Eight (Z)-isomers of lycopene were prepared by stereocontrolled syntheses and fully characterized by '€1-NMR, "C-NMR, mass, and UVjVIS spectroscopy: (5Z)-, (72)

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Synthesis of Optically Active Natural Carotenoids and Structurally Related Compounds. VIII. Synthesis of (3S,3′S)‐7,8,7′,8′‐Tetradehydroastaxanthin and (3S,3′S)‐7,8‐Didehydroastaxanthin (Asterinic Acid) The synthesis of all‐trans‐(3S,3′S)‐3,3′‐dihydroxy‐7,8, 7′,8′‐tetradehydro‐β, β‐carotene‐4,4′‐dione (1), of all‐trans‐(3S,3′S)‐3,3′‐dihydroxy‐7, 8‐didehydro‐β,β‐carotene‐4,4′‐dione (2) (asterinic acid = mixture of 1 and 2), and of their 9,9′‐di‐cis‐ and 9‐cis‐isomers is reported starting from (4′S)(2E)‐5‐(4′‐hydroxy‐2′, 6′,6′‐trimethyl‐3′‐oxo‐l′‐cyclohexenyl)‐3‐methyl‐2‐penten‐4‐ynal (8). The absolute configuration (3S,3′S) for both components 1 and 2 of asterinic acid ex Asterias rubens is confirmed on the basis of spectroscopic and direct comparison.

Synthesis of Optically Active Natural Carotenoids and Structurally Related Compounds. IX. Synthesis of (3R)‐Hydroxyechinenone, (3R, 3′R)‐ and (3R, 3′S)‐Adonixanthin, (3R)‐Adonirubin, Their Optical Antipodes and Related Compounds The synthesis of racemic and optically active hydroxyechinenone (12–14), adonixanthin (16–19), adonirubin (22–24), meso‐astaxanthin (26) and their corresponding diosphenols 15, 20, 21, 25, 27, 28, and 29) by Wittig reaction is reported, starting from suitable C15‐phosphonium salts and C10‐aldehydes.

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Contribution to the Analytical Separation and the Synthesis of 3‐Hydroxy‐4‐oxocarotenoids (3RS,3′RS)‐Astaxanthin (= 3,3′‐dihydroxy‐β,β‐carotene‐4,4′‐dione, 1:1‐mixture of racemate and meso‐form; 1) can be separated into its optical isomers (3S,3′S)‐1a, (3R,3′R)‐1b and meso‐(3R,3′S)‐1c via the corresponding diastereomeric di‐(−)‐camphanates. Some aspects of the configurational stability of astaxanthin are discussed. ‐ HPLC. analysis of the (−)‐camphanates of 3‐hydroxy‐4‐oxocarotenoids provides, in suitable cases and supported by spectroscopic data, an analytical method for the simultaneous determination of constitution and chirality.

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