Conformations of dehydrophenylalanine containing peptides.

Abstract

Three tripeptides containing a central Z‐dehydrophenylalanine residue (Δ z ‐Phe), Boc‐L‐Phe‐Δ z ‐Phe‐X‐OMe (X = L‐Val 1, L‐Leu 2 and X = L‐Ala 3) have been synthesized and their solution conformations investigated by 270 MHz 1 H NMR spectroscopy. In all three peptides, conformations involving the X residue NH in an intramolecular hydrogen bond were favoured in CDCl 3 solutions. Studies of the nuclear Overhauser effect (NOE) provided support for a Type II β turn conformation in these peptides with Phe and Δ z ‐Phe occupying the i + 1 and i + 2 positions, respectively. Significantly different conformations lacking any intramolecular hydrogen bonds were observed for peptide 1 in (CD 3 ) 2 SO. NOE results were consistent with a significant population of molecules having semi‐extended conformations (ø > 100°) at the Δ z ‐Phe residue.