Semiquinone production by lipophilic o-naphthoquinones

Several β-lapachone analogues, the o-naphthoquinones CG 10-248, CG 9-442 and CG 8-935, were reduced to their semiquinones by sodium borohydride, the liver NADPH-P450 reductase system and Crithidia fasciculata cells, in anaerobic solutions. ESR spectra of the radical anions showed hyperfine spin couplings located at protons of the naphthalene ring. Borohydride reduction of another o-naphthoquinone, mansonone E, yielded spin couplings located at the naphthalene and methyl groups protons. The symmetrical polarized carbonyl groups were essential for electron capture and semiquinone production. These observations support the idea that quinones are capable of redox-cycling and oxygen radical generation.