28 Synthesis and Structure Elucidation of Novel Ecdysteroids, Abutasterone and Gerardiasterone
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The stereocontrolled introduction of side chains into steroids has been widely investigated due to the discovery of physiologically active steroids, such as ecdysone, brassinolide, and withanolide, which have highly oxygenated side chains. Synthesis and structure elucidation of two novel ecdysteroids, abutasterone and gerardiasterone, are described. 1. Synthesis and Structure Elucidation of Abutasterone Side Chain Abutasterone, isolated from the Amazonian plant Abuts velutina, is a novel ecdysteroid and its structure elucidated by spectral means except the stereochemistry at C-24. Both (24R)- and (24S)-tetraols(3,4) were prepared employing hydroxylation of the lactone (7) with MoOPH. Since the NMR spectrum of 3 was close to that of abutasterone, the stereochemistry of the 24-position was deduced to be R cofiguration. 2. Synthesis and Structure Elucidation of Gerardiasterone Gerardiasterone is a new ecdysteroid with a 20,22,23,25-tetra-hydroxylated side chain from the Mediterranean zoanthid Gerardia savaglia. The configurations on the side chain have not been established. Preparation of four model compounds(14-17) among eight possible diastereomers suggested that the stereochemistry on the side chain could be 20R, 22R, 23S configurations. Thus, synthesis of (20R,22R,23S)-gerardiasterone(35) was achieved by stereoselective hydroxylation of 22E-olefin(34) as a key step. The NMR spectrum of 35 was identical with that of natural gerardiasterone.
