Synthesis and Biological Evaluation of a Novel Series of Heterobivalent Muscarinic Ligands Based on Xanomeline and 1‑[3-(4-Butylpiperidin-1-yl)propyl]-1,2,3,4-tetrahydroquinolin-2-one (77-LH-28-1)

Novel bitopic hybrids, based on the M₁/M₄ muscarinic acetylcholine receptor (mAChR) orthosteric agonist xanomeline (<b>1</b>) and the putative M₁ mAChR allosteric agonist 1-[3-(4-butylpiperidin-1-yl)­propyl]-1,2,3,4-tetrahydroquinolin-2-one (77-LH-28-1, <b>3</b>) connected by an aliphatic linker of variable length, were prepared. The novel heterobivalent hybrids <b>4a</b>–<b>f</b> along with the intermediate alcohols <b>5a</b>–<b>f</b> were pharmacologically evaluated in radioligand binding assays and some of them for their functional efficacies in bioluminescence resonance energy transfer (BRET)-based assays to give an insight into the structure–activity relationships of bivalent and linker-attached compounds in mAChRs. The hybrid <b>4d</b> exhibited high efficacy for β-arrestin2 engagement in M₁ mAChR and alcohol <b>5c</b> behaved much like <b>3</b> at M₁ mAChR and showed full antagonism in both G_i activation and β-arrestin2 engagement at M₄ mAChR. Moreover, docking simulations on the M₁ mAChR model were performed to elucidate how the binding mode of the proposed compounds is influenced by the linker length

Chiral Resolution and Serendipitous Fluorination Reaction for the Selective Dopamine D3 Receptor Antagonist BAK2-66

The improved chiral synthesis of the selective dopamine D3 receptor (D3R) antagonist (<i>R</i>)-<i>N</i>-(4-(4-(2,3-dichlorophenyl)­piperazin-1-yl)-3-hydroxybutyl)­1<i>H</i>-indole-2-carboxamide (<b>(</b><i><b>R</b></i><b>)-PG648</b>) is described. The same chiral secondary alcohol intermediate was used to prepare the enantiomers of a 3-F-benzofuranyl analogue, <b>BAK 2-66</b>. The absolute configurations of the 3-F enantiomers were assigned from their X-ray crystal structures that confirmed retention of configuration during fluorination with <i>N</i>,<i>N</i>-diethylaminosulfur trifluoride (DAST). <b>(</b><i><b>R</b></i><b>)-BAK2-66</b> showed higher D3R affinity and selectivity than its (<i>S</i>)-enantiomer; however, it had lower D3R affinity and enantioselectivity than <b>(</b><i><b>R</b></i><b>)-PG648</b>. Further, importance of the 4-atom linker length between the aryl amide and 4-phenylpiperazine was demonstrated with the 4-fluorobutyl-product (<b>8</b>)

Pharmacological and Physicochemical Properties Optimization for Dual-Target Dopamine D₃ (D₃R) and μ‑Opioid (MOR) Receptor Ligands as Potentially Safer Analgesics

A new generation of dual-target μ opioid receptor (MOR) agonist/dopamine D3 receptor (D3R) antagonist/partial agonists with optimized physicochemical properties was designed and synthesized. Combining in vitro cell-based on-target/off-target affinity screening, in silico computer-aided drug design, and BRET functional assays, we identified new structural scaffolds that achieved high affinity and agonist/antagonist potencies for MOR and D3R, respectively, improving the dopamine receptor subtype selectivity (e.g., D3R over D2R) and significantly enhancing central nervous system multiparameter optimization scores for predicted blood–brain barrier permeability. We identified the substituted trans-(2S,4R)-pyrrolidine and trans-phenylcyclopropyl amine as key dopaminergic moieties and tethered these to different opioid scaffolds, derived from the MOR agonists TRV130 (3) or loperamide (6). The lead compounds 46, 84, 114, and 121 have the potential of producing analgesic effects through MOR partial agonism with reduced opioid-misuse liability via D3R antagonism. Moreover, the peripherally limited derivatives could have therapeutic indications for inflammation and neuropathic pain

1,4-Dioxane, a Suitable Scaffold for the Development of Novel M₃ Muscarinic Receptor Antagonists

In this study the modulation of the pharmacological profile from agonist to antagonist was successfully obtained by replacing the methyl group in position 6 of the 1,4-dioxane scaffold of the potent M₂/M₃ muscarinic agonist <b>1</b> with bulkier groups. In particular, the 6,6-diphenyl substitution provided the potent M₃ preferring antagonist (±)-<b>17</b>, which in in vivo study proved to be effective in reducing the volume-induced contractions of rat urinary bladder and was devoid of cardiovascular effects

Pharmacological and Physicochemical Properties Optimization for Dual-Target Dopamine D₃ (D₃R) and μ‑Opioid (MOR) Receptor Ligands as Potentially Safer Analgesics

A new generation of dual-target μ opioid receptor (MOR) agonist/dopamine D3 receptor (D3R) antagonist/partial agonists with optimized physicochemical properties was designed and synthesized. Combining in vitro cell-based on-target/off-target affinity screening, in silico computer-aided drug design, and BRET functional assays, we identified new structural scaffolds that achieved high affinity and agonist/antagonist potencies for MOR and D3R, respectively, improving the dopamine receptor subtype selectivity (e.g., D3R over D2R) and significantly enhancing central nervous system multiparameter optimization scores for predicted blood–brain barrier permeability. We identified the substituted trans-(2S,4R)-pyrrolidine and trans-phenylcyclopropyl amine as key dopaminergic moieties and tethered these to different opioid scaffolds, derived from the MOR agonists TRV130 (3) or loperamide (6). The lead compounds 46, 84, 114, and 121 have the potential of producing analgesic effects through MOR partial agonism with reduced opioid-misuse liability via D3R antagonism. Moreover, the peripherally limited derivatives could have therapeutic indications for inflammation and neuropathic pain

Pharmacological and Physicochemical Properties Optimization for Dual-Target Dopamine D₃ (D₃R) and μ‑Opioid (MOR) Receptor Ligands as Potentially Safer Analgesics

A new generation of dual-target μ opioid receptor (MOR) agonist/dopamine D3 receptor (D3R) antagonist/partial agonists with optimized physicochemical properties was designed and synthesized. Combining in vitro cell-based on-target/off-target affinity screening, in silico computer-aided drug design, and BRET functional assays, we identified new structural scaffolds that achieved high affinity and agonist/antagonist potencies for MOR and D3R, respectively, improving the dopamine receptor subtype selectivity (e.g., D3R over D2R) and significantly enhancing central nervous system multiparameter optimization scores for predicted blood–brain barrier permeability. We identified the substituted trans-(2S,4R)-pyrrolidine and trans-phenylcyclopropyl amine as key dopaminergic moieties and tethered these to different opioid scaffolds, derived from the MOR agonists TRV130 (3) or loperamide (6). The lead compounds 46, 84, 114, and 121 have the potential of producing analgesic effects through MOR partial agonism with reduced opioid-misuse liability via D3R antagonism. Moreover, the peripherally limited derivatives could have therapeutic indications for inflammation and neuropathic pain

Structure–Activity Relationships in 1,4-Benzodioxan-Related Compounds. 11. Reversed Enantioselectivity of 1,4-Dioxane Derivatives in α₁‑Adrenergic and 5‑HT_1A Receptor Binding Sites Recognition

5-HT_1A receptor and α₁-adrenoreceptor (α₁-AR) binding sites recognized by the 1,4-dioxanes <b>2</b>–<b>4</b> display reversed stereochemical requirements. (<i>S</i>)-<b>2</b> proved to be a potent 5-HT_1A receptor agonist highly selective over α₁-AR subtypes. Chirality influenced the anticancer activity of <b>3</b> and <b>4</b> in human prostate cancer cells (PC-3): (<i>R</i>)-<b>4</b>, eutomer at the α_1d-AR subtype, was the most potent. The decreased effect of <b>4</b> and (<i>R</i>)-<b>4</b> in α_1d-AR silenced PC-3 cells confirmed that their anticancer activity was α_1d-AR-dependent

1‑[3-(4-Butylpiperidin-1-yl)propyl]-1,2,3,4-tetrahydroquinolin-2-one (77-LH-28-1) as a Model for the Rational Design of a Novel Class of Brain Penetrant Ligands with High Affinity and Selectivity for Dopamine D₄ Receptor

In the present article, the M₁ mAChR bitopic agonist 1-[3-(4-butylpiperidin-1-yl)­propyl]-1,2,3,4-tetrahydroquinolin-2-one (77-LH-28-1, <b>1</b>) has been demonstrated to show unexpected D₄R selectivity over D₂R and D₃R and to behave as a D₄R antagonist. To better understand the structural features required for the selective interaction with the D₄R and to obtain compounds unable to activate mAChRs, the aliphatic butyl chain and the piperidine nucleus of <b>1</b> were modified, affording compounds <b>2</b>–<b>14</b>. The 4-benzylpiperidine <b>9</b> and the 4-phenylpiperazine <b>12</b> showed high D₄R affinity and selectivity not only over the other D₂-like subtypes, but also over M₁–M₅ mAChRs. Derivative <b>12</b> was also highly selective over some selected off-targets. This compound showed biased behavior, potently and partially activating G_i protein and inhibiting β-arrestin2 recruitment in functional studies. Pharmacokinetic studies demonstrated that it was characterized by a relevant brain penetration. Therefore, <b>12</b> might be a useful tool to better clarify the role played by D₄R in disorders in which this subtype is involved

Highly Selective Dopamine D₃ Receptor (D₃R) Antagonists and Partial Agonists Based on Eticlopride and the D₃R Crystal Structure: New Leads for Opioid Dependence Treatment

The recent and precipitous increase in opioid analgesic abuse and overdose has inspired investigation of the dopamine D₃ receptor (D₃R) as a target for therapeutic intervention. Metabolic instability or predicted toxicity has precluded successful translation of previously reported D₃R-selective antagonists to clinical use for cocaine abuse. Herein, we report a series of novel and D₃R crystal structure-guided 4-phenylpiperazines with exceptionally high D₃R affinities and/or selectivities with varying efficacies. Lead compound <b>19</b> was selected based on its in vitro profile: D₃R <i>K</i>_i = 6.84 nM, 1700-fold D₃R versus D₂R binding selectivity, and its metabolic stability in mouse microsomes. Compound <b>19</b> inhibited oxycodone-induced hyperlocomotion in mice and reduced oxycodone-induced locomotor sensitization. In addition, pretreatment with <b>19</b> also dose-dependently inhibited the acquisition of oxycodone-induced conditioned place preference (CPP) in rats. These findings support the D₃R as a target for opioid dependence treatment and compound <b>19</b> as a new lead molecule for development

Novel Bivalent Ligands Based on the Sumanirole Pharmacophore Reveal Dopamine D₂ Receptor (D₂R) Biased Agonism

The development of bivalent ligands has attracted interest as a way to potentially improve the selectivity and/or affinity for a specific receptor subtype. The ability to bind two distinct receptor binding sites simultaneously can allow the selective activation of specific G-protein dependent or β-arrestin-mediated cascade pathways. Herein, we developed an extended SAR study using sumanirole (<b>1</b>) as the primary pharmacophore. We found that substitutions in the <i>N</i>-1- and/or <i>N</i>-5-positions, physiochemical properties of those substituents, and secondary aromatic pharmacophores can enhance agonist efficacy for the cAMP inhibition mediated by G_i/o-proteins, while reducing or suppressing potency and efficacy toward β-arrestin recruitment. Compound <b>19</b> was identified as a new lead for its selective D₂ G-protein biased agonism with an EC₅₀ in the subnanomolar range. Structure–activity correlations were observed between substitutions in positions <i>N</i>-1 and/or <i>N</i>-5 of <b>1</b> and the capacity of the new bivalent compounds to selectively activate G-proteins versus β-arrestin recruitment in D₂R-BRET functional assays