Dehydro-dermorphins. III. Circular dichroism investigation of conformation in solution

Dehydropeptide analogs of dermorphin (H-Tyr-D-Ala-Phe-Gly-Tyr-Pro-Ser-NH2) and N-terminal fragments containing one or two dehydrophenylalanine residues in the 3rd and/or 5th position, have been investigated by means of CD spectroscopy. The results indicate that the above dehydropeptides can adopt different conformations in alcohol and water solutions. In methanol and trifluoroethanol, the CD spectra are mainly consistent with the presence of folded structures, probably stabilized by intramolecular hydrogen bonds. In water, conversely, CD data indicate disruption of ordered structures and formation of preferentially extended flexible conformations. Models of the involved folded structures are tentatively proposed, taking into account the geometric features of dehydro residues and their tendency to favor hydrogen-bonded 10-membered rings.