Aromatic interactions with naphthylalanine in a β‐hairpin peptide

Stable peptides have been explored as epitope mimics for protein–protein and protein–nucleic acid interactions; however, presentation of a regular structure is critical. Aromatic interactions are ubiquitous and are competent at stabilizing a β‐hairpin fold. The greatest stabilization has been reported from pairs of tryptophan side chains. Naphthylalanine residues are often used as tryptophan replacements, but it is not clear if 1‐naphthylalanine or 2‐naphthylalanine is adequate at replicating the geometry and stability observed with tryptophan aromatic interactions. Herein, a 12‐residue peptide has been constructed with laterally disposed aromatic amino acids. A direct comparison is made between tryptophan and other bicyclic, unnatural amino acids. Significant stabilization is gained from all bicyclic amino acids; however, geometric analysis shows that only 1‐naphthylalanine adopts a similar edge to face geometry as tryptophan, whereas the 2‐naphthylalanine appears most similar to a substituted phenylalanine. Copyright © 2013 European Peptide Society and John Wiley & Sons, Ltd.