Opioid peptides. Structure-activity relationships in dermorphin tetrapeptides. I.

Characterisation and pharmacological data of twelve synthetic tetrapeptide analogs of dermorphin (opioid heptapeptide) are reported. An N-terminal tetrapeptide free acid or ester is less potent that the corresponding amide. Whereas substitution of Gly4 by another aminoacid residue is well tolerated, substitution of D-Ala2 by D- or L-alpha-aminoxypropionic acid causes a complete loss of activity. Finally, guanidination of the tetrapeptides results in an increase of peripheral and central opioid activity.