Design, synthesis and antifungal activity of indole derivatives containing 1,3,4-oxadiazole

In this study, 21 indole derivatives containing 1,3,4-oxadiazole were designed and synthesized, the results of the biological activity test showed that the target compounds had certain antifungal activity against 12 plant pathogenic fungi in vitro, among which. E1 showed excellent bioactivity against Botrytis cinerea (B.c.), Tomato Botrytis cinerea (F.M.) and Phomopsis sp (P.s.), with median effective concentration (EC50) values of 2.8, 5.1 and 5.2 µg/mL, which are higher than those of the control drug azoxystrobin (Az) at 15.2, 31.2 and 15.2 µg/mL. In vivo tests on blueberry leaves, tomato leaves and kiwifruit showed that E1 at 200 µg/mL offered stronger protective effect against B.c. (91.9 %) than Az (83.8 %) in blueberry leaves, F.M. (83.3 %) than Az (72.9 %) in tomato leaves and P.s. (89.3 %) than Az (86.9 %) in kiwifruit. Scanning electron microscope (SEM) experiments showed that B.c. hyphae treated with E1 had abnormal shrinkage and obvious morphological changes. The results of the mechanism study showed that E1 could change the integrity of the cell wall and cell membrane of pathogen B.c., which led to the increase in malondialdehyde (MDA), cell leakage and permeability and the rupture of the cell membrane. Because of their strong antifungal effects on plant fungus, indole derivatives containing 1,3,4-oxadiazole were predicted to develop into novel fungicides.