Robert K. Müller

Some recent advances in the synthesis of natural carotenoids

Abstract The total syntheses of naturally occurring (3R,3′R)-zeaxanthin, (3S,3′S)-astaxanthin, (3S,3′S)-asterinic acid and of some related xanthophylls are discussed. Asymmetric hydroboration has been applied to the total synthesis of all configurational isomers of zeaxanthin. The total synthesis of natural actinioerythrin is described and the absolute configuration confirmed by X-ray crystallographic analysis of an intermediate. The optical resolution of α-hydroxy-carbonyl compounds via (−)-camphanic acid esters appears to be generally applicable and can be used as an analytical method for the determination of the optical purity of α-hydroxy-carbonyl carotenoids. Some technological applications are indicated.

RECENT ADVANCES IN THE SYNTHESIS AND ANALYSIS OF 3,4-OXYGENATED XANTHOPHYLLS

Abstract The progress made within the last three years in the synthesis and analysis of astaxanthin and of other related 3,4-oxygenated xanthophylls is reviewed. This includes preparatively attractive routes to all optical isomers of adonirubin, 3-hydroxy echinenone, and of adonixanthin. (3R,3′R)-, (3S,3′S)-, as well as meso-(3R,3′S)-astaxanthin could be separated by HPLC when (3RS,3′RS)-astaxanthin (a 1:1 mixture of race-mate and meso-form) was first converted into the corresponding diaste-reomeric di-(-)-camphanates. The usefulness of this accurate analytical method for the separation of optical isomers of astaxanthin was demonstrated by the analysis of various astaxanthin samples from different natural sources. Surprisingly, some of these were found to be mixtures of the three optical isomers. The extension of this separation technique to other 3-hydroxy-4-oxo carotenoids provided, in combination with spectroscopic data, an excellent analytical method for the determination of the constitution, chirality and purity of these carotenoids.