Sesquiterpenoids with Phytotoxic and Antifungal Activities from a Pathogenic Fungus Aspergillus alabamensis

Five new carotane sesquiterpenoids (asperalacids A–E (1–5)), one new tricyclic sesquiterpenoid (4-hydroxy-5(6)-dihydroterrecyclic acid A (6)), and two known analogues (7–8) were obtained from a seagrass-derived fungus Aspergillus alabamensis, which was speculated to be a phytopathogenic fungus, isolated from the necrotic leaves of Enhalus acoroides. The structures of 1–6 were established by a combination of spectroscopic methods, including comprehensive NMR analysis, mass spectrometry, conformational analysis, NMR computational methods, and ECD calculations. Compound 4, with higher inhibitory activity on wheat (Triticum aestivum L.) root and shoot elongation than the positive control terbutryn, a broad-spectrum systemic herbicide, is a new natural plant growth inhibitor. Compound 5, belonging to the rare glycosylated sesquiterpenoid class, represents the first example of glycosylated carotane sesquiterpenoid whose sugar moiety was identified as α-d-glucose. Compounds 1–4 and 6 displayed weak to potent antimicrobial activity against the plant pathogenic fungi Fusarium oxysporum, Fusarium graminearum, and Penicillium italicum and the Gram-positive bacteria Bacillus subtilis and Staphylococcus aureus.