title: Synthesis and evaluation of potential affinity labels derived from endomorphin-2.
abstract: In an attempt to identify potential peptide-based affinity labels for opioid receptors, endomorphin-2 (Tyr-Pro-Phe-PheNH2), a potent and selective endogenous ligand for mu-opioid receptors, was chosen as the parent peptide for modification. The tetrapeptide analogs were prepared using standard Fmoc-solid phase peptide synthesis in conjunction with incorporation of Fmoc-Phe(p-NHAlloc) and modification of the p-amino group. The electrophilic groups isothiocyanate and bromoacetamide were introduced into the para position on either Phe3 or Phe4; the corresponding free amine-containing peptides were also prepared for comparison. The peptides bearing an affinity label group and their free amine analogs were evaluated in a radioligand-binding assay using Chinese hamster ovary (CHO) cells expressing mu- and delta-opioid receptors. Modification on Phe4 was better tolerated than on Phe3 for mu-receptor binding. Among the analogs tested, [Phe(p-NH2)4]endomorphin-2 showed the highest affinity (IC50 = 37 nm) for mu-receptors. The Phe(p-NHCOCH2Br)4 analog displayed the highest mu-receptor affinity (IC50 = 158 nm) among the peptides containing an affinity label group. Most of the compounds exhibited negligible binding affinity for delta-receptors, similar to the parent peptide.
authors.affiliation: Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, Baltimore, USA.
authors.forename: H
authors.initials: H
authors.lastname: Choi
authors.forename: T F
authors.initials: TF
authors.lastname: Murray
authors.forename: J V
authors.initials: JV
authors.lastname: Aldrich
mesh_terms: D000345:Affinity Labels / Q000138:chemical synthesis* / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D020128:Inhibitory Concentration 50; D009842:Oligopeptides / Q000737:chemistry* / Q000378:metabolism; D010446:Peptide Fragments / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism; D011869:Radioligand Assay; D017465:Receptors, Opioid, delta / Q000378:metabolism; D017450:Receptors, Opioid, mu / Q000378:metabolism
chemical_list: D000345:Affinity Labels; D009842:Oligopeptides; D010446:Peptide Fragments; D017465:Receptors, Opioid, delta; D017450:Receptors, Opioid, mu; C105294:endomorphin 2