Research progress of nitroxide radical derivatives and their biological activities

Nitroxide radicals are a kind of stable organic free radicals. Due to the presence of N-O· and unpaired electrons in its structure, it has many characteristics, and thus can be used as a spin marker to explore the mechanism of biological reactions; with its magnetic properties, it can be used for the development of multifunctional magnetic molecular materials and used as a polymerization inhibitor and catalyst in organic reactions. More importantly, it has a variety of biological activities such as anti-oxidation and anti-tumor, and so has attracted much attention in the research and development of new drugs. For example, the spin labeling of nitroxide radicals on anticancer drug podophyllotoxin can enhance the efficacy and reduce the toxicity, and can be easily to be absorbed by the body, thus obtaining a new anti-cancer drug 4-4″-(2″,2″,6″,6″-tetramethyl-1″-piperidinyloxy nitroxide radical) amino-4′-demethyl epipodophyllotoxin(GP-7). It is an effective way to seek new drugs by introducing pharmacophore to modify nitroxide radicals or it can be spin-labeled on active natural products to obtain new compounds with high efficiency and low toxicity. The research progress of derivatives and its biological activitives of nitroxide radicals are summarized, aiming to provide theoretical basis for the developing and utilizing of nitroxide radicals and searching for new drugs.