55(P20) 保護基を用いない有機合成 : 水溶液中でのClavicipitic Acidの全合成(ポスター発表の部)

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Protection of the reactive functional groups such as hydroxyl, amino, or carboxyl group is essential for the organic synthesis in order to surpress the side reaction and to realize the easy handling in organic solvent. But a protecting group causes sometimes serious problems; for example, increase of the reaction steps (protection and deprotection) or difficulty of the deprotection of a complex compound. Therefore, if the methodology for the synthesis without protecting groups would have been established, it would greatly contribute to the organic chemistry. We wish to present here the one-pot synthesis of optically active clavicipitic acid (1) without using protecting group from free amino acid, 4-bromotryptophan (2). Palladium-catalyzed vinylation (Heck reaction) of optically active 4-bromotryptophan (2) with 3,3-dimethylallylacicohol (3) in the presence of 0.1eq. of palladium acetate, K_2CO_3 (KHCO_3 or NaOH) and water soluble ligand, TPPTS in aqueous solution at 130℃ for 6h gave the potassium salt of 4-(3-hydroxy-3,3-dimethylpropen-1-yl)-tryptophan (4) in good yield (91%). When AcONa, NaHCO_3, or Et_3N was used as a base, the reaction did not proceed satisfactorily. The cyclization of 4 to clavicipitic acid (1) proceeded smoothly by heating in 50% acetic acid (50℃, 3h). Furthermore, one-pot reaction of Heck reaction of 2 followed by cyclization gave the optically active clavicipitic acid (1) in 61% yield without racemization. Since we were interested in the fact that no racemization occurred under such a strong basic condition at high temperature during Heck reaction, racemization test of L-tryptophan was accomplished in the presence of K_2CO_3 in various solvent or AcOH solution at 130℃. As a result, racemization was largely surpressed in aqueous solution under acidic or basic condition.
天然有機化合物討論会の論文
1997-07-20

55(P20) 保護基を用いない有機合成 : 水溶液中でのClavicipitic Acidの全合成(ポスター発表の部)

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