Per-Residue Program of Multiple Backbone Dihedral Angles of β-Peptoids via Backbone Substitutions

Unique folded structures of natural and synthetic oligomers are the most fundamental basis for their unique functions. N-Substituted β-peptides, or β-peptoids, are synthetic oligomers with great potential to fold into diverse three-dimensional structures because of the existence of four rotatable bonds in a monomer with highly modular synthetic accessibility. However, the existence of the four rotatable bonds poses a challenge for conformational control of β-peptoids. Here, we report a strategy for per-residue programming of two dihedral angles of β-peptoids, which is useful for restricting the conformational space of the oligomers. The oligomer was found to form a unique loop conformation that is stabilized by the backbone rotational restrictions. Circular dichroism and NMR spectroscopic analyses and X-ray crystallographic analysis of the oligomer are presented. The strategy would significantly facilitate the discovery of many more unique folded structures of β-peptoids.