Discovery of Acaricidal,\nInsecticidal, and Fungicidal\nCandidates Inspired by Natural Ethyl Cinnamate Compounds Isolated\nfrom Polygonum orientale L.

As a continuation of our research on the pesticide development\nof Polygonum orientale L., the chemical\nconstituents of the seeds of P. orientale were systematically investigated. Eleven natural compounds (<b>PO-1</b> to <b>PO-11</b>) were isolated from the EtOAc extract\nof P. orientale. Notably, compound <b>PO-9</b> and its dimeric compound <b>PO-10</b> were first\nisolated from P. orientale and possessed\nexcellent acaricidal activity against Tetranychus cinnabarinus. With <b>PO-9</b> and <b>PO-10</b> as the lead compounds,\ntwo series of cinnamate derivatives were further synthesized, and\ntheir acaricidal, insecticidal, and fungicidal activities were evaluated\nsystematically. The insecticidal activity results showed that dimeric\nderivative <b>NKY-70</b> displayed the highest acaricidal activity\nagainst T. cinnabarinus and insecticidal\nactivities against Brevicoryne brassicae and Myzus persicae. Furthermore,\nmost of these compounds showed excellent <i>in vitro</i> antifungal activity against plant fungi. Compound <b>NKY-66</b> displayed the highest and broad spectrum of antifungal activity\nagainst 23 fungi, and the respective EC<sub>50</sub> values were 0.09,\n0.08, 0.12, 0.18, 0.12, and 0.09 mg/mL against Valsa\nmali, Fusarium oxysporum f. sp. cucumerinum, Fusarium graminearum, Magnaporthe oryzae, Colletotrichum capsici, and Phytophthora\ninfestans, which were more potent than those of chlorothalonil\nand procymidone. Moreover, the <i>in vivo</i> fungicidal\nevaluation also demonstrated that compound <b>NKY-66</b> could\neffectively control plant fungal diseases in the greenhouse and in\nthe field, such as damping off, powdery mildew, and cucumber downy\nmildew. Therefore, these findings implied that the cinnamate derivative <b>NKY-66</b> displayed superior <i>in vitro</i> and <i>in vivo</i> fungicidal activities and could be a potential candidate\nagainst plant fungal diseases.