Obtaining new flavanones exhibiting antifungal activities by methyltrioxorhenium-catalyzed epoxidation–methanolysis of flavones

New 3-hydroxy-2-methoxyflavanones have been obtained through epoxidation–methanolysis of the corresponding flavone with urea–hydrogen peroxide (UHP)/methyltrioxorhenium (CH3ReO3, MTO) catalytic system in methanol as nucleophilic solvent. After acetylation of the reaction mixtures, the corresponding cis- and trans-3-acetoxy-2-methoxyflavanones have been isolated and characterized by spectroscopic analyses. Their antifungal activity has been tested in vitro against three fungal strains of common saprotrophic soil and seed fungi, such as Trichoderma koningii, Fusarium solani and Cladosporium herbarum, potentially pathogenic for humans. Some aspects of the structure–activity relationship of the most active compounds have been evaluated. The mycelial growth of T. koningii and C. herbarum has been totally inhibited from cis-3-acetoxy-2,6-dimethoxyflavanone 7c and cis-3-acetoxy-2,7-dimethoxyflavanone 13c at the lowest concentration (0.5×10−4 M).