Regioselective nitration of purine nucleosides: synthesis of 2-nitroadenosine and 2-nitroinosine

Nitration reactions of 6-substituted purine nucleosides with tetrabutylammonium nitrate/trifluoroacetic anhydride (TBAN/TFAA) have been studied. This nitrating mixture selectively nitrates C-6 substituted purines at the 2-position, but the method is limited to substrates without NH or OH substituents. Acetylated 6-chloropurine riboside was cleanly nitrated (DCM, 0°C, 71%) and converted to nitro substituted adenosine and inosine in a few simple steps.