Natural Science Faculty, UFPA, ICEN, Belém, PA, 66075-110, Brazil.
Department of Chemistry, UFJ, Jataí, GO, 75801-615, Brazil.
J Mol Model. 2021 Mar 31;27(4):116. doi: 10.1007/s00894-021-04725-0.
The determination of an absolute configuration is a challenge in the structure elucidation of chiral natural products. With advancements in computational chemistry of chiroptical spectroscopy, the time-dependent density functional theory (TDDFT) calculation has emerged as a very promising tool. This paper attempts to illustrate the applicability of computational approaches in comparison with experimental data to understand the conformation, interaction, and stabilization of the loliolide's isomers. The quantum chemical calculations were used from optimized geometries of the (6R,7aS)-, (6S,7aR)-, (6R,7aR)-, and (6S,7aS)-6-hydroxy-4,4,7a-trimethyl-6,7-dihydro-5H-1-benzofuran-2-one. The spectroscopic values were obtained for C NMR isotropic shielding by GIAO method in mPW1PW91/cc-pVTZ level, in TDDFT at the ωB97X-D/cc-pVTZ level to the circular dichroism, and in theoretical analyses of non-covalent interaction to study the isomer's stability. The TDDFT calculation of circular dichroism can be used to quantify the individual isomers and the nature of excitation in the molecule. The (6R,7aS) and (6R,7aR) isomers present a higher stability due to electronegativity associated at the hydroxyl group.
确定绝对构型是手性天然产物结构阐明中的一个挑战。随着手性光学光谱计算化学的进步，含时密度泛函理论（TDDFT）计算已成为一种非常有前途的工具。本文试图说明计算方法在与实验数据进行比较时的适用性，以了解毛叶丁香烯异构体的构象、相互作用和稳定化。使用量子化学计算从（6R，7aS）-、（6S，7aR）-、（6R，7aR）-和（6S，7aS）-6-羟基-4,4,7a-三甲基-6,7-二氢-5H-1-苯并呋喃-2-酮的优化几何结构进行了计算。通过 GIAO 方法在 mPW1PW91/cc-pVTZ 水平上获得了 C NMR 各向同性屏蔽的光谱值，在 ωB97X-D/cc-pVTZ 水平上在 TDDFT 中获得了圆二色性的光谱值，并在非共价相互作用的理论分析中研究了异构体的稳定性。圆二色性的 TDDFT 计算可用于定量确定各个异构体和分子中激发的性质。由于与羟基相关的电负性，（6R，7aS）和（6R，7aR）异构体呈现出更高的稳定性。
