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The bright orange-red color of the toadstool Tricholoma aurantium is due to the benzotropolone pigment aurantricholone (1). The compound is at least partially present as the calcium salt. Minor pigments are the yellow 2H-furo[3,2-b]benzopyran-2-one derivatives aurantricholides A (7a) and B (7b), which exhibit strong green fluorescences. Their structures have been established by total syntheses.
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Klostermeyer et al. (2000) studied this question.
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