1,3,4-Oxadiazole Derivatives as Plant Activators for Controlling Plant Viral Diseases: Preparation and Assessment of the Effect of Auxiliaries.

Plant viral diseases cause the loss of millions of dollars to agriculture around the world annually. Therefore, the development of highly efficient, ultra-low-dosage agrochemicals is desirable for protecting the health of crops and ensuring food security. Herein, a series of 1,3,4-oxadiazole derivatives bearing an isopropanol amine moiety was prepared, and the inhibitory activity against tobacco mosaic virus (TMV) was assessed. Notably, compound A 14 exhibited excellent anti-TMV protective activity with an EC 50 value of 137.7 mg L -1 , which was superior to that of ribavirin (590.0 mg L -1 ) and ningnanmycin (248.2 mg L -1 ). Moreover, the anti-TMV activity of some compounds could be further enhanced (by up to 5-30%) through supplementation with 0.1% auxiliaries. Biochemical assays suggested that compound A 14 could suppress the biosynthesis of TMV and induce the plant's defense response. Given these merits, designed compounds had outstanding bioactivities and unusual action mechanisms and were promising candidates for controlling plant viral diseases.