Please use this identifier to cite or link to this item: http://hdl.handle.net/10397/10713
Title: Structure-activity study of endomorphin-2 analogs with C-terminal modifications by NMR spectroscopy and molecular modeling
Authors: Wang, CL
Yao, JL
Yu, Y
Shao, X
Cui, Y
Liu, HM
Lai, LH
Wang, R
Keywords: C-terminal modification
Conformation
Endomorphin-2
Molecular modeling
NMR spectroscopy
Issue Date: 2008
Publisher: Pergamon-Elsevier Science Ltd
Source: Bioorganic and medicinal chemistry, 2008, v. 16, no. 12, p. 6415-6422 How to cite?
Journal: Bioorganic and Medicinal Chemistry 
Abstract: Endomorphin-2 (EM-2) is a putative endogenous μ-opioid receptor ligand. To get insight into the important role of C-terminal amide group of EM-2, we investigated herein a series of EM-2 analogs by substitution of the C-terminal amide group with -NHNH2, -NHCH3, -N(CH3)2, -OCH3, -OCH2CH3, -OC(CH3)3, and -CH2-OH. Their binding affinity and bioactivity were determined and compared. Despite similar (analogs 1, 4, and 7) or decreased (analogs 2, 3,5, and 6) μ affinity in binding assays, all analogs showed low guinea pig ileum (GPI) and mouse vas deferens (MVD) potencies compared to their parent peptide. Interestingly, as for analogs 2 and 3 (a single and double N-methylation of C-terminal amide), the potency order with the Ki (μ) values was 2 > 3; for the C-terminal esterified analogs 4-6, the potency order with the Ki (μ) values was 4 > 5 > 6. Thus, we concluded that the steric hindrance of C-terminus might play an important role in opioid receptor affinity. We further investigated the conformational properties of these analogs by 1D and 2D 1H NMR spectroscopy and molecular modeling. Evaluating the ratios of cis- and trans-isomers, aromatic interactions, dihedral angles, and stereoscopic views of the most convergent conformers, we found that modifications at the C-terminal amide group of EM-2 affected these analog conformations markedly, therefore changed the opioid receptor affinity and in vitro bioactivity.
URI: http://hdl.handle.net/10397/10713
DOI: 10.1016/j.bmc.2008.05.001
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