Structure-activity relationships of novel endomorphin-2 analogues with N-O turns induced by α-aminoxy acids

Endomorphin-2 (H-Tyr-Pro-Phe-Phe-NH2, EM-2) is a putative endogenous mu-opioid receptor ligand. To study the structure-activity relationship against its receptor, we introduced N-O turns into EM-2 and got the analogues with potent affinities for p-opioid receptor. Our results indicated that N-O turn structures at the PrO2-aminoxy-Phe(3) position of EM-2 analogues played important roles for their affinities. These novel analogues with N-O turns provided a new approach to develop potent analgesics related to EM-2. (c) 2005 Elsevier Ltd. All rights reserved.