In the course of study to develop new herbicidal compounds, we found that some 4-thiazolone derivatives possessed herbicidal activity against several paddy weeds. As a result of a structure-activity relation study, 5-(2-chloroethyl)-5-methyl-2-(3-methyl-2,3-dihydro-1,4-benzoxazin-4-yl)-4-thiazolone (CMT) was selected as one of the potential herbicides for rice. CMT showed potent herbicidal activity against paddy weeds, especially barnyardgrass (Echinochloa oryzicola) and three-square grass (Scirpus juncoides). The herbicidal activity of CMT appeared to be caused by specific inhibition in the growing tissues. Electron microscopic observations of CMT-treated barnyardgrass revealed that exposure to 10 μM CMT for 4 hr caused swelling of the endoplasmic reticulum (ER) and Golgi apparatus, the separation of plasma membranes from cell walls, and an accumulation of small vesicles in the plasma membrane-cell wall interspace. These findings suggest that CMT acts primarily as an inhibitor of the secretory pathway, resulting in a dysfunction of cell wall biosynthesis.
