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

Abstract

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: EC₅₀=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′-CF₃ and 4′-CF₃ derivatives, 39 and 40, respectively, had the lowest EC₅₀ 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 OCH₃ or CH₃ group at the 5-position accelerated the activity, as the (4′-OCH₃, 5-OCH₃) derivative 41 and (4′-OCH₃, 5-CH₃) derivative 45 were, respectively, 4–5 times more potent than the 4′-OCH₃ derivative (S)-5.