Biological characterization of fusapyrone and deoxyfusapyrone, two bioactive secondary metabolites of Fusarium semitectum

Fusapyrone (1) and deoxyfusapyrone (2), two alpha-pyrones originally isolat ed from rice cultures of Fusarium semitectum, were tested in several biolog ical assays. Compounds 1 and 2 showed considerable antifungal activity agai nst several plant pathogenic and/or mycotoxigenic filamentous fungi, althou gh they were inactive toward yeasts isolated from plants and the Gram-posit ive bacterium Bacillus megaterium in disk diffusion assays. Compound 1 was consistently more active than 2. Among the tested fungi, Fusarium species w ere the least sensitive to the two pyrones, while Alternaria alternata, Asc ochyta rabiei, Aspergillus flavus, Botrytis cinerea, Cladosporium cucumerin um, Phoma tracheiphila, and Penicillium verrucosum were the most sensitive. Compounds 1 and 2 also showed good inhibitory activity toward agents of hu man mycoses. Aspergilli were the most sensitive, while some species-specifi c variability was found among the Candida spp. In an Artemia salina larvae bioassay, 1 was not toxic at the highest concentration tested (500 mu M), w hereas the LC50 of 2 was 37.1 mu M (21.8 mu g/mL). Neither 1 nor 2 was phyt otoxic in a panel of assays that monitored plant-cell toxicity, as well as wilt-, chlorosis-, and necrosis-inducing activity. Moreover, 2 stimulated t he root elongation of tomato seedlings at doses of 10 and 100 mu M. In cons ideration of the biological activities evidenced in this study, 1 and 2 app ear to be potential candidates for biotechnological applications, as well a s good models for studies on mechanism(s) of action and structure-activity relationships.