Abstract: Described herein are novel 6-alkylthio and 6-arylalkylthio purine 3',5' cyclic nucleotides variously exhibiting adenyl cyclase and (in animal studies) tumor inhibitory properties, interferon potentiation, antiviral activity, and the ability to activate adenosine 3',5'-cyclic phosphate-dependent protein kinase while enjoying resistance to phosphodiesterase hydrolysis superior to that of its naturally occuring analog. The compounds are obtained by alkylation of the corresponding 6-thio nucleotide, which is in turn provided by a novel synthetic route.