title: Conformational Restriction and Enantioseparation Increase Potency and Selectivity of Cyanoguanidine-Type Histamine H4 Receptor Agonists.
abstract: 2-Cyano-1-[4-(1H-imidazol-4-yl)butyl]-3-[2-(phenylsulfanyl)ethyl]guanidine (UR-PI376, 1) is a potent and selective agonist of the human histamine H4 receptor (hH4R). To gain information on the active conformation, we synthesized analogues of 1 with a cyclopentane-1,3-diyl linker. Affinities and functional activities were determined at recombinant hHxR (x: 1-4) subtypes on Sf9 cell membranes (radioligand binding, [(35)S]GTPγS, or GTPase assays) and in part in luciferase assays on human or mouse H4R (HEK-293 cells). The most potent H4R agonists among 14 racemates were separated by chiral HPLC, yielding eight enantiomerically pure compounds. Configurations were assigned based on X-ray structures of intermediates and a stereocontrolled synthetic pathway. (+)-2-Cyano-1-{[trans-(1S,3S)-3-(1H-imidazol-4-yl)cyclopentyl]methyl}-3-[2-(phenylsulfanyl)ethyl]guanidine ((1S,3S)-UR-RG98, 39a) was the most potent H4R agonist in this series (EC50 11 nM; H4R vs H3R, >100-fold selectivity; H1R, H2R, negligible activities), whereas the optical antipode proved to be an H4R antagonist ([(35)S]GTPγS assay). MD simulations confirmed differential stabilization of the active and inactive H4R state by the enantiomers.
authors.affiliation: Institute of Pharmacy, Pharmaceutical/Medicinal Chemistry, Faculty of Chemistry and Pharmacy, University of Regensburg , Universitätsstraße 31, D-93053 Regensburg, Germany.
authors.forename: Roland
authors.initials: R
authors.lastname: Geyer
authors.affiliation: Institute of Pharmacy, Pharmaceutical/Medicinal Chemistry, Faculty of Chemistry and Pharmacy, University of Regensburg , Universitätsstraße 31, D-93053 Regensburg, Germany.
authors.forename: Uwe
authors.initials: U
authors.lastname: Nordemann
authors.affiliation: Institute of Pharmacy, Pharmaceutical/Medicinal Chemistry, Faculty of Chemistry and Pharmacy, University of Regensburg , Universitätsstraße 31, D-93053 Regensburg, Germany.
authors.forename: Andrea
authors.initials: A
authors.lastname: Strasser
authors.affiliation: Institute of Pharmacy, Pharmaceutical/Medicinal Chemistry, Faculty of Chemistry and Pharmacy, University of Regensburg , Universitätsstraße 31, D-93053 Regensburg, Germany.
authors.forename: Hans-Joachim
authors.initials: HJ
authors.lastname: Wittmann
authors.affiliation: Institute of Pharmacy, Pharmaceutical/Medicinal Chemistry, Faculty of Chemistry and Pharmacy, University of Regensburg , Universitätsstraße 31, D-93053 Regensburg, Germany.
authors.forename: Armin
authors.initials: A
authors.lastname: Buschauer
mesh_terms: D000818:Animals; D006146:Guanidines / Q000737:chemistry* / Q000494:pharmacology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D057809:HEK293 Cells; D017442:Histamine Agonists / Q000737:chemistry / Q000494:pharmacology*; D006801:Humans; D007093:Imidazoles / Q000737:chemistry* / Q000494:pharmacology*; D051379:Mice; D008958:Models, Molecular; D008968:Molecular Conformation; D056004:Molecular Dynamics Simulation; D011487:Protein Conformation; D011869:Radioligand Assay; D043562:Receptors, G-Protein-Coupled / Q000819:agonists* / Q000737:chemistry* / Q000378:metabolism; D011968:Receptors, Histamine / Q000737:chemistry* / Q000378:metabolism; D000074040:Receptors, Histamine H4; D061987:Sf9 Cells; D018411:Spodoptera; D013237:Stereoisomerism; D013329:Structure-Activity Relationship
chemical_list: C574160:2-cyano-1-(4-(1H-imidazol-4-yl)butyl)-3-((2-phenylthio)ethyl)guanidine; D006146:Guanidines; C418607:HRH4 protein, human; D017442:Histamine Agonists; D007093:Imidazoles; D043562:Receptors, G-Protein-Coupled; D011968:Receptors, Histamine; D000074040:Receptors, Histamine H4; C000611070:UR-RG98; D016244:Guanosine 5'-O-(3-Thiotriphosphate); C004711:dicyandiamido