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 (<b>6a-j</b>, <b>7i,j</b>, <b>8i,j</b>, and <b>9i,j</b>) 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, <i>Phytophthora capsici</i> and <i>Fusarium graminearum</i> we assessed. Amongst evaluated compounds, 1) Compounds <b>6a</b> and <b>6e</b> displayed good anti-oomycete against <i>P. capsici</i>, with EC₅₀ values of 116.50 and 88.86 mg/L, respectively. 2) Compounds <b>6e</b> and <b>7i</b> exhibited prominent anti-fungal against <i>F. graminearum</i>, 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 <i>P. capsici</i> and <i>F. graminearum</i>. 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.