Novel ferrocenyl nitroxides: Synthesis, structures, electrochemistry and antioxidative activity

Novel ferrocenyl nitroxides 3−6 were prepared as models for studying the linkage structure–activity relationship. Single-crystal X-ray structures of compounds 4 and 5 were determined and comparatively studied. The in vitro antioxidative activities (e.g. scavenging superoxide anion and hydroxide radical) of compounds 3−6 and 4-ferrocenamido-2,2,6,6-tetramethyl-piperidin-oxy (2) were evaluated. Compounds 3 and 5 exhibit high scavenging activities in low concentration. Results from electrochemistry and UV/Vis spectroscopy show that the redox property and antioxidative activity are closely related to the structure of the linkage bridging ferrocene and cyclic nitroxide moieties. The results further indicate that the ferrocene moiety plays a principal role in antioxidation. The modification of linkage was found to be able to decrease the ferrocene/ferrocenium potential and improve the antioxidative activity effectively.