Stable Helical Secondary Structure in Short-Chain N,N′-Linked Oligoureas Bearing Proteinogenic Side Chains

Closely related to the (P)2.614 helix of γ‐peptides: Heptamer 1 bearing side chains of Ala, Val, and Tyr adopts a stable 2.5‐helical secondary structure in solution that is characterized by a pitch of approximately 5.1 Å and by the simultaneous presence of 12‐ and 14‐membered hydrogen‐bonded rings. Thus N,N′‐linked oligoureas belong to the growing family of non‐natural non‐peptide oligomers with defined and predictable secondary structure.