Novel 1,3,4-thiadiazol derivatives including α-lipoic acid: Synthesis, characterization, and antioxidant properties

Abstract

In this study, new 1,3,4-thiadiazole-2-amine derivatives containing different substitution groups were synthesized in order to increase the free radical quenching ability of α-lipoic acid. The target thiadiazole amines were derived from thiosemicarbazide reagent. Structural analysis for the synthesized compounds (1–8) was carried out using modern spectroscopic techniques including FTIR, NMR, EIMS spectral analyses. The antioxidant properties of each molecule were elucidated by calculating% inhibition as well as significant IC50 values using the 1,1-diphenyl-2-picryl hydrazyl (DPPH) free radical scavenging method. The antioxidant activities of the compounds were compared against ascorbic acid, a water-soluble antioxidant, and against α-lipoic acid, the starting molecule of the synthesis step, which actually showed a low DPPH quenching activity. While lipoic acid had a reference standard value of 15,625.02±0.96 µM, compound 8 was the compound with the highest antioxidant activity with an IC50 value of 433.69±0.04 µM. The obtained data suggested that the (NH) proton in the thiadiazole structure bound to lipoic acid plays an important role in binding to the DPPH radical. This study may provide a source for the synthesis of α-lipoic acid-based thiadiazole derivatives, new compounds with antioxidant properties that can be used in medicine and pharmacy.