51 Withanolidesの合成研究(5) : Withaferin Aの全合成
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概要
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In the course of synthetic studies on withanolides, we have been working on the total synthesis of withaferin A (1). In this paper, a synthetic procedure for the side-chain moiety of withaferin A, 22R-δ-lactone (13), and its application to the total synthesis of withaferin A are described. As a model compound, the 22R-lactones (13 and 15) were synthesized from i-steroidal 22S,23-epoxide (6). The epoxide 6 was converted to trisubstituted 22R-lactone (8) through 4 stages, which involved intramolecular cyclization. The 25-alkyl group was successfully introduced by 25-sulfenylation followed by alkylation and dehydrosulfenylation. Thus, after reduction of 8, the resultant lactone (10) was transformed into tetrasubstituted 22R-δ-lactone (13), which had the identical structure with withaferin A side-chain. Total synthesis of withaferin A was carried out starting from bisnorcholenic acid (16) (Scheme 1). 1α-Acetoxy compound (18) was obtained through the 7 steps from 16. Oxidation of 22-ene (19) with OsO_4 followed by tosylation gave 22S-ol (20), which was converted to trisubstituted 22R-δ-lactone (22) via 21. Reduction of 22, sulfenylation, and subsequent hydroxymethylation gave 25-phenylthio-25-hydroxy-methyl compound (24), which was transformed into 5,6-epoxide (25). Oxidation followed by opening of the epoxide by PhSH afforded vic 5α-hydroxy sulfide (26), which was converted to 6β-PhS-dienone (27). This compound has the identical side-chain lactone with 1. Derivation of 27 to 1 is under investigation.
- 天然有機化合物討論会の論文
- 1981-09-10
著者
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平山 匡男
明治製菓・生科研
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池川 信夫
Laboratory Of Chemistry For Natural Products Tokyo Institute Of Technology
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蒲生 啓司
Department Of Chemistry Tokyo Institute Of Technology
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池川 信夫
東京工大 理
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池川 信夫
東工大・理
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蒲生 啓司
東工大・理
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平山 匡男
明治製菓・中研
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