Synthesis, reactivity and conformational preferences of novel enediynyl peptides: a possible scaffold for beta-sheet capping turns

Novel enediynyl tripeptides 2(a-c) in fully protected forms have been prepared via a sequence of palladium(o)-based Sonogashira coupling. The thermal reactivity of these peptides was shown to be dependent upon the nature of the side chain in the amino acids. Analysis of the CD-spectra of these peptides as well as the variation of chemical shifts with temperature revealed the presence of a beta-sheet nucleating conformation in equilibrium with a conformation induced by H-bond formation between the CO and NH belonging to the enediynyl amino acid.