Ascandinines A–D, Indole Diterpenoids, from the Sponge-Derived Fungus Aspergillus candidus HDN15-152

Four new indole diterpenoids, ascandinines A–D (1–4), were isolated from an Antarctic sponge-derived fungus Aspergillus candidus HDN15-152. Their structures, including absolute configurations, were established based on NMR data, computational calculations, and biosynthetic considerations. Ascandinine A (1) possesses an unprecedented 2-oxabicyclo[2.2.2]­octan-3-ol motif embedded in a pentacyclic ring system, while compounds 2–4 represent a rare type of indole diterpenoid featuring the 6/5/5/6/6/6/6-fused ring system. Compound 3 displayed anti-influenza virus A (H1N1) activity with an IC50 value of 26 μM, while compound 4 showed cytotoxicity against HL-60 cells with an IC50 value of 7.8 μM.