When not to rely on Boltzmann populations. Automated CASE-3D structure elucidation of hyacinthacines through chemical shift differences,Magnetic Resonance in Chemistry

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When not to rely on Boltzmann populations. Automated CASE-3D structure elucidation of hyacinthacines through chemical shift differences
Magnetic Resonance in Chemistry ( IF 1.9 ) Pub Date : 2019-11-10 , DOI: 10.1002/mrc.4951
Armando Navarro-Vázquez ₁

Affiliation

An Akaike Information Criterion (AIC) procedure (CASE‐3D) has been successfully applied to the NMR based configurational assignment of reported hyacinthacines (1–3,5–8), recently target of configurational analysis using the popular DP4+ methodology. The present analysis makes use of reported 1H and 13C shifts and, in some particular cases, a few 3JHH couplings. The difficulty in proper computational prediction of relative energies, in molecules capable of inter‐molecular hydrogen bonding, introduces large errors in the prediction of conformationally averaged NMR properties in methods based on Boltzmann averaging such as DP4 or DP4+. In contrast CASE‐3D conformational amplitudes are free parameters in the model. Here we show that the CASE‐3D conformational model selection strategy, when combined with a larger energy cutoff in the molecular‐modelling conformational exploration, was sufficient to correctly assign the relative configuration in five of seven cases. Introduction of more information, either by supplementing 1H and 13C data with a few J‐couplings, or using a cutoff based on computed DFT energies for the definition of the conformational ensembles, allowed the safe assignment of configuration for all compounds.

中文翻译：

何时不依赖玻尔兹曼种群。通过化学位移差异自动解析风信子的 CASE-3D 结构

Akaike 信息准则 (AIC) 程序 (CASE-3D) 已成功应用于已报告的风信子 (1-3,5-8) 的基于 NMR 的构型分配，这是最近使用流行的 DP4+ 方法进行构型分析的目标。本分析利用报告的 1H 和 13C 位移，在某些特定情况下，使用一些 3JHH 耦合。在能够分子间氢键的分子中，相对能量的正确计算预测的困难在基于玻尔兹曼平均的方法（如 DP4 或 DP4+）中的构象平均 NMR 特性的预测中引入了很大的误差。相比之下，CASE-3D 构象振幅是模型中的自由参数。在这里，我们展示了 CASE-3D 构象模型选择策略，当在分子建模构象探索中结合更大的能量截断时，足以在七种情况中的五种情况下正确分配相对构型。引入更多信息，通过用一些 J 耦合补充 1H 和 13C 数据，或使用基于计算的 DFT 能量的截止值来定义构象集合，允许对所有化合物进行构型的安全分配。

更新日期：2019-11-10

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