The spiropiperidine-3,3′-oxindole scaffold: a type II β-turn peptide isostere

An unprecedented chiral spiropiperidine oxindole system was synthesized starting from enantiopure quaternary 3-aminooxindole and relying on a ring closing metathesis as the key step. This compound acts as an highly constrained Freidinger γ-lactam, adopting a type II β-turn conformation in solution, as assessed by modelling and spectroscopical studies.