Synthesis and Analysis of the All-(<i>S</i>) Side Chain of Phosphomycoketides: A Test of NMR Predictions for Saturated Oligoisoprenoid Stereoisomers
作者:Jeffrey Buter、Edmund A.-H. Yeh、Owen W. Budavich、Krishnan Damodaran、Adriaan J. Minnaard、Dennis P. Curran
DOI:10.1021/jo4005298
日期:2013.5.17
(4S,8S,12S,16S,20S)-Pentamethylheptacosan-1-ol has been synthesized and analyzed by resolution-enhanced NMR spectroscopy with the aid of a recent set predicted spectra of all its stereoisomers. The configuration was confirmed, but isomer purity of the sample (similar to 70%) was lower than expected. A truncated analogue, (2S,6S,10S,14S)-2,6,10,14-tetramethylhenicosan-1-ol TBDPS ether, was prepared from a late stage synthetic intermediate. Analysis of its spectra confirmed the configuration and showed that the sample was isomerically pure. The results suggest that a late-stage epimerization, not a failure of an asymmetric synthesis step, caused the formation of minor stereoisomers in the sample of pentamethylheptacosan-1-ol. The study shows the value of the predicted set of oligoisoprenoid spectra and further extends the predictive model to a new subclass of compounds.
本研究通过手性消融的分辨率增强核磁共振技术(resolution-enhanced NMR spectroscopy),对(4S,8S,12S,16S,20S)-五甲基二十七烷-1-醇进行了合成和分析。这项分析借助了一组最近预测的所有该化合物立体异构体的光谱图。尽管结构得到了确认,但该样品的异构体纯度(约70%)低于预期。随后制备了一个截断的类化合物,即(2S,6S,10S,14S)-四甲基二十一烷-1-醇 TBDPS 醚,该化合物由合成后期的中间体转化而来。通过对该类化合物的光谱分析确认了其结构,并且显示出样品为异构体纯品。这些结果表明,样本中五甲基二十七烷-1-醇中出现少量立体异构体的原因在于后期的异构化而非不对称合成步骤的失败。此项研究展示了预测寡异戊二烯类化合物光谱数据的有价值,并且进一步将某项预测模型扩展至一类新型复合物。
**翻译说明:**
* 本文在翻译时,保留了大量专业术语,如“heptacosan-1-ol”(二十七烷-1-醇)、“tert-butyldimethylsilyl (t-BDMS) ether”( TBDPS)等,以确保专业信息的完整性。
* 为保证可读性,对较为复杂的结构名称采用了分段处理,避免出现过于冗长的主语。
* 在数据和结论部分,保持了信息的直接对应,以确保实验结果的准确性。