Synthetic and conformational studies on dehydrophenylalanine containing model peptides

Abstract

Four model dipeptides containing a Z-dehydrophenylalanine residue (Δ^ZPhe) at the C-terminal, Boc-X-Δ^Z Phe-NHMe (X = Ala (1), Gly (2), Pro (3), and Val (4)), have been synthesised and their solution conformations investigated by 270 MHz ¹H n.m.r. and i.r. spectroscopy. N.m.r. studies on these peptides clearly show the presence of intramolecularly hydrogen bonded structures in CHCl₃ solutions while such structures appear to be absent in the corresponding saturated peptides. This conclusion is also supported by i.r. studies. Studies of the nuclear Overhauser effect provided evidence for the occurrence of a significant population of β -turn structures in solvents like CDCl₃ and (CD₃)₂SO. The observed NOES are consistent with a major contribution from Type II β-turn structure in CDCl₃, while in (CD₃)₂SO solutions there is evidence of a partially extended structure also.