Synthesis and Herbicidal Activities of Novel Substituted Acetophenone Oxime Esters of Pyrithiobac

A series of substituted acetophenone oxime esters of Pyrithiobac were synthesized as potential herbicides. The structures of the synthesized new compounds were confirmed by H-1 NMR, C-13 NMR, HRMS, and X-ray single-crystal diffraction (XRD). The pre-emergence and post-emergence herbicidal activity studies show that 4-CF3 (6 f), 4-NO2 (6 i), 4-NH2 (6 j), 4-F (6 l), and 2,4-2OCH(3) (6 s) substituted acetophenone oxime esters of Pyrithiobac exhibit better pre-emergence and post-emergence herbicidal activities against monocotyledon and dicotyledon weeds than other synthesized new compounds. In pre-emergence herbicidal activity study, 6 f, 6 i, 6 j, 6 l, and 6 s exhibit similar herbicidal activities against monocotyledon and dicotyledon weeds as compared to Staple (Pyrithiobac-sodium). In post-emergence herbicidal activity study, 6 f, 6 i, 6 j, 6 l, and 6 s exhibit similar herbicidal activities against dicotyledon weeds and better herbicidal activities against monocotyledon weeds as compared to Staple. Compounds 6 i and 6 l with high herbicidal activities and similar binding mode with acetolactate synthase as compared to Staple were further subjected to crop safety study. The results show that the safety of compound 6 l to cotton is as good as Staple and better than 6 i. The present work indicates that compound 6 l may serve as a new candidate for potential herbicides.