34 高速な脱水縮合法を用いる天然ラクトン類の環骨格形成反応(口頭発表の部)
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概要
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Recently, we have developed a new and rapid lactonization of ω-hydroxycarboxylic acids using symmetric substituted benzoic anhydrides such as 2-methyl-6-nitrobenzoic anhydride (MNBA) as a condensation reagent. This protocol could be performed using a very simple procedure and the desired lactones are obtained within a very short time under mild conditions since the reaction quickly proceeds by the promotion of a catalytic amount of basic catalysts such as DMAP or its N-oxide (DMAPO). In this presentation, we will report an effective method for the synthesis of the several cyclic compounds including natural 8-, 9-, 14- or 29-membered ring lactone moiety using the effective lactonization protocol accelerated by MNBA as part of our continuous efforts for the application of the new synthetic methodology to produce peculiarly structural lactones. I. First, erythronolide A, a 14-membered lactone ring moiety of antibiotic erythromycin A, is prepared from the corresponding seco-acids including a variety of functionalities through the mixed-anhydride method using MNBA combined with basic catalyst. Although the reaction of a substrate protected by benzylidene acetal group with free tert-hydroxyl groups affords the desired lactone in low yield, the substrate protected with MOM group on the tert-hydroxyl groups is converted to the 14-membered lactone in good yield. II. Next, an effective method for the total synthesis of 2-hydroxy-24-oxooctacosanolide, a defensive salivary secretion of the African termite Pseudacanthoterme springer, has been developed. The key lactonization to form a 29-membered ring lactone core is performed using MNBA with a catalytic amount of DMAPO. III. Octalactin A, an anti-tumor agent having an 8-membered lactone moiety, is stereoselectively prepared by means of stereoselective C-C bond forming reactions using asymmetric catalysts. The medium-sized lactone part is effectively constructed by way of the new and rapid mixed-anhydride lactonization using MNBA with a catalytic amount of DMAP or DMAPO. The use of only 5mol% of DMAP or 2mol% of DMAPO rapidly promotes formation of the medium-sized ring of the octalactins indicating the remarkable efficiency of the new lactonization protocol. IV. Finally, the total synthesis ofpseudo-2-epibotcinolide through several featured synthetic approaches is attained. First, a chiral linear precursors of the 9-membered ring compounds is stereoselectively constructed by the combination of the asymmetric aldol strategy for producing β-hydroxy ester units. The key cyclization reaction to form the 9-membered ring lactone moiety is efficiently achieved by the extremely facile and powerful mixed-anhydride method promoted by MNBA with basic promoters.
- 天然有機化合物討論会の論文
- 2006-09-15
著者
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福井 博喜
東京理科大学理学部
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椎名 勇
東京理科大学理学部
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福井 博喜
東理大理
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椎名 勇
東理大理
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椎名 勇
Department Of Applied Chemistry Faculty Of Science Tokyo University Of Science
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佐々木 茜
東理大理
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小宮山 友理
東理大理
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人見 誠一
東理大理
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鈴木 亮輔
東理大理
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加藤 孝
東理大理
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