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°C yielded the guaninium salts 9 and 13. The salts were consequently transformed by phase transfer hydrogenation into N7- and N9-isomers 10 and 14, respectively, in a highly regioselective manner. A convenient deoxygenation of both derivatives, achieved via the corresponding O6-arenesulfonates, into 2-aminopurine potential prodrugs was also established.