Free radical trapping agents

PBN), a free radical trapping agent, reduces the occurrence of thalidomide embryopathy, suggesting that the mechanism is free radical-mediated oxidative DNA damage (108). 

Folinic acid (leucovorin) reduces the toxicity of methotrexate because it provides an active form of folate to normal (nonneo-plastic) cells, resulting in leucovorin rescue. Dexrazoxane is a free radical trapping agent that is thought to reduce the cardiotoxicity of anthracyclines (eg, doxorubicin). Mercaptoethanesulfonate (mesna), which inactivates acrolein, is available for protection against hemorrhagic cystitis in patients treated with cyclophosphamide and related drugs. 

Cerovive (NXY-059) A free radical-trapping agent Lees et al. (2006), Shuaib et al. (2007)... 

Nitrone-Based Free Radical Traps as Neuroprotective Agents in Cerebral Ischemia and Other Pathologies... 

Electron-spin resonance (ESR) indicated free radicals in a brown polymer (mean ca 1 kDa by field-desorption MS) from a glucose-4-chloroaniline model system.185 Such free radicals (see Chapter 2) could be a source of visible colour. Exposure of the melanoidin to nitric oxide, a radical-trapping agent, diminished the ESR signal by 48% and changed the colour to red-brown. 

Chain reaction may be inhibited by agents acting as free-radical traps. They may also exhibit induction periods, that is, delayed onset of the reaction. An induction period may be caused by a trace inhibitor that must first be destroyed by the free radicals, or actually reflect autocatalytic behavior. Yet another possible mechanism is the reversible formation of a metastable compound from free radicals, acting as a free-radical sink until filled. 

In a number of reactions, use of classical spin trapping agents led to the ESR observation of spin adducts, which were due to the presence of free radicals. For example, the presence of phenyl-tert-butylnitroxide was considered as a proof of the intermediacy of phenyl radicals in the reaction of diphenyliodonium salts with phenolate anions leading to aiylphenyl ethers. However, the qualitative observation of free radical species cannot be considered as a proof of a radical mechanism, as they can result from a competitive decomposition pathway. Two major experimental iq)proaches were used to determine the real influence of free radical species a) quantitative evaluation of the efrect of the addition of free radical traps and b) the use of substrates containing internal traps. 

Radical involvement is indicated also by the inhibitory effect of radical trapping agents and product analysis, since 10-15% of the products from cumene hydroperoxide decomposition induced by the organic sulfur compounds result from free-radical processes (2). Acids will... 

The free radical trapping reaction (kxf) of Scheme 3 involves a collisionally formed cage pair (where the trapping agent (T) and the alkyl (R ) radical are the chemically reactive components) which is formally identical to that for free radical self-termination discussed above. Scheme 4 provides this... 

First Generation Monomeric HALS. Several decades ago, physical organic chemists were entranced by the concept of stable free radicals and their potential as radical trapping agents. References on the use of nitroxyls as potential stabilizers for plastics had already been cited in the patent literature (44). 

The first example of a cyclization of fluorine-containing 5-hexenyl radicals was the study of the radical-iniOated cyclodimenzation reaction of 3,3,4,4-tetra-fluoro-4-iodo-1-butene. In this reaction, the intermediate free radical adds either to more of the butene or to an added unsaturated species [54, 55] (equation 56). Electron-deficient alkenes are not as effective trapping agents as electron-nch alkenes and alkynes [55]. 

ESR studies on the initial free radicals were carried out by using MNP(2-methyl-2-nitrosopropane) or DMPO (5,5-dimethylpyrroline N-oxide) as the spin-trapping agent. The reactions are shown as ... 

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