Conformations of dehydrophenylalanine containing peptides: nmr studies of an acyclic hexapeptide with two Δz‐Phe residues

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Abstract
The conformation of an acyclic dehydrophenylalanine (Δz‐Phe) containing hexapeptide, Boc‐Phe‐Δz‐Phe‐Val‐Phe‐Δz‐Phe‐Val‐OMe, has been investigated in CDCl3 and (CD3)2SO by 270‐MHz 1H‐nmr. Studies of NH group solvent accessibility and observation of interresidue nuclear Overhauser effects (NOEs) suggest a significant solvent‐dependent conformational variability. In CDCl3, a population of folded helical conformations is supported by the inaccessibility to solvent of the NH groups of residues 3–6 and the detection of several NiH ⟷ Ni+1H NOEs. Evidence is also obtained for conformational heterogeneity from the detection of some CH ⟷ Ni+1H NOEs characteristic of extended strands. In (CD3)2SO, the peptide largely favors an extended conformation, characterized by five solvent‐exposed NH groups and successive CH ⟷ Ni+1 H NOEs for the L‐residues and CH ⟷ Ni+1H NOEs for the Δz‐Phe residues. The results suggest that Δz‐Phe residues do not provide compelling conformational constraints.

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