Theoretical and NMR Conformational Studies of ß-Proline Oligopeptides With Alternating Chirality of Pyrrolidine Units.

ABSTRACT

Synthetic ß-peptides are potential functional mimetics of native α-proteins. A recently developed, novel, synthetic approach provides an effective route to the broad group of ß-proline oligomers with alternating patterns of stereogenic centers. Conformation of the pyrrolidine ring, Z/E isomerism of ß-peptide bonds, and hindered rotation of the neighboring monomers determine the spatial structure of this group of ß-proline oligopeptides. Preferences in their structural organization and corresponding thermodynamic properties are determined by NMR spectroscopy, restrained molecular dynamics and quantum mechanics. The studied ß-proline oligopeptides exist in dimethyl sulfoxide solution in a limited number of conformers, with compatible energy of formation and different spatial organization. In the ß-proline tetrapeptide with alternating chirality of composing pyrrolidine units, one of three peptide bonds may exist in an E configuration. For the alternating ß-proline pentapeptide, the presence of an E configuration for at least of one ß-peptide bond is mandatory. In this case, three peptide bonds synchronously change their configurations. Larger polypeptides may only exist in the presence of several E configurations of ß-peptide bonds forming a wave-like extended structure.