Design, Synthesis, and Biological Activity Studies of Myricetin Derivatives Containing a Diisopropanolamine Structure

A series of myricetin derivatives containing diisopropanolamine were designed and synthesized. The in vitro inhibitory effects of the target compounds on 9 fungal pathogens and 3 bacterial pathogens were also evaluated. <b>A12</b> had the best inhibitory effect against <i>Xanthomonas oryzae</i> <i>pv. oryzae</i> (<i>Xoo</i>), with an EC₅₀ value of 4.9 μg/mL, which was better than zinc-thiazole (ZT: EC₅₀ = 7.3 μg/mL) and thiodiazole-copper (TC: EC₅₀ = 65.5 μg/mL); <b>A25</b> had the best inhibitory effect against <i>Phomopsis sp</i>. (<i>Ps</i>), with an EC₅₀ value of 17.2 μg/mL, which was better than azoxystrobin (Az: EC₅₀ = 22.3 μg/mL). In vivo inhibition tests were performed on kiwifruit for <b>A25</b> and rice leaves for <b>A12</b>. At 200 μg/mL, the curative activity of <b>A12</b> against rice leaf blight was 40.7%, which was better than that of ZT (37.2%) and TC (32.9%), and the protective activity of <b>A12</b> was 44.8%, which was better than that of ZT (39.5%) and TC (34.6%). The curative activity of <b>A25</b> against kiwi soft rot disease was 70.1%, which was better than that of Az (62.8%). Preliminary elucidation of the possible mechanisms of action was carried out by experiments on fluorescence microscopy, scanning electron microscopy, formation of biofilms, density functional theory calculations, and so on.