Analysis ofN-amino-imidazolin-2-one peptide turn mimic 4-position substituent effects on conformation by X-ray crystallography

Abstract

N-Amino-imidazolin-2-ones, a new class of turn mimics onto which side chains of different amino acids may be added conveniently, have been analyzed by X-ray crystallography. 4-Methyl and 4-benzyl N-amino-imidazolin-2-one tetrapeptide models 2 and 3 were examined to study the influence of the 4-position substituent on turn conformation and the chi dihedral angle of the neighbouring C-terminal residue side-chain. The nature of the 4-position substituent caused substantial effects on the ψ(i + 2) main chain and C-terminal Phe χ(1) side-chain dihedral angle values, giving a preference for β- and γ-turn conformers for the methyl- and benzyl-substituted imidazolin-2-ones, respectively. Conformational analysis in the solid state has provided insight to guide application of N-amino-imidazolin-2-ones in peptide mimicry.