Structure-activity relationship of the aromatic moiety of 6-substituted 5,6-dihydro-2-pyrone to find the novel compound showing higher plant growth inhibitory activity.

In the course of our research on the structure-activity relationship of 5,6-dihydro-2H-pyran-2-one, (S)-6-[(R)-2-hydroxy-6-(4-fluorophenyl)hexyl]- 5,6-dihydro-2H-pyran-2-one was found to show 2-3-fold more potent plant growth inhibitory activity against Italian ryegrass shoots (IC50 = 95 μM) and roots (IC50 = 17 μM) than compound bearing unsubstituted phenyl group. The small electron withdrawing atom at 4-position of the benzene ring caused the higher activity.