摘要:
Analogues of endomorphin-2 (EM-2: Tyr-Pro-Phe-Phe-NH2) (1) were designed to examine the importance of each residue on mu-opioid receptor interaction. Replacement of Tyr(1) by 2',6'-dimethyl-L-tyrosine (Dmt) (9-12) exerted profound effects: [Dmt(1)]EM-2 (9) elevated mu-opioid affinity 4.6-fold (K(i)mu = 0.15 nM) yet selectivity fell 330-fold as delta-affinity rose (K(i)delta = 28.2 nM). This simultaneous increased mu- and delta-receptor bioactivities resulted in dual agonism (IC50 = 0.07 and 1.87 nM, respectively). While substitution of Phe(4) by a phenethyl group (4) decreased mu affinity (K(i)mu 13.3 nM), the same derivative containing Dmt (12) was comparable to EM-2 but also acquired weak delta antagonism (pA(2) = 7.05). H-1 NMR spectroscopy revealed a trans configuration (1:2 to 1:3, cis/trans) in the Tyr-Pro amide bond, but a cis configuration (5:3 to 13:7, cis/trans) with Dmt-Pro analogues. (C) 2003 Elsevier Science Ltd. All rights reserved.