System-oriented optimization of multi-target 2,6-diaminopurine derivatives: Easily accessible broad-spectrum antivirals active against flaviviruses, influenza virus and SARS-CoV-2.

The worldwide circulation of different viruses coupled with the increased frequency and diversity of new out- breaks, strongly highlight the need for new antiviral drugs to quickly react against potential pandemic pathogens. Broad-spectrum antiviral agents (BSAAs) represent the ideal option for a prompt response against multiple viruses, new and re-emerging. Starting from previously identified anti-flavivirus hits, we report herein the identification of promising BSAAs by submitting the multi-target 2,6-diaminopurine chemotype to a system-oriented optimization based on phenotypic screening on cell cultures infected with different viruses. Among the synthesized compounds, 6i showed low micromolar potency against Dengue, Zika, West Nile and Influenza A viruses (IC50 = 0.5–5.3 μM) with high selectivity index. Interestingly, 6i also inhibited SARS-CoV-2 replication in different cell lines, with higher potency on Calu-3 cells that better mimic the SARS-COV-2 infection in vivo (IC50 = 0.5 μM, SI = 240). The multi-target effect of 6i on flavivirus replication was also analyzed in whole cell studies (in vitro selection and immunofluorescence) and against isolated host/viral targets.