Frankia sp.G2 (ORS 020604), grown for one month without shaking, produced a mixture of 2 quinonoid pigments.The structure of one, G-2N, was shown by chemical and physical methods to be 2-methyl-4,7,9,12-tetrahydroxy-5,6-dihydro benzo[a]naphthacene-8,13-dione.The other, G-2A, has the same structure with the addition of a carboxyl group at position 10 or 11.Natural quinones with this ring system have not been reported previously.
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Gerber et al. (1984) studied this question.