Absolute Konfiguration von Antheraxanthin, « cis ‐Antheraxantliirt» und der diastereomeren Mutatoxanthine

Absolute Configuration of Antheraxanthin, ‘ cis ‐Aritheraxanthin’ and of the Stereoisomeric Mutatdxanthins The assignement of structure 2 to antheraxanthin (all‐ E )‐(3 S , 5 R , 6 S , 3′ R )‐5,6‐epoxy‐5,6‐dihydro‐β,β‐carotene‐3,3′‐diol and of 1 to ‘ cis ‐antheraxanthin’ (9 Z )‐(3 S , 5 R , 6 S , 3′ R )‐5,6‐epoxy‐5,6‐dihydro‐β,β‐carotene‐3,3′‐diol is based on chemical correlation with (3 R , 3′ R )‐zeaxanthin and extensive 1 H‐NMR. measurements at 400 MHz. ‘Semisynthetic antheraxanthin’ ( = ‘antheraxanthin B’) has structure 6 . For the first time the so‐called ‘mutatoxanthin’, a known rearrangement product of either 1 or 2 , has been separated into pure and crystalline C(8)‐epimers (epimer A of m.p. 213° and epimer B of m.p. 159°). Their structures were assigned by spectroscopical and chiroptical correlations with flavoxanthin and chrysanthemaxanthin. Epimer A is (3 S , 5 R , 8 S , 3′ R )‐5,8‐epoxy‐5,8‐dihydro‐β,β‐carotene‐3,3′‐diol ( 4 ; = (8 S )mutatoxanthin) and epimer B is (3 S , 5 R , 8 R , 3′ R )‐5,8‐epoxy‐5,8‐dihydro‐β,β‐carotene‐3,3′‐diol ( 3 ; = (8 R )‐mutatoxanthin). The carotenoids 1 – 4 have a widespread occurrence in plants. We also describe their separation by HPLC. techniques. CD. spectra measured at room temperature and at − 180° are presented for 1 – 4 and 6 . Antheraxanthin ( 2 ) and (9 Z )‐antheraxanthin ( 1 ) exhibit a typical conservative CD. The CD. Spectra also allow an easy differentiation of 6 from its epimer 2 . The isomeric (9 Z )‐antheraxanthin ( 1 ) shows the expected inversion of the CD. curve in the UV. range. The CD. spectra of the epimeric mutatoxanthins 3 and 4 (β end group) are dissimilar to those of flavoxanthin/chrysanthemaxanthin (ε end group). They allow an easy differentiation of the C (8)‐epimers.