Compositions for the treatment or prophylaxis of viral infections

A method of treatment of viral infection with the Varicella Zoster virus, comprising administering to a human or non-human animal patient in need of such treatment an effective amount of a compound of formula (III):

• wherein
• X is O, S, NH or CH2;
• Y is O, S or NH;
• Z is O, S or CH2;
• R1 is C1-8 alkyl;
• at least one of R2 and R3 is H—[R4—R5]n—R6—, in which:
• H—[R4—R5]n— comprises an oligopeptide,
• R4 is an amino acid,
• R5 is an amino acid selected from the group consisting of proline, alanine, hydroxyproline, dihydroxyproline, thiazolidinecarboxylic acid (thioproline), dehydroproline, pipecolic acid (L-homoproline), azetidinecarboxylic acid, aziridinecarboxylic acid, glycine, serine, valine, leucine, isoleucine and threonine,
• R6 is a neutral, non-polar amino acid moiety that is bonded to R5 by a peptide bond, and
• n is 1, 2, 3, 4 or 5;
• and
• the other of R3 and R2 is H—[R4—R5]n—R6— or H;
• or a pharmaceutically acceptable salt thereof.