Mu opioid receptor antagonist 4 (compound 31) is a potent and selective μ opioid receptor (MOR) antagonist with a K i of 0.38 nM and an EC 50 of 1.07 nM. Mu opioid receptor antagonist 4 has remarkable CNS antagonism against morphine, and precipitated fewer withdrawal symptoms than Naloxone. Mu opioid receptor antagonist 4 Mu opioid receptor antagonist 4 can be used for researching opioid use disorders (OUD).