Synthesis of 13C-labeled carotenoids and retinoids

A three-part strategy has been developed to study molecular interactions in biological systems at the atomic level. First, isotopically labeled carotenoids and retinoids are prepared by organic total synthetic schemes with labels at predetermined atomic positions and combinations of positions. Subsequently, the labeled compounds are incorporated in the biological system. Finally, the system is studied by isotope sensitive spectroscopic techniques. In this paper, the synthesis of 10-fold C-13-labeled retinal palmitate and beta-carotene alpha-crustacyanin carotene for nutritional studies is discussed. Also, the scheme to label the end positions of astaxanthin and canthaxanthin with C-13 for spectroscopic investigations of alpha-crustacyanin with isotope labels in the chromophore is given. The synthesis of 10-methyl retinal is discussed, starting from isotopically labeled synthons obtained via schemes to C-13-labeled natural retinal. Finally, the possibility for spectroscopic studies of carotene and retino proteins via an expression of apoproteins by way of genetic techniques in the post-genomic era is discussed.