Absolute Konfiguration von α-Zeacarotin, α-Apo-8-carotinal und α-Apo-8-carotinol

α-Zeacarotene, isolated from corn gluten, has been shown to have the same absolute configuration at C(6) as natural (+)-α-carotene. Chiroptical comparison was made with the derived α-apo-8-carotenole. The same chirality has been found with δ-, ε-carotene, lutein, semi-α-carotenone, zeinoxanthin, crocoxanthin and β,ε-carotene-2-ol. Therefore, biological cyclisation of the acyclic precursor to the α-ionone ring seems to be stereospecific and is probably different (enantiomeric) to that leading to β-ionone derivatives. Cotton effects of carotenoids have for the first time been measured in the visible region. All carotenoids examined with C(6)-R-chirality show a positive effect at their longest absorption band.