Design, synthesis and biological activity of novel (Z)-N-(2,6-dioxo-5-phenyl-1,2,3,5,6,7,8,9-octahydro-4H-chromeno2,3-dpyrimidin-4-ylidene)-4-methylbenzenesulfonamide compounds

To discover new and highly effective herbicidal compounds, 29 (Z)-N-(2,6-dioxo-5-phenyl-1,2,3,5,6,7,8,9-octahydro-4H-chromeno2,3-dpyrimidin-4-ylidene)-4-methylbenzenesulfonamide derivatives (Ⅵaa-Ⅵbc) were designed and synthesized. The structures of these compounds were characterized by melting point, ¹H NMR, ¹³C NMR, and HRMS. The spatial configuration of compound Ⅵan was determined using X-ray single crystal diffraction. The herbicidal activity of these compounds was tested using the plate method with barnyard grass and piemarker as target weeds. The target compounds exhibited inhibition rates of over 70% against barnyard grass, with compound Ⅵak showing 85% inhibition at a concentration of 200 mg/L, but the inhibitory effect on the piemarker was slightly lower. The inhibitory medium concentration (IC₅₀) of compound Ⅵak on seed germination of barnyard grass was 113 mg/L. Crop safety experiments showed that compound Ⅵak at a dosage of 500 or 1000 mg/L caused varying degrees of phytotoxicity to maize, rice, and rapeseed. However, the phytotoxicity to soybean was the lowest among these crops and significantly lower than the control herbicide bensulfuronmethyl·pretilachlor. Transmission electron microscopy showed that the chloroplasts of barnyard grass were broken and dispersed, most chloroplast envelope changed from elongated to oval, osmophilic particles appeared in the chloroplast, the lamella of the inner capsule disappeared, and the matrix stack was scattered, including a large number of large vesicles when barnyard grass seeds were treated with compound Ⅵak. The enzyme activity assay showed that compound Ⅵak at 50-450 mg/L showed a trend of slow increase to CAT acitivity and H₂O₂ content at first and then stable. It can be concluded that compound Ⅵak may inhibit the growth of barnyard grass by destroying chloroplast structure and affecting CAT activity and H₂O₂ content, thus providing lead compounds for the development of barnyard grass.