Synthesis of N-substituted indole-2-carboxamides and investigation of their biochemical responses against free radicals.

The antioxidant role of novel N-substituted indole-2-carboxamides (I2CDs) was investigated for their inhibitory effects on superoxide anion (O2-) and lipid peroxidation (LP). Among the synthesized I2CDs, 3, 4, 6, 8 and 9 significantly inhibited O2*- with an inhibition range at 70-98%. Examination of substituent effects on activity showed that both the ortho- and para- positions of the benzamide residue needs to be dichlorinated in order to get a maximum inhibitory effect on superoxide anion. In general, halogenated derivatives were found more active then the non-halogenated ones. However, none of the I2CDs had a significant inhibitory effects on the level of lipid peroxidation; only compounds 7 and 10 moderately decreased LP levels by over 50% at 10(-3) M concentrations.