Synthesis and radical-addition stereochemistry of two trimethyl-1-pyrroline 1-oxides as studied by EPR spectroscopy

Abstract

A two-step synthetic route has been applied to the preparation of two five-membered ring nitrone spin traps, 3,5,5-trimethyl-1-pyrroline 1-oxide (3-Me-DMPO) and 4,5,5-trimethyl-1 -pyrroline 1-oxide (4-Me-DMPO). A general method has been developed for the purification of the aqueous nitrone solution, which is suitable for the trapping of radicals present in biological processes. The EPR spin-trapping stereochemistry of 3- and 4-Me-DMPO has been investigated. The addition of the radicals ˙OH, RC˙HOH, tetrahydrofuranyl and ˙OBu^t, to Me-DMPO is stereoselective or stereospecific. Hydrogen atom addition to 3-Me-DMPO and 4-Me-DMPO gives aminoxyls 9 and 10, respectively, which each contain two non-equivalent β-protons.