Structure-Antifungal Activity Relationship of Fluorinated Dihydroguaiaretic Acid Derivatives and Preventive Activity against Alternaria alternata Japanese Pear Pathotype.

The structure-activity relationship of the antifungal fluorinated dihydroguaiaretic acid derivatives was evaluated. Some of the newly synthesized lignan compounds were found to show higher antifungal activity against phytopathogenic fungi such as Alternaria alternata (Japanese pear and apple pathotypes) and A. citri than the lead compound, 3-fluoro-3'-methoxylignan-4'-ol (3). The broad antifungal spectrum of 3'-hydroxyphenyl derivative 16 was observed, and the 3'-fluoro-4'-hydroxyphenyl derivative 38 was found to show the highest activity against the A. alternata Japanese pear pathotype, with an EC50 value of 11 μM. The preventive effect of the potent lignan on the infection of A. alternata in the Japanese pear's leaves was also shown.