Effect of further substitutions at 5-, 6-, 7-, or 8-position of 3-[3-(4-methoxyphenyl)-1-hydroxyprop-2-yl]coumarin on phytotoxicity

Derivatives of the coumarin ring in (R)-3-[3-(4-methoxyphenyl)-1-hydroxyprop-2-yl]coumarin 2, which is a lignan structure, were synthesized to clarify their structure–phytotoxicity relationships. The growth-inhibitory activity of the 8-OCH(3) derivative 8 (IC(50)=228 µM) was more potent against the roots of lettuce seedlings than the compound without substituents 2. As for the roots of Italian ryegrass seedlings, the presence of the methoxy group at the 7- or 8-position was extremely effective for inhibiting growth (7-OCH(3) 7: IC(50)=121 µM, 8-OCH(3) 8: 56.7 µM). Methyl derivatives at the 5- or 8-position showed activity levels similar to those of the compound without substituents 2 (5-CH(3) 13: IC(50)=214 µM, 8-CH(3) 16: IC(50)=225 µM). The activities of OH- and F-derivatives were not observed or were lower.