The present invention is directed to compounds compositions and methods for treating or preventing cancer and viral infections in particular HIV HCV Norovirus Saporovirus cytomegalovirus (CMV) herpes viruses (HSV 1 HSV 2) Dengue virus Yellow fever or HBV in human patients or other animal hosts. The compounds are certain A^ hydroxycytidine nucleosides derivatives modified monophosphate and phosphonates prodrugs analogs 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 cytomegalovirus (CMV) herpes viruses (HSV 1 HSV 2) Dengue virus Yellow fever and HBV.