Synthesis of a 6-methyl-7-deaza analogue of adenosine that potently inhibits replication of polio and dengue viruses

Bioisosteric deaza analogues of 6-methyl-9-β-d-ribofuranosylpurine, a hydrophobic analogue of adenosine, were synthesized and evaluated for antiviral activity. Whereas the 1-deaza and 3-deaza analogues were essentially inactive in plaque assays of infectivity, a novel 7-deaza-6-methyl-9-β-d- ribofuranosylpurine analogue, structurally related to the natural product tubercidin, potently inhibited replication of poliovirus (PV) in HeLa cells (IC₅₀ = 11 nM) and dengue virus (DENV) in Vero cells (IC₅₀ = 62 nM). Selectivity against PV over cytotoxic effects to HeLa cells was >100-fold after incubation for 7 h. Mechanistic studies of the 5′-triphosphate of 7-deaza-6-methyl-9-β-d-ribofuranosylpurine revealed that this compound is an efficient substrate of PV RNA-dependent RNA polymerase (RdRP) and is incorporated into RNA mimicking both ATP and GTP.