Prodrugs of Formula I, their uses, their intermediates, and their method of manufacture are described: ##STR00001## wherein: M and V are cis to one another and MPO.sub.3H.sub.2 is a phosphonic acid selected from the group consisting of 9-(2-phosphonylmethoxyethyl)adenine, (R)-9-(2-phosphonylmethoxy propyl)adenine, 9-(2-phosphonylmethoxyethyl)guanine, 9-(2-phosphonylmethoxy ethyloxy)adenine, 9-(2-phosphonylmethoxyethyl)-2,6-diaminopurine, (S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine, (S)-9-(3-hydroxy-2-phosphonylmethoxypropyl)adenine, 9-(3-hydroxy-2-phosphonylmethoxypropyl)guanine, and (S)-9-(3-fluoro-2-phosphonyl methoxypropyl)adenine; V is selected from a group consisting of phenyl, 2-pyridyl, 3-pyridyl, 4-pyridyl, 2-furanyl, 3-furanyl, 2-thienyl, and 3-thienyl, all optionally substituted with 1-3 substituents selected from a group consisting of F, Cl, Br, C1-C3 alkyl, CF.sub.3 and OR.sup.6; R.sup.6 is selected from the group consisting of C1-C3 alkyl, and CF.sub.3; and pharmaceutically acceptable salts thereof.