P-9 イネファイトアレキシン関連ジテルペンの合成研究(ポスター発表の部)

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Phytoalexins are antimicrobial secondary metabolites that are biosynthesized de novo and accumulated in plants after exposure to pathogens. They have been suggested to serve as plant antibiotics in defense systems of plants. But the detail of their biosyntheses still remains obscure. To clarify the biosyntheses of phytoalexins in rice plant, we became interested in the syntheses of the diterpens related to rice phytoalexins. 1. Synthetic studies on phytocassanes. In 1995, Koga and co-workers isolated phytocassans (1) from rice plant as a novel rice phyoalexin. The relative stereochemistry of the natural product was reported, but the absolute configuration of that has not been determined. For the purpose of determining the absolute configuration of the phytocassane group of phytoalexins, the naturally occurring (-)-phytocassane D (1) was synthesized from (R)-Wieland-Miescher ketone basing on the preliminary model synthesis of the unnatural (+)-2-deoxyphytocassane A (12). Phytocassanes were shown to possess ent-cassane skeleton by comparing thier CD spectra with those of synthetic phytocassanes of known absolute configuration. 2. Total synthesis of ent-cassa-12,15-diene. A hypothetical biosynthetic intermediate leading to (-)-phytocassane D (1) was identified in the suspension-cultured rice cells and proposed to be ent-cassa-12,15-diene (27) as a candidate. However only a few structural information was available because of the difficulty of purification of the compound. Our total synthesis of 27 proved the structure of the unknown compound. 3. Development of novel methodology for the synthesis of tricyclic diterpenoid. A versatile methodology for the synthesis of various tricyclic diterpenoids via B-alkyl-Suzuki-Miyaura coupling as a key step was developed. By using this methodology, the total syntheses of putative biosynthetic intermediates of the rice phytoalexins, (±)-sandracopimaradiene (36) and (±)-9β-H-pimara-7,15-diene (39) were accomplished.
2005-09-15

P-9 イネファイトアレキシン関連ジテルペンの合成研究(ポスター発表の部)

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