Design, synthesis, and evaluation of polycyclic pyridone derivatives as potent influenza inhibitors

Pandemics caused by influenza viruses remain a serious public health concern worldwide, despite the approval of many antiviral agents, in which baloxavir marboxil (BXM) as the first cap-dependent endonuclease (CEN) inhibitor demonstrates excellent efficacy. Clinical trials have shown that BXM faces emerging resistance (e.g., I38T mutation), compromising its efficacy against variants and urging the development of more effective inhibitors. In this study, a series of novel substituted polycyclic pyridone derivatives were designed and synthesized by replacing the dibenzothiepin scaffold of baloxavir with a dibenzocycloheptene to improve antiviral activities and reduce stereochemical complexity. The lead compound KJ001-12a exhibited potent antiviral activities against influenza A and B strains. Meanwhile, molecular docking and molecular dynamics simulations provided supportive evidence that compounds with a dibenzocycloheptene scaffold may be less affected by the hydrophobic interactions induced by the I38T mutation, which is consistent with the results of the cytopathic effect assay. By contrast, structure-activity relationship (SAR) analysis revealed that chiral analogs require chiral resolution for optimal efficacy, and that the R,S diastereomer is the most potent configuration among these chiral derivatives, though these chiral derivatives showed slightly reduced activity compared to the achiral KJ001-12a. Influenza polymerase inhibitory activity assay and quantitative real-time PCR assays confirmed that KJ001-12a significantly inhibits the activity of RNA-dependent RNA polymerase and reduce viral M2 mRNA and vRNA expression. Furthermore, KJ001-12a demonstrated favorable bioavailability (F = 40.25% in rats) and metabolic stability, outperforming baloxavir in pharmacokinetic profiles. These findings highlight KJ001-12a as a promising candidate with favorable resistance and pharmacokinetic properties worthy of further development.