New nonacyclic duclauxin derivatives with potent anti-influenza activities from Antarctic fungus Penicillium sp. CPCC 401065.

Four new duclauxin derivatives, spiroduclauxins A-D (1-4) along with six known duclauxin analogs (5-10) have been obtained from Antarctic fungus Penicillium sp. CPCC 401065. Compounds 1-4 were rare nonacyclic duclauxin derivatives fused with [6,5]-spiroketal ring system. Their structures and absolute configurations were determined on the detailed analysis of comprehensive spectroscopic data, electronic circular dichroism, and quantum chemical calculations. Compounds 1-3 showed excellent anti-influenza A virus (IAV) activities with the EC50 values of 0.07, 0.21, 0.50 μM, respectively. Mechanistic studies revealed that 2 inhibits IAV replication by targeting the viral RNA transcription stage 2-6 h post-infection, without affecting early viral ribonucleoprotein (RNP) nuclear import. Further investigation using an IAV minigenome system confirmed that 2 suppressed viral RNA accumulation in a dose-dependent manner, correlating with a significant reduction in the protein levels of the RNA-dependent RNA polymerase (RdRp) subunits PA and PB2, while PB1 and NP remained unchanged, indicating targeted disruption of the polymerase complex. Broad-spectrum evaluation demonstrated that 2 effectively inhibits multiple influenza strains, including H1N1 (EC50: 0.16-0.36 μM), H3N2 (EC50: 0.16 μM), and influenza B viruses (EC50: 1.32-2.31 μM). In contrast, 2 showed only marginal or no inhibitory activity against other RNA viruses (HCoV-OC43, EV71, and Zika virus), confirming its selective anti-influenza mechanism. Collectively, this study provides the first report of duclauxin derivatives as broad-spectrum anti-influenza agents that function by disrupting the stability of the viral RdRp complex, thereby inhibiting viral RNA transcription and replication.