Herbicide potential of new phytotoxins structurally based on plant allelochemicals

Abstract

Agriculture requires the development of new herbicides to control weeds. The synthesis of molecules totally or partially based on the combination of basic allelochemical structures viz.,chalcone, pyrimidine and diphenyl ether skeletons may provide phytotoxic compounds more active and environmentally friendly than present herbicides. In this work, chloride aryl pyrimidine benzyl ether (CAPBE) compounds 4a-4f and diphenyl pyrimidine propenone (DPPP) compounds 6a-6g were synthesized and tested on barnyardgrass (Echinochloa cruss-galli) and rape (Brassica napus). These compounds were designed by combining the pyrimidine-diphenyl ether and pyrimidine-chalcone structures, respectively. The herbicidal activity was tested in Petri dish bioassays at 100 mg/L, 10 mg/L and 1 mg/L. The CAPBE compound 4b bearing a 2,4-fluoride substitution in the benzyl ring, exerted the strongest herbicidal activity at 100 mg/L. The CAPBE structure by itself and its benzyl substituted derivatives 4-NO2 (4c) and 4-OCF3 (4e) had the strongest herbicidal activity to barnyardgrass, while the remaining CAPBE compounds, were similarly inhibitory to both test species. The DPPP compounds showed selective herbicidal activity on rape, with compound 6a as the most phytotoxic. However, phytotoxicity decreased with substitutions in the phenyl propenone moiety of the DPPP skeleton. Compounds 4b and 6a deserve further investigations as herbicide lead molecules.