A compound of the formula: ** Formula ** or a pharmaceutically acceptable salt thereof, optionally in a pharmaceutically acceptable carrier or diluent, wherein: The base is a pyric or pyrimidine base； R1 is independently H； phosphate； acyl； I rent； sulfonate ester, benzyl, wherein the phenyl group is unsubstituted or substituted with one or more substituents selected from the group consisting of hydroxyl, amino, alkylamino, arylamino, alkoxy, aryloxy, nitro, cyano, sulphonic acid, sulfate, acid phosphonic, phosphate or phosphonate； a lipid； an amino acid； a carbohydrate； a peptide； a cholesterol； R6 is alkyl； R7 and R9 are independently hydrogen, OR1, hydroxy, alkyl, lower alkyl, alkenyl, alkynyl, Br-vinyl, -O (alkenyl), NO2, NH2, -NH (lower alkyl), -N (lower alkyl) 2； and R10 is H, alkyl, chlorine, bromine or iodine； wherein the alkyl is unsubstituted or substituted with one or more substituents selected from the group consisting of hydroxyl, amino, alkylamino, arylamino, alkoxy, aryloxy, nitro, cyano, sulfonic acid, sulfate, phosphonic acid, phosphate or phosphonate； wherein the aryl is phenyl, biphenyl or naphthyl, unsubstituted or substituted with one or more substituents selected from the group consisting of hydroxyl, amino, alkylamino, arylamino, alkoxy, aryloxy, nitro, cyano, sulphonic acid, sulfate, phosphonic acid, phosphate or phosphonate； and wherein the acyl is a carboxylic acid ester in which the non-carbonyl moiety of the ester group is selected from linear, branched or cyclic alkyl or lower alkyl, alkoxyalkyl, including methoxymethyl, aralkyl including benzyl, aryloxyalkyl, aryl including optionally substituted phenyl with chlorine, bromine, fluorine, iodine, C1 to C4 alkyl or C1 to C4 alkoxy, sulfonate esters including sulfonate esters including methanesulfonyl ester, mono, di or triphosphate, trityl or monomethoxytrityl ester, substituted benzyl, trialkylsilyl or diphenylmethylsilyl ester ； for use in a method for the treatment of a hepatitis C viru
