Synthesis and Spin-Trapping Properties of a New Spirolactonyl Nitrone

Spin trapping using electron paramagnetic resonance (EPR) spectroscopy is commonly employed for the identification of transient radicals in chemical and biological systems. A spirolactonyl-nitrone with rigid H-bond acceptor, 7-oxa-1-azaspiro[4.4]non-1-en-6-one 1-oxide, CPCOMPO, has been synthesized and characterized, and its spin-trapping properties were investigated. The rate of formation of CPCOMPO−O2H was determined using competition kinetics between the superoxide/hydroperoxyl radical (O2•-/HO2•) trapping by CPCOMPO and the spontaneous dismutation of this radical in aqueous media. The rate constant of 60 M-1·s-1 is the highest rate constant thus far observed at neutral pH for any nitrones using the kinetic method employed. Decay kinetics were also experimentally investigated for CPCOMPO−O2H. The effect of rigid H-bond acceptor on the stability of the CPCOMPO−O2H were computationally rationalized and compared to that of EMPO−O2H, which has flexible H-bond acceptor, and results show the need of a “loose” H-bond acceptor for improved adduct stability.