The present invention is directed to compounds, compositions and methods for treating or preventing cancer and viral infections, in particular, HIV, HCV, Norovirus, Saporovirus, HSV-1, HSV-2, Dengue virus, Yellow fever, and HBV in human patients or other animal hosts. The compounds are certain 6-substituted purine monophosphates, and pharmaceutically acceptable, salts, prodrugs, and other derivatives thereof. In particular, the compounds show potent antiviral activity against HIV-1, HIV-2, HCV, Norovirus, Saporovirus, HSV-1, HSV-2, Dengue virus, Yellow fever, and HBV.
