Quinone pigments from higher plants and marine animals
The chemical constituents of Ventilago maderaspatana and V. calyculata have been examined and a large number of novel quinones have been identified in the extracts. Sixteen new isochromanquinones, five new isofuranquinones and four new miscellaneous naphtho- and anthraquinones were characterised. The discovery of both naphthoquinones and anthraquinones in the same species is highly unusual and the large number of isochromanquinones obtained from such a limited-source is unprecedented, isochromanquinones themselves being uncommon structures in nature. A review of other naturally occurring isochromanquinones is presented. From the Mexican plant Lantana achyrantifolia two mixtures of isomeric furanonaphthoquinones were obtained. Structures for these quinones were deduced from spectroscopic data and syntheses were attempted to provide supporting evidence. The dihydro- precursors of one pair of isomers were obtained but the final oxidation of these compounds to the natural products was prevented by lack of time and material. Following reports that the wood of the olive (Oleo eurapaea) contained an eczematogenous constituent, an attempt was made to isolate the compound(s) responsible. The known coumarin, scopoletin, was obtained from the wood but gave negative results in skin-sensitisation tests. A second eczematogenous compound, primetin, from the primrose Primula mistassinica was suspected to be active in vivo as the corresponding quinone. Primetin quinone was successfully produced from primetin and this proved to be significantly more active in skin-sensitising tests than primetin. The sea-urchins, Benthodytes typica and B. lingua (Holothuroidea), were studied in order to determine the compound(s) responsible for their deep red colour. A known polyhydroxynaphthoquinone and its dimer were obtained and characterised. The dimer had not previously been reported. The feather-star Antedon bifida (Crinoidea) was also examined in order to determine the nature of the major colouring constituent(s). No compounds were obtained in a pure state from the extract but the main pigment appears to be a polyhydroxyquinone which may be bound up with one or more polypeptide chains as a chromoprotein.