Hydroxy-Substituted Heteroarylpiperazines: Novel Scaffolds for β‑Arrestin-Biased D2R Agonists

By means of a formal structural hybridization of the antipsychotic drug aripiprazole and the heterocyclic catecholamine surrogates present in the β2-adrenoceptor agonists procaterol and BI-167107 (4), we designed and synthesized a collection of novel hydroxy-substituted heteroarylpiperazines and heteroarylhomopiperazines with high dopamine D2 receptor (D2R) affinity. In contrast to the weak agonistic behavior of aripiprazole, these ligands are capable of effectively mimicking those interactions of dopamine and the D2R that are crucial for an active state, leading to the recruitment of β-arrestin-2. Interestingly, some ligands show considerably lower intrinsic activity in guanine nucleotide exchange experiments at D2R and consequently represent biased agonists favoring β-arrestin-2 recruitment over canonical G protein activation. The ligands’ agonistic properties are substantially driven by the presence of an endocyclic H-bond donor.