Semi-synthesis and characterization of some new matrine derivatives as insecticidal agents

BACKGROUND: Matrine is an important traditional plant-derived insecticide with broad-spectrum activity. However, due to its moderate activity, matrine is mainly applied in combination with other pesticides. In order to discover new potential natural-product-based crop protection agents, a series of matrine derivatives characterized by cyclohexylamine group were synthesized to screen their insecticidal activity against seven typically agricultural pests. 

RESULTS: The structural configurations of compounds were characterized by IR, ¹H NMR, ¹³C NMR, MS and XRD, with the pure yields of 42%, 65% and 71%, respectively. Although all compounds showed poor insecticidal activity against five lepidoptera pests, the compounds 2 and 4 displayed remarkable insecticidal activities against Lipaphis erysimi and Mulberry Root-Knot Nematode with a concentration-dependent manner within 0.5~1.5 mg/ mL. Compared with matrine (60%), compounds 2 and 4 exhibited potent insecticidal activities against L. erysimi, with a corrected mortality of 83.3% and 89.7%, respectively. They also showed excellent control effects on Mulberry Root-Knot Nematode, with corrected mortality as high as 88% and 80%, respectively. 

CONCLUSION: All four synthesized matrine derivatives showed poor insecticidal activity against five lepidoptera pests, but the compounds 2 and 4 exhibited much stronger insecticidal activities against L. erysimi and Mulberry Root-Knot Nematode than matrine. Combined with the structural characteristics of compounds 1~4, we conclude that 4-methylcyclohexylamine, not the carbon disulfide group or cyclohexylamine group alone, mainly contributed to the improvement of insecticidal activities of matrine derivatives against these two agricultural pests. This work provides a direction and foundation for structural optimization of the matrine pesticides in the future.