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 alpha-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 1,1diphenyl-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 alpha-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 mu M, compound 8 was the compound with the highest antioxidant activity with an IC50 value of 433.69 +/- 0.04 mu M. The obtained data suggested that the (N-H) 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 alpha-lipoic acid-based thiadiazole derivatives, new compounds with antioxidant properties that can be used in medicine and pharmacy.