Electron spin resonance studies and theoretical quantum calculations of free radicals generated from anthracenetrione by electrochemical and microsomal reduction

The ESR spectra of radicals obtained by electrolytic reduction of 4,4-dimet hylanthracene- 1,9,10 (4H)-trione (1) and the regioisomeric quinones 8-acet yloxymethyl-4,4,5-trimethyl- (2), and 5-acetyloxy-methyl-4,4,8-trimethyl-(4 H)-1.9,10-anthracenetrione (3) were measured in DMSO and analyzed by quantu m chemical calculations. The electrochemistry of these compounds was charac terized using cyclic voltammetry, in DMSO and DMF solvents and compared wit h nifurtimox. The quinones were also reduced by microsomal NADPH-cytochrome P-450 reductase and the corresponding radicals species were also detected by ESR spectroscopy. AMI, INDO, and ADF calculations were performed to obta in the optimized geometries, theoretical hyperfine constants, and spin dist ributions, respectively. Density functional theory was used to rationalize the reduction potential of these compounds. (C) 2001 Elsevier Science B.V. All rights reserved.