N-[[1-(2-phenylethyl)pyrrolidin-2-yl]methyl]cyclohexanecarboxamides as selective 5-HT1A receptor agonists

Positron Emission Tomography (PET) Imaging Tracers for Serotonin Receptors

Serotonin (5-hydroxytryptamine, 5-HT) and 5-HT receptors (5-HTRs) have crucial roles in various neuropsychiatric disorders and neurodegenerative diseases, making them attractive diagnostic and therapeutic targets. Positron emission tomography (PET) is a noninvasive nuclear molecular imaging technique and is an essential tool in clinical diagnosis and drug discovery. In this context, numerous PET ligands have been developed for "visualizing" 5-HTRs in the brain and translated into human use to study disease mechanisms and/or support drug development. Herein, we present a comprehensive repertoire of 5-HTR PET ligands by focusing on their chemotypes and performance in PET imaging studies. Furthermore, this Perspective summarizes recent 5-HTR-focused drug discovery, including biased agonists and allosteric modulators, which would stimulate the development of more potent and subtype-selective 5-HTR PET ligands and thus further our understanding of 5-HTR biology.

Dopamine and Dopamine-Related Ligands Can Bind Not Only to Dopamine Receptors

The dopaminergic system is one of the most important neurotransmitter systems in the central nervous system (CNS). It acts mainly by activation of the D₁-like receptor family at the target cell. Additionally, fine-tuning of the signal is achieved via pre-synaptic modulation by the D₂-like receptor family. Some dopamine drugs (both agonists and antagonists) bind in addition to DRs also to α₂-ARs and 5-HT receptors. Unfortunately, these compounds are often considered subtype(s) specific. Thus, it is important to consider the presence of these receptor subtypes in specific CNS areas as the function virtually elicited by one receptor type could be an effect of other—or the co-effect of multiple receptors. However, there are enough molecules with adequate specificity. In this review, we want to give an overview of the most common off-targets for established dopamine receptor ligands. To give an overall picture, we included a discussion on subtype selectivity. Molecules used as antipsychotic drugs are reviewed too. Therefore, we will summarize reported affinities and give an outline of molecules sufficiently specific for one or more subtypes (i.e., for subfamily), the presence of DR, α₂-ARs, and 5-HT receptors in CNS areas, which could help avoid ambiguous results.

Exploring the antiplatelet activity of serotonin 5-HT2A receptor antagonists bearing 6-fluorobenzo[d]isoxazol-3-yl)propyl) motif- as potential therapeutic agents in the prevention of cardiovascular diseases

Small drug-like molecules that can block the function of serotonin 5-HT_2A receptors have garnered considerable attention due to their ability to inhibit platelet aggregation and the possible prevention of atherosclerotic lesions. Although clinical data provided compelling evidence for the efficacy of this approach in the prevention of various cardiovascular conditions, the chemical space of 5-HT_2A receptor antagonists is limited to ketanserin and sarpogrelate. To expand the portfolio of novel chemical motifs with potential antiplatelet activity, we evaluated the antiplatelet activity of a series of 6-fluorobenzo[d]isoxazole derivatives that possess a high affinity for 5-HT_2A receptor. Here we describe in vitro studies showing that 6-fluorobenzo[d]isoxazole derivatives exert promising antiplatelet activity in three various in vitro models of platelet aggregation, as well as limit serotonin-induced vasoconstriction. Compound AZ928 showed in vitro activity greater than the clinically approved drug sarpogrelate. In addition to promising antiplatelet activity, the novel series was characterized by a favorable safety profile. Our findings show that the novel series exerts promising antiplatelet efficacy while being deprived of potential side effects, such as hemolytic activity, which render these compounds as potential substances for further investigation in the field of cardiovascular research.

New piperidinyl- and 1,2,3,6-tetrahydropyridinyl-pyrimidine derivatives as selective 5-HT1A receptor agonists with highly potent anti-ischemic effects

A series of new piperidinyl- and 1,2,3,6-tetrahydropyridinyl-pyrimidine derivatives were synthesized. Among these compounds, 4-methyl-2-(1,2,3,6-tetrahydropyridin-4-yl)pyrimidine derivative 23 (SUN N5147) exhibited sub-nanomolar affinity for 5-HT1A receptor with 1000-fold selectivity over both dopamine D2 and alpha1-adrenergic receptors and remarkable neuroprotective activity in a transient middle cerebral artery occlusion (t-MCAO) model.

Synthesis and evaluation of (11)C-labeled (S)-N-[[1-(2-phenylethyl) pyrrolidin-2-yl]methyl]-3-methylthiobenzamide as a PET 5-HT(1A) receptor ligand

We prepared 5-HT(1A) receptor ligands (S)-N-[[1-(2-phenylethyl)pyrrolidin-2-yl]methyl]-3-[11C]methylthiobenzamide ([11C](S)-PPMMB) (Ki = 4.3 nM) and the less active [(11)C](R)-PPMMB (Ki = 160 nM) by reduction of the disulfide dimer and subsequent [(11)C]methylation of demethyl (S)- and (R)-PPMMB, respectively. Both radioligands showed similar brain distribution in mice with relatively higher affinity for the hippocampus being rich in 5-HT(1A) receptors than for other brain regions. Uptake of [(11)C](S)-PPMMB was not reduced by carrier-loading nor by pretreatment with 5-HT(1A) receptor ligands. [(11)C](S)-PPMMB is therefore not a suitable radioligand for mapping 5-HT(1A) receptors using positron emission tomography.

Initial structure-activity relationship studies of a novel series of pyrrolo[1,2-a]pyrimid-7-ones as GnRH receptor antagonists

Initial SAR studies on 1-aminomethyl-2-aryl-3-cyano-pyrrolo[1,2-a]pyrimid-7-one-6-carboxylates as human GnRH receptor antagonists were discussed. 2-(2-Methylaminoethyl)pyridine was discovered to be a key feature for generating active compounds. The best compound from the series had 25 nM (K(i)) binding affinity to human GnRH receptor.

N-[1-(2-Phenylethyl)pyrrolidin-3-yl]-1-adamantanecarboxamides as novel 5-HT2 receptor antagonists

A series of 1-adamantanecarboxamides was synthesized and examined for their potency as a selective 5-HT2 receptor antagonist. We found (S)-N-[1-[2-(4-fluorophenyl)ethyl]pyrrolidin-3-yl]-1-adamantane carboxamide hydrochloride hydrate (10-(S), Y-39241) to have a high affinity and selectivity for 5-HT2 receptors, and this potent anti-platelet effect of Y-39241 was confirmed both in vitro and in vivo.