Synthese von optisch aktiven, natürlichen Carotinoiden und strukturell verwandten Naturprodukten. VIII. Synthese von (3S,3′S)‐7,8,7′,8′‐Tetradehydroastaxanthin und (3S,3′S)‐7,8‐Didehydroastaxanthin (Asterinsäure)

Abstract

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.

X-ray crystal structures of diacetates of 6-s-cis and 6-s-trans astaxanthin and of 7,8-didehydroastaxanthin and 7,8,7′,8′-tetradehydroastaxanthin: comparison with free and protein-bound astaxanthins

“…Samples of synthetic, optically pure (3S,3 0 S)-(2) and (3S,3 0 S)-(3) (Bernhard et al, 1980) were obtained from Hoffmann-La Roche, Basle, and recrystallized from acetone/ water and dichloromethane/hexane, respectively, by vapourdiffusion techniques, the latter at 278 K.…”

Total Synthesis of Capsanthin Using Lewis Acid-Promoted Regio- and Stereoselective Rearrangement of Tetrasubstituted Epoxide.

“…Treatment of the epoxide 12 with SnCl 4 followed by desilylation yielded the regio-and stereoselective rearranged product 13 15) in good yield, which was then condensed with the Wittig salt 16 16) in the presence of NaOMe as a base followed by one-pot treatment with ion exchange resin, Dowex 50W-X8 (H ϩ ), to give a mixture of the all-E C 25 -apocarotenal 14a (39%), the 11Z isomer 14b (28%) and 13Z one 14c (9%). Both isomers 14b and 14c could be transformed (64% from 14b; 70% from 14c) into the desired all-E one 14a by palladium-catalyzed isomerization.…”

“…The resulting TBS ether 10 was then treated with m-chloroperbenzoic acid (m-CPBA) to give a mixture of the anti(a)-epoxide 11a (28%) and syn(b)-epoxide 11b (54%). Reduction of 11a with LiAlH 4 followed by MnO 2 -oxidation gave the C 15 -epoxy-aldehyde 12 in 98% yield.Treatment of the epoxide 12 with SnCl 4 followed by desilylation yielded the regio-and stereoselective rearranged product 13 15) in good yield, which was then condensed with the Wittig salt 16 16) in the presence of NaOMe as a base followed by one-pot treatment with ion exchange resin, Dowex 50W-X8 (H ϩ ), to give a mixture of the all-E C 25 -apocarotenal 14a (39%), the 11Z isomer 14b (28%) and 13Z one 14c (9%). Both isomers 14b and 14c could be transformed (64% from 14b; 70% from 14c) into the desired all-E one 14a by…”

Carotenoids and Related Polyenes, Part 12 First Total Synthesis and Absolute Configuration of 3'-Deoxycapsanthin and 3,4-Didehydroxy-3'-deoxycapsanthin

“…Wittig condensation of the C 15 -aldehyde 6a with the C 10 -phosphonium salt 19 17) in the presence of NaOMe as a base, followed by one-pot treatment with ion exchange resin (Dowex 50W-X8, H ϩ ), provided an isomeric mixture of C 25 -apocarotenals. Preparative HPLC (PHPLC) provided the all-E isomer 17 (42%) and an isomeric mixture (18%), which thermodynamically isomerized while standing in ethereal solution at room temperature (rt) for 1 d to yield the desired all-E isomer 17 (7% from 6a).…”