3-AZIDO PURINE NUCLEOSIDES

The present invention relates to 3 min -azido purine nucleosides of formula (I) and their use in medical therapy, particularly for the treatment or prophylaxis of human immunodeficiency virus and hepatitis B virus infections, to methods for their preparation and to compositions containing them. wherein R represents halogen; C1-6 alkoxy; C3-6 cycloalkoxy; aryloxy or arylalkoxy in which the aryl may optionally be substituted with C1-6 alkyl, C1-6 alkoxy, halogen, nitro or hydroxyl; amino which is substituted by one or two substituents indepently selected from C1-6 alkyl, aryl, aralkyl including aracycloalkyl and C3-6 cycloalkyl; or a 4- to 6- membered heterocyclic ring containing at least one nitrogen atom which ring is bonded to the purine base via a/the nitrogen atom; or a pharmaceutically acceptable derivative thereof.