Regioselective functionalization of guanine: Simple and practical synthesis of 7-and 9-alkylated guanines starting from guanosine

Reaction of N2-acetyl-9- and/or -7-benzylated guanines 8 and 12 with selected alkylating agents in 1-methyl-2-pyrrolidone at 120 degreesC yielded the guaninium salts 9 and 13. The salts were consequently transformed by phase transfer hydrogenation into N-7- and N-9-isomers 10 and 14, respectively, in a highly regioselective manner. A convenient deoxygenation of both derivatives, achieved via the corresponding O-6-arenesulfonates, into 2-aminopurine potential prodrugs was also established.