Compounds which are active against viruses have the following Formulas: wherein B is 2-aminopurine-9-yl, which may be unsubstituted or substituted in the 6 position with NHR1, OR2, or SR3; R1 is selected from the group consisting of alkyl, alkenyl, alkynyl, and C4-18 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; R2 is selected from the group consisting of C2-18 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 R3 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.