Alkaline opening of imidazole ring of 7-methylguanosine. 2. Further studies on reaction mechanisms and products.

High performance liquid chromatography (HPLC) was used to follow the kinetics of the alkaline induced opening of the imidazole ring of 7-methyl-guanosine (7-meGuo). The kinetics show an initial rapid formation of a major transient intermediate and some minor products that were chromatographically separable into seven peaks. This phase of the reaction is followed by the formation of a dominant pyrimidine derivative whose liquid chromatography retention time in a 6% methanol, 0.01 M NH4H2PO4 (pH 5.1) solvent is 6 min; during the rest of the reaction time this dominant species of ring opened 7-methylguanine (7-meGua), one formylated and another deformylated. Schiff's reaction demonstrated that the species in the second HPLC peak is the formylated one. The ring opened 7-methylguanine (rom7Gua) released by formamidopyrimidine (FAPy)-DNA glycosylase was shown to coelute with the formylates species. These results demonstrate that the enzyme excises formylated rom7Gua from DNA Analysis of rom7Gua by NMR showed that there are two signals assignable to methyl protons and two to formyl protons. These chemical shifts were interpreted as being due to the opening of the imidazole ring at two sites and to the formation of formylated and deformylated rom7Gua.