LAUSR

Abstract Four new series of diastereomeric β,γ-di- and β,γ-tetrapeptides derived from conveniently protected (1 R ,2 S )- and (1 S ,2S)-2-aminocyclobutane-1-carboxylic acid and cis - and trans -γ-amino- l -proline joined in alternation have been synthesized. High resolution NMR experiments show that peptides containing trans -cyclobutane amino acid residues adopt a more folded structure in solution than those containing a cis -cyclobutane residue, which adopt a strand-like structure. The cis/trans relative configuration of the cyclobutane residue is the origin of the folding pattern of each peptide due to either intra- or inter-residue hydrogen-bonded ring formation, whereas the cis/trans isomerism of the γ-amino- l -proline residue does not have a significantly relevant role on the folding ability of these peptides.