Institut für Organische Chemie und Biochemie, Albert-Ludwigs-Universität Freiburg, Albertstr. 21, 79104 Freiburg i. Br., Germany.
Chemistry. 2012 Jun 4;18(23):7071-81. doi: 10.1002/chem.201103988. Epub 2012 Apr 27.
The determination of the relative configuration of 1,3-dimethyl-substituted alkyl chains is possible by interpretation of (1)H NMR shift differences. Additionally, assignments are feasible in a variety of deuterated solvents, because the corresponding shift differences are not significantly influenced by the solvent. The trends for Δδ values depending on functional groups adjacent to the stereogenic centers are shown. Based on a thorough comparison with literature data, the relative configuration of natural products can be predicted. For this purpose, we derived an empirical rule for the ranges in which Δδ values usually occur. Furthermore, we were able to proof the validity of our method by the successful prediction of the relative configuration for the polyketide natural product xylarinic acid A, which was confirmed by the asymmetric total synthesis of its enantiomer. Based on the proposed simple analysis of published (1)H NMR data and the determination of the relevant chemical-shift differences, we predicted the relative configurations of several previously unassigned natural products.
通过对 (1)H NMR 位移差异的解释，可以确定 1,3-二甲基取代烷基链的相对构型。此外，在各种氘代溶剂中进行分配也是可行的，因为相应的位移差异不会受到溶剂的显著影响。本文展示了与立体中心相邻官能团有关的 Δδ 值趋势。通过与文献数据的彻底比较，可以预测天然产物的相对构型。为此，我们得出了一个经验规则，用于确定 Δδ 值通常出现的范围。此外，我们还通过成功预测多酮天然产物木聚糖酸 A 的相对构型来证明我们方法的有效性，该天然产物的对映体通过不对称全合成得到证实。基于对已发表的 (1)H NMR 数据的简单分析和相关化学位移差异的确定，我们预测了几个以前未分配的天然产物的相对构型。
