Geministatins: new depside antibiotics from the fungus Austroacremonium gemini

Two new depside antibiotics, geministatins A (1) and B (2), were isolated from the fungus Austroacremonium gemini MST-FP2131 (Sordariomycetes, Ascomycota), which was recovered from rotting wood in the wet tropics of northern Australia. The structures of the geministatins were elucidated by detailed spectroscopic analysis, chemical degradation and comparison with literature values. Chemical degradation of 1 and 2 yielded three new analogues, geministatins C–E (3–5), as well as a previously reported compound dehydromerulinic acid A (6). Compounds 1, 2 and 6 exhibited antibacterial activity against the Gram-positive bacteria Bacillus subtilis (MIC 0.2–1.6 µg mL⁻¹) and Staphylococcus aureus (MIC 0.78–6.3 µg mL⁻¹), including methicillin-resistant S. aureus (MRSA), while 4 exhibited antifungal activity against the yeast Saccharomyces cerevisiae (MIC 13 µg mL⁻¹).