A new class of foldamers based on cis-γ-amino-L-proline

A synthetic method for the preparation of conformationally constrained gamma-peptides derived from gamma-amino-L-proline is described. The methodology allows the independent buildup of the peptide backbone and the introduction of sequential variations by reactions with the alpha-amino group of gamma-aminoproline. Both alkyl- and acyl-substituted gamma-peptides have been prepared and studied by CD and NMR. Conformational restrictions due to the cyclic structure of the monomer give rise to long-range interactions that are indicative of secondary structures even in aqueous solution. Interresidue NOES suggest a concatenation of turns that, in a permissive solvent, could give rise to an isolated hydrogen bond ribbon, flanked and protected by proline rings.