27 Fudecaloneの合成と立体配置の決定(口頭発表の部)

抄録

Fudecalone was isolated by Omura et al. in 1995 from a culture broth of Penicillium sp. FO-2030 as an anticoccidial sesquiterpene. The structure was elucidated mainly by NMR experiments and the conformation was reported to be A. However, our synthetic Fudecalone, which has the same configuration as reported, showed the other conformation B and the NMR spectral data were not identical. According to MM3 calculation, B was more stable than A. So, we thought interesting that Fudecalone existed as an unstable conformation because of the extra-high energy barrier between A and B, and investigated conformational isomerization from B to A. The selenide 11, whose conformation was determined to be nonsteroid type (A) by NOE experiments, was prepared in seven steps from the intermediate 8 with B type conformation. But after oxidative elimination, the conformation returned to A type, so we doubted the proposed relative stereochemistry and attempted to synthesize transoctalone (C). We adopted the intermediate 8 again, isomerized its octalone skeleton from cis to trans and converted the trans-isomer (14) into 16, whose NMR spectral data were identical with those of the natural Fudecalone. In addition to that, NOE experiment revealed the hydroxy group of hemiacetal to be β-oriented. In conclusion, we synthesized Fudecalone as a racemate and determined its relative configuration as 1S^*, 3aS^*, 6aS^* and 10aS^*. The synthesis of optically active compound is now in progress.