Design, synthesis, and biological evaluation of novel penindolone derivatives as potential inhibitors of hemagglutinin-mediated membrane fusion.

Development and design of anti-influenza drugs with novel mechanisms is of great significance to combat the ongoing threat of influenza A virus (IAV). Hemagglutinin (HA) is regarded as a potential target for the therapy of IAV. Our previous research led to the discovery of penindolone (PND), a new diclavatol indole adduct, as an HA targeting leading compound exhibited anti-IAV activity. To enhance the bioactivity and understand the structure-activity relationships (SARs), 65 PND derivatives were designed and synthesized, and the anti-IAV activities as well as the HA targeting effects were systematically investigated in this study. Among them, compound 5g possessed high affinity to HA and was more effective than PND in terms of inhibiting HA-mediated membrane fusion. Compound 5g may act on the trypsin cleavage site of HA to exhibit a strong inhibition on membrane fusion. In addition, oral administration of 5g can significantly reduce the pulmonary virus titer, attenuate the weight loss, and improve the survival of IAV-infected mice, superior to the effects of PND. These findings suggest that the HA inhibitor 5g has potential to be developed into a novel broad-spectrum anti-IAV agent in the future.