Mechanism and intermediate for formation of 2'-deoxyoxanosine

A reaction mechanism for the direct formation of 2'-deoxyoxanosine (dOxo) from 2'-deoxyguanosine (dGuo) by nitrous acid (HNO2) or nitric oxide (NO) was explored by using guanosine (Guo) and its methyl derivatives. HNO2 treatment of 1-methylguanosine (1-Me-Guo) indicated that the exocyclic amino nitrogen (N5) of dOxo originates from imino nitrogen (N1) of dGuo. A short-lived intermediate detected in the Guo-HNO2 system by reversed phase (RP) HPLC was converted into oxanosine (Oxo) and xanthosine (Xao) at neutral pH. Based on these findings, we discuss the reaction mechanism for the formation of dOxo.