Synthesis of four diastereomeric enkephalins incorporating cyclopropyl phenylalanine

Four diastereomeric D-Ala2,Leu5-enkephalins have been synthesized and their CD spectra and rat brain binding affinities determined. Only the peptides containing Z-cyclopropyl phenylalanine residues showed strong binding affinity. No correlation between CD spectra and bioactivity could be made.