Eight new dermorphin tetrapeptides, X-Tyr-D-MetO-Phe-aa-Y (X= H, H2N= C (NH); aa= Gly, 2-aminoethanol, sarcosine; Y= NHz, NH--11, were prepared and teated for opioid activity. They show doee-related naloxone-reversible opioid effects in vitro and in vivo. H-Tyr-D- MetO-Phe-Gly-NH2 (I)(guinea pig ileum ICw= 13.6 n M tail-flick EDM= 1.97 pmol/mouse, icv, and 0.65 pmol/kg, sc), though less effective in the pheriphery, has central activities higher ...
