Synthesis of Z-Protected Aib- and Phe(2Me)-Containing Pentapeptides and Their Crystal Structures

Abstract

A series of pentapeptide derivatives containing alpha,alpha-disubstituted alpha-amino acids have been prepared by a combination of the 'azirine/oxazolone method' and segment condensations. X-Ray crystal-structure determinations of the molecular structures confirmed the presence of helical conformations stabilized by beta-turns of type III or III’. Pentapeptides containing (R)-Phe(2Me) form a right-handed helix, whereas those containing (S)-Phe(2Me) adopt a left-handed helical structure.