Synthesis and characterisation of novel 4,6-dimethoxyindole-7-and-2-thiosemicarbazone derivatives: Biological evaluation as antioxidant and anticholinesterase candidates

Two sets of novel indole-based thiosemicarbazone systems 8a-d and 9a-d are prepared by the Schiff base condensation reaction of indole carbaldehydes 4 and 6 with a range of thiosemicarbazides 7a-d in high yields and purity. The antioxidant properties of the synthesised compounds 8a-d and 9a-d are determined by employing three different assays, namely 2,2-diphenyl-1-picrylhydrazyl hydrate-free radical scavenging, ABTS [2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)] cationic radical decolarization and cupric ion reducing antioxidant capacity. The anticholinesterase properties of the products are investigated by acetylcholinesterase and butyrylcholinesterase enzyme inhibition assays. The methyl-substituted compounds 8b and 9b display the highest inhibition for the ABTS assay and absorbance values for the cupric ion reducing antioxidant capacity assay, while compound 9c shows the best activity for 2,2-diphenyl-1-picrylhydrazyl hydrate assay. Moderate inhibition of acetylcholinesterase and butyrylcholinesterase is determined in the case of compound 8b.