Formation of s-triazines during aerial oxidation of 8-oxo-7,8-dihydro-2'-deoxyguanosine in concentrated ammonia.

After automated DNA synthesis, oligodeoxynucleotides containing 8-oxoguanine are sensitive to aerial oxidation when subjected to the basic conditions necessary for deprotection and release of the oligomer from the control pore glass support. The major oxidation products of this heterocyclic moiety have been characterized by permitting 8-oxo-7,8-dihydro-2'-deoxyguanosine to react with oxygen in the presence of 28% aqueous ammonia at room temperature. Products were isolated by reverse phase HPLC and analyzed by electrospray ionization-mass spectrometry and gas chromatography-mass spectrometry of the trimethylsilyl-derivatives. 2-Amino-4-hydroxy-s-triazine-6-carboxylic acid and 2-amino-4-hydroxy-6-carbamyl-s-triazine were identified by these techniques and standards were synthesized. In addition, GC-MS analysis revealed other oxidation products, including urea, guanidine and 2-deoxyribose, which were not observed by HPLC because these compounds are transparent in the UV region of the spectrum. Both s-triazines were also observed when a purified, synthetic oligodeoxynucleotide containing a single 8-oxoguanine moiety was exposed to the same conditions. Oxidation of 8-oxoguanine appears to parallel the uric acid oxidation pathway, and a mechanistic scheme is proposed to account for the products of degradation.