Crystal structures of peptidic catalysts of the H‐ d Pro‐Pro‐Xaa type

Crystal structures of catalytically active tripeptides of the general type H‐dPro‐Pro‐Xaa and related N‐acetylated analogs were compared. The influence of acylation at the N‐terminus, the nature of the C‐terminal residue, coordinating groups, and intramolecular hydrogen bonds on the conformation of the tripeptides was examined. Regardless of the presence or absence of stabilizing intramolecular H‐bonds or n → π* interactions, all of the analyzed peptides share a β‐turn‐like conformation, which highlights the structural rigidity of the d Pro‐Pro motif and its value for conformational preorganization. The C‐terminal residues and coordinating moieties were found to affect the turn‐conformation, which suggests that H‐ d Pro‐Pro‐Xaa type peptides are sufficiently flexible to adopt distinctly different but related conformations.