6 Clerodane diterpene化合物の絶対配置について : X線解析及びCDスペフトルの矛盾する結果に対する立体配座からの解明

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Absolute configuration of clerodin 1 and caryoptin 9 which were decided by D.H.R. Barton et al. and G.A. Sim et al. and the authors, respectively, were recently corrected by N. Harada and H. Uda and D. Rogers et al. However, at this time, a new problem arised from the above conclusion, i.e., the results of the ketone Cotton effects of their ketone derivatives were in conflict with the conclusion of X-ray analysis. We calculated the minimized energy of an imaginary compound 16a and 6-keto derivs. 11a and 12a by molecular mechanics (program: MM2), to begin with. The calculated results showed that 16a was stable with a chair conformation about a B ring, but 11a and 12a were stable for the boat conformation (Table 1). Further-more, the result of the calculation revealed that caryoptin derivs. 17a and 18a were also retained the boat form on the B ring as the stable conformer. The facts were confirmed by the X-ray analysis of 18a. Therefore, we concluded that the inversion of the Cotton curve for the ketone derivs. was caused by the conformational change to the boat form on the B ring. Furthermore, in the calculation of the steric energy for 19a, 20a, and 22a, it showed that their B ring prefered the chair form as the stable conformer. However, a stable conformer of 21a took on the boat form for the B ring. For confirmation of it clerodin was derived to 21a and 22a. As we would expect, they showed (+) and (-) Cotton curve, respectively. From the above results, it was concluded that complex and subtle steric interactions caused conformational change at the B ring.
天然有機化合物討論会の論文
1981-09-10

6 Clerodane diterpene化合物の絶対配置について : X線解析及びCDスペフトルの矛盾する結果に対する立体配座からの解明

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