Discovery of anti-phytopathogenic fungal activity of a new type of (S)-coumarin bearing a phenylpropanoid unit at the 3-position.

The enantiospecific anti-phytopathogenic fungal activity of a new type of coumarin bearing a phenylpropanoid unit at the 3-position was found. (S)-3-[1-Methoxy-3-(4-methoxyphenyl)prop-2-yl]coumarin ((S)-5: EC(50)=16.5 µM) was 30 times more effective than the (R)-form against the Alternaria alternata Japanese pear pathotype. Derivatives bearing different substituents on the 7'-aromatic ring and the coumarin ring were synthesized to discover the more potent compounds. The 3'-CF(3) and 4'-CF(3) derivatives, 39 and 40, respectively, had the lowest EC(50) values (1-2 µM) in this project, suggesting that the size of the electron-withdrawing and hydrophobic substituents at these positions gave an advantage. On the coumarin ring, the presence of the OCH(3) or CH(3) group at the 5-position accelerated the activity, as the (4'-OCH(3), 5-OCH(3)) derivative 41 and (4'-OCH(3), 5-CH(3)) derivative 45 were, respectively, 4-5 times more potent than the 4'-OCH(3) derivative (S)-5.