Compounds which are active against viruses have the following formulas:
##STR00001## wherein B is a purine or pyrimidine heterocyclic ring or
base. In a preferred embodiment, the purine include 6-aminopurine
(adenine), 6-hydroxypurine (hypoxanthine), 2-amino-6-hydroxypurine
(guanine), 2,6-diamino-purine, 2-amino-6-azidopurine, 2-amino-6-halo
substituted purines such as 2-amino-6-chloropurine,
2-amino-6-fluoropurine, 2-amino-6-alkoxypurines such as
2-amino-6-methoxypurine, 2-amino-6-cyclopropylaminopurine,
2-amino-6-alkylamino or 2-amino-6-dialkylamino substituted purines,
2-amino-6-thiopurine, 2-amino-6-alkylthio substituted purines,
3-deazapurines, 7-deazapurines and 8-azapurines. The pyrimidine
incorporates cytosine, uracil and thymine, 5-halo substituted cytosines
and uracils, 5-alkyl substituted cytosines and uracils including
derivatives with a saturated or unsaturated alkyl group and
6-azapyrimidines.