Antimicrobial Dolabellanes and Atranones from a Marine-Derived Strain of the Toxigenic Fungus Stachybotrys chartarum

Three new dolabellane-type diterpenoids (13) and three new atranones (46) were isolated and identified from a marine-derived strain of the toxigenic fungus Stachybotrys chartarum. The planar and relative structures of 16 were elucidated using extensive spectroscopic methods, and their absolute configurations were fully confirmed via single-crystal X-ray diffraction analysis. Structurally, compounds 2 and 3 have a 1,14-seco dolabellane-type diterpenoid skeleton; compound 4 is the first C23 atranone featuring a propan-2-one motif linked to a dolabellane-type diterpenoid by a carbon–carbon bond; compound 5 represents the first example of a C24 atranone with a 2-methyltetrahydrofuran-3-carboxylate motif fused to a dolabellane-type diterpenoid at C-5–C-6. In an in vitro antimicrobial activity assay, compound 2 was active against Acinetobacter baumannii and Enterococcus faecalis with MIC values of 16 and 32 μg/mL, respectively, while compound 4 exhibited significant inhibitory activities against Candida albicans, Enterococcus faecalis, and methicillin-resistant Staphylococcus aureus (MRSA) with MIC values of 8, 16, and 32 μg/mL, respectively.