53 ブラシノライドおよびその類縁体の立体選択的合成

概要

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Brassinolide (1), a plant growth promoting steroid, has contiguous four chiral centers in its side chain and 22R, 23R, and 24S-configurations are required to exhibit its physiological activity. The key feature of our approach to the synthesis of brassinolide is based on the stereoselective reduction of the 4-ylidenetetronate (9) to control the stereochemistry of the contiguous four acyclic chiral centers in one-step. The requisite 4-ylidenetetronate (9) prepared from pregnenolone by several steps, was hydrogenated over 5% rhodium-alumina to give the saturated lactone (10) as the sole product, which was further converted into the triol (36), a key intermediate for the synthesis of brassinolide. The syntheses of (22S,23S,24R)-epibrassinolide (46) and 26,27-bisnorbrassinolide (53) have also been achieved by application of the above synthetic strategy. Thus, we could develop a novel stereoselective construction of steroidal side chain bearing polyhydroxy group, and could achieve the stereocontrolled syntheses of brassinolide and its analogues.
天然有機化合物討論会の論文
1986-09-09