DREADD agonist 21 is a potent human muscarinic acetylcholine M3 receptors (hM3Dq) agonist (EC 50 =1.7 nM). DREADD agonist 21 does not activate the human M3 receptor (hM3). In addition to being inactive at hM3, DREADD agonist 21, a potent full agonist of hM3Dq (EC 50 =1.7 nM), is only 3.5-fold selective for hM3Dq over H1, 40-fold selective over 5HT2A, 100-fold selective over 5HT2C, and 165-fold selective over α1A. DREADD agonist 21 shows high binding affinities to 5HT2A and 5HT2C serotonin receptor, α1A adrenergic receptor, and H1 histamine receptor with K i values of 66, 170, 280, and 6 nM, respectively [1]. DREADD agonist 21 potently activates hM1Dq, hM3Dq, and hM4Di. DREADD agonist 21 binds to hM1, hM4, hM1Dq and hM4Di receptors with pK i s of 5.97, 5.44, 7.20, and 6.75, respectively. DREADD agonist 21 potently activates hM3Dq in Chinese hamster ovary (CHO) cells transfected cells in vitro with a pEC 50 of 8.48±0.05. DREADD agonist 21 is a highly selective and potent agonist for muscarinic DREADDs (pEC 50 for hM1Dq=6.54 and that for hM4Di=7.77 in pERK assays) [2].

DREADD agonist 21 (0.3, 1.0, and 3.0 mg/kg; i.p.) activates neuronal hM3Dq in mice [2]. DREADD agonist 21 has excellent bioavailability, pharmacokinetic properties, and brain penetrability. DREADD agonist 21 (0.1, 1, and 10 mg/kg; i.p.) shows 95.1% plasma protein binding and 95% brain protein bounding in mice [2].