The overall goal of this project is to produce drug-like small molecule agonists of the MAS1 receptor with suitable brain exposure to better understand the role of this orphan GPCR in neuropsychiatric conditions, such as post- traumatic stress syndrome (PTSD). There is a paucity of high-quality probes of MAS1 that can enable successful in vivo pharmacological studies to elucidate the role of this protein in the central nervous system (CNS). Studies from several groups using transgenic animals indicate deletion of this receptor produces a pro-anxiogenic phenotype. These studies point to a possible role of MAS1 agonists in resolving mental diseases associated with heightened response to aversive stimuli such PTSD. We developed an HTS assay for MAS1 and conducted a screening campaign using a diversity set of 30,000 compounds. Three different scaffolds were identified, of which one particular pyrazole scaffold has many advantageous properties that can enable rapid development of CNS- penetrant high-quality MAS1 probes with good drug-like properties. Through early SAR studies, congeners of this scaffold have been identified that are more potent than commonly utilized small molecule activators of MAS1. Three aims are proposed for this project: Aim 1. Synthesis and Optimization of the lead scaffold RU-70. A series of pyrazole analogs are proposed to further improve potency, CNS exposure, and limit metabolism. Computational approaches such as docking, and pharmacophore mapping will augment the design flow. Aim 2. Pharmacological and ADMET characterization of MAS1 ligands. We will use MAS1 functional assays to rank- order novel ligands. A suite of ADMET studies will identify leads that have good drug-like in vitro properties. Suitable compounds will advance to rodent pharmacokinetic (PK) studies to establish their in vivo suitability for efficacy testing. Further de-risking will involve off-target profiling of mature leads as appropriate. Aim 3 Determine in vivo efficacy of novel MAS1 ligands on behavior and neural activity. We will determine whether innate or learned responses to aversive stimuli and associated calcium dynamics in the dentate gyrus are altered by MAS1 activation through our novel MAS1 ligands. These studies will provide a clear indication of whether pharmacological activation of MAS1 in the CNS can potentially provide a therapeutic opportunity for PTSD and other psychiatric disorders. Successful completion of this innovative project can lead to the development of a first in class therapy that has the potential to help many patients across the world.