Compounds which are active against viruses have the following Formulas: ##STR00001## wherein B is 2-aminopurine-9-yl, which may be unsubstituted or substituted in the 6 position with NHR.sub.1, OR.sub.2, or SR.sub.3; R.sub.1 is selected from the group consisting of alkyl, alkenyl, alkynyl, and C.sub.4-18 cycloalkyl, any of which may be optionally substituted with one or more members of the group consisting of hydroxy, halo, amino, acyl, cycloalkyl, heterocyclyl and aryl; R.sub.2 is selected from the group consisting of C.sub.2-18 alkyl, alkenyl, alkynyl, and cycloalkyl, any of which may be branched or unbranched and optionally substituted with one or more members of the group consisting of hydroxy, halo, amino, acyl, cycloalkyl, heterocyclyl, and aryl; and R.sub.3 is selected from the group consisting of alkyl, alkenyl, alkynyl, and cycloalkyl, any of which may be branched or unbranched and optionally substituted with one or more members of the group consisting of hydroxy, halo, amino, acyl, cycloalkyl, heterocyclyl and aryl.