Design and Synthesis of 3-Carene-Derived Amide-Thiourea/Nanochitosan Complexes with Excellent Laccase Inhibitory Activity and Sustained Releasing Performance for Crop Protection.

The discovery of natural product-derived novel nanopesticide systems can effectively address the adverse effects caused by the improper use of traditional fungicides. In this research, 33 novel 3-carene-derived amide-thiourea derivatives - were designed using laccase as the biological target, synthesized from natural renewable forest biomass resource 3-carene as the starting material, and structurally confirmed by Fourier-transform infrared spectroscopy, nuclear magnetic resonance, high-resolution mass spectrometry, and single crystal X-ray diffraction. The antifungal activity of the target compounds against eight plant pathogenic fungi was evaluated, and the results presented that target compound exhibited excellent and broad-spectrum antifungal activity against the eight tested phytopathogenic fungi. Furthermore, the important contribution of the -dimethylcyclopropane structure in the antifungal activity of compound was revealed through two negative controls without the -dimethylcyclopropane structure. Besides, compound also demonstrated a prominent laccase inhibitory activity. The fluorescence quenching of the laccase with compound , the chelating characteristics of compound , and the interaction mode between the laccase and compound presented that the target compound probably exhibited excellent antifungal activity by acting on the laccase target. Cytotoxicity assay revealed that compound had a low cytotoxicity for LO2 and HEK293T cell lines. On the other hand, to further improve the application potential of compound , the 3-carene molecular skeleton containing -dimethylcyclopropane ring was grafted onto chitosan, and two nanopesticide carriers CACS and CATCS with sustained releasing performance were synthesized for loading compound . 3-Carene-derived nanochitosan carrier CATCS showed a relatively regular, loose, and porous reticular structure, which displayed high dispersibility and good thermostability. In addition, this carrier had a higher drug-loading capacity and sustained releasing performance than that of the unmodified chitosan. This research identified that the target compound could be used as a promising lead compound for fungicide against the laccase target, meanwhile, the complex /CATCS deserved further study as a nanopesticide candidate.