Cyclic α,β-Tetrapeptoids: Sequence-Dependent Cyclization and Conformational Preference

The presence of at least one <i>N</i>-Cα branched side chain is crucial for successful cyclization of α,β-tetrapeptoids. The <i>ctct</i> amide sequence revealed in the crystal structure of the 14-membered cyclotetrapeptoid <b>8</b> is also the most populated conformation in solution and is reminiscent of the predominant amide arrangement of the 12-membered cyclic tetrapeptides (CTPs)