Synthesen der enantiomeren Aleuriaxanthine. Nachweis eines vorherrschenden (Z)-Aleuriaxanthins inAleuria

Syntheses of the Enantiomeric Aleuriaxanthins. Detection of a Predominant (Z)-Aleuriaxanthin in Aleuria The 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.