Compounds of the formula (I) including any possible stereoisomers thereof, wherein: R1 is hydrogen or halo; R4 is a monophosphate, diphosphate or triphosphate ester; or R4 is a group of formula (II) R7 is optionally substituted phenyl; naphthyl; indolyl or N-C1-C6alkyloxycarbonyl- indolyl; R8 is hydrogen, C1-C6alkyl, benzyl; R8' is hydrogen, C1-C6alkyl, benzyl; or R8 and R8' together with the carbon atom to which they are attached form C3-C7cycloalkyl; R9 is C1-C10alkyl, benzyl, or optionally substituted phenyl; or a pharmaceutically acceptable salt or solvate thereof. pharmaceutical formulations and the use of compounds I as HCV inhibitors.