Spin trapping of superoxide and hydroxyl radicals with substituted pyrroline 1-oxides.

The synthesis of three nitrones, 5-butyl-5-methyl-1-pyrroline 1-oxide (BMPO), 5,5-dipropyl-1-pyrroline 1-oxide (DPPO), and 2-aza-2-cyclopentenespirocyclopentane 2-oxide (CPPO), was conducted with use of the zinc/ammonium chloride reduction of appropriately substituted gamma-nitrocarbonyl compounds. The lipophilicity of these nitrones was estimated by determining their partition coefficients in a 1-octanol/water system. These nitrones were found to possess more lipophilic character than the most frequently used cyclic nitrone, 5,5-dimethyl-1-pyrroline 1-oxide (DMPO), which exhibits a partition coefficient of only 0.02. Hyperfine coupling constants for the spin trapping of superoxide and hydroxyl radical by the various nitrones were determined. The rate of spin trapping of superoxide with each nitrone was conducted by competitive kinetics with superoxide dismutase (SOD). In addition, the ability of DPPO and BMPO to spin trap free radicals generated during the metabolism of menadione by rat enterocyte cells was investigated. From these studies, DPPO and BMPO appear to be more suitable spin traps than DMPO when one is interested in monitoring free radicals generated intracellularly.