Shan Hui, Wilson William K, Kamaric Emma
Org Lett. 2020 Mar 6;22(5):1714-1719. doi: 10.1021/acs.orglett.9b04566. Epub 2020 Feb 18.
The current scientific consensus generally assigns incorrect C20 configurations to taraxastane-3β,20-diols and their oxo derivatives reported in 32 articles. Definitive configurations established here by NOESY, quantum mechanical NMR predictions, and C NMR γ-gauche effects warrant updating of the many erroneous structures. Suggestions to improve NMR structure determinations of such nonpolar polycyclic natural products include acquiring 2D spectra at higher resolution, suppressing zero-quantum coherence in NOESY, and judging proposed NOE correlations against H-H distances.
目前的科学共识通常给32篇文章中报道的蒲公英甾烷-3β,20-二醇及其氧代衍生物指定了错误的C20构型。本文通过NOESY、量子力学NMR预测和碳核磁共振γ-gauche效应确定的明确构型，保证了对许多错误结构的更新。改善此类非极性多环天然产物NMR结构测定的建议包括以更高分辨率采集二维光谱、在NOESY中抑制零量子相干，以及根据H-H距离判断提出的NOE相关性。
