Abstract
Seven 4-amino-5-substituted-1,2,4-triazole-3-thione Schiff base compounds were synthesized reacting 4-amino-5-substituted-1,2,4-triazole-3-thione with dichloro-substituted 5-pyrimidines, and the structures were verified by elemental analysis and spectroscopic techniques (FT-IR, 1H NMR). Additionally, in vitro antifungal activities of the compounds (named F1~F2; A1~A5) against Grape anthracnose and Wheat gibberellic have been evaluated. The compounds of F1, A4 and A5 were found to be potentially effective antifungal agents against Grape anthracnose, while the others showed the low bioactivity. The antifungal activity of all compounds against Wheat gibberellic were superior to that of fluconazole (standard drug, SD). Particularly, compounds of F1, A1, A4 and A5 exhibited a broad-spectrum antifungal activity against two fungus as compared to the others. Therefore, molecular docking study was carried out to explore the potential interaction between ligands and Fusarium graminearum (PDB ID: 5E9H). The results showed that four compounds had higher affinity compared with fluconazole and form the stable complex with the receptor. Besides, the frontier molecular orbitals (FMOs) and molecular electrostatic potentials (MEP) of four compounds with broad-spectrum antimicrobial activity were also calculated with DFT/ B3LYP /6-31G (d, p) method. The energy gap values (△ELUMO-HOMO) of all the synthesized compounds ranged from 3.307-3.375 eV, which was lower than that of SD (6.248 eV). Additionally, according to MEP the electrophile reaction of 5-substituted groups was beneficial to improving the biological activity against Wheat gibberellic and Grape anthracnose.
Highlights
The long-term and extensive use of pesticides will significantly increase the side effects and drug resistance of some crops [1]
Novel Schiff base compounds containing 1,2,4-triazole and pyrimidine heterocycles were synthesized by the method of splicing active substructures, and the structures were confirmed by series characterization
The results revealed that the compounds of F1, A4, and A5 had good antifungal activity against Grape anthracnose, while all compounds had stronger antimicrobial activity against Wheat gibberellic than fluconazole
Summary
The long-term and extensive use of pesticides will significantly increase the side effects and drug resistance of some crops [1]. Nitrogen-containing heterocyclic compounds, such as pyrimidine and triazole, are widely used in pesticides because of their broad-spectrum, high-efficiency and low-toxic biological activities. They can be used as fungicides, insecticides, herbicides, plant growth regulators and so on [5-9]. Pyrimidine composed of two nitrogen atoms and four carbon atoms is a kind of six-membered heterocyclic ring with conjugated π bond, which widely exists in human body and organism. Pyrimidine compounds and their derivatives are a kind of very important active substances in the field of pesticides and medicine, with broad-spectrum biological activities. The compounds of Schiff base show the extensive applications in medicinal, agricultural and pharmaceutical fields and become one of the important class of organic compounds because of the existence of azomethine group (N=CH) in the structure that is essential for biological activity [11-13]
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