspects of metal-catalysed oxyradical reactions. As such one will find discussions of structures of metal complexes, rate constants and reduction potentials, not unlike our review of 1985 [34], Two areas related to the role of transition metals in radical chemistry and biology have been reviewed recently these are the metal-ion-catalysed oxidation of proteins [35] and the role of iron in oxygen-mediated toxicities [36]. These topics will not be discussed in detail in this review. Related to this work is a review on the role of transition metals in autoxidation reactions [37]. Additional information can be obtained from Afanas ev s two volumes on superoxide [38,39], This subject is also treated in a more general and less quantitative manner by Halliwell and Gutteridge [40],... 

Ribonucleotide reductase catalyses the reduction of the four common ribonucleotides to their corresponding deoxyribonucleotides, an essential step in DNA synthesis. All four ribonucleotides are reduced by the same enzyme [77], The enzyme (250 000 mol. wt.) is a complex of two proteins Mi which contains substrate and redox-active sulphydryl groups and M2 which contains both a (x-oxo-bridged binuclear iron centre (Fig. 5) [77] and a tyrosine moiety sidechain which exists as a free radical stabilised by the iron centre [78], This radical, which is only 5.3 A away from iron centre 1, has access to the substrate-binding pocket and is essential for enzyme activity. Electrons for the reduction reaction are supplied from NADPH via thioredoxin, a small redox-active protein. 

Biotin synthase (BioB) is a Fe S protein that catalyses a presumed radical-mediated insertion of a sulfur atom between the saturated C-6 and C-9 carbon atoms of dethiobiotin. Ugulava et aV have measured equilibrium reduction potentials and monitored cluster conversions by UV/vis, and by X-band EPR spectroscopy between 5 and 50 K. [Fe2S2] and [Fe4S4] clusters and free ferric iron were detected. Overall the authors suggested that the dominant stable cluster state for BioB was a dimer containing two [Fe2S2] and two [Fc4S4] + clusters. 

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