Photochemically Reversible Dimer Electroreduction Product of 2-Oxopurine

The electrochemical reduction of 2-oxopurine in buffered aqueous medium was found to proceed via two successive one-electron additions. The initial one-electron step involves the addition of a proton, leading to formation of a free radical which rapidly dimerizes. At more negative potentials, reduction leads to formation of l,6-dihydro-2-oxopurine. The product of reduction on wave I was isolated and identified by various spectroscopic techniques as the dimer 6,6'-bis( l ,6-dihydro-2-oxopurine). In neutral aqueous medium this dimer reduction product (but not the product of reduction on wave II, l,6-dihydro-2-oxopurine) underwent quantitative photochemical dissociation to the parent 2-oxopurine, with a quantum yield at 254 nm of 0.03. The dimer reduction product also quantitatively regenerated the parent monomer in an alkali-catalyzed reaction at room temperature. The proposed mechanism of the reduction reaction, and susceptibility of the reduction product to photodissociation, is compared with the corresponding behaviour of other purine, and pyrimidine, derivatives.