2-, 6-, And 8-alkylated (methyl, ethyl, and vinyl) adenosine analogues were synthesized by a palladium-catalyzed cross-coupling of a tetraalkyltin with the halogenated purine nucleosides. The synthesis of the 8-substituted analogues was accomplished using a transient protection procedure. The 6-alkylated-9-beta-D-ribofuranosylpurines as well as 2-ethyladenosine were cytotoxic at relatively low concentrations (0.8-10 micrograms/mL). 8-Methyladenosine was a potent and selective inhibitor of vaccinia virus, whereas 8-ethyl- and 8-vinyladenosine were specifically inhibitory to respiratory syncytial virus. 8-Vinyladenosine displayed particular activity against herpes simplex virus (type 1).