21 Graphislactone類および関連化合物の合成(口頭発表の部)
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概要
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In 1997, Tanahashi et al. isolated four phenolics from the cultured lichen mycobiont of Graphis scripta var. pulverulenta, which were called graphislactones A-D. Since two of them, graphislactones C and D, were found to exhibit anti-tumor activity against the human bladder cancer cell, our interest has focused on the total synthesis of the graphislactones. In this report, we describe their synthesis through a Pd-mediated biaryl coupling reaction of phenyl benzoate derivatives as the key step. For their structural features, the graphislactones A-C have highly oxygenated 6H-dibenzo[b,d]pyran-6-one skeletons. To obtain these compounds, we envisioned phenyl benzoate derivatives as good precursors. These esters would be prepared by a simple esterification between the corresponding phenols and benzoic acids furnishing the required functionalities on each aromatic ring. Initially, as the precursors of the six-membered ring lactones 15, 20, and 22, the phenyl benzoate derivatives 14, 19, and 21 were prepared respectively. The Pd-mediated biaryl coupling reaction was successful to afford the desired products, which were transformed into graphislactones through the deprotection process. On the other hand, graphislactone D has a different ring system from the above graphislactone A-C. We thought that the core skeleton, 5H-dibenzo[c,e]oxepin-7-one, would be synthesized by the reconstruction of the lactone ring from the 6H-dibenzo[b,d]pyran-6-one. Thus, the lactone 25 was envisioned as a key intermediate for graphislactone D. After transformation into 25 by a similar route to graphislactone C, the treatment of the resulting 25 with an excess amount of K_2CO_3 in MeOH was effective for the direct formation of the seven-membered ring lactone 27. Final deprotection of the benzyl group was also successful, and the synthesis of graphislactone D was accomplished. The synthesis of ulocladol, which is significantly related to graphislactone D, will be also discussed.
- 天然有機化合物討論会の論文
- 2005-09-15
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