In aqueous solution and using molecular oxygen as electron acceptor, the antitumor drug 9- hydroxyellipticine (9-OH-E) undergoes a spontaneous oxidation to give hydrogen peroxide (H, O,), the quinone imine 9-oxoellipticine (g-oxo-E), and a dimer of 9-OH-E (9-OH-E2). Electron paramagnetic resonance (EPR) experiments performed either in alkaline MezSO or in phosphate buffer in the presence of the spin trap 5, 5-dimethylpyrroline 1-oxide (DMPO) ...