Inverse γ‐Turn‐Inspired Peptide: Synthesis and Analysis of Segetalin A Indole Hemi­aminal

Abstract

AbstractSubstitution of a peptide bond for an imine transforms the irreversible macrocyclization of peptides into a reversible process. The inherent cyclization tendency of a linear peptide is then analyzable through the equilibrium between the aldehyde and the imine by virtue of the higher reactivity of the corresponding linear peptide aldehyde. The tryptophan side chain of segetalin A aldehyde forms a 12‐membered cyclic indole hemiaminal instead of the 18‐membered macrocyclic imine expected. Herein, we analyzed this uncommon hemiaminal that shows that the biosynthesis of cyclic peptides is not necessarily based on linear precursor peptides with a high inherent macrolactamization tendency.