Structural studies of [2',6'-dimethyl-L-tyrosine1]endomorphin-2 analogues: enhanced activity and cis orientation of the Dmt-Pro amide bond |
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Authors: | Okada Yoshio Fujita Yoshio Motoyama Takashi Tsuda Yuko Yokoi Toshio Li Tingyou Sasaki Yusuke Ambo Akihiro Jinsmaa Yunden Bryant Sharon D Lazarus Lawrence H |
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Affiliation: | Faculty of Pharmaceutical Sciences, Department of Medicinal Chemistry, Kobe Gakuin University, Nishi-ku, Kobe 651-2180, Japan. okada@pharm.kobegakuin.ac.jp |
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Abstract: | Analogues of endomorphin-2 (EM-2: Tyr-Pro-Phe-Phe-NH(2)) (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 (IC(50)=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). 1H 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. |
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