Plant Growth Suppressive Activity of ( R )-3-(7'-Aryl-9'-hydroxyprop-8'-yl)coumarin, Structural Isomer of Z -2-Hydroxybenzylidene-γ-butyrolactone-type Lignan.

3-(7'-Aryl-9'-hydroxyprop-8'-yl)coumarin, which is a structural isomer of a -2-hydroxybenzylidene-γ-butyrolactone-type lignan, was stereoselectively synthesized and subjected to plant growth regulation examination. ()-4'-Methoxyphenyl derivative showed stereospecific plant growth suppressive activity. The significance of the presence of hydroxy group at the 9'-position for the activity was clarified. The effect of the substituent at the 7'-aryl group was also shown. The 3'-methoxy, 4'-methoxy, and 4'-trifluoromethyl derivatives , , and led to the most significant growth suppression of Italian ryegrass roots. The 2'-methoxy derivative and 4'-methoxy derivative provided the most growth suppressive activity against lettuce shoots and roots, respectively.