Highly Conjugated Ergosterols with Anti‐Influenza Virus Activity from the Marine‐Derived Fungus Eutypella sp. F0219

one rare 15‐nor‐cadinane sesquiterpenoid (1), one new chromene amide derivative (2), and one new highly conjugated ergosterol steroid (3), along with three known compounds (4–6) were isolated from the marine‐derived fungus Eutypella sp. F0219. Their chemical structures including absolute configurations were established by HR‐ESIMS, extensive 1D and 2D NMR investigations, and electronic circular dichroism (ECD) calculations. All compounds were evaluated for their anti‐influenza A virus and anti‐influenza B virus activities against the A/PR/8/34 (H1N1), ZX1109 (H1N1, oseltamivir resistant virus), HK68 (H3N2), and B/Florida/78/2015 strains. Compounds 3 and 4 showed significant antiviral activities against those four virus strains with EC50 values ranging from 2.07 to 11.3 μM. Most notably, compound 3 exhibited potent anti‐influenza B virus activity against B/Florida/78/2015 strain with EC50 value of 2.27±1.76 μM, versus the postive control (oseltamivir, EC50 = 7.14±1.94 μM).