期刊
MAGNETIC RESONANCE IN CHEMISTRY
卷 58, 期 2, 页码 139-144出版社
WILEY
DOI: 10.1002/mrc.4951
关键词
CASE; DP4; GIAO; stereochemistry; Structural elucidation
资金
- Chamada Universal MCTIC/CNPq [426216/2018-0]
- Auxilio para Projeto de Pesquisa [APQ-0507-1.06/15]
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 H-1 and C-13 shifts and, in some particular cases, a few (3)J(HH) 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 H-1 and C-13 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.
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