RESUMEN
Development of synthetic procedures for the preparation of 1,3,4-oxadiazole derivatives has always been in the interest of researchers as a result of their widespread biological activities. In this study, an ultrasound-assisted procedure was proposed for the synthesis of 1,3,4-oxadiazol-2-amines form the reaction of hydrazides and cyanogen bromide. They were efficiently produced in 81-93% yields in the presence of ethanol and potassium bicarbonate as the reaction media and the base, respectively. Their antioxidant properties were determined via DPPH free radical scavenging method as one of the most basic steps in identifying other related biological effects. IC50 values were in the range of from 0.237 to 0.863 mM. The synthesized 1,3,4-oxadiazoles are protective agents against oxidative stress, and can be used in the treatment of cancer, candidiasis, diabetes, neurodegenerative and inflammatory diseases. Furthermore, bond dissociation energies (BDEs) and electron densities based NCI (non-covalent interactions) were calculated using density-functional theory (DFT) to understand the observed reactivities. It was found that reversible dipole-dipole forces play a key role in most interactions.
RESUMEN
One of the goals of green chemistry is to use environmentally friendly solvents or remove and reduce the volume of harmful spent solvents. In this study, a novel process for the synthesis of 5-substituted 1,3,4-oxadiazole-2-thiol derivatives was proposed via ultrasound-assisted reaction of aryl hydrazides with CS2 (1:1 molar ratio) in some drops of DMF in the absence of basic or acidic catalysts. They were produced in good to excellent yields under easy workup and purification conditions. In order to prove the usefulness of the prepared compounds, their antioxidant, antibacterial, and antifungal potentials were screened by DPPH free radical scavenging, serial twofold microdilution and streak plate methods. Acceptable to significant inhibitory activities were observed with synthesized heterocycles. The results showed that 5-(4-fluorophenyl)-1,3,4-oxadiazole-2-thiol (3c) is an broad-spectrum antimicrobial agent. Many of them displayed remarkable antioxidant properties comparable to standard controls (ascorbic acid and α-tocopherol). Synthesized 1,3,4-oxadiazoles are also potent candidates to treat cancer, Parkinson, inflammatory, and diabetes diseases. Eighteen 5-substituted 1,3,4-oxadiazole-2-thiol derivatives as potent antimicrobial and antioxidant agents were prepared via a new, efficient and green procedure.
