Department of Chemistry, University of Minnesota , 207 Pleasant Street, SE, Minneapolis, Minnesota 55455, USA.
J Nat Prod. 2012 Jul 27;75(7):1326-31. doi: 10.1021/np300248w. Epub 2012 Jun 25.
Phomopsichalasin was isolated and assigned structure 1 over 15 years ago. Analysis of its proton NMR data led us to hypothesize that not all aspects of the relative configuration of this structure were correct. We have used both empirical and computational methods to propose an alternative structure. Diaporthichalasin was reported several years ago, and its structure was assigned as 7, a diastereomer of structure 1, and confirmed by a single-crystal X-ray study. We have shown that diaporthichalasin and phomopsichalasin are identical; that is, both have structure 7. Additional aspects of NMR interpretation that provide guidance for avoiding some of the pitfalls that can lead to incorrect structure assignments are discussed. These recommendations/reminders include (i) the use of complementary solvents for acquiring NMR data that break accidental chemical shift degeneracy, (ii) the importance of assigning coupling constants as extensively as possible, and (iii) exercising caution when interpreting correlations in 2D spectra where overlapping resonances are involved.
多年前，我们分离得到并确定了化合物 Phomopsichalasin 的结构为 1。对其质子 NMR 数据的分析使我们假设该结构的相对构型并非完全正确。我们已使用经验和计算方法提出了一种替代结构。几年前曾报道过 Diaporthichalasin，其结构被确定为 7，为结构 1 的非对映异构体，并通过单晶 X 射线研究得到证实。我们已经证明 Diaporthichalasin 和 Phomopsichalasin 是相同的，即两者都具有结构 7。此外，我们还讨论了一些 NMR 解释方面的内容，这些内容为避免导致错误结构归属的一些陷阱提供了指导。这些建议/提示包括：（i）使用互补溶剂获取 NMR 数据，以打破偶然的化学位移简并性；（ii）尽可能广泛地分配偶合常数的重要性；（iii）在涉及重叠共振的二维谱中解释相关时要谨慎。
