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Kinobscurinone, a benzo[ b]fluorenone quinone previously reported to be “NMR silent”, affording neither 1H- nor 13C NMR spectra under a variety of conditions, has now been shown to exist in part as a free radical under ambient conditions. The gvalue for kinobscurinone was found to be 2.0052; no hyperfine splitting was observed. ESR signals were similarly observed for three other substituted benzo[ b]fluorene quinones.

Incorporations of sodium [1,2-13C2]acetate and sodium [1-13C,18O2]acetate confirmed that murayaquinone, produced by Streptomyces murayamaensis, is a polyketide. However, the labeling patterns revealed that a simple folding of the decaketide intermediate does not lead directly to the final phenanthrene skeleton. Instead a different phenanthrene is apparently formed that undergoes an oxidative cleavage, isomerization, and re-closure to a new phenanthrene skeleton.

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