Synthesis, anti-oomycete and anti-fungal activities of novel paeonol ester derivatives containing a schiff base

To discover biorational natural product-based pesticides, a series of paeonol ester derivatives containing a Schiff base (6a-j, 7i,j, 8i,j, and 9i,j) were prepared, and their structures were well characterised by ¹H NMR and HRMS. Furthermore, bioactivities of these compounds as anti-oomycete and anti-fungal agents against two serious agricultural diseases, Phytophthora capsici and Fusarium graminearum we assessed. Amongst evaluated compounds, 1) Compounds 6a and 6e displayed good anti-oomycete against P. capsici, with EC₅₀ values of 116.50 and 88.86 mg/L, respectively. 2) Compounds 6e and 7i exhibited prominent anti-fungal against F. graminearum, with EC₅₀ values of 66.73 and 29.33 mg/L, respectively. 3) This study suggested that the introduction of nitro at the C5 position of paeonol could improve its bioactivity against P. capsici and F. graminearum. The results of this study pave the way for further design and development of paeonol derivatives as plant anti-oomycetes and anti-fungal agents in crop protection.