5 海洋光合成色素フコキサンチンの全合成(口頭発表の部)

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The allenic carotenoid fucoxanthin 1 is known as an auxiliary light harvesting pigment for photosynthesis in the sea. We have accomplished the first total synthesis of optically active 1. In order to construct the fucoxanthin skeletal compound 2, two kinds of Wittig salts 3 and 5 were synthesized from the common intermediate 9a, which was prepared from the optically active hydroxy ketone 6 in good yield. Stereoselective DIBAL reduction of the anti-epoxide 11b derived from 9a in two steps and subsequent MnO_2 oxidation gave the allenic aldehyde 13, which was converted to the allenic Wittig salt 5. Rearrangement of the α-acetylenic alcohol 9a to the α,β-unsaturated ketone 14 catalyzed by oxometallic derivatives and subsequent iodine-catalyzed isomerization of the 6,7-exo-double bond into the 5,6-endo position provided the intermediate 15, leading to the 8-oxo-Wittig salt 3. The 8-oxo-Wittig salt 3 was condensed with the dialdehyde 4 to yield an isomeric mixture of 8-oxo-apocarotenals 16 and 17. Palladium-catalyzed isomerization of the mixture gave the all-E-isomer 16 as a sole product. Condensation between the TES ether 18 of 16 and the allenic Wittig salt 5 followed by reacetylation of 3'-hydroxyl group and deprotection of silyl group gave the skeletal compound 2. Epoxidation of the 5,6-double bond in 2 provided fucoxanthin 1. Spectral properties of the synthetic 1 were identical with those of the natural specimen.
天然有機化合物討論会の論文
1993-09-10

5 海洋光合成色素フコキサンチンの全合成(口頭発表の部)

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