Biochemical studies suggest a direct relationship between the radical scavenging activity of paracetamol (I) and its antipyretic and analgesic action. To evaluate the effect of chemical modifications on the radical scavenging activity of compounds of type I, analogues 1-14 were prepared and submitted to a stable free radical (DPPH; 1,1-diphenyl-2-picryl-hydrazyl) assay. All paracetamol derivatives showed a significant higher efficiency than the parent compound. This study showed that radical scavenging activity can be increased by decreasing the phenolic ortho substituents steric hindrance or by introducing substituents on the acyl moiety like an indazole ring or the ionic N-methyl morpholinium group. A significant activating effect was also observed by replacing the 1,4-acylamidophenol with a 1,4-acylamidonaphthol system. (C) 2012 Elsevier Ltd. All rights reserved.