(A) Activity of compounds 1, 24, 46, 49, 53, 54, and quinpirole in the D2R-mediated Gi/o coupled isoproterenol-stimulated cAMP production assay using HEK293T cells expressing D2R and GloSensor-22F. All six tested compounds were partial agonists compared to quinpirole (EC50 = 1.7 nM), which was used as a positive control. (B) Activity of compounds 1, 24, 46, 49, 53, 54, and quinpirole in the D2R-mediated β-arrestin-2 translocation Tango assay using HTLA cells transfected with a D2V2-TCS-tTA construct. 1 recruited β-arrestin weakly and other five compounds did not substantially recruit β-arrestin compared to the full agonist quinpirole (EC50 = 0.8 nM). Data are representative of at least three independent experiments performed in triplicate. (C) Bias plot of compounds 1, 24, 46, 49, 53, 54, and quinpirole in the D2R-mediated cAMP inhibition GloSensor assay versus the D2R-mediated β-arrestin-2 translocation Tango assay. Quinpirole shows equal activity in both assays, but compounds 1, 24, 46, 49, 53, and 54 cluster toward G protein activation.