Synthesis of highly 13C enriched carotenoids: access to carotenoids enriched with 13C at any position and combination of positions

Carotenoids and their metabolites are essential factors for the maintenance of important life processes such as photosynthesis. Animals cannot synthesize carotenoids de novo, they must obtain them via their food. In order to make intensive animal husbandry possible and maintain human and animal health synthetic nature identical carotenoids are presently commercially available at the multi-tonnes scale per year. Synthetically accessible 13C enriched carotenoids are essential to apply isotope sensitive techniques to obtain information at the atomic level without perturbation about the role of carotenoids in photosynthesis, nutrition, vision, animal development, etc. Simple highly 13C enriched C1, C2 and C3 building blocks are commercially available via 99% 13CO. The synthetic routes for the preparation of the 13C enriched building blocks starting from the commercially available systems are discussed first. Then, how these building blocks are used for the synthesis of the various 13C enriched carotenoids and apocarotenoids are reviewed next. The synthetic Schemes that resulted in 13C enriched β-carotene, spheroidene, β-cryptoxanthin, canthaxanthin, astaxanthin, (3R,3'R)-zeaxanthin and (3R,3'R,6'R)-lutein are described. The Schemes that are reviewed can also be used to synthetically access any carotenoid and apocarotenoid in any 13C isotopically enriched form up to the unitarily enriched form.