Design of novel hexahydropyrazinoquinolines as potent and selective dopamine D3 receptor ligands with improved solubility

New tetrahydroisoquinoline-based D3R ligands with an o-xylenyl linker motif

The effect of rigidification of the n-butyl linker region of tetrahydroisoquinoline-containing D₃R ligands via inclusion of an o-xylenyl motif was examined in this study. Generally, rigidification with an o-xylenyl linker group reduces D₃R affinity and negatively impacts selectivity versus D₂R for compounds possessing a 6-methoxy-1,2,3,4,-tetrahydroisoquinolin-7-ol primary pharmacophore group. However, D₃R affinity appears to be regulated by the primary pharmacophore group and high affinity D₃R ligands with 6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline and 6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline primary pharmacophore groups were identified. The results of this study also indicate that D₃R selectivity versus the σ₂R is dictated by the benzamide secondary pharmacophore group, this being facilitated with 4-substituted benzamides. Compounds 5s and 5t were identified as high affinity (K_i < 4 nM) D₃R ligands. Docking studies revealed that the added phenyl ring moiety interacts with the Cys181 in D₃R which partially accounts for the strong D₃R affinity of the ligands.

Tranylcypromine substituted cis-hydroxycyclobutylnaphthamides as potent and selective dopamine D₃ receptor antagonists

We report a class of potent and selective dopamine D₃ receptor antagonists based upon tranylcypromine. Although tranylcypromine has a low affinity for the rat D₃ receptor (K_i = 12.8 μM), our efforts have yielded (1R,2S)-11 (CJ-1882), which has K_i values of 2.7 and 2.8 nM at the rat and human dopamine D₃ receptors, respectively, and displays respective selectivities of >10000-fold and 223-fold over the rat and human D₂ receptors. Evaluation in a β-arrestin functional assay showed that (1R,2S)-11 is a potent and competitive antagonist at the human D₃ receptor.

Quinoline- and isoquinoline-sulfonamide analogs of aripiprazole: novel antipsychotic agents?

The introduction of typical antipsychotics over six decades ago signaled an important milestone in psychiatry. However, second-generation antipsychotics ameliorated the positive symptoms of schizophrenia but displayed limited effectiveness for the negative and cognitive symptoms. In addition, while the newer antipsychotics produced fewer motor side effects, the atypical antipsychotics still induced weight gain and endocrinopathies. In recent years, a third generation of antipsychotics was identified. Aripiprazole was the first approved drug acting as a D2 partial agonist/functionally selective ligand. This review presents the state of the development of novel antipsychotic dopaminergic and non-dopaminergic agents, supported by an overview of the compounds evaluated under advanced preclinical and clinical development (e.g., cariprazine and brexpiprazole). In line with the recent trends in the development of modern atypical antipsychotics, we present our strategic development of long-chain arylpiperazine-derived quinoline- and isoquinoline-sulfonamide displaying a multireceptor binding profile and partial D2 receptor agonism.

High-affinity and selective dopamine D₃ receptor full agonists

We have designed, synthesized and evaluated a series of new compounds with the goal to identify potent and selective D(3) ligands. The two most potent and selective new D(3) ligands are compounds 38 and 52, which bind to the D(3) receptors with a K(i) value of <nM and display a selectivity of 450-494 times over the D(2) receptors and >10,000 times over the D(1) receptors. Both 38 and 52 are full agonists with high potency at the D(3) receptor in a D(3) functional assay.

Chemical Modifications on 4-Arylpiperazine-Ethyl Carboxamide Derivatives Differentially Modulate Affinity for 5-HT1A, D4.2, and α2A Receptors: Synthesis and In Vitro Radioligand Binding Studies

A series of substituted 4-aryl-piperazine-ethyl heteroarylcarboxamides were prepared and tested in in vitro radioligand binding studies. The presence of a quinoxaline has a favourable impact in terms of serotonin 5-HT1A versus dopamine D4.2 receptor selectivity. Compounds with a 3-CF3 group at the distal phenyl ring are the most effective in terms of affinity and selectivity for 5-HT1A versus D4.2 receptors. A 4-phenyl-1,2,3,6-tetrahydropyridine in place of the corresponding 4-phenyl-piperazine side chain is also favourable not only for the affinity for 5-HT1A and D4.2 receptors but also in some cases for α 2A-adrenoceptors.

Design, synthesis, and evaluation of potent and selective ligands for the dopamine 3 (D3) receptor with a novel in vivo behavioral profile

A series of compounds structurally related to pramipexole were designed, synthesized, and evaluated as ligands for the dopamine 3 (D3) receptor. Compound 12 has a K(i) value of 0.41 nM to D3 and a selectivity of >30000- and 800-fold over the D1-like and D2 receptors, respectively. Our in vivo functional assays showed that this compound is a partial agonist at the D3 receptor with no detectable activity at the D2 receptor.

Asymmetric synthesis of chiral piperazinylpropylisoxazoline ligands for dopamine receptors

The asymmetric synthesis of chiral piperazinylpropylisoxazoline analogues, (R)-(+)-1, 2 and (S)-(-)-1, 2 was accomplished through a seven-step sequence of reactions, which involved asymmetric 1,3-dipolar cycloaddition, alkyl chain extension, and reductive amination as key reactions. Chiral ligands (R)-(+)-1, 2 exhibited the higher binding affinity and selectivity for the D(3) receptor over the D(4) receptor than (S)-(-)-1, 2 ligands.

Dopamine D3 receptor ligands—Recent advances in the control of subtype selectivity and intrinsic activity

Various pharmacological studies have implicated the dopamine D(3) receptor as an interesting therapeutic target in the treatment of different neurological disorders. Because of these putative therapeutic applications, D(3) receptor ligands with diverse intrinsic activities have been an active field of research in recent years. Separation of purely D(3)-mediated drug effects from effects produced by interactions with similar biogenic amine receptors allows to verify the therapeutic impact of D(3) receptors and to reduce possible side-effects caused by "promiscuous" receptor interactions. The requirement to gain control of receptor selectivity and in particular subtype selectivity has been a challenging task in rational drug discovery for quite a few years. In this review, recently developed structural classes of D(3) ligands are discussed, which cover a broad spectrum of intrinsic activities and show interesting selectivities.