Using DP4+ probability for structure elucidation of sesquiterpenic lactones: The case of (−)-Istanbulin A,Journal of Physical Organic Chemistry

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Using DP4+ probability for structure elucidation of sesquiterpenic lactones: The case of (−)-Istanbulin A
Journal of Physical Organic Chemistry ( IF 1.9 ) Pub Date : 2021-08-28 , DOI: 10.1002/poc.4282
Diego D. Colasurdo ₁ , Luz A. Arancibia ₂ , Mariana L. Naspi _{2,

3} , Sergio L. Laurella ₁

Affiliation

Theoretical calculations have become a crucial support for experimental data when it comes to confirming and/or rejecting molecular structure. Quantum calculations have therefore become essential for other research fields, such as total synthesis of natural products or the study of their mechanisms of action, among others. In this communication, four different parameters are used for the confirmation of the structure of (−)-Istanbulin A, testing the experimental NMR data against eight possible stereoisomers. (−)-Istanbulin A is a natural product (an eremophilane) extracted from the aerial parts of Senecio filaginoides DC (an endemic plant from Patagonia Argentina) that has proven successful as antibacterial and antifungal agent. The structures of the eight possible stereoisomers were optimized by means of DFT calculations (B3LYP/6-311+G[d,p] in vacuum), and then their isotropic shielding tensors were obtained using GIAO-B3LYP/6-31+G(d,p) method in chloroform. Isotropic shielding values of ¹H and ¹³C were converted into chemical shifts by subtraction of TMS analog values. The eight sets of calculated data were compared with the spectroscopic chemical shifts in order to find the most probable structure. This was made by means of the parameters R² (correlation coefficient), MAE (mean absolute error), CMAE (corrected mean absolute error), and DP4+ probability. While R², MAE, and CMAE afford uncertain results which do not permit confirmation of the molecular structure, DP4+ predicts the isomer of configuration (4S,5R,8R,10S) with more than 99% probability. These results open the possibility of applying DP4+ method for confirming the relative configuration of other istanbulins (and probably other eremophilanes).

中文翻译：

使用 DP4+ 概率解析倍半萜内酯的结构：(-)-Istanbulin A 的案例

在确认和/或拒绝分子结构时，理论计算已成为实验数据的重要支持。因此，量子计算对于其他研究领域变得必不可少，例如天然产物的全合成或其作用机制的研究等。在此通讯中，四个不同的参数用于确认 (-)-Istanbulin A 的结构，针对八种可能的立体异构体测试实验 NMR 数据。(−)-Istanbulin A 是一种天然产物（一种 eremophilane），是从千叶千里光的地上部分提取的DC（来自阿根廷巴塔哥尼亚的特有植物）已被证明是成功的抗菌和抗真菌剂。通过DFT计算(真空中B3LYP/6-311+G[d,p])优化了8种可能的立体异构体的结构，然后使用GIAO-B3LYP/6-31+G( d,p) 氯仿中的方法。通过减去 TMS 模拟值，将¹ H 和¹³ C 的各向同性屏蔽值转换为化学位移。将八组计算数据与光谱化学位移进行比较，以找到最可能的结构。这是通过参数R ²（相关系数）、MAE（平均绝对误差）、CMAE（校正后的平均绝对误差）和 DP4+ 概率。虽然R ²、MAE 和 CMAE 提供了无法确认分子结构的不确定结果，但 DP4+ 以超过 99% 的概率预测了构型 (4S,5R,8R,10S) 的异构体。这些结果开启了应用 DP4+ 方法来确认其他伊斯坦布尔素（可能还有其他 eremophilanes）的相对构型的可能性。

更新日期：2021-08-28

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