Local and Tunable n→π* Interactions Regulate Amide Isomerism in the Peptoid Backbone

We report that n→π* interactions are operative in peptoids and play a major role in controlling amide isomerism. These interactions can be tuned using α-chiral amide side chains known to promote peptoid folding. To our knowledge, this is the first report of n→π* interactions between amides in non-prolyl systems. Furthermore, we have characterized an n→π* interaction between backbone carbonyls and side chain aromatic rings that can dramatically stabilize the cis-amides required for peptoid helix formation. The tunability of both types of n→π* interactions in peptoids has significant implications for peptoid folding and could be exploited for the design of new peptoid architectures.