Quinolizidine Alkaloids with Antiviral and Insecticidal Activities from the Seeds of <i>Sophora tonkinensis</i> Gagnep

Abstract

The discovery of novel, effective, and botanical pesticides is one of the main strategies for modern plant protection and insect pest control. During the search for novel botanical pesticides from natural sources, the seeds of <i>Sophora tonkinensis</i> were systematically investigated to obtain 11 new matrine-type alkaloids (<b>1</b>-<b>11</b>), including one novel matrine-type alkaloid featuring an unprecedented 5/6/6/6 tetracyclic skeleton (<b>1</b>), along with 16 known compounds (<b>12</b>-<b>27</b>). Their structures were elucidated by comprehensive spectroscopic data analysis (IR, UV, NMR, and HRESIMS), ECD calculations, and single-crystal X-ray diffraction. The anti-tobacco mosaic virus (TMV) activity and insecticidal activities against <i>Aphis fabae</i> and <i>Tetranychus urticae</i> of the compounds were also respectively screened using the half-leaf method and spray method. Biological tests indicated that compounds <b>2</b>, <b>4</b>, <b>6</b>, and <b>26</b> displayed significant anti-TMV biological activities compared with the positive control ningnanmycin. Compounds <b>7</b>, <b>17</b>, and <b>26</b> presented moderate activities against <i>A. fabae</i> with LC₅₀ values of 38.29, 18.63, and 23.74 mg/L, respectively. Moreover, compounds <b>13</b> and <b>26</b> exhibited weak activities against <i>T. urticae</i>.