Synthesis, Anti‐Oomycete and Anti‐Fungal Activities of Anhydride Derivatives of Oleanolic Acid

AbstractOleanolic acid is a pentacyclic triterpenoid extracted and isolated from the fruit of plants in the Ligustrum lucidum Ait. in the family Oleaceae. To discover biorational natural product‐based pesticides, a series of oleanolic acid derivatives containing anhydride active skeletons were prepared by ingeniously introducing an active acyloxy group at its C‐28 carboxyl position, and their structures were well characterized by 1H‐NMR, 13C NMR, HRMS, and m.p. The stereochemical configuration of compound 8 e was confirmed using single‐crystal X‐ray diffraction. Furthermore, bioactivities of these compounds as anti‐oomycete and anti‐fungal agents against two serious agricultural pests, Phytophthora capsici (P. capsici) and Fusarium graminearum (F. graminearum) we assessed. Amongst evaluated compounds, 1) Compounds 8 h and 8 j displayed significant anti‐oomycete against P. capsici, with EC50 values of 54.73 and 65.15 mg/L, respectively. 2) The target compounds have obvious selectivity, and their anti‐oomycete activity is significantly better than their anti‐fungal activity. 3) Interestingly, there are significant differences in the structure‐activity relationship of different substituents or the same substituent at different positions anti‐oomycete and anti‐fungal against P. capsici and F. graminearum, respectively. The study provides an idea for further exploring the bioactivities of 28‐acyloxyoleanolic acid derivatives, and develops the application of 28‐acyloxyoleanolic acid derivatives containing anhydride in agriculture.