Design, Synthesis, and Bioactivity of Eighteen Novel 2H-1,4-Benzoxazin-3(4H)-one Containing a Propanolamine Moiety

To develop a novel skeleton for broad-spectrum pesticides with high-efficiency against tea tree diseases, a series of aniline 2H-1,4-benzoxazin-3(4H)-one derivatives containing a propanolamine structure was synthesized and confirmed by ¹ H-NMR, ¹³ C-NMR, ¹⁹ F-NMR, HRMS, and single-crystal diffraction analysis. Bioactivities were evaluated against tobacco mosaic virus (TMV, the model virus), three kinds of bacteria, and five typical plant fungi. Bioassay results showed that compound 2i (EC₅₀ =395.05 μg/mL) had the best curative activity against TMV, 3d (EC₅₀ =45.70 μg/mL) had the best inhibitory activity against Pseudomonas syringae pv. Actinidiae, and 3a (EC₅₀ =13.53 μg/mL) had the best inhibitory activity against Pestalotiopsis trachicarpicola. Scanning electron microscope morphological observation of P. trachicarpicola treated with 0, 100, and 200 μg/mL 3a revealed dried, flattened and folded outer walls of the hyphae at higher concentrations, leading to inhibition of fungal growth. The broad-spectrum bioactivities (against viruses, bacteria and fungi) of this series of target compounds indicate that these 2H-1,4-benzoxazin-3(4H)-one derivatives containing a propanolamine moiety are potential skeletons for developing pesticides with wide-ranging activities against various tea tree diseases.