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

Abstract

Syntheses of the Enantiomeric Aleuriaxanthins. Detection of a Predominant (Z)‐Aleuriaxanthin in AleuriaThe enantiomeric C₁₀‐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.