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’ (9Z)-(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 ¹H-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 (9Z)-antheraxanthin ( 1 ) exhibit a typical conservative CD. The CD. Spectra also allow an easy differentiation of 6 from its epimer 2 . The isomeric (9Z)-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.