ESR investigation of 5,8-quinolinequinone semiquinone as a streptonigrin model compound

Streptonigrin, an aminoquinone, is a potent antitumor antibiotic. Its use in the clinical treatment against cancers is limited by its cytotoxic side effects. It is believed that the biological activity of streptonigrin involves the semiquinone. Streptonigrin semiquinone was made by reducing it with sodium borohydride in the presence of air, and the electron spin resonance (esr) spectra were determined as a function of temperature in four detergent systems: three neutral (non-ionic) detergents TRITON X-100, octyl ~-D-glucopyranoside (OG) and octyl P-D-thioglucopyranoside (OSGP); one cationic hexadecyltrimethylammonium bromide (CTAB) in aqueous media at pHl-1.00. The temperature variations for all four detergents were set at 2�, 5� and thereafter at 5� increments up to 60� C. The coupling cons tan ts between the unpaired electron and the amino protons become nondegenerate as the temperature decreases. The assigned hyperfine coupling constants were confirmed by reproducing the experimental esr spectrum with a computer simulated esr spectrum. Deuterated streptonigrin semiquinone was generated with sodium borodeuteride in CTAB/D2 0, and the esr spectra were recorded as a function of temperature as above. The esr spectra obtained confirmed the assigned coupling constants for non-deuterated semiquinone m CTAB. The effects on the esr spectra of streptonigrin semiquinone in sodium dodecyl sulfate (SDS), CTAB and TRITON X- 100 at elevated ionic strengths was determined. We have prepared and characterized the esr spectra of 5,8-quinolinequinone semiquinone in various solvents as a model for streptonigrin. The esr spectra of 5,8-quinoline semiquinone in comparison to streptonigrin was sensitive toward substitution of the quinolinequinone moiety. A metal binding precursor of 5,8-quinolinequinone toward the semiquinone complex has been prepared.