Pyxiferin

This structure had been erroneously assigned to pyxiferin... 

Diquinone Only one lichen compound, pyxiferin, has been identified as a diquinone. If pyxiferin were formed by oxidative coupling of acetate-polymalonate-derived units, the first ring would arise by decarboxylation. 

Huneck (77(5) reported that the structure (201) proposed for pyxiferin was incorrect. The metabolite was found to be identical with chiodectonic acid, identified as a naphthoquinone derivative, although no structure has yet been proposed. 

Fig. 4. Structural relationships and possible formation of the five types of condensation products of orsellinic acid (6) or its homologues taking place in lichens. (9a) = olivetoric acid, (9b) = dihydropicrolichenic acid, (10) = physodic acid, (11) = picrolichenic acid, (12) = pannaric acid, (13) = pyxiferin.

Fig. 7. Possible biosynthesis of pyxiferin (16a) and structures of the fungal dibenzoquinones phoenicin (16b) and oosporein (16c). Labeling pattern in fungal toluquinone fumigatin (17) after incubation with [2- C]orsellinic acid.

K+ red to violet Anthraquinones, bisanthraquinones, terphenylquinones, naphthoquinones, pyxiferin... 

In 1965 Chandrasenan et al. (65) proposed structure 514 for pyxiferin, the main pigment from Pyxine coccifera. This substance was subsequently synthesized (see Scheme 159) and found to differ from natural pyxiferin. Later on Huneck (380) identified pyxiferin with chiodectonic acid and proposed structure 515 for this pigment. 

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