Computer-Aided Discovery of Aromatic l-[alpha]-Amino Acids as Agonists of the Orphan G Protein-Coupled Receptor GPR139

GPR139 is an orphan G protein-coupled receptor expressed mainly in the central nervous system. We developed a pharmacophore model based on known GPR139 surrogate agonists which led us to propose aromatic-containing dipeptides as potential ligands. Upon testing, the dipeptides demonstrated agonism in the Gq pathway. Next, in testing all 20 proteinogenic l-α-amino acids, L-tryptophan and l-phenylalanine were found to have EC50 values of 220 and 320 μM, respectively, making them the first putative endogenous agonists for GPR139.