Combined work by some of us has led to the recent synthesis of aza-C-nucleosides 1 and 2 (“immucillins”). These compounds, and their 5'-monophosphate esters, are extremely powerful inhibitors of human purine nucleoside phosphorylase (PNP), protozoan nucleoside hydrolases, and purine phosphoribosyltransferases. 1 Inhibitors of PNP have become targets for drug design, because they are expected to selectively control the proliferation of ...