Solution conformation and synthesis of a linear heptapeptide containing two dehydrophenylalanine residues separated by three L-amino acids
A heptapeptide containing two dehydrophenylalanine residues, Boc-Gly-ΔzPhe-Ala-Phe-Leu-ΔzPhe-Ala-NHMe (Boc = t-butoxycarbonyl) has been synthesised and its solution conformation investigated using 500 MHz 1H NMR and IR spectroscopy. 1H NMR studies of the solvent accessibility of NH resonances and observation of successive Ni,H ↔ Ni+1H nuclear Overhauser effects (NOEs) suggest the presence of a significant population of folded, helical structures in CDCl3. A 5→1 intramolecular hydrogen bonding pattern provides evidence in favour of an α-helix conformation. In (CD3)2SO, although the peptide largely favours the helical conformation, observation of a few CiαH ↔ Ni+1H NOEs gives an indication of some conformational heterogeneity. IR studies in chloroform have provided supporting evidence in favour of these conclusions. Dehydrophenylalanine residues may be of potential use in designing peptides with preferred secondary structures.