Radical trap hydrazine

Alkyl radicals are conveniently generated by photodecomposition of azoalkanes. A kinetic study of the rearrangement of cyclopropyl radicals (1), obtained by photolysis of the azoalkanes (2), has been described. Particularly high radical concentrations leading to a dramatic change in the product ratio of tetrakis(pentafluoro-ethyl)hydrazine and perfluorobutane have been achieved in the pulsed laser excitation of perfluoroazoethane. On photolysis, azosulphonates also function as radical traps, with the formation of hydrazyl radicals as reactive intermediates. ... 

Closely related routes to alkoxyamines have also been described by Studer and Grubbs research groups. They both used nitroso compounds as radical traps. Studer et used the reaction between hydrazine and lead oxide to promote the alkyl radical formation, whereas Grubbs et generated the alkyl radical by reaction of an alkyl bromide with copper(I) complex. The advantage of this technique relies on the in situ production of the nitroxide. However, yields for alkoxyamines are often moderate and the method is limited to alkoxyamines beating two identical alkyl groups in the stracture. 

In earlier studies the in vitro transition metal-catalyzed oxidation of proteins and the interaction of proteins with free radicals have been studied. In 1983, Levine [1] showed that the oxidative inactivation of enzymes and the oxidative modification of proteins resulted in the formation of protein carbonyl derivatives. These derivatives easily react with dinitrophenyl-hydrazine (DNPH) to form protein hydrazones, which were used for the detection of protein carbonyl content. Using this method and spin-trapping with PBN, it has been demonstrated [2,3] that protein oxidation and inactivation of glutamine synthetase (a key enzyme in the regulation of amino acid metabolism and the brain L-glutamate and y-aminobutyric acid levels) were sharply enhanced during ischemia- and reperfusion-induced injury in gerbil brain. 

The reversible dissociation of colorless tetraphenylhydrazine into the green diphenylaminyl (15) at 100°C was discovered by Wieland in 1911 (equation 7), and extended the free radical concept to nitrogen. These radicals are trapped by nitric oxide to give diphenylnitrosoamine (16), and the rate of this reaction was used to show the rate of dissociation of the hydrazine. ... 

The reaction of oxyhaemoglobin with phenylhydrazine was studied in whole blood samples (Maples et al., 1988). Hydrazine-based drugs induce destruction of red blood cells with resulting haemolytic anaemia. Using DMPO as a trap, nitroxide radicals were detected, but these had solid-state or immobilized spectra with broad parallel and perpendicular features. Whilst no firm identification is possibly based on ESR spectra, except that the trapped radical must be a high polymer, various lines of evidence lead to the conclusion that the adduct was formed from a sulphydryl radical on oxyhaemoglobin. Chloroform extracts gave the phenyl radical adduct in accord with in vitro studies. 

Aliphatic amines are mainly converted to a-substituted products [99,100], whereby especially the a-methoxylation leads to valuable reagents for synthesis. The intermediate iminium salts can be directly trapped by silyl enol ethers to form Mannich bases [108]. If the a-position is blocked or steric conditions favor it, N,N coupling to hydrazo or azo compounds occurs (Table 5, numbers 17-19). 1,1-Disubstituted hydrazines are dimerized to tetrazenes in fair to excellent yields (Table 5, numbers 20-24). The intermediate diaze-nium ions can attack enolizable carbonyl compounds to form aza-Mannich bases [109]. Arylazonaphthols undergo anodic oxidation, producing radical cations. These couple to biphenylbisazo compounds (up to 34%) or can be trapped by anisidine to form azodiphe-nylamines (up to 74%) [110a]. 

Sinha, B. K. Activation of hydrazine derivatives to free radicals in the perfused rat liver a spin-trapping study. Biochim. Biophys. Acta 1987, 924, 261-269. 

ESR investigations of microsomal drug oxidation have been reported. For example, the microsomal enzyme mixed function amine oxidase converts hindered hydroxyl-amines to the corresponding ESR-detectable nitroxides. From a comparison of rates of nitroxide and superoxide production, it has been concluded [177] that oxidation of the hydroxylamine is mediated solely by enzyme-generated superoxide radical. In addition, it appears that some oxidations mediated by cytochrome P-450 may occur, at least in part, by a one-electron mechanism. Oxidation of several dihydropyridine derivatives and some substituted hydrazines in the presence of spin traps has given spectra of spin-adducts consistent with radical production from the P-450 substrates [178]. Cumene hydroperoxide has been shown to support the P-450-catalyzed oxidation of aminopyrine to its radical cation [179]. 

The observation of 4 -hydroxylated abasic site 23 allowed to propose the mechanism summarized in Fig. 7 in association to the observation of similar oxidation products previously characterized with Fe-bleomycin or neocarzi-nostatin (4,7). It results in the initial formation of a C4 radical 6 due to H4 abstraction by activated Cu(phen)2. Then a C4 -hydroxylated compound is probably formed. It allows the release of the nucleobase and the formation of 4 -hydroxylated abasic site 23 that is not associated to DNA cleavage. This site was trapped by the authors as a pyridazine after reaction with hydrazine followed by an enzymatic digestion to nucleosides. Oyushi and Sugiyama proposed that a C4 carbocation was involved as intermediate in the reaction, as for Cl -DNA oxidation performed by activated Cu(phen)2. This hypothesis needs, however, to be confirmed since other evolutions of the C4 radical 6, producing also C4 -hydroxylated site, have been proposed with other chemical nucleases (4). However, in the case of DNA oxidation by activated Cu(phen)2 this oxidation pathway seemed minor when compared to the pathway leading to the formation of phosphoglycolate fragment 11. 

The products of the decomposition the tetraazacycloheptene are the five-membered ring hydrazine plus other, as yet unidentified, materials. When the decomposition was carried out in a large excess of a-methylstyrene some of the initial bi-radical was trapped as a radical addition product. 

Generation of Aryl Radicals. Treatment of arylboronic acids or arylhydrazinium hydrochlorides with Mn(OAc)3 results in the formation of the corresponding aryl radicals. When reactions are done in heteroaromatic solvents, the radical is trapped to afford the corresponding aryl-substituted heterocycle (eq 43). When benzene is used as the solvent, the biaryl is obtained in high (95%) and good (75%) yields for the boronic acid and hydrazine derivatives, respectively. 

---