| abstract |
1. The compound of formula (IVa): or a pharmaceutically acceptable salt thereof, wherein the base is a purine or pyrimidine base; R and R together form a cyclic 3 ', 5'-phosphate ester; R is halogen; Y is independently H, F, Cl, Br or I.2. The compound according to claim 1, where R is F.3. A pharmaceutical composition comprising an effective amount of a compound or a pharmaceutically acceptable salt thereof of claim 1 or 2 in a pharmaceutically acceptable carrier for the treatment of Flaviviridae infection. The pharmaceutical composition of claim 3, wherein the carrier is suitable for oral delivery. The pharmaceutical composition according to claim 3, containing effective for treating a host infected with West Nile virus, yellow fever virus, dengue virus or BVDV, an amount of a compound or a pharmaceutically acceptable salt thereof. The composition of claim 3, wherein the Flaviviridae virus is hepatitis C.7 virus. The pharmaceutical composition according to claim 3, wherein the compound or a pharmaceutically acceptable salt thereof is presented in unit dosage form. The composition of claim 7, wherein the unit dosage form contains 0.1-50 mg or 50-1000 mg of the compound or a pharmaceutically acceptable salt thereof. The composition of claim 7, wherein said unit dosage form is a tablet or capsule. The pharmaceutical composition of claim 3, further comprising a second antiviral agent. The pharmaceutical composition of claim 10, wherein the second antiviral agent is selected from the group consisting of interferon, ribavirin, interleukin, NS3 protease inhibitor, cysteine protease inhibitor, phenanthrenone, thiazolidine derivative, thiazolidine, benzanilide, helicazide inhibitor |