Design, Synthesis, Anti-Oomycete, and Insecticidal Activities of 3β-Acyloxy-18β-Glycyrrhetinic Acid Derivatives

18β-Glycyrrhetinic acid (GA) is a pentacyclic triterpenoid compound mainly extracted from the roots of the leguminous plant licorice. To discover botanical pesticides, twelve 3β-acyloxy-18β-glycyrrhetinic acid derivatives ( 3a – l ) were synthesized, and their structures were characterized by 1 H NMR, 13 C NMR, and HR–MS. In addition, we assessed the bioactivities of these title compounds as anti-oomycete and insecticidal agents against two serious agricultural pests, Phytophthora capsici and Mythimna separata . Amongst all tested target compounds, (1) Six compounds 3d , 3e , 3h , 3i , 3j , and 3k indicated promising anti-oomycete activity against P. capsici , with EC 50 values of 28.27, 29.36, 23.88, 20.03, 23.07, and 25.93 mg/L, respectively. (2) Six compounds showed significant insecticidal activity, the final mortality rates of 3b , 3c , 3f , 3g , 3i , and 3l were 66.7%, 55.6%, 63.0%, 60.7%, 51.9%, and 75.6%, respectively. The anti-oomycete and insecticidal activities of the title compounds were closely related to R, which has a significant impact on its activity. Graphical