Department of Chemistry and Industrial Chemistry, University of Pisa, Via G. Moruzzi 13, 56124 Pisa, Italy.
Mar Drugs. 2018 Oct 16;16(10):388. doi: 10.3390/md16100388.
The circular dichroism (CD) exciton chirality method (ECM) is a very popular approach for assigning the absolute configuration (AC) of natural products, thanks to its immediacy and ease of application. The sign of an exciton couplet (two electronic CD bands with opposite sign and similar intensity) can be directly correlated with the molecular stereochemistry, including the AC. However, a correct application of the ECM necessitates several prerequisites: knowledge of the molecular conformation; knowledge of transition moment direction; and preeminence of the exciton coupling mechanism with respect to other sources of CD signals. In recent years, by using quantum-chemical CD calculations, we have demonstrated that some previous applications of ECM were wrong or based on incorrect assumptions. In a recent publication of this journal (, , (4), 121), the ECM was employed to assign the AC of a marine metabolite, laucysteinamide A. This is a further case of incorrect application of the method, where none of the aforementioned prerequisites is fully met. Using this example, we will discuss the criteria required for a correct application of the ECM.
圆二色性（CD）激子手性方法（ECM）是一种非常流行的用于确定天然产物绝对构型（AC）的方法，这要归功于其直接性和易于应用。两个具有相反符号和相似强度的电子 CD 带的激子偶合可以直接与分子立体化学相关联，包括 AC。然而，ECM 的正确应用需要满足几个前提条件：分子构象的知识；跃迁矩方向的知识；以及与其他 CD 信号源相比，激子耦合机制的优势。近年来，通过使用量子化学 CD 计算，我们已经证明了 ECM 的一些先前应用是错误的，或者是基于不正确的假设。在本期刊的最近一篇出版物中（[1]，[2]，[3]，[4]，121），ECM 被用于确定海洋代谢产物 laucysteinamide A 的 AC。这是 ECM 方法不正确应用的另一个例子，其中没有完全满足上述前提条件。我们将使用这个例子来讨论正确应用 ECM 所需的标准。
