36 多官能性カロテノイド・ペリジニンの立体化学を制御した全合成(口頭発表の部)

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Peridinin (1), which was isolated from fish-water dinoflagellates causing red tide, has been known as an auxiliary light harvesting pigment for photosynthesis in the sea. The structure of this carotenoid was determined by Jensen's group in 1980. This molecular is highly oxidized unique C37 nor-carotenoid containing allene and ylidenebutenolide functions in the conjugated main polyene chain, in addition to the functionalized cyclohexane rings at both ends of the molecular. The first synthesis of peridinin was reported by Ito and co-workers in 1993. In that synthesis, however, the control of stereochemistry and therefore the yields were left out of consideration. For the stereocontrolled synthesis of peridinin, the questions are the following: (1) stereocontrolled construction of the all-trans-conjugated olefin chain containing the (Z)-γ-ylidenebutenolide moiety, and of the asymmetric allene function, and(2)stereocontrolled construction of the oxygen functions at the terminal cyclohexane ring. We resolved these questions and overcomed problems by effectively utilizing our own or new synthetic methods, and achieved the highly efficient total synthesis of peridinin by controlling the stereochemistry of six asymmetric carbons and six of seven geometries of the double bonds in this particular molecular. In this conference, we disclose in detail our synthetic efforts on the total synthesis of peridinin. The highly stereoselective introduction of the oxygen functions at a cyclohexane terminal was actually realized with the Sharpless asymmetric epoxidation by finding the strictly precise reaction conditions, and the key intermediate, (-)-epoxyaldehyde E was prepared in high purity. The allene half-segment A of peridinin was synthesized from the compound E by a transformation into the acetylene derivative 4, followed by the Sonogashira coupling with the conjugated vinyl iodide 5, and then S_N2' hydride reduction. The ylidenebutenolide segment Y was efficiently synthesized from the same compound E by a coupling of our own furan-Wittig reagent W followed by ^1O_2 oxygenation, acetylene formation, and then novel and effective three-step one-pot formation of the (Z)-ylidenebutenolide moiety. Finally, the both of segment A and Y was successfully coupled by utilizing the modified Julia-Kocienski olefination. The 15Z-peridinin thus obtained stereoselectively, gradually isomerized into all-trans-peridinin at room temperature. Thus, we achieved the stereocontrolled efficient synthesis of peridinin. The knowledge obtained from our present synthesis is believed to essencially contribute to the polyfunctional carotenoid synthesis.
天然有機化合物討論会の論文
2001-09-01

36 多官能性カロテノイド・ペリジニンの立体化学を制御した全合成(口頭発表の部)

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