Pharmacological and Physicochemical Properties Optimization for Dual-Target Dopamine D3 (D3R) and μ-Opioid (MOR) Receptor Ligands as Potentially Safer Analgesics

A new generation of dual-target μ opioid receptor (MOR) agonist/dopamine D 3 receptor (D 3 R) antagonist/partial agonists with optimized physicochemical properties was designed and synthesized. Combining in vitro cell-based on-target/off-target affinity screening, in silico computer-aided drug design, and BRET functional assays, we identified new structural scaffolds that achieved high affinity and agonist/antagonist potencies for MOR and D 3 R, respectively, improving the dopamine receptor subtype selectivity (e.g., D 3 R over D 2 R) and significantly enhancing central nervous system multiparameter optimization scores for predicted blood–brain barrier permeability. We identified the substituted trans -(2 S,4 R )-pyrrolidine and trans -phenylcyclopropyl amine as key dopaminergic moieties and tethered these to different opioid scaffolds, derived from the MOR agonists TRV130 ( 3 ) or loperamide ( 6 ). The lead compounds 46, 84, 114, and 121 have the potential of producing analgesic effects through MOR partial agonism with reduced opioid-misuse liability via D 3 R antagonism. Moreover, the peripherally limited derivatives could have therapeutic indications for inflammation and neuropathic pain.