Identification of the Major Product of Guanine Oxidation in DNA by Ozone.

Ozonolysis of guanosine formed the 5-carboxamido-5-formamido-2-iminohydantoin (2Ih) nucleoside along with trace spiroiminodihydantoin (Sp). On the basis of literature precedent, we propose an unconventional ozone mechanism involving incorporation of only one oxygen atom of O 3 to form 2Ih with evolution of singlet oxygen responsible for Sp formation. The increased yield of Sp in the buffered 1 O 2 -stabilizing solvent D 2 O, formation of 2Ih in a short oligodeoxynucleotide, and 18 O-isotope labeling provided evidence to support this mechanism. The elusiveness and challenges of working with 2Ih are described in a series of studies on the significant context effects on the half-life of the 2Ih glycosidic bond.