Phosphoramidate derivatives of nucleoside compounds of formula I derived from bases such as adenine and guanine have enhanced therapeutic potency, in particular, enhanced potency with respect to the prophylaxis or treatment of a viral infection such as hepatitis C virus. The glycoside moiety of the nucleoside compound is suitably substituted at the β-2 position with methyl and the phosphoramidate group suitably comprises 1-naphthyI linked by -O- to the P atom.
