Discovery, optimization, and characterization of novel D2 dopamine receptor selective antagonists

Abstract

The D2 dopamine receptor (D2 DAR) is one of the most validated drug targets for neuropsychiatric and endocrine disorders. However, clinically approved drugs targeting D2 DAR display poor selectivity between the D2 and other receptors, especially the D3 DAR. This lack of selectivity may lead to undesirable side effects. Here we describe the chemical and pharmacological characterization of a novel D2 DAR antagonist series with excellent D2 versus D1, D3, D4, and D5 receptor selectivity. The final probe 65 was obtained through a quantitative high-throughput screening campaign, followed by medicinal chemistry optimization, to yield a selective molecule with good in vitro physical properties, metabolic stability, and in vivo pharmacokinetics. The optimized molecule may be a useful in vivo probe for studying D2 DAR signal modulation and could also serve as a lead compound for the development of D2 DAR-selective druglike molecules for the treatment of multiple neuropsychiatric and endocrine disorders.

Figure 1

Known chemical series of selective D₂ versus D₃ DAR antagonists. Superscript “a” indicates that additional information is in Table S15 in Supporting Information.

Figure 2

(A) Structure of the hit compound 1. (B) Graphical representation of the dose–response curves of 1 in D₂ Ca²⁺ assay (green, AC₅₀ = 0.280 ± 0.012 μM), D₂ β-arrestin assay (blue, AC₅₀ = 2.89 ± 0.25 μM), and D₃ β-arrestin assay (red, AC₅₀ = 5.76 ± 1.18 μM). (C) Graphical representation of the dose–response curves of 1 in binding assays for D₁ (black), D₂ (blue, K_i = 0.30 ± 0.09 μM), D₃ (red, K_i = 1.9 ± 0.9 μM), D₄ (green), and D₅ (brown).

Figure 3

(A) Preparative chiral HPLC separation of the original racemic hit 1 and absolute stereochemistry assignment. (B) Single crystal X-ray structure of the inactive enantiomer ((R)-59).

Scheme 1. General Synthetic Route for Analogues Shown in Tables 1–3

Scheme 2. General Synthetic Routes (A) for Analogues Shown in Table 4, (B) for Analogues Shown in Table 5, and (C) for Analogues Shown in Table 6

Figure 4

SAR summary.

Figure 5

X-ray crystal structure of 65. X-ray parameters are listed in the Supporting Information.

Figure 6

Mean plasma and brain concentration–time profiles of 65 after an ip dose of 30 mg/kg in male C57BL/6 mice (N = 3). The mice appeared less active at 5 min after dosing, and it lasted for about 2 h. The ip dosing solution was prepared in 10% NMP + 20% PEG 400 + 70% of 25% HP-β-CD in water. Full PK parameters are listed in the Supporting Information.