123(P-62) ビサボラン型セスキテルペノイド,ケイモノフィロンEの全合成(ポスター発表の部)

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Cheimonophyllons (1-6) are six new bisabolane type sesquiterpenoids, which exhibit nematicidal, weak antifungal and antibacterial as well as cytotoxic activities. The major product, cheimonophyllon A (1), is the most active against nematodes and microorganisms. On the other hand, cheimonophyllon E (5) possesses most stereogenic centers in the highly oxygenated 7-oxabicyclo[4.3.0]nonane core. Interested in these intriguing structures and biological activities, we have been investigating the synthetic study on cheimonophyllons. We present herein the total synthesis of cheimonophyllon E (5). We first examined a racemic synthesis of cheimonophyllon E. The aldol reaction of commercially available enone 15 and aldehyde 16 with LDA at ?18℃ afforded an inseparable mixture of 17-syn and 17-anti (1.2:1). Benzoylation of the mixture provided 18-syn as a single isomer, after silica gel chromatography. Reduction of enone 18-syn under Luche's conditions gave the desired isomer 19 with a high level of diastereoselectivity. Oxidation of allylic alcohol 21, derived from 19, with VO(acac)_2 provided anti-epoxide 22 predominantly. Introduction of a methylene group was carried out by Peterson olefination to give γ-hydroxy-α-methylene-epoxide 26. Treatment of 26 with a catalytic amount of CSA underwent an intramolecular cyclization as a result of the epoxy ring opening. As expected, the 5-exo product 27 was obtained exclusively. Finally, oxidation of 27 followed by dihydroxylation with OsO_4-NMO afforded (±)-cheimonophyllon E (5). We next explored the synthesis of an optical active cheimonophyllon E. We found that the alcohol 27 was acylated with (S)-O-acetylmandelic acid giving separable diastereomers 30 and 31. Dibal-H reduction of 31 provided (+)-27, which was eventually converted into (+)-cheimonophyllon E, the natural enantiomer.
2000-10-01

123(P-62) ビサボラン型セスキテルペノイド,ケイモノフィロンEの全合成(ポスター発表の部)

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