Design, efficient synthesis, and anti-HIV activity of 4'-C-cyano- and 4'-C-ethynyl-2'-deoxy purine nucleosides

Some 4'-C-ethynyl-2'-deoxy purine nucleosides showed the most potent anti-HIV activity among the series of 4'-C-substituted 2'-deoxynucleosides whose 4'-C-substituents were methyl, ethyl, ethynyl and so on. Our hypothesis is that the smaller the substituent at the C-4' position they have, the more acceptable biological activity they show. Thus, 4'-C-cyano-2'-deoxy purine nucleosides, whose substituent is smaller than the ethynyl group, will have more potent antiviral activity. To prove our hypothesis, we planned to develop an efficient synthesis of 4'-C-cyano-2'-deoxy purine nucleosides (4'-CNdNs) and 4'-C-ethynyl-2'-deoxy purine nucleosides (4'-EdNs). Consequently, we succeeded in developing an efficient synthesis of six 2'-deoxy purine nucleosides bearing either a cyano or an ethynyl group at the C-4' position of the sugar moiety from 2'-deoxyadenosine and 2,6-diaminopurine 2'-deoxyriboside. Unfortunately, 4'-C-cyano derivatives showed lower activity against HIV-1, and two 4'-C-ethynyl derivatives suggested high toxicity in vivo.