Absolute Konfiguration von Loroxanthin (=(3 R , 3′ R , 6′ R )‐β, ϵ‐Carotin‐3, 19, 3′‐triol)

Absolute Configuration of Loroxanthin (=(3 R , 3′ R , 6′ R )‐β, ϵ‐Carotene‐3, 19, 3′‐triol) ‘Loroxanthin’, isolated from Chlorella vulgaris , was separated by HPLC. methods in two major isomers, a mono‐ cis ‐loroxanthin and the all‐ trans ‐form. Solutions of the pure isomers easily set up again a mixture of the cis / trans ‐isomers. Extensive 1 H‐NMR. spectral measurements at 400 MHz allowed to establish the 3′, 6′‐ trans ‐configuration at the ϵ‐end group in both isomers and the (9 E )‐configuration in the mono‐ cis ‐isomer. The absolute configurations at C(3) and C(6′) were deduced from CD. correlations with synthetic (9 Z , 3 R , 6′ R )‐β, ϵ‐carotene‐3, 19‐diol ( 5 ) and (9 E , 3 R , 6′ R )‐β, ϵ‐carotene‐3, 19‐diol ( 6 ), respectively. Thus, all‐ trans ‐loroxanthin ( 3 ) is (9 Z , 3 R , 3′ R , 6′ R )‐β, ϵ‐carotene‐3, 19, 3′‐triol and its predominant mono‐ cis ‐isomer is (9 E , 3 R , 3′ R , 6′ R )‐β, ϵ‐carotene‐3, 19, 3′‐triol ( 4 ). Cooccurrence in the same organism and identical chirality at all centers suggest that loroxanthin is biosynthesized from lutein ( 2 ).