Design of high affinity cyclic pentapeptide ligands for j-opioid receptors M.J. Przydzial I.D. Pogozheva J.C. Ho K.E. Bosse E. Sawyer J.R. Traynor H.I. Mosberg Authors' affiliations: M.J. Przydzial, I.D. Pogozheva, J.C. Ho and H.I. Mosberg, Department of Medicinal Chemistry, College of Pharmacy, University of Michigan, Ann Arbor, MI 48109, USA K. E. Bosse, E. Sawyer and J. R. Traynor, Department of Pharmacology, University of Michigan, Ann Arbor, MI 48109, USA Correspondence to: H.I. Mosberg Department of Medicinal Chemistry College of Pharmacy University of Michigan 428 Church St Ann Arbor MI 48109-1065 USA Tel.: (734) 764-8117 Fax: (734) 763-5595 E-mail: him@umich.edu Key words: cyclic peptides; G protein-coupled receptor; j-opioid receptor; opioid ligands Abstract: Using results from our previously reported cyclic opioid peptide series and reliable models for l-, d-, and j-opioid receptors (MOR, DOR, and KOR, respectively) and their complexes with peptide ligands, we have designed and synthesized a series of cyclic pentapeptides of structure Tyr-c[D-Cys-Phe-Phe-X]-NH 2 , cyclized via disulfide, methylene, or ethylene dithioethers, and where X ¼ D- or L-Cys; or D- or L-penicillamine (Pen; b,b-dimethylcysteine). Determination of binding affinities to MOR, DOR, and KOR revealed that members of this series with X ¼ D- or L-Cys display KOR affinities in the low nanomolar range, demonstrating that a ÔDPDPE-likeÕ tetrapeptide scaffold is suitable not only for DOR and MOR ligands, but also for KOR ligands. The cyclic pentapeptides reported here are not, however, selective for KOR, rather they display significant selectivity and high affinity for MOR. Indeed, peptide 8, Tyr-c[D-Cys-Phe-Phe-Cys]-NH 2 -cyclized via a methylene dithioether, shows picomolar binding affinity for MOR (K l i ¼ 16 pM) with more than 100-fold selectivity for MOR vs. DOR or KOR, and may be of interest as a high affinity, high selectivity MOR ligand. Nonetheless, the high affinity KOR peptides in this series represent excellent leads for the development of structurally related, selective KOR ligands designed to exploit structurally specific features of KOR, MOR, and DOR. Abbreviations: CHO, Chinese hamster ovary; C6, rat C6 glioma; EL, extracellular loop; Pen, penicillamine; RP-HPLC, reverse phase high- performance liquid chromatography; TM, transmembrane a-helix. Dates: Received 27 July 2005 Accepted 24 August 2005 To cite this article: Przydzial, M.J., Pogozheva, I.D., Ho, J.C., Bosse, K.E., Sawyer, E., Traynor, J.R. & Mosberg, H.I. Design of high affinity cyclic pentapeptide ligands for j-opioid receptors. J. Peptide Res., 2005, 66, 255–262. DOI 10.1111/j.1399-3011.2005.00295.x Ó 2005 The Authors Journal compilation Ó 2005 Blackwell Munksgaard. Introduction Understanding the differences in structure and function of opioid receptors and of the modes of their interactions with ligands is fundamental for rational design of safer analge- 255