SAR Exploration of Tight-Binding Inhibitors of Influenza Virus PA Endonuclease

Significant efforts have been reported on the development of influenza antivirals including inhibitors of the RNA-dependent RNA polymerase PA N-terminal (PA N ) endonuclease. Based on recently identified, highly active metal-binding pharmacophores (MBPs) for PA N endonuclease inhibition, a fragment-based drug development campaign was pursued. Guided by coordination chemistry and structure-based drug design, MBP scaffolds were elaborated to improve activity and selectivity. Structure–activity relationships were established and used to generate inhibitors of influenza endonuclease with tight-binding affinities. The activity of these inhibitors was analyzed using a fluorescence-quenching-based nuclease activity assay, and binding was validated using differential scanning fluorometry. Lead compounds were found to be highly selective for PA N endonuclease against several related dinuclear and mononuclear metalloenzymes. Combining principles of bioinorganic and medicinal chemistry in this study has resulted in some of the most active in vitro influenza PA N endonuclease inhibitors with high ligand efficiencies.