Solution-state conformations of natural products from chiroptical spectroscopy: the case of isocorilagin.
Org Biomol Chem
; 14(13): 3369-75, 2016 Apr 07.
Article
em En
| MEDLINE
| ID: mdl-26946940
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 ß-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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01-internacional
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MEDLINE
Assunto principal:
Taninos
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Produtos Biológicos
Idioma:
En
Ano de publicação:
2016
Tipo de documento:
Article