名称:
Bifunctional [2‘,6‘-Dimethyl-l-tyrosine]endomorphin-2 Analogues Substituted at Position 3 with Alkylated Phenylalanine Derivatives Yield Potent Mixed μ-Agonist/δ-Antagonist and Dual μ-Agonist/δ-Agonist Opioid Ligands
摘要:
Endomorphin-2 (H-Tyr-Pro-Phe-Phe-NH2) and [Dmt(1)]EM-2 (Dmt = 2',6'-dimethyl-L-tyrosine) analogues, containing alkylated Phe(3) derivatives, 2'-monomethyl (2, 2'), 3',5'- and 2',6'-dimethyl (3, 3', and 4', respectively), 2',4',6'-trimethyl (6, 6'), 2'-ethyl-6'-methyl (7, 7'), and 2'-isopropyl-6'-methyl (8, 8') groups or Dmt (5, 5'), had the following characteristics: (i) [Xaa(3)]EM-2 analogues exhibited improved mu- and delta-opioid receptor affinities. The latter, however, were inconsequential (K-i(delta) = 491-3451 nM). (ii) [Dmt(1),Xaa(3)]EM-2 analogues enhanced mu- and delta-opioid receptor affinities (K-i(mu) = 0.069-0.32 nM; K-i(delta) = 1.83-99.8 nM) without kappa-opioid receptor interaction. (iii) There were elevated mu-bioactivity (IC50 = 0.12-14.4 nM) and abolished delta-agonism (IC50 > 10 mu M in 2', 3', 4', 5', 6'), although 4' and 6' demonstrated a potent mixed mu-agonism/delta-antagonism (for 4', IC50 mu = 0.12 and pA(2) = 8.15; for 6', IC50 mu = 0.21 nM and pA(2) = 9.05) and 7' was a dual mu-agonist/delta-agonist (IC50 mu = 0.17 nM; IC50 delta = 0.51 nM).