17O NMR studies on polycyclic quinones, hydroxyquinones and related cyclic ketones: Models for anthracycline intercalators

Abstract

AbstractThe 17O chemical shifts for six cyclic ketones which serve as models for quinones, viz. cyclohex‐2‐enone (1), α‐tetralone (2), anthrone (3), 4H‐pyran‐4‐one (4), 1‐benzopyran‐4(4H)‐one (5), xanth‐9‐enone (6), and for six quinones, viz. benzoquinone, naphthoquinone, anthraquinone, 2,5‐dihydroxybenzoquinone 5,8‐dihydroxynaphthoquinone and 1,4‐dihydroxyanthraquinone, were measured in toluene at 90°C. A shielding effect of approximately 50 ppm per fused benzene ring was noted for the quinones and related carbocyclic ketones; however, the analogous series of heterocyclic fused ring ketones 4–6 showed only a slight fused‐ring effect on the carbonyl chemical shift. A single 17O resonance was observed for 2,5‐dihydroxybenzoquinone (358 ppm) and 5,8‐dihydroxynaphthoquinone (283 ppm), indicating rapid proton exchange between the oxygen atoms of these compounds. However, 1,4‐dihydroxyanthraquinone gave two discrete 17O signals at 441 and 87 ppm, indicating that in this case proton exchange between oxygen atoms is slow.