Rational design and synthesis of l-carvone-derived 4-methyl-1,2,4-triazole-thioether/nanochitosan complexes as potent nanopesticides for sustainable and efficient herbicidal application†

Natural product-based nanopesticide is an effective and sustainable approach for solving the environmental issues caused by the application of current commercial herbicides. In this study, 21 novel L-carvone-derived 4-methyl-1,2,4-triazole-thioether derivatives 5a–5u were rationally designed by transketolase-based in silicon virtual screening, synthesized, and structurally characterized using FT-IR spectroscopy, ¹H/¹³C NMR spectroscopy, and HRMS technique. Besides, the herbicidal activity of the target compounds against Brassica campestris and Echinochloa crusgalli L. was evaluated, and the bioassay results revealed that compound 5a with the most significant herbicidal and TK-inhibition activities could serve as a potential TK inhibitor and could serve as a leading compound for further study of green herbicides. Subsequently, the molecular skeletons of chitosan and L-carvone were incorporated for developing high-efficiency nanopesticide carriers, and thus samples 7a–7d were synthesized by N-alkylation of chitosan and characterized using various methods. Compared with unmodified chitosan, L-carvone-derived nanochitosan carrier 7b with the micro-morphologies of nubby lumps and porous surfaces exhibited higher dispersibility and similar thermostability. Finally, L-carvone-derived 4-methyl-1,2,4-triazole-thioether/nanochitosan complexes 7b/5a, 7c/5a, and 7d/5a with better 5a-loading capacities and multi-stage sustained releasing performances were constructed, and the herbicidal activities of 7b/5a and 7d/5a against Brassica campestris were evaluated in the petri dish and greenhouse. It was found that 7b/5a and 7d/5a exhibited significant herbicidal activities. Among them, 7b/5a had great potential as a green and eco-friendly nanopesticide for weed control.