Design, synthesis and herbicidal activity of novel N-(5-(3,5-dinitrophenyl)thiazol-2-yl)-2-phenoxyacetamide compounds

In order to discover highly active herbicidal compounds, 29 derivatives of N-(5-(3,5-dinitrophenyl)thiazol-2-yl)-2-phenoxyacetamide (Ⅵaa-Ⅵbc) were synthesized and characterized by ¹H NMR,¹³C NMR, and HRMS. The spatial configuration of compound Ⅵaa was determined using X-ray single crystal diffraction. Barnyard grass and lettuce were used as target organisms for herbicidal activity testing using a Petri dish method. The results showed that most of the target compounds exhibited inhibition rates of over 70% against barnyard grass and lettuce at a concentration of 100 mg/L. Stem and leaf spray experiments demonstrated that compounds Ⅵam, Ⅵas, Ⅵat, Ⅵav, and Ⅵaw inhibited the fresh weight of dicotyledonous plant lettuce by over 80% at a concentration of 375 g/hm², with compound Ⅵas showing 100% inhibition. Crop safety experiments have demonstrated that compound Ⅵas at a dosage of 750 g/hm² causes varying degrees of phytotoxicity to maize, sorghum, rice, soybeans, flax, and rapeseed. However, the phytotoxicity to sorghum is the lowest among these crops and notably lower than the control herbicide 2,4-D. The results of the transmission electron microscope analysis showed that treatment of lettuce leaves with a concentration of 18.17 g/hm² for 72 hours, the chloroplast membrane of the leaves twisted and deformed, the thylakoid layers of the chloroplasts were disorganized, and partial vesicles underwent rupture. Enzyme activity measurement results showed that compound Ⅵas exhibited a stimulatory effect followed by suppression on catalase (CAT) and hydrogen peroxide (H₂O₂). It can be inferred that compound VIas inhibits the normal growth of lettuce by damaging the chloroplast structure and affecting the activity of CAT and H₂O₂, showing an initial promotion followed by inhibition effect.