Conformational preferences ofN-acetyl-N′-methylprolineamide in different media: a¹H NMR and theoretical investigation

Abstract

The conformational preferences and role of non-covalent interactions on the geometries of Ac–Pro–NHMe were elucidated in isolated phase and solution.

Enantiopure 5-CF3–Proline: Synthesis, Incorporation in Peptides, and Tuning of the Peptide Bond Geometry

“…11%) of the cis conformer for the 5-CF 3 -proline derivatives 13 and 14 (Table ). , In D 2 O an increase of the cis amide bond ratio of the methylamide 13 could be explained by the breaking of the intramolecular H bond stabilizing the trans amide bond conformation. The increased trans amide conformation for the methyl ester 14 could be explained by a stronger polar n → π* interaction between the oxygen atom lone pair of the acetate and the carbonyl of the methylester …”

“…Our main observations with these compounds were the increased cis amide bond content and an unexpected decrease of the trans to cis amide bond isomerization energy. 22,23 We report herein the thermodynamic study of the N-acetyl-5-CF 3proline methylamide 13, which is considered as a tripeptide model (Table As already observed both in the nonfluorinated 24 and in the fluorinated CF 3 -and CF 2 Hpseudoproline series, 22,23 the cis/trans amide bond ratio can be affected by an intramolecular H bond between the Cterminal amide NH and the carbonyl of the N-terminal acetyl group. To evaluate the impact of this H bond on the conformational behavior, we also considered the proline methyl ester 14.…”