Design, synthesis, and biological evaluation of a novel library of indole‐benzoxazole derivatives as potential antifungal and antibacterial agents

Abstract BACKGROUND Plant diseases threaten global agriculture. A series of 22 novel indole‐benzoxazole derivatives were synthesized to evaluate their antimicrobial potential against eight plant pathogenic fungi and three bacteria. RESULTS Several compounds exhibited potent antimicrobial activity. Specifically, C12 showed high efficacy against Phomopsis sp. (EC₅₀ = 5.1 μg mL −1 vs azoxystrobin 44.7 μg mL −1 ) and Rhizoctonia solani (EC₅₀ = 7.9 μg mL −1 vs 17.3 μg mL −1 ). C4 strongly inhibited Xanthomonas axonopodis pv. citri (EC₅₀ = 8.5 μg mL −1 vs thiodiazole copper 73.3 μg mL −1 ). In vivo assays confirmed their superior curative and protective efficacy. Mechanistic studies revealed that C12 acted by disrupting cell wall/membrane integrity, while C4 functioned by suppressing biofilm formation and reducing extracellular polysaccharide production. CONCLUSION C12 and C4 demonstrate promising antimicrobial potential through distinct action mechanisms, providing valuable candidates for the development of new plant disease control agents. © 2026 Society of Chemical Industry.