Indole/Indazole Derivatives Containing Imine Fragment as Potential Inhibitors Against Phytopathogenic Oomycetes, Structure‐Function Analysis, and Theoretical Investigations

ABSTRACT A series of novel fluorescent indole/indazole derivatives ( A1 – A7 ) and complexes ( B1 – B5) containing imine fragment were synthesised, antimyoocete bioassays exhibited that compounds A1 and A5 could selectively inhibit the in vitro growth of Phytophthora capsici ( P. capsici ), with the EC 50 value of 4.4 and 2.6 µg/mL which was similar to that of metalaxyl (2.3 µ g/mL). Complexes B1 – B5 obtained by chelating the compounds with Cu 2+ ion and their structures were preliminarily determined by fluorescence titration. The complex B1 demonstrated superior protective and curative efficacy (91.45% and 83.75%) on pepper leaves against P. capsici compared to the control treatment metalaxyl (80.05% and 76.15%). Scanning electron microscopy (SEM) and cell membrane permeability experiments synergistic demonstrated that the compound B1 induced mycelial deformation and wrinkling, thereby inhibiting oomycete growth. Theoretical calculations indicated that the compounds with lower energy of LUMO orbital are more readily bound to the proteins of strain, thereby exhibiting superior efficacy against oomycetes. In addition, the complex B1 is nontoxic to those specific nontarget organisms. This research introduced imine fragment into different modification sites on indole/indazole scaffold, providing a distinctive strategy for developing novel pesticides based on benzoheterocyclic ring fragment that simultaneously exhibit antioomycete properties.