P-30 ニトロンの環化付加を用いるMaremycin類の合成(ポスター発表の部)
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概要
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Maremycins 1-6 are diketopiperazines obtained from the culture broths of marine Streptomyces species. The stereochemistries of maremycins were tentatively proposed on the basis of molecular mechanics calculations and spectroscopic data of compounds 1 and 2. The fact that structurally related diketopiperazine FR900452 (7) is a potent and specific inhibitor of platelet-activating factor (PAF) also interests us in bioactivities of compounds 1-6. We present here the first synthesis of maremycins A (1) and D_1 (5) by using cycloaddition of 3-ethylideneindolin-2-one 10 with cyclic nitrone 11, and confirmed stereostructures of maremycins. When a mixture of 3-ethylidene-1-methylindolin-2-one (10) and nitrone 11 in toluene was heated at 60℃ for 48h, smooth cycloaddition occurred to afford a 22:78 mixture of cycloadducts 12 and its regioisomer 13 in 94% yield. Unfortunately, the desired cycloadduct 12 was the minor isomer, so we further examined the reaction conditions such as Lewis acids, temperatures, and solvents. After experimentation, we found that use of hexane or THF as a solvent afforded a 1:1 mixture of 12 and 13, although Lewis acids did not work. It was also found that undesired adduct 13 could be transformed to desired adduct 12 via cycloreversion-recycloaddition. Since cycloadduct 12 has the correct stereochemistry for maremycins A (1) and D_1 (5), synthesis of 1 and 5 was readily achieved by elaboration including hydrogenolysis, condensation with Boc-S-Me-L-Cys (16), diketopiperazine formation and oxidative desulfurization.
- 天然有機化合物討論会の論文
- 2008-09-01
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