In hopes of finding better therapeutic agents for AIDS, a wide variety of sugar-modified nucleosides have been prepared. Thionucleosides in which oxygen of the sugar ring has been replaced by sulfur have shown interesting biological a~ tivities.“~ It has been demonstrated that 4 '-thioadenosine, which is a potent inhibitor of S-adenosylhomocysteine hydrolase, e rapidly undergoes phosphorylation to ita triphosphate. The resistance of ...