Identification of alkyl radicals derived from an allergenic cyclic tertiary allylic hydroperoxide by combined use of radical trapping and ESR studies

Alkyl radicals derived from 1-(1-hydroperoxy-1-methylethyl)cyclohexene, an allergenic cyclic tertiary allylic hydroperoxide, were identified using a combination of radical trapping and ESR studies. Radical trapping experiments were carried out in aqueous acetonitrile solutions containing the stable scavenger agent 1,1,3,3-tetramethylisoindolin-2-yloxyl, and light, heat and TPP–Fe3+ were used as radical inducers. ESR spin-trapping studies were performed on the allylic alcohol precursor of the hydroperoxide, which generated the same allyloxyl radical by in situ photolysis of the corresponding nitrite formed in the presence of t-BuONO (which also played the role of spin-trap). The formation and trapping of carbon-centered radicals derived from the allyloxyl radical, as well as from the peroxyl radical, are described. The generation of these highly reactive radicals in the epidermis could lead to the formation of antigenic structures, the first step of the allergic contact dermatitis mechanism.