Synthesis and antioxidant evaluation of novel indole-3-acetic acid analogues

Indole-3-acetic acid (1) on reaction with thionyl chloride, afforded 2-(1H-indol-3-yl)acetyl chloride (2), which was further treated with aniline and various substituted anilines through base condensation reaction to obtain respected indole-3-acetic acid derivatives (3-9). The structures of all new compounds were elucidated by elemental analysis, Mass, IR, 1H NMR and 13C NMR and spectroscopic techniques. All the compounds were screened for their antioxidant activities by applying in vitro methods like 2,2-diphenyl-1-picryl hydrazyl (DPPH) free radical scavenging assay and inhibition of microsomal lipid peroxidation (LPO) assay. Butylated hydroxy anisole (BHA) was used as a reference antioxidant compound and the comparative study with newly synthesized compounds was also done. Among the analogues, compound 9 bearing electron donating methoxy substituent in addition to the phenolic moiety showed predominant activity. It is conceivable from these studies that the coupling of aniline and substituted anilines is the most important feature for the significant antioxidant activity of indole-3-acetic acid analogues studied.