Compounds which are active against viruses have the following formulas: 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
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