Antifungal Macrocyclic Trichothecenes from the Insect-Associated Fungus Myrothecium roridum

Three new macrocyclic trichothecenes possessing rare 6'-ketal moieties, roridoxins A-C (1-3), and five known compounds (4-8) were isolated from the insect-associated fungus Myrothecium roridum. Their structures were confirmed by a combination of NMR and HRESIMS data, while their absolute configurations were unambiguously determined by single-crystal X-ray analysis and electronic circular dichroism experiments. Trichothecenes 1 and 3 showed potent antifungal activities against four strains of phytopathogenic fungi. In addition, 1, 3, 5, and 6 were found to significantly inhibit the cell growth of Candida albicans with minimal inhibitory concentration values from 8.8 to 18.5 μg/mL. Moreover, they were able to inhibit the biofilm formation of C. albicans better than the positive control.