V. Torbeev, Erik Fumi, Marc-Olivier Ebert
Dec 1, 2012
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0
Influential Citations
8
Citations
Journal
Helvetica Chimica Acta
Abstract
α-Methyl-L-proline is an α-substituted analog of proline that has been previously employed to constrain prolyl peptide bonds in a trans conformation. Here, we revisit the cis-trans prolyl peptide bond equilibrium in derivatives of α-methyl-L-proline, such as N-Boc-protected α-methyl-L-proline and the hexapeptide H-Ala-Tyr-αMePro-Tyr-Asp-Val-OH. In Boc-α-methyl-L-proline, we found that both cis and trans conformers were populated, whereas, in the short peptide, only the trans conformer was detected. The energy barrier for the cis-trans isomerization in Boc-α-methyl-L-proline was determined by line-shape analysis of NMR spectra obtained at different temperatures and found to be 1.24 kcal/mol (at 298 K) higher than the corresponding value for Boc-L-proline. These findings further illuminate the conformationally constraining properties of α-methyl-L-proline.