Discovery of New Antifungal Polyketides Cladrioides A-N against Phytopathogenic Fungi from LD-8.

During the search for natural fungicides, 14 new australifungin analogues cladrioides A-S (-) and two known ones ( and ) were obtained from LD-8. Their structures were elucidated by comprehensive analysis of NMR and HRESIMS data, as well as ECD calculations. Compounds and possess a novel 6/6/5-fused tricyclic scaffold. Most of the compounds exhibited remarkable antifungal activities against the tested phytopathogenic fungi. Among them, compounds , , and showed excellent activities with IC values ranging from 1.71 to 16.63 μg/mL. Their inhibitory activities against . and . were higher than that of the commercial fungicide hymexazol. Compound displayed potent antifungal activity against . at 100 μg/mL with an inhibitory rate of 96.82%. The structure-activity relationship of antifungal australifungin analogues was analyzed for the first time. Therefore, our study provides promising candidates for the development of new fungicides for plant protection.