Oxalierpenes A and B, Unusual Indole-Diterpenoid Derivatives with Antiviral Activity from a Marine-Derived Strain of the Fungus Penicillium oxalicum

Oxalierpenes A and B (1 and 2), two unusual indole-diterpenoid derivatives, were obtained from the marine-derived fungus Penicillium oxalicum. The absolute configurations of 1 and 2 were elucidated by calculated TDDFT ECD and DP4plus methods. Oxalierpene A (1) represents the first indole-diterpenoid derivative with a five-membered ring of 4-hydroxy-5,5-dimethyldihydrofuran-3-one as a side chain. Oxalierpene B (2) has a unique 6/5/6/5/5/6/6/5/5 ring system. Compounds 1 and 2 showed antiviral activity against the H1N1 virus and respiratory syncytial virus (RSV), with IC50 values ranging from 2.8 to 9.4 μM.