Synthesis And Fungicidal Activity Of Novel2,5-Disubstituted-1,3,4-Oxadiazoles Containing Benzimidazole Moiety

The study of the synthetic methods and the biological activity of heterocyclic compoundshas always been one of the most active and important research subject in the organicchemistry, pesticide chemistry and medical chemistry, and a great deal of literature reportedthat many heterocyclic compounds had good antifungal bioactivities. In recent yearsheterocyclic compounds were used in the fields of medicine and pesticides more and morewidely. In numerous developed heterocyclic compounds,1,3,4-oxadiazole derivatives andbenzimidazole derivatives have received increasing interests because of their potentialbiological activities such as insecticidal, antibacterial(antifungal), anti-inflammatory,antiviral and anticancer activities.By consulting concerned literatures, we comprehensively reviewed the biologicalactivities and synthetic methods of1,3,4-oxadiazole derivatives and benzimidazolederivatives. In order to seek pesticides with good biological activities, we have modified themain structure of1,3,4-oxadiazole by Bioisosterism Principles and Structure Link Way, andintroduce benzimidazole moiety into1,3,4-oxadiazole. Nine novel compounds of2-(1H-benzimidazol-2-yl)-5-substitutedthio-1,3,4-oxadiazole (Ⅰ) and nine novel compounds of2-[1-(4-fluorobenzyl)-(1H-benzimidazol-2-yl)]-5-substitutedthio-1,3,4-oxadiazole (Ⅱ) weresynthesized from1H-benzimidazole-2-carbonyl hydrazine, carbon disulfide and alkyl halideor benzyl halide by multi-step reactions.In this paper, we simplified the post-treatment and improved the yield of the targetcompounds by discussing the synthetic process of target compounds and intermediates indetail and making some improvement. Structures of eighteen novel compounds werecharacterized by IR,1H NMR spectra and elemental analysis. Based on the idiographicstructure, we discuss synthes in condition, spectrum properties and physic-chemicalconstant of the target compounds at last. In the article, the biological activities of the target compounds were determined bybioassay standard method (the mycelium growth rate method) created by national “85”novel pesticide. The antifungal activities of two series compounds(Ⅰ, Ⅱ) against Botrytiscinerea pers and Rhizoctonia cereailes were respectively tested, and the results indicatedthat they had good antifungal activity against Botrytis cinerea pers and Rhizoctoniacereailes, the EC50values of Ⅰ_b, Ⅱ_b, Ⅱ_c, Ⅱ_e, Ⅱ_f, Ⅱ_hto Botrytis cinerea pers is2.70,5.63,3.08,1.31,6.07and6.26μg/mL and the EC50values of Ⅱ_fto Rhizoctonia cereailes is0.04μg/mL,which is less than that of carbendazim (7.40μg/mL and0.13μg/mL). The results indicatethat the activies are increased when we modify the main structure of1,3,4-oxadiazolederivatives by Bioisosterism Principles, and connected benzimidazole with the mainstructure.