The Chemistry and Stereochemistry of Cercosporin

The structure of cercosporin, a deep red photosensitizing pigment isolated from the cultured mycelia of Cercospora kikuchii (Matsumoto et Tomoyasu) Gardner, has been elucidated as 1,12-bis(2-hydroxypropyl)-2,11-dimethoxy-6,7-methylenedioxy-4,9-dihydroxyperylene-3,10-quinone(Ia). All substituents are symmetrically arranged and the molecule has a two-fold rotation axis. An unusual seven-membered methylenedioxy bridged system endows the molecule with the inherently dissymmetric nature. Isocercosporin(Ib), a stereoisomer of Ia, was separated and the stereochemistry and the molecular dissymmetry of both isomers were also discussed.