SYNTHESIS OF ISOTOPICALLY LABELED CAROTENOIDS - INVESTIGATIONS ON STRUCTURE AND FUNCTION OF CAROTENOPROTEINS AT THE ATOMIC-LEVEL

A three-part strategy has been developed to study molecular interactio ns in biological systems. Isotopically labelled carotenoids or other s ubstances are prepared by organic total synthesis in specific isotopic ally labelled form. These small molecules are used to assemble the act ive biological system, which is then studied by physical techniques. A general synthetic scheme for the synthesis of carotenoids, both symme trical and asymmetrical, selectively labelled with C-13 at predetermin ed positions in the C-10-central part, is presented. The synthetic sch eme is based on the C-15 + C-10 + C-15 strategy. For symmetrical carot enoids the C-10-dialdehyde, 2,7-dimethylocta-2,4,6-triene-1,8-dial 1, is used. For asymmetrical carotenoids two novel synthons are introduce d: 2,7-dimethylocta-2,4,6-triene-8-alnitrile 2 and methoxy-N,2,7-trime thylocta-2,4,6-triene-8-alamide 3. The use of these synthons is illust rated by the synthesis of labelled beta-carotene 4, astaxanthin 5 and spheroidene 6. Some of the structural and functional results that have been obtained by this strategy in the fields of photosynthesis and vi sion, are given.