Talarergosteroids A–C: Three Unusual Steroid-Polyketone Conjugates with Antifungal Activity from a <i>Kandelia Obovata</i> Derived Fungus <i>Talaromyces</i> sp

Three previously undescribed steroid-polyketone conjugates, talarergosteroids A-C (<b>1</b>-<b>3</b>), together with talarergosteroid D (<b>4</b>), which was first identified from a natural source, were isolated from a <i>Kandelia Obovata</i> derived fungus <i>Talaromyces</i> sp. SCNU-F0041. Compounds <b>1</b> and <b>2</b> bear a complicated 6/6/6/5/6/6 hexacyclic ring system characterized by an oxaspiro[5.5]undecane architecture. Compound <b>3</b> possesses a benzofuran moiety substituted at C-3 in ergosterol. The structures of the new compounds were identified by comprehensive spectroscopic analysis, X-ray diffraction, and electronic circular dichroism (ECD) calculation. Talarergosteroid B (<b>2</b>) showed significant inhibitory activity against the agricultural plant pathogen <i>Fusarium oxysporum</i> f. sp. <i>lycopersici</i> (MIC = 0.78 μg/mL), outperforming the positive control carbendazim (MIC = 1.56 μg/mL). Preliminary research disclosed that compound <b>2</b> may inhibit the spore germination progress, malform the fungal mycelium, and damage the organelle. These results indicate that compound <b>2</b> could be a potential fungicidal lead compound against <i>Fusarium oxysporum</i> f. sp. <i>lycopersici</i>.