New acylphloroglucinol-sesquiterpenoid adducts with antiviral activities from Dryopteris atrata

Seven new 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 NMR-DP4 + probability analysis and ECD calculations. These structures represent a rarer subclass of carbon skeleton of acylphloroglucinol-sesquiterpenoid adducts with a furan ring linking the acylphloroglucinol and sesquiterpenoid moieties. Among them, compounds 1–6 are the first examples of acylphloroglucinol-sesquiterpenoid adducts with dimeric acylphloroglucinol incorporated into the aristolane- or rulepidanol-type sesquiterpene, and compound 7 features a hydroxylated monomeric acylphloroglucinol motif. A preliminary evaluation of their antiviral activities showed that compounds 1–6 displayed stronger activities against respiratory syncytial virus (RSV) with IC₅₀ values ranging from 0.75 to 3.12 μmol·L⁻¹ than the positive control of ribavirin.