cis-Stereoisomers of β-carotene and its congeners in the alga Dunaliella bardawil, and their biogenetic interrelationships

The acyclic carotenoids phytoene and phytofluene, which are precursors of 9-cis-β-carotene produced by the alga Dunaliella bardawil, have been separated and characterised. Spectroscopic data, and comparison with synthetic model compounds and corresponding carotenoids found in the fruits of the Tangerine tomato Lycopersicon esculentum var., establish that the pigments have the stereochemistries 15-cis-6 and 9-cis-11 respectively. The data suggest that phytoene 6 is the clear branch point for the formation of 9-cis-β-carotene 2 in D. bardawil. In addition, spectroscopic data for β-carotene isolated from D. bardawil showed that it was isomerically pure 9-cis-β-carotene 2.