Quinolizidine Alkaloids and Isoflavones from the Herb of Thermopsis lupinoidesand Their Antiviral, Antifungal, and Insecticidal Activities

As part of our ongoing investigation of natural bioactive substances from the genus Thermopsisof the tribe Fabaceae for agricultural protection, the chemical constituents of the herb Thermopsis lupinoideswere systematically investigated, which led to the isolation of 39 quinolizidine alkaloids (QAs) (1–39), including 14 new QAs (1–14) and 14 isoflavones (40–53). Their structures were elucidated through comprehensive spectroscopic data analysis (IR, UV, NMR, HRESIMS), ECD calculations, and X-ray crystallography. The antitomato spotted wilt virus (TSWV) and antifungal (against Botrytis cinerea, Gibberella zeae, Phytophythora capsica, and Alternaria alternata) and insecticidal (against Aphis fabaeand Tetranychus urticae) activities of the isolated compounds were screened using the lesion counting method, mycelial inhibition assay, and spray method, respectively. The bioassay results showed that 34exhibited excellent protective activity against TSWV, with an EC50value of 36.04 μg/mL, which was better than that of the positive control, ningnanmycin (86.03 μg/mL). The preliminary mechanistic exploration illustrated that 34induced systemic acquired resistance in the host plant by acting on the salicylic acid signaling pathway. Moreover, 1showed significant antifungal activity against B. cinerea(EC50value of 20.83 μg/mL), while 2exhibited good insecticidal activity against A. fabae(LC50value of 24.97 μg/mL). This research is promising for the invention of novel pesticides from QAs with high efficiency and satisfactory ecological compatibility.