Non-food renewable and bioactive products for pesticides: Synthesis, anti-oomycete and anti-fungal activities of 9R-acyloxyquinine derivatives bearing an 1,3,4-oxadiazole moiety

Quinine is the main alkaloids in the bark of Cinchona and its homologous plants of Rubiaceae. To discover biorational natural product-based pesticides, a series of 9 R -acyloxyquinine derivatives containing 1,3,4-oxadiazole moieties were prepared by ingeniously introducing an active ester group and a 1,3,4-oxadiazole five membered heterocyclic ring at its C-9 position, and their structures were well characterized by 1 H NMR, 13 C NMR, HRMS, and m.p. The stereochemical configuration of target compound 6 t was unambiguously subjected to single-crystal X-ray diffraction. Furthermore, bioactivities of these compounds as anti-oomycete and anti-fungal agents against two serious agricultural diseases, Phytophthora capsici and Fusarium graminearum we assessed. Among all tested compounds, 1) Compounds 6c and 6d displayed promising anti-oomycete against P. capsici , with EC 50 values of 38.42 and 35.49 mg/L, respectively. 2) Compound 6i exhibited promising anti-fungal against F. graminearum , with an EC 50 value of 29.92 mg/L. Moreover, some interesting results of structure-activity relationships were also observed. The results of this study pave the way for further design, structural modification, and development of quinine derivatives as plant anti-oomycetes and anti-fungal agents in crop protection.