Chemical and biological studies on nucleic acids and derivatives. Progress report, October 1, 1974--April 30, 1975

Ultraviolet irradiation of N-hydroxyxanthines in the solid state induces a radical that was assigned as an acyl amidogen radical in which the unpaired electron density is partially delocalized throughout the π-cloud of the purine ring. The radical is reduced in the presence of water. In the presence of methanol this process is also accompanied by some 8-substitution. Photochemical deoxygenation in solution was found to proceed from either the nonionized N-hydroxyl tautomer or the conjugate anion of N-hydroxypurines. Reduction is the sole photoreaction of the former, while intramolecular migration of the oxygen is the main photoprocess of the latter with photoreduction a minor result. The comparison of the photochemistry of the N-hydroxypurine anion to that of the corresponding purine N-oxide was documented with a study of suitable model purine 1-oxides. A unique photorearrangement of 1-hydroxyxanthine to the oncogenic 3-isomer was examined and is deduced to be a two step process