Inhibitory Activity of N-Substituted-2-piperidones with a 1,4-Benzodioxan Ring on Germination of Barnyardgrass

A variety of 3-substituted-2-piperidones and related compounds were evaluated for their activity to inhibit germination of barnyardgrass (Echinochloa utilis) seeds. 3-[1-(1,4-Benzodioxan-6-yl)-1-hydroxymethyl]-N-benzyl-2-piperidone (22) showed extremely high inhibitory activity. Studies on the structure-activity relationship indicated that a 1,4-benzodioxan ring, a hydroxy substituent at the α-position of the benzyl group and a 2-piperidone ring were significant for higher activity. Of the compounds tested, 3-[1-(l,4-benzodioxan-6-yl)-l-hydroxymethyl]-N-cinnamyl-2-piperidone (55) was the most effective, showing more than 90% germination inhibition at 1 nM. In both compounds 22 and 55, only erythro isomers inhibited germination of barnyardgrass seeds, while threo isomers were inactive even at 1 µM. This result indicated that the stereochemistry of 1,4-benzodioxan moiety in the erythro isomer, which is fixed by an intramolecular hydrogen bond between the hydroxy group and the carbonyl group, was essential for activity. The erythro-22 and 55 were less active against rice seeds when compared to barnyardgrass.