Discovery of Pyridyl-Benzothiazol Hybrids as Novel Protoporphyrinogen Oxidase Inhibitors via Scaffold Hopping

In order to discover novel protoporphyrinogen oxidase (PPO) inhibitors with excellent herbicidal activity, a series of structurally novel 6-(pyridin-2-yl) benzothiazole derivatives were designed based on the scaffold hopping strategy. The in vitro experiments demonstrated that the newly synthesized compounds exhibited noteworthy inhibitory activity against Arabidopsis thaliana PPO (AtPPO), with IC50 values ranging from 0.06 to 1.36 μM. Preliminary postemergence herbicidal activity tests and crop safety studies indicated that some of our compounds exhibited excellent herbicidal activity and crop safety. For instance, compound (rac)-7as exhibited superior herbicidal activities to commercially available flumioxazin (FLU) and saflufenacil (SAF) at all the tested concentrations and showed effective herbicidal activities even at a dosage as low as 18.75 g ai/ha. Meanwhile, compound (rac)-7as showed good crop safety for wheat at a dosage as high as 150 g of ai/ha. Although the absolute configuration of compound 7as has no obvious effect on its herbicidal activity, compound (R)-7as showed a slightly higher crop safety than compound (S)-7as. Molecular simulation studies of Nicotiana tabacum PPO (NtPPO) and our candidate compounds showed that the benzothiazole moiety of compounds (R)-7as or (S)-7as formed multiple π–π stacking interactions with FAD, and the pyridine ring generated π–π stacking with Phe-392. Our finding proved that the pyridyl–benzothiazol hybrids are promising scaffolds for the development of PPO-inhibiting herbicides.