9 The Structure of Flavoskyrin
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Previously a structural formula (V) was proposed for flavoskyrin, a yellow pigment of Penicillium islandicum Sopp. NRRL 1175. In relation with the revised structure of rugulosin (I) and luteoskyrin (II), the structure of (-) flavoskyrin has been reexamined. Flavoskyrin has now been found to be a dimeric compound having a molecular formula, C_<30>H_<24>O_<10>. On treatment with thionyl chloride in pyridine (-) flavoskyrin is converted into (+) dianhydrorugulosin ((+) dichrysophonol (8, 8')). By the action of pyridine (-) flavoskyrin affords dianhydrorugulosin and (-) rugulosin. The synthetic compounds (VIII), (XII) and (XIII) which were used as the model compounds for flavoskyrin have now been proved by the Mass and MNR spectra to be dimers. The comparative studies using UV, IR, NMR and Mass spectra have led the new structure XVIa for flavoskyrin. The mechanism of dimerization reaction of the synthetic model compoumds has also been discussed.
