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Updated: Mar 24, 2026

Spatial Separation of Molecular Conformers and Clusters
Published on: January 9, 2014
Solution-state conformations of natural products from chiroptical spectroscopy: the case of isocorilagin
R F Sprenger1, S S Thomasi, A G Ferreira
1Department of Chemistry, Federal University of São Carlos, UFSCar. Rod. Washington Luís km 235, São Carlos, SP 13565-305, Brazil. joaombj@hotmail.com quezia@pq.cnpq.br.
Abstract:
Isocorilagin, the α-anomer of the ellagitannin corilagin, has been frequently reported in the literature as a constituent of various plant species. Its identification is based mainly on the smaller value for the coupling constant of its anomeric proton when compared to that of corilagin. A careful investigation of the corilagin structure in both methanol and DMSO solutions using NMR, electronic and vibrational CD, and DFT and MD calculations confirmed that isocorilagin is the result of a solvent-induced conformational transition of corilagin, rather than its diastereoisomer. Corilagin changes from B1,4 and (o)S5 conformations of the β-glucose core in DMSO-d6 to an inverted (1)C4 conformation in methanol-d4, which accounts for NMR observables attributed to the alleged α-anomer. This misassignment reinforces the risks of relying upon a single technique for structural elucidation and stereochemical analysis of complex natural products, especially those containing saccharide moieties.
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