Stable Helical Secondary Structure in Short-Chain N,N′-Linked Oligoureas Bearing Proteinogenic Side Chains Access to both the Bruker ARX 500 facilities of the Service Commun de RMN (Faculté de Chimie, Strasbourg) and the Bruker DRX 600 NMR facilities of the Service Commun de Biophysicochimie des Interactions Moléculaires (Université Henri Poincaré, Nancy I) were deeply appreciated.