Quinolizidine Alkaloids with Antitomato Spotted Wilt Virus and Insecticidal Activities from the Seeds of <i>Thermopsis lanceolata</i> R. Br

Abstract

As part of our ongoing investigation of pesticide active quinolizidine alkaloids (QAs) from the family Fabaceae, the chemical constituents of the seeds of <i>Thermopsis lanceolata</i> R. Br. were systematically investigated. Bioassay-guided fractionation and purification of the crude extract led to the isolation of seventeen new QAs (<b>1</b>-<b>17</b>), including three new naturally occurring compounds (<b>15</b>-<b>17</b>), along with 15 known compounds (<b>18</b>-<b>32</b>). Their structures were elucidated by comprehensive spectroscopic data analysis (IR, UV, NMR, and HRESIMS) and quantum chemistry calculations (¹³C NMR and ECD). The antitomato spotted wilt virus activities and insecticidal activities against <i>Aphis fabae</i>, <i>Nilaparvata lugens</i> (Stal), and <i>Tetranychus urticae</i> of compounds <b>1</b>-<b>32</b> were screened using the lesion counting method, spray method, and rice-stem dipping method, respectively. Biological tests indicated that compounds <b>6, 9</b>, <b>10</b>, and <b>18</b> displayed significant anti-TSWV activities compared with the positive control ningnanmycin. Compounds <b>3</b>, <b>4</b>, and <b>5</b> showed better insecticidal activities against <i>A. fabae</i> with LC₅₀ values of 10.07, 12.07, and 6.56 mg/L, respectively. Moreover, compounds <b>5</b>, <b>18</b>, and <b>24</b> exhibited moderate insecticidal activities against <i>N. lugens</i> (Stal) with LC₅₀ values of 37.91, 53.44, and 31.21 mg/L, respectively. Furthermore, compounds <b>9</b> and <b>10</b> exhibited moderate insecticidal activities against <i>T. urticae</i>.