A novel metal-free low molecular weight superoxide dismutase mimic.

2-Ethyl-1-hydroxy-2,5,5-trimethyl-3-oxazolidine (OXANOH), the one-electron reduction product of the stable nitroxide radical, 2-ethyl-2,5,5-trimethyl-3-oxazolidinoxyl (OXANO), is reportedly oxidized by superoxide, and its oxidation has been proposed as a method for assaying superoxide. We find that superoxide can both reduce OXANO and oxidize OXANOH. The respective rate constants, k1 and k2, were determined using two superoxide-generating systems (xanthine oxidase/xanthine as well as ionizing radiation). OXANOH oxidation and OXANO reduction are both inhibitable by superoxide dismutase, pH-dependent (4.5-9.3), and result in a steady state distribution of [OXANO] and [OXANOH], independent of their initial concentrations, i.e. the OXANO/OXANOH couple exhibits a metal-independent superoxide dismutase-like function. Thus it provides a prototype for future development of improved low molecular weight superoxide dismutase mimics which will also function in cellular hydrophobic (aprotic) compartments such as membranes.