Design, Synthesis of Dienthiazole Derivatives, and Evaluation of Aphicidal Activity

Nitrogen-containing heterocycles have attracted attention for the development of chemicals because of their many types, high physiological activities, and ease of synthesis. Aphids are severe pests found worldwide that cause serious losses in crop yield and quality every year. In this study, a series of novel dienolone thiazole derivatives were synthesized using dienolone acetate as the parent molecule. The synthesis involved bromination, Hantzsch reaction, esterification, deprotection, and other reactions. The structure of the compounds was determined using proton and carbon-13 nuclear magnetic resonance, high-resolution mass spectrometry, and single-crystal diffraction. The synthesized compounds exhibited excellent insecticidal activities against five species of aphids, including <i>Schizaphis graminum</i>, <i>Brevicoryne brassicae</i>, <i>Aphis gossypii</i>, <i>Aphis citricola</i> Van der, and <i>Myzus persicae</i>. The median lethal concentration values of the compound <b>H-13</b> for <i>S. graminum</i>, <i>B. brassicae</i>, <i>A. gossypii</i>, <i>A. citricola</i> Van der, and <i>M. persicae</i> were 8.72, 13.77, 14.17, 12.96, and 12.35 μg/mL, respectively. The mode of action test results indicated that compound <b>H-13</b> had superior contact and systemic activity against <i>M. persicae</i>, similar to the positive control flonicamid. Furthermore, a field trial showed that the control effect of compound <b>H-13</b> at 100 μg/mL concentration was comparable to that of flonicamid against <i>M. persicae</i>. The mortality was 85.6% and 90.3% after 7 and 14 days, respectively. Finally, to further explore the action mechanism of these compounds, the insecticidal activity of compounds <b>H-13</b> (strong) and <b>H-24</b> (weak) on aphid protease was determined. Compound <b>H-13</b> was found to have a significant inhibitory effect on the strong alkaline tryptase activity. Compound <b>H-13</b> might cause aphid poisoning and death by inhibiting the trypsin activity. This study provided important insights for the discovery and development of new insecticides.