A compound for use in the treatment or prophylaxis of viral infections such, for example as chicken pox or shingles caused by the Varicella Zoster virus, said compound having the general formula (II): wherein X is O, S, NH or CH2, Y is O, S or NH, Z is O, S or CH2, R1 is C1-6 alkyl, preferably n-alkyl, e.g., n-pentyl or n-hexyl, and one of R2 and R3 is OH, and the other of R3 and R2 is a neutral, non-polar amino acid moiety, or a pharmaceutically acceptable salt or hydrate thereof. Said neutral, non-polar amino acid moiety R2 or R3 may be (IV): in which R4, R5, R6 and R7 are each independently H or C1-2 alkyl. In preferred embodiments, one of R2 or R3 is valine, leucine, isoleucine or alanine, particularly valine.
