%0 Journal Article
%A Suardíaz Delrío, Reynier
%A Maestre, Mitcheell
%A Suárez, Ernesto
%A Bernardo, Yamilet
%A Alonso-Becerra, Esther
%A Pérez, Carlos
%T Molecular dynamics and NMR analysis of the configurational C assignment of epimeric 22,23-epoxides of stigmasterol
%D 2008
%@ 1089-5639
%U https://hdl.handle.net/20.500.14352/92796
%X The determination of the stereochemistry of brasinosteroid analogs with 22,23-epoxide groups can be easily achieved by means of 13C NMR spectroscopy. Here, we provide a rationalization of the 13C chemical shift pattern found in 22R,23R- and 22S,23S-epoxides of stigmasterol, based on the analysis of γ effects. (22S,23S)- and (22R,23R)-3β-acetoxystigmast-22,23-epoxy-5,6β-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 γ interactions affecting the chemical shift of interest. We demonstrate that the differences between the 13C chemical shift patterns of 22R,23R and 22S,23S isomers arise from γ effects as the result of diverging local conformations around the C17−C20 and C20−C22 bonds.
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