Absolute Konfiguration von α‐Doradexanthin und von Fritschiellaxanthin, einem neuen Carotinoid aus Fritschiella tuberosa I YENG

Absolute Configuration of α‐Doradexanthin and of Fritschiellaxanthin, a New Carotenoid from Fritschiella tuberosa IYENG. Fritschiellaxanthin, a new oxocarotenoid produced by the green alga Fritschiella tuberosa, in a nitrogen‐deficient medium is now shown to be (3 S, 3′ R, 6′ R)‐3, 3′‐dihydroxy‐β, ϵ‐caroten‐4‐one (4b). It is not identical with α‐Doradexanthin (5b) previously found in goldfish (Carassius auratus) and to which we assign the (3 S, 3′ S, 6′ R)‐chirality. Consequently, fritschiellaxanthin and α‐Doradexanthin are C(3′)‐epimers of lutein‐4‐on. Furthermore, the so‐called ′lutein′ from goldfish has now been found to be identical with 3′‐epilutein (3). Therefore, fritschiellaxanthin is probably biogenetically derived from lutein (2), whereas α‐Doradexanthin is formed from 3′‐epilutein (3) with 3, O‐didehydrolutein (=(3R, 6′R)‐3‐hydroxy‐β, ϵ‐caroten‐3′‐one10) as a precursor. For comparison, optically active 10 and 3 have been prepared from lutein (2) and are fully characterised.