New acylphloroglucinol-sesquiterpenoid adducts with antiviral activities from Dryopteris atrata

Seven novel acylphloroglucinol-sesquiterpenoid adducts, designated as dryatraols J–P (1–7), were isolated from the rhizomes of Dryopteris atrata (Wall. ex Kunze) Ching. The structures, including absolute configurations, were elucidated using comprehensive spectroscopic data, calculated (¹³C Nuclear Magnetic Resonance-Diastereotopic Probability Assignment Plus) ¹³C NMR-DP4+ probability analysis, and ECD calculations. These structures represent a rare subclass of carbon skeleton of acylphloroglucinol-sesquiterpenoid adducts with a furan ring connecting the acylphloroglucinol and sesquiterpenoid moieties. Notably, compounds 1–6 are the first reported examples of acylphloroglucinol-sesquiterpenoid adducts with dimeric acylphloroglucinol incorporated into the aristolane- or rulepidanol-type sesquiterpene, while compound 7 features a hydroxylated monomeric acylphloroglucinol motif. A preliminary evaluation of their antiviral activities revealed that compounds 1–6 exhibited more potent activities against respiratory syncytial virus (RSV) with IC₅₀ values ranging from 0.75 to 3.12 μmol·L⁻¹ compared to the positive control, ribavirin.