Design, Synthesis, and Anti-Oomycete and Antifungal Activities of Novel Paeonol Derivatives Containing a Pyrazole Ring.

Paeonol is the main active ingredient in the Chinese medicinal herb peony root bark. To discover biorational natural product-based fungicides, 25 paeonol derivatives (-) containing a pyrazole ring were designed and synthesized by ingeniously introducing a pyrazole five-membered heterocyclic ring, and their structures were well characterized by H NMR, C NMR, high-resolution mass spectrometer (HRMS), and m.p. The stereochemical configurations of six target compounds, , , , , , and , were unambiguously subjected to single-crystal X-ray diffraction. Furthermore, we evaluated the bioactivities of these target compounds as anti-oomycete and antifungal agents against two serious agricultural diseases, and . Among all tested compounds, (1) nine compounds -, , , , , , displayed promising anti-oomycete against , with EC values ranging from 22.1 to 34.5 mg/L, and the protective effect of the target compounds against further confirmed the above results. (2) Six compounds , , , , , displayed promising antifungal against , with EC values ranging from 38.2 to 86.0 mg/L. Moreover, some interesting results of structure-activity relationships were also observed. The results of this study pave the way for further design, synthesis, and development of paeonol derivatives as potential botanical anti-oomycete and antifungal agents in crop protection.