Studies on the Metabolites of Aspergillus versicolor (Vuillemin) Tiraboschi

Part V. Isolation and Structures of Three New Metabolites, Versicolorins A, B and C

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Three new pigments, named versicolorins A, B and C, as metabolites from the mycelium of Aspergillus versicolor have been isolated. Versicolorin A, C₁₈H₁₀O₇, is fine orange yellow needles, m. p. 289°C (decomp.), [α]D-354°. It is an anthraquinoid pigment having three hydroxyl groups and a vinyl ether system contained in a five-membered ring. Versicolorin A trimethyl ether was hydrogenated to a dihydro-derivative, and by oxidation gave 3, 5-dimethoxyphthalic acid and a hydroxy acid which may be 1, 6, 8-trimethoxy-3-hydroxy anthraquinone-2-carboxylic acid. These chemical behavior and NMR data show that versicolorin A probably has the structure of (I). Versicolorin B, C₁₈H₁₂O₇, is fine orange yellow needles, m. p., 298°C (decomp.), [α]D-223° Its trimethyl ether is identical with that of dihydroversicolorin A. Therefore, the structure (II) could be assigned to versicolorin B. Versicolorin C, C₁₈H₁₂O₇, is orange red needles, m. p.>310°C, [α]D 0° Comparison of optical properties, IR and NMR spectra of versicolorin B and its methyl ether with those of versicolorin C and its methyl ether indicates that versicolorin C is very probably a racemate of versicolorin B.