Molecular dynamics and NMR analysis of the configurational 13C assignment of epimeric 22,23-epoxides of stigmasterol.
J Phys Chem A
; 112(36): 8333-6, 2008 Sep 11.
Article
em En
| MEDLINE
| ID: mdl-18700734
ABSTRACT
The determination of the stereochemistry of brasinosteroid analogs with 22,23-epoxide groups can be easily achieved by means of (13)C NMR spectroscopy. Here, we provide a rationalization of the (13)C chemical shift pattern found in 22R,23R- and 22S,23S-epoxides of stigmasterol, based on the analysis of gamma effects. (22S,23S)- and (22R,23R)-3beta-acetoxystigmast-22,23-epoxy-5,6beta-diol were used in the study as model compounds. Our methodology starts with a conformational search by means of molecular dynamics and NMR (NOE contacts) spectroscopy, which is followed by the analysis of the different gamma interactions affecting the chemical shift of interest. We demonstrate that the differences between the (13)C chemical shift patterns of 22R,23R and 22S,23S isomers arise from gamma effects as the result of diverging local conformations around the C17-C20 and C20-C22 bonds.
Texto completo:
1
Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Estigmasterol
/
Isótopos de Carbono
/
Espectroscopia de Ressonância Magnética
/
Clorofórmio
/
Compostos de Epóxi
Idioma:
En
Ano de publicação:
2008
Tipo de documento:
Article