Design, Synthesis, and Antifungal Activity of Polyacetylenic Alcohol Derivatives and Stereoisomers against Phytopathogenic Fungi

Falcarindiol is active against phytopathogenic fungi. In the present study, racemic falcarindiol analogs (8a–8q) were designed, synthesized, and tested for their activities against eight economically significant phytopathogenic fungal species. The compound 8o displayed the best antifungal activities and up to 54.6-fold in vitro potency improvement against Phytophthora capsici than the natural product stipudiol. Its half-maximum effective concentrations ranged from 4 to 23 μg/mL against all tested fungal species. Racemic 8o was 195-fold more potent than the fungicide carbendazim against P. capsici in vitro. The isomer (1S, 6S)-8o exhibited an EC50 of 1.10 and 2.70 μg/mL against Monilia fructigena and P. capsici, respectively, which was 47 and 11 times lower than (1R, 6S)-8o and (1S, 6R)-8o. In addition, in vivo bioassay results showed that (1S, 6S)-8o had high antifungal activity against infection of M. fructigena and P. capsici to apricot and pepper fruits and pepper plants, which the efficacy was similar or better than carbendazim. The high potency and selectivity of 8o stereoisomers against the phytopathogens warrant an interest in elucidating the molecular target for fungicide development.