6-Chloro-2-fluoropurine is a heterocyclic building block.1,2It has been used in the synthesis of purine nucleosides that inhibit cyclin-dependent kinases (CDKs)in vitro.16-Chloro-2-fluoropurine has also been used in the synthesis of purine nucleosides that are active against HIV-1 and hepatitis B virus (HBV)in vitro.2