Melanocortin Tetrapeptide Ac-His-DPhe-Arg-Trp-NH<sub>2</sub> Modified at the Para Position of the Benzyl Side Chain (DPhe): Importance for Mouse Melanocortin-3 Receptor Agonist versus Antagonist Activity Bettina Proneth Irina D. Pogozheva Federico P. Portillo Henry I. Mosberg Carrie Haskell-Luevano 10.1021/jm800291b.s001 https://acs.figshare.com/articles/journal_contribution/Melanocortin_Tetrapeptide_Ac_His_DPhe_Arg_Trp_NH_sub_2_sub_Modified_at_the_Para_Position_of_the_Benzyl_Side_Chain_DPhe_Importance_for_Mouse_Melanocortin_3_Receptor_Agonist_versus_Antagonist_Activity/2911591 The melanocortin-3 and -4 receptors (MC3R, MC4R) have been implicated in energy homeostasis and obesity. Whereas the physiological role of the MC4R is extensively studied, little is known about the MC3R. One caveat is the limited availability of ligands that are selective for the MC3R. Previous studies identified Ac-His-DPhe(p-I)-Arg-Trp-NH<sub>2</sub>, which possessed partial agonist/antagonist pharmacology at the mMC3R while retaining full nanomolar agonist pharmacology at the mMC4R. These data allowed for the hypothesis that the DPhe position in melanocortin tetrapeptides can be used to examine ligand side-chain determinants important for differentiation of mMC3R agonist versus antagonist activity. A series of 15 DPhe<sup>7</sup> modified Ac-His-DPhe<sup>7</sup>-Arg-Trp-NH<sub>2</sub> tetrapeptides has been synthesized and pharmacologically characterized. Most notable results include the identification of modifications that resulted in potent antagonists/partial agonists at the mMC3R and full, potent agonists at the mMC4R. These SAR studies provide experimental evidence that the molecular mechanism of antagonism at the mMC3R differentiates this subtype from the mMC4R. 2008-09-25 00:00:00 nanomolar agonist pharmacology SAR mMC 3R MC 3R MC 4R MC 3R 15 DPhe 7 mMC 4R Benzyl Side Chain mMC 3R agonist