Water elimination and rearrangement reactions

While OH radicals readily add to double bonds, they undergo electron transfer reactions with reluctance. This implies that, since there is evidence that heteroatom-centered radicals are formed from guanine and adenine derivatives (see also below), the precursor of the intermediates must under these conditions be an OH-adduct radical rather than the radical cation. Rapid transformation has been observed with adenosine and guanosine. Part of this is attributed to solvent-catalyzed water elimination such as in reaction (73) [5]. In the case of acid catalysis, the intermediate is a radical cation (see below). It can be seen that OH-adducts with OH attached in several different positions lead to a single anhydro radical. 

It appears that the OH-adduct radicals to the pyrimidinic cycle are denied the option of undergoing fragmentation of the purine skeleton since this would require the transformation of a 7t radical into a o radical. 

This barrier does not exist for the C(8)-OH adduct [c/. reaction (74)]. This radical can moreover undergo the 1,2-H-shift reaction (75), leading to a species whose reduction [reaction (80)] gives rise [reaction (79)] to a product that can hydrolyze to an amino-formamidopyrimidine, FAPY. These are well-documented purine radiolysis products. In the presence of an oxidant, e.g. Fe(CN)6, these transformation reactions (ring-opening and/or 1,2-H-shift) can 

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