All of α-Carotene and Its Derivatives Have a Sole Chirality?

Abstract

Distribution of a-carotene and its derivatives is reported to be limited in some taxonomic groups of phototrophic organisms. In addition, C-6′ in a-carotene between e-end group and conjugated double bonds is chiral, (6′R) - and (6′S)-types. The chirality was not systematically investigated, and the reported algae and land plants contained only (6′R)-type of a-carotene and/or its derivatives. To confirm the reliability of chirality, we re-examined distribution of a-carotene and its derivatives, and analyzed their C-6′ chirality using circular dichroism or nuclear magnetic resonance spectra after purification of the carotenoids. We found a-carotene and/or its derivatives from Rhodophyceae (macrophytic type), Cryptophyceae, Euglenophyceae, Chlorarachniophyceae, Prasinophyceae, Chlorophyceae, Ulvophyceae, Charophyceae, and land plants, while we could not detected them from Glaucophyceae, Rhodophyceae (unicellular type), Chryosophyceae, Raphidophyceae, Bacillariophyceae, Phaeophyceae, Xanthophyceae, Eustigmatophyceae, Haptophyceae, and Dinophyceae. Further, loroxanthin, siphonaxanthin, and their fatty acid esters, which are synthesized from lutein, were found from Euglenophyceae, Chlorarachniophyceae, Prasinophyceae, Chlorophyceae, and Ulvophyceae. We analyzed chirality of a-carotene and/or its derivatives from around 40 species described above, and found they had only (6′R)-type.