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

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