作者:Shi-Man Hui、Koon-Sin Ngo、Geoffrey D. Brown
DOI:10.1039/a702714a
日期:——
Treatment of artemisinin 1 with acid leads to either a cyclohexane dione degradation product 10, which is a useful intermediate for biosynthetic studies of artemisinin, or to a decalin system which has undergone epimerization 8. It is shown by NMR spectroscopy, chemical reactions and molecular modelling that the bulky 7-substituent in the epimerized decalin series (8, 17, 14) adopts an axial solution conformation and that this is thermodynamically favoured over the natural configuration for which this substituent is equatorial (11, 15, 13). Conversely, for the cyclohexane dione series, the natural configuration in which the 7-substituent is equatorial is more favoured. Reasons for the differing conformational preferences in the two series, which are ultimately responsible for promoting epimerization, are discussed and a simple spectroscopic procedure for identification of epimerized products is presented.
用酸处理青蒿素 1 可以得到环己烷二酮降解产物 10(这是研究青蒿素生物合成的有用中间体),也可以得到经过外延化的蜕皮素体系 8。核磁共振光谱、化学反应和分子建模表明,在表聚蜕皮素系列(8、17、14)中,笨重的 7-取代基采用轴向溶液构象,与该取代基为赤道构象的天然构型(11、15、13)相比,这种构象在热力学上更有利。相反,在环己烷二酮系列中,7-取代基为赤道型的天然构型更受青睐。本文讨论了这两个系列中存在不同构象偏好的原因,这些偏好最终导致了环化反应的发生,并介绍了一种用于识别环化产物的简单光谱程序。