I am a little confused between Guanine-N7-oxide and Guanine-N3-oxide synthetic procedures? Please let me know, under which conditions Guanine-N3-oxide forms solely. If possible, please provide me a reference which can sort out this confusion.
I don't think you would be able to obtain guanine-N3 oxide without side products. You might have to use some enzymatic reactions (with such selectivities as Xanthine-Oxidase or the opposite ones).