Synthesen der enantiomeren Aleuriaxanthine. Nachweis eines vorherrschenden ( Z )‐Aleuriaxanthins in Aleuria

Syntheses of the Enantiomeric Aleuriaxanthins. Detection of a Predominant ( Z )‐Aleuriaxanthin in Aleuria The enantiomeric C 10 ‐building blocks 9 ((+)‐(2 E , 6 R)‐6, 7‐dihydroxy‐3, 7‐di methyl‐2‐octen‐l‐yl acetate) and ent ‐ 9 , and 11 ((+)‐(2 E , 6 R )‐3, 7‐dimethyl‐2, 7‐octadien‐l, 6‐diyl diacetate) and ent ‐ 11 , prepared from the optically active epoxy‐geraniols 7 and ent ‐ 7 , respectively, have been used for the syntheses of (2′ R )‐aleuriaxanthin ( 1 ) and (2′ S )‐aleuriaxanthin ( ent ‐ 1 ). At room temperature aleuriaxanthin exhibits no significant CD. nor ORD. However, at −180° a very distinct CD. was observed, which in the UV. range showed a surprising resemblance to that of (3 R , 3′ R )‐zeaxanthin. By direct comparison of 1 with aleuriaxanthin isolated from Aleuria aurantia [2], the (2′ R )‐chirality assigned to the latter by Liaaen‐Jensen et al. [5] is confirmed. HPLC. separation of the mixture of carotenoids from Aleuria shows the presence of a predominant ( Z )‐aleuriaxanthin of yet undetermined structure.