Novel Substituted Imidazo[2,1-b][1,3,4]Thiadiazole Derivatives: Synthesis, Characterization, Molecular Docking Study, and Investigation of Their In Vitro Antifungal Activities

Abstract

In this study, a new series of substituted imidazo[2,1-b][1,3,4]thiadiazole derivatives were synthesized. To this end, first 2-amino-1,3,4-thiadiazole derivatives (compounds 2a and 2b), the starting materials, were synthesized with high yields (82% and 79%, respectively). Then imidazo[2,1-b][1,3,4]thiadiazole derivatives (4-16), the target compounds, were synthesized from reactions of 2-amino-1,3,4-thiadiazole derivatives (2a and 2b) with 2-bromoacetophenone derivatives (3a-3i) (in yields of 52% to 71%). All of the synthesized compounds were characterized by H-1 NMR, C-13 NMR, Fourier transform infrared, elemental analysis, mass spectroscopy, and X-ray diffraction analysis (compounds 4-12, 14, and 15) techniques. In vitro antifungal activity tests were performed for all of the synthesized compounds. Inhibition zones, percentage of inhibition, minimum fungicidal activity, minimum inhibitory concentration, and lethal dose values of the target compounds were determined against some plant pathogens. According to the results of the biological activity tests, all of the synthesized compounds showed moderate to high levels of antifungal activity. Theoretical calculations were performed to support the experimental results. The geometric parameters of selected compounds (5, 6, and 8) were optimized using the density functional theory B3LYP/6-31G(d) method in the Gaussian 09W package program, and the frontier molecular orbitals (highest occupied molecular orbital-lowest unoccupied molecular orbital) were calculated theoretically. Finally, molecular docking studies were performed for antifungal activity studies of the selected compounds and to determine whether or not these compounds could be inhibitor agents for the 2RKV protein structure.