New analogues (compounds 6, 7 and 9) of the mono- (8) and diphosphate (10) bioactive forms of the antiherpes drug acyclovir are described. In compound 6, the monophosphate moiety of 8 was replaced by an aminosulfonyloxy group, while in compounds 7 and 9, a phosphonoacetamidoxy and an O-ethyl phosphonoacetamidoxy moiety are, respectively present instead of the diphosphate one of 10. None of the compounds synthesized proved to possess an appreciable activity on herpes simplex virus (HSV) or human immunodeficiency virus (HIV).