Synthesis and biological evaluation of novel (thio)semicarbazone-based benzimidazoles as antiviral agents against human respiratory viruses

Respiratory RNA viruses are responsible for recurrent acute respiratory illnesses that stillrepresent a major medical need. Previously we developed a large variety of benzimidazole derivativesable to inhibit these viruses. Herein, two series of (thio)semicarbazone- and hydrazone-basedbenzimidazoles have been explored, by derivatizing 5-acetyl benzimidazoles previously reported by us,thereby evaluating the influence of the modification on the antiviral activity. Compounds6,8,16and17,bearing the 5-(thio)semicarbazone and 5-hydrazone functionalities in combination with the 2-benzylring on the benzimidazole core structure, acted as dual inhibitors of influenza A virus and humancoronavirus. For respiratory syncytial virus (RSV), activity is limited to the 5-thiosemicarbazone(25) and 5-hydrazone (22) compounds carrying the 2-[(benzotriazol-1/2-yl)methyl]benzimidazolescaffold. These molecules proved to be the most effective antiviral agents, able to reach the potencyprofile of the licensed drug ribavirin. The molecular docking analysis explained the SAR of thesecompounds around their binding mode to the target RSV F protein, revealing the key contacts forfurther assessment. The herein-investigated benzimidazole-based derivatives may represent valuablehit compounds, deserving subsequent structural improvements towards more efficient antiviralagents for the treatment of pathologies caused by these human respiratory viruses.