Novel antiviral compounds of Formula (I): wherein: A represents hydroxy; R1 represents aryl, heteroaryl bonded through a ring carbon atom, or heterocyclyl bonded through a ring carbon atom, C1-6alkyl or —C5-9cycloalkyl, each of which may be optionally substituted; R2 represents substituted phenyl, or —(CH2)nC5-7cycloalkyl optionally substituted on the cycloalkyl; R3 represents heterocyclyl or heteroaryl; optionally substituted phenyl or optionally substituted —C1-6alkyl; R4 represents hydrogen; and salts, solvates and esters thereof processes for their preparation, pharmaceutical compositions comprising them, and methods of using them in HCV treatment are provided.