Protoporphyrinogen oxidase (PPO, E.C. 1.3.3.4) is known as a key action target for several structurally diverse herbicides. As a continuation of our research work on the development of new PPO-inhibiting herbicides, a series of novel 3-(2′-halo-5′-substituted-benzothiazol-1′-yl)-1-methyl-6-(trifluoromethyl)pyrimidine-2,4-diones 9 were designed and synthesized. The bioassay results indicated that a number of the newly synthesized compounds exhibited higher inhibition activity against tobacco PPO (mtPPO) than the controls, saflufenacil and sulfentrazone. Compound 9F-5 was ident...