New N- and O-arylpiperazinylalkyl pyrimidines and 2-methylquinazolines derivatives as 5-HT7 and 5-HT1A receptor ligands: Synthesis, structure-activity relationships, and molecular modeling studies

Advances in drug design and therapeutic potential of selective or multitarget 5-HT1A receptor ligands

5-HT1A receptor (5-HT1A-R) is a serotoninergic G-protein coupled receptor subtype which contributes to several physiological processes in both central nervous system and periphery. Despite being the first 5-HT-R identified, cloned and studied, it still represents a very attractive target in drug discovery and continues to be the focus of a myriad of drug discovery campaigns due to its involvement in numerous neuropsychiatric disorders. The structure-activity relationship studies (SAR) performed over the last years have been devoted to three main goals: (i) design and synthesis of 5-HT1A-R selective/preferential ligands; (ii) identification of 5-HT1A-R biased agonists, differentiating pre- versus post-synaptic agonism and signaling cellular mechanisms; (iii) development of multitarget compounds endowed with well-defined poly-pharmacological profiles targeting 5-HT1A-R along with other serotonin receptors, serotonin transporter (SERT), D2-like receptors and/or enzymes, such as acetylcholinesterase and phosphodiesterase, as a promising strategy for the management of complex psychiatric and neurodegenerative disorders. In this review, medicinal chemistry aspects of ligands acting as selective/preferential or multitarget 5-HT1A-R agonists and antagonists belonging to different chemotypes and developed in the last 7 years (2017-2023) have been discussed. The development of chemical and pharmacological 5-HT1A-R tools for molecular imaging have also been described. Finally, the pharmacological interest of 5-HT1A-R and the therapeutic potential of ligands targeting this receptor have been considered.

A new paradigm shift in antidepressant therapy? From dual-action to multitarget-directed ligands

Major Depressive Disorder is a chronic, recurring, and potentially fatal disease affecting up to 20% of the global population. Since the monoamine hypothesis was proposed more than 60 years ago, only a few relevant advances have been achieved, with very little disease course changing, from a pharmacological perspective. Moreover, since negative efficacy studies with novel molecules are frequent, many pharmaceutical companies have put new studies on hold. Fortunately, relevant clinical studies are currently being performed, and extensive striving is being developed by universities, research centers, and other public and private institutions. Depression is no longer considered a simple disease but a multifactorial one. New research fields are emerging in what could be a paradigm shift: the multitarget approach beyond monoamines. In this review, we summarize the present and the past of antidepressant drug discovery, with the aim to shed some light on the current state of the art in clinical and preclinical advances to face this increasingly devastating disease.

Examination of the Novel Sigma-1 Receptor Antagonist, SI 1/28, for Antinociceptive and Anti-allodynic Efficacy against Multiple Types of Nociception with Fewer Liabilities of Use

Neuropathic pain is a significant problem with few effective treatments lacking adverse effects. The sigma-1 receptor (S1R) is a potential therapeutic target for neuropathic pain, as antagonists for this receptor effectively ameliorate pain in both preclinical and clinical studies. The current research examines the antinociceptive and anti-allodynic efficacy of SI 1/28, a recently reported benzylpiperazine derivative and analog of the S1R antagonist SI 1/13, that was 423-fold more selective for S1R over the sigma-2 receptor (S2R). In addition, possible liabilities of respiration, sedation, and drug reinforcement caused by SI 1/28 have been evaluated. Inflammatory and chemical nociception, chronic nerve constriction injury (CCI) induced mechanical allodynia, and adverse effects of sedation in a rotarod assay, conditioned place preference (CPP), and changes in breath rate and locomotor activity were assessed after i.p. administration of SI 1/28. Pretreatment with SI 1/28 produced dose-dependent antinociception in the formalin test, with an ED50 (and 95% C.I.) value of 13.2 (7.42-28.3) mg/kg, i.p. Likewise, SI 1/28 produced dose-dependent antinociception against visceral nociception and anti-allodynia against CCI-induced neuropathic pain. SI 1/28 demonstrated no impairment of locomotor activity, conditioned place preference, or respiratory depression. In summary, SI 1/28 proved efficacious in the treatment of acute inflammatory pain and chronic neuropathy without liabilities at therapeutic doses, supporting the development of S1R antagonists as therapeutics for chronic pain.

Therapeutic potential of quinazoline derivatives for Alzheimer's disease: A comprehensive review

Quinazolines are considered as a promising class of bioactive heterocyclic compounds with broad properties. Particularly, the quinazoline scaffold has an impressive role in the design and synthesis of new CNS-active drugs. The drug-like properties and pharmacological characteristics of quinazoline could lead to different drugs with various targets. Among CNS disorders, Alzheimer's disease (AD) is a progressive neurodegenerative disorder with memory loss, cognitive decline and language dysfunction. AD is a complex and multifactorial disease therefore, the need for finding multi-target drugs against this devastative disease is urgent. A literature survey revealed that quinazoline derivatives have diverse therapeutic potential for AD as modulators/inhibitors of β-amyloid, tau protein, cholinesterases, monoamine oxidases, and phosphodiesterases as well as other protective effects. Thus, we describe here the most relevant and recent studies about anti-AD agents with quinazoline structure which can further aid the development and discovery of new anti-AD agents.

Chemical update on the potential for serotonin 5-HT6 and 5-HT7 receptor agents in the treatment of Alzheimer's disease

Despite the better understanding of the mechanisms underlying Alzheimer's Disease (AD) and launched clinical trials, no AD-modifying treatment based on a synthetic drug has been introduced for almost twenty years. The serotonin 5-HT₆ and 5-HT₇ receptors turned out to be promising biological targets for modulation of central nervous system dysfunctions including cognitive impairment. Within this paper, we evaluate the pharmacological potency of both, 5-HT₆R and 5-HT₇R, agents in search for novel AD treatment. An overview of chemical structures of the 5-HTRs ligands with simultaneous procognitive action which have undergone preclinical and clinical studies within the last 10 years has been performed.

In Vitro Antioxidant and Anti-Glycation Activity of Resveratrol and Its Novel Triester with Trolox

Resveratrol (RSV) is well known for its many beneficial activities, but its unfavorable physicochemical properties impair its effectiveness after systemic and topical administration; thus, several strategies have been investigated to improve RSV efficacy. With this aim, in this work, we synthesized a novel RSV triester with trolox, an analogue of vitamin E with strong antioxidant activity. The new RSV derivative (RSVTR) was assayed in vitro to evaluate its antioxidant and anti-glycation activity compared to RSV. RSVTR chemical stability was assessed at pH 2.0, 6.8, and 7.2 and different storage temperatures (5 °C, 22 °C, and 37 °C). An influence of pH stronger than that of temperature on RSVTR half-life values was pointed out, and RSVTR greatest stability was observed at pH 7.2 and 5 °C. RSVTR showed a lower antioxidant ability compared to RSV (determined by the oxygen radical absorbance capacity assay) while its anti-glycation activity (evaluated using the Maillard reaction) was significantly greater than that of RSV. The improved ability to inhibit the glycation process was attributed to a better interaction of RSVTR with albumin owing to its increased topological polar surface area value and H-bond acceptor number compared to RSV. Therefore, RSVTR could be regarded as a promising anti-glycation agent worthy of further investigations.

Impact of N-Alkylamino Substituents on Serotonin Receptor (5-HTR) Affinity and Phosphodiesterase 10A (PDE10A) Inhibition of Isoindole-1,3-dione Derivatives

In this study, a series of compounds derived from 4-methoxy-1H-isoindole-1,3(2H)-dione, potential ligands of phosphodiesterase 10A and serotonin receptors, were investigated as potential antipsychotics. A library of 4-methoxy-1H-isoindole-1,3(2H)-dione derivatives with various amine moieties was synthesized and examined for their phosphodiesterase 10A (PDE10A)-inhibiting properties and their 5-HT_1A and 5-HT₇ receptor affinities. Based on in vitro studies, the most potent compound, 18 (2-[4-(1H-benzimidazol-2-yl)butyl]-4-methoxy-1H-isoindole-1,3(2H)-dione), was selected and its safety in vitro was evaluated. In order to explain the binding mode of compound 18 in the active site of the PDE10A enzyme and describe the molecular interactions responsible for its inhibition, computer-aided docking studies were performed. The potential antipsychotic properties of compound 18 in a behavioral model of schizophrenia were also investigated.

Antidepressant-like activity and safety profile evaluation of 1H-imidazo[2,1-f]purine-2,4(3H,8H)-dione derivatives as 5-HT1A receptor partial agonists

Current antidepressant therapy has several disadvantages related to the properties of antidepressants. Considering their unfavourable features, the process of searching for new antidepressant drugs with better safety and tolerability requires consistent efforts and many complementary studies. Serotonin 5-HT_1A receptor is considered as an interesting target of antidepressant therapy. In the present study, the intrinsic activity at different signaling pathways coupled to serotonin 5-HT_1A receptor, antidepressant-like and pharmacokinetic properties, and the safety profile of two novel imidazopurine-2,4-dione derivatives, namely compounds AZ-853 (8-(4-(4-(2-fluorophenyl)piperazin-1-yl)butyl)-1,3-dimethyl-1H- imidazo[2,1-f]purine-2,4(3H,8H)-dione) and AZ-861 (1,3-dimethyl-8-(4-(4-(3-(trifluoromethyl)phenyl)piperazin-1-yl)butyl)-1H-imidazo[2,1-f]purine-2,4(3H,8H)-dione), were studied in animal models through in vitro and in vivo experiments. We demonstrated that AZ-853 and AZ-861, which structurally differ by one substituent and its placement in the phenyl ring, showed varied functional, pharmacological, and pharmacokinetic properties as well as side effect profiles. AZ-861 exhibited stronger agonistic action in all functional assays. After acute and repeated administration in mice, both compounds showed antidepressant-like activity in the forced swim test, which was partially mediated by 5-HT_1A receptor activation. AZ-853 showed a more potent antidepressant-like effect, presumably due to its better penetration into brain structures. Both compounds did not show anticholinergic properties, but after repeated administration, they induced weak sedation and lipid metabolism disturbances without affecting serum glucose level. The stronger α₁-adrenolytic effect of AZ-853 is responsible for decreased systolic blood pressure, and in contrast to AZ-861, AZ-853 induced weight gain in mice. The interesting comparative pharmacological profiles of AZ-853 and AZ-861 encourage to conduct further experiments to fully understand their mechanisms and differences in action.

Discovery of a Highly Selective Sigma-2 Receptor Ligand, 1-(4-(6,7-Dimethoxy-3,4-dihydroisoquinolin-2(1H)-yl)butyl)-3-methyl-1H-benzo[d]imidazol-2(3H)-one (CM398), with Drug-Like Properties and Antinociceptive Effects In Vivo

The sigma-2 receptor has been cloned and identified as Tmem97, which is a transmembrane protein involved in intracellular Ca²⁺ regulation and cholesterol homeostasis. Since its discovery, the sigma-2 receptor has been an extremely controversial target, and many efforts have been made to elucidate the functional role of this receptor during physiological and pathological conditions. Recently, this receptor has been proposed as a potential target to treat neuropathic pain due to the ability of sigma-2 receptor agonists to relieve mechanical hyperalgesia in mice model of chronic pain. In the present work, we developed a highly selective sigma-2 receptor ligand (sigma-1/sigma-2 selectivity ratio > 1000), 1-(4-(6,7-dimethoxy-3,4-dihydroisoquinolin-2(1H)-yl)butyl)-3-methyl-1H- benzo[d]imidazol-2(3H)-one (CM398), with an encouraging in vitro and in vivo pharmacological profile in rodents. In particular, radioligand binding studies demonstrated that CM398 had preferential affinity for sigma-2 receptor compared with sigma-1 receptor and at least four other neurotransmitter receptors sites, including the norepinephrine transporter. Following oral administration, CM398 showed rapid absorption and peak plasma concentration (Cmax) occurred within 10 min of dosing. Moreover, the compound showed adequate, absolute oral bioavailability of 29.0%. Finally, CM398 showed promising anti-inflammatory analgesic effects in the formalin model of inflammatory pain in mice. The results collected in this study provide more evidence that selective sigma-2 receptor ligands can be useful tools in the development of novel pain therapeutics and altogether, these data suggest that CM398 is a suitable lead candidate for further evaluation.

Exploring 1-adamantanamine as an alternative amine moiety for metabolically labile azepane ring in newly synthesized benzo[d]thiazol-2(3H)one σ receptor ligands

In this work we report the structure-activity relationships, binding properties, and metabolic stability studies of a series of benzo[d]thiazol-2(3H)one as sigma receptors (σRs) ligands. Specifically, to improve the metabolic stability of the cyclic amine fragment of our lead compound (SN56), the metabolically unstable azepane ring was replaced with a 1-adatamantamine moiety. Within the synthesized analogs, compound 12 had low nanomolar affinity for the σ₁R (K _i = 7.2 nM) and moderate preference (61-fold) over the σ₂R. In vitro metabolic stability studies showed a slight improvement of the metabolic stability for 7-12, even though an extensive metabolism in rat liver microsomes is being observed. Furthermore, metabolic soft spot identification of 12 suggested that the N-methyl group of the adamantyl moiety is a major site of metabolism.

Synthesis, in vitro and in vivo characterization of new benzoxazole and benzothiazole-based sigma receptor ligands

A new set of 5-chlorobenzoxazole- and 5-chlorobenzothiazole-based derivatives containing the azepane ring as a basic moiety was designed, synthesized and evaluated through binding assays to measure their affinity and selectivity towards σ₁ and σ₂ receptors. Compounds 19, 22 and 24, with a four units spacer between the bicyclic scaffold and the azepane ring, showed nanomolar affinity towards both receptor subtype and the best K_i values (K_i σ₁ = 1.27, 2.30, and 0.78 and K_i σ₂ = 7.9, 3.8, and 7.61 nM, respectively). Evaluation of cytotoxic and apoptotic effects in MCF-7 human cancer cells was useful to assess σ₂ receptor activity, while an in vivo mice model of inflammatory pain allowed to analyze σ₁ receptor pharmacological properties. In vitro and in vivo results suggested that compound 19 is a σ₁/σ₂ agonist, compound 24 a σ₁ antagonist/σ₂ agonist, whereas compound 22 might act as σ₁ antagonist/σ₂ partial agonist. Due to their pharmacological profile, a potential therapeutic application in cancer of aforesaid novel σ₁/σ₂ receptor ligands, especially 22 and 24, is proposed.

Structure-Activity Relationships and Therapeutic Potentials of 5-HT7 Receptor Ligands: An Update

Serotonin 5-HT₇ receptor (5-HT₇R) has been the subject of intense research efforts because of its presence in brain areas such as the hippocampus, hypothalamus, and cortex. Preclinical data link the 5-HT₇R to a variety of central nervous system processes including the regulation of circadian rhythms, mood, cognition, pain processing, and mechanisms of addiction. 5-HT₇R blockade has antidepressant effects and may ameliorate cognitive deficits associated with schizophrenia. 5-HT₇R has been recently shown to modulate neuronal morphology, excitability, and plasticity, thus contributing to shape brain networks during development and to remodel neuronal wiring in the mature brain. Therefore, the activation of 5-HT₇R has been proposed as a therapeutic approach for neurodevelopmental and neuropsychiatric disorders associated with abnormal neuronal connectivity. This Perspective celebrates the silver jubilee of the discovery of 5-HT₇R by providing a survey of recent studies on the medicinal chemistry of 5-HT₇R ligands and on the neuropharmacology of 5-HT₇R.

Structural determinants influencing halogen bonding: a case study on azinesulfonamide analogs of aripiprazole as 5-HT1A, 5-HT7, and D2 receptor ligands

A series of azinesulfonamide derivatives of long-chain arylpiperazines with variable-length alkylene spacers between sulfonamide and 4-arylpiperazine moiety is designed, synthesized, and biologically evaluated. In vitro methods are used to determine their affinity for serotonin 5-HT_1A, 5-HT₆, 5-HT₇, and dopamine D₂ receptors. X-ray analysis, two-dimensional NMR conformational studies, and docking into the 5-HT_1A and 5-HT₇ receptor models are then conducted to investigate the conformational preferences of selected serotonin receptor ligands in different environments. The bent conformation of tetramethylene derivatives is found in a solid state, in dimethyl sulfoxide, and as a global energy minimum during conformational analysis in a simulated water environment. Furthermore, ligand geometry in top-scored complexes is also bent, with one torsion angle in the spacer (τ₂) in synclinal conformation. Molecular docking studies indicate the role of halogen bonding in complexes of the most potent ligands and target receptors.

The impact of the halogen bonding on D2 and 5-HT1A/5-HT7 receptor activity of azinesulfonamides of 4-[(2-ethyl)piperidinyl-1-yl]phenylpiperazines with antipsychotic and antidepressant properties

A series of azinesulfonamides of long-chain arylpiperazine derivatives with semi-rigid alkylene spacer was designed, synthesized, and biologically evaluated using in vitro methods for their affinity for dopaminergic D₂ and serotoninergic 5-HT_1A, 5-HT_2A, 5-HT₆ and 5-HT₇ receptors. Docking to homology models revealed a possible halogen bond formation in complexes of the most potent ligands and the target receptors. The study allowed for the identification of compound 5-({4-(2-[4-(2,3-dichlorophenyl)piperazin-1-yl]ethyl)piperidin-1-yl}sulfonyl)quinoline (21), which behaved as D₂, 5-HT_1A and 5-HT₇ receptor antagonist. In preliminary in vivo studies, compound 21 displayed distinct antipsychotic properties in the MK-801-evoked hyperactivity test in mice at a dose of 10mg/kg, and exerted antidepressant-like effect in a forced swim test in mice (MED=0.625mg/kg, i.p.).