Quinones polycyclic pigments

Orphan skeletons are emphasized in boldfece characters. Found both in the Tertiary and the Triassic eras, they have no equivalent in extant organisms and cannot be accounted for by di enetic transformations alone. They comprise xanthenoxanthene quinones, quincyte pigments of likely polyketide origin (Prowse 1991), and three series of isoprenoids polycyclic hydrocarbons from the... 

Isoviolanthrone is described as a highly anellated polycyclic quinone system , essentially two benzanthrone molecules joined asymmetrically. This compound was first synthesised in 1907 and has long been known as a vat dye. However, it is the dichloro-derivative which is best known as a pigment, affording the reddish violet colour known as isoviolanthrone violet. Cl Pigment Violet 31 Colour Index, 1971 Wich, 1973 Herbst and Hunger, 1997). 

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