Structure activity relationship exploration of 5-hydroxy-2-(3-phenylpropyl)chromones as a unique 5-HT2B receptor antagonist scaffold

Antagonists for the serotonin receptor 2B (5-HT_2B) have clinical applications towards migraine, anxiety, irritable bowl syndrome, and MDMA abuse; however, few selective 5-HT_2B antagonists have been identified. Previous studies from these labs identified a natural product, 5-hydroxy-2-(2-phenylethyl)chromone (5-HPEC, 2) as the first non-nitrogenous ligand for the 5-HT_2B receptor. Studies on 5-HPEC optimization led to the identification of 5-hydroxy-2-(3-phenylpropyl)chromone (5-HPPC, 3), which showed a tenfold improvement in binding affinity over 2 at 5-HT_2B. This study aimed to further improve receptor pharmacology of this unique scaffold. Guided by molecular modeling studies modifications at the C-3′ and C-4′ positions of 3 were made to probe their effects on ligand binding affinity and efficacy. Among the derivatives synthesized 5-hydroxy-2-(3-(3-cyanophenyl)propyl)chromone (5-HCPC, 3d) showed the most promise with a multifold improvement in binding affinity (pK_i = 7.1 ± 0.07) over 3 with retained antagonism.     

Synthesis and pharmacological evaluation of new arylpiperazines. 3-{4-[4-(3-chlorophenyl)-1-piperazinyl]butyl}-quinazolidin-4-one — a dual serotonin 5-HT1A/5-HT2A receptor ligand with an anxiolytic-like activity

On the basis of systematic studies on the structure–activity relationships in arylpiperazine group of serotonin ligands, 12 new derivatives containing quinazolidin-4(3H)-one (1–4), 2-phenyl-2,3-dihydrophthalazine-1,4-dione (5–8) or 1-phenyl-1,2-dihydropyridazine-3,6-dione (9–12) fragments were synthesized. The majority of the tested compounds (2, 4, 7, 8 and 10–12) showed a high affinity for 5-HT_1A receptors (K_i=11–54 nM) and two (1, 2) were found active at 5-HT_2A sites (16 and 68 nM, respectively). All the new 5-HT_1A ligands tested in vivo revealed an antagonistic activity at postsynaptic 5-HT_1A receptors, and three of them behaved as agonists at presynaptic ones. Additionally, both the meta-chlorophenylpiperazine derivatives containing quinazolidin-4-one fragment showed features of 5-HT_2A receptor antagonists. The dual 5-HT_1A/5-HT_2A receptor ligand (2) was further tested for its potential psychotropic activity. It showed a distinct anxiolytic-like activity in a conflict drinking test in rats and the observed effect was more potent in terms of the active dose, than that produced by diazepam (used as a reference drug).     

Synthesis and structure–activity relationships of new carbonyl guanidine derivatives as novel dual 5-HT2B and 5-HT7 receptor antagonists

To identify potent dual 5-HT_2B and 5-HT₇ receptor antagonists, we synthesized a series of novel carbonyl guanidine derivatives and examined their structure–activity relationships. Among these compounds, N-(9-hydroxy-9H-fluorene-2-carbonyl)guanidine (10) had a good in vitro profile, that is, potent affinity for human 5-HT_2B and 5-HT₇ receptor subtypes (K_i = 1.8 nM and K_i = 17.6 nM, respectively) and high selectivity over 5-HT_2A, 5-HT_2C, α₁, D₂ and M₁ receptors. Compound 10 also showed a suppressing effect on 5-HT-induced dural protein extravasation in guinea pigs when orally administered.     

Novel N-biphenyl-2-ylmethyl 2-methoxyphenylpiperazinylalkanamides as 5-HT7R antagonists for the treatment of depression

5-HT₇ receptor (5-HT₇R) is a promising target for the treatment of depression and neuropathic pain. 5-HT₇R antagonists exhibited antidepressant effects, while the agonists produced strong anti-hyperalgesic effects. In our efforts to discover selective 5-HT₇R antagonists or agonists, N-biphenylylmethyl 2-methoxyphenylpiperazinylalkanamides 1 were designed, synthesized, and biologically evaluated against 5-HT₇R. Among the synthesized compounds, N-2′-chlorobiphenylylmethyl 2-methoxyphenylpiperazinylpentanamide 1–8 showed the best binding affinity with a K_i value of 8.69 nM and it was verified as a novel antagonist according to functional assays. The compound 1–8 was very selective over 5-HT_1DR, 5-HT_2AR, 5-HT₃R, 5-HT_5AR and 5-HT₆R and moderately selective over 5-HT_1AR, 5-HT_1BR and 5-HT_2CR. The novel 5-HT₇R antagonist 1–8 exhibited an antidepressant effect at a dose of 25 mg/kg in the forced swimming test in mice and showed a U-shaped dose–response curve which typically appears in 5-HT₇R antagonists such as SB-269970 and lurasidone.     

Acidic biphenyl derivatives: Synthesis and biological activity of a new series of potent 5-HT4 receptor antagonists

Serotonin (5-hydroxytryptamine, 5-HT) is an important signaling molecule in the central nervous system (CNS) and in non-neuronal tissues and organs. Serotonin mediates a positive chronotropic and inotropic response through 5-HT₄ receptors in the atrium and ventricle of the heart. Recent investigations have revealed increased expression of the 5-HT_4(b) isoform in cardiomyocytes of chronic arrhythmic and failing hearts, and that the use of 5-HT₄ receptor antagonists may be beneficial for treating these conditions. The 5-HT₄ receptor possesses a transmembrane (TM) binding site important for ligand affinity and recognition, as well as a capacity to accommodate bulky ligands. A new series of peripherally-acting 5-HT₄ receptor antagonists were prepared by combining the acidic biphenyl group from the class of angiotensin II receptor blockers (ARBs) with the SB207266 (piboserod) scaffold. The new compounds were pharmacologically evaluated and carboxylic acid 21 was identified as a potent and promising 5-HT₄ receptor antagonist with moderate affinity for the AT₁ receptor. The permeability of carboxylic acid 21 in a Caco-2 assay was low and the corresponding prodrug esters 23a–f were therefore prepared. The pharmacokinetics of methyl ester 20 and n-butyl ester 23c were evaluated in a rat model, revealing incomplete metabolism to carboxylic acid 21. However, methyl ester 20 is a potent 5-HT₄ receptor antagonist with binding affinities in the low picomolar range. Methyl ester 20 has promising oral bioavailability and pharmacokinetics and may target 5-HT₄ receptors in both CNS and peripheral organs.     

Novel multitarget 5-arylidenehydantoins with arylpiperazinealkyl fragment: Pharmacological evaluation and investigation of cytotoxicity and metabolic stability

On the basis of the structures of serotonin modulators or drugs (NAN-190, buspirone, aripiprazole) and phosphodiesterase 4 (PDE4) inhibitors (rolipram, RO-20-1724), a series of novel multitarget 5-arylidenehydantoin derivatives with arylpiperazine fragment was synthesized. Among these compounds, 5-(3,4-dimethoxybenzylidene-3-(4-(4-(2,3-dichlorophenyl)piperazine-1-yl)butyl)-imidazolidine-2,4-dione (13) and 5-(3-cyclopentyloxy-4-methoxybenzylidene-3-(4-(4-(2-methoxyphenyl)piperazine-1-yl)butyl)-imidazolidine-2,4-dione (18) were found to be the most promising showing very high affinity toward 5-HT_1A and 5-HT₇ receptors (K_i = 0.2–1.0 nM) but a negligible inhibitory effect on PDE4. The high affinity of the compounds for 5-HT_1A and 5-HT₇ receptors was further investigated by computer-aided studies. Moreover, compounds 13 and 18 showed no significant cytotoxicity in the MTT assay, but high clearance in the in vitro assay. In addition, these compounds behaved like 5-HT_1A and 5-HT₇ receptor antagonists and exhibited antidepressant-like activity, similar to the reference drug citalopram, in an animal model of depression.     

5-HT1A and 5-HT2A receptors affinity,docking studies and pharmacological evaluation of a series of 8-acetyl-7-hydroxy-4-methylcoumarin derivatives

In this work we describe the synthesis, docking studies and biological evaluation of a focused library of novel arylpiperazinyl derivatives of 8-acetyl-7-hydroxy-4-methylcoumarin. The new compounds were screened for their 5-HT_1A and 5-HT_2A receptor affinity. Among the evaluated compounds, six displayed high affinities to 5-HT_1A receptors (4a-0.9?nM, 6a-0.5?nM, 10a-0.6?nM, 3b-0.9?nM, 6b-1.5?nM, 10b-1?nM). Compound 6a and 10a bearing a bromo- or methoxy- substituent in ortho position of the piperazine phenyl ring, were identified as potent antagonists of the 5-HT_1A receptors. In the tail suspension test, mice injected with 6a showed a dose-dependent increase in depressive-like behavior that was related to a decrease in locomotor activity. Compound 10a did not decrease or prolong immobility time nor did it affect home cage activity. Molecular docking studies using 5-HT_1A and 5-HT_2A homology models revealed structural basis of the high affinity of ortho-substituted derivatives and subtle changes in amino acid interactions patterns depending on the length of the alkyl linker.     

Synthesis and pharmacological evaluation of optically pure,novel carbonyl guanidine derivatives as dual 5-HT2B and 5-HT7 receptor antagonists

A series of 9-disubstituted N-(9H-fluorene-2-carbonyl)guanidine derivatives have been discovered as potent and orally active dual 5-HT_2B and 5-HT₇ receptor antagonists. Upon screening several compounds, N-(diaminomethylene)-4′,5′-dihydro-3′H-spiro[fluorene-9,2′-furan]-2-carboxamide (17) exhibited potent affinity for both 5-HT_2B (K_i = 5.1 nM) and 5-HT₇ (K_i = 1.7 nM) receptors with high selectivity over 5-HT_2A, 5-HT_2C, α₁, D₂ and M₁ receptors. Optical resolution of the intermediate carboxylic acid 16 via the formation of diastereomeric salts using chiral alkaloids gave the optically pure compounds (R)-17 and (S)-17. Both enantiomers suppressed 5-HT-induced dural protein extravasation in guinea pigs in a dose-dependent manner and the amount of leaked protein was suppressed to near normal levels when orally administrated at 10 mg/kg. (R)-17 and (S)-17 were therefore selected as candidates for human clinical trials.     

Model studies on a synthetically facile series of N-substituted phenyl-N′-pyridin-3-yl ureas leading to 1-(3-pyridylcarbamoyl) indolines that are potent and selective 5-HT2C/2B receptor antagonists

A model series of 5-HT_2C antagonists have been prepared by rapid parallel synthesis. These N-substituted phenyl-N′-pyridin-3-yl ureas were found to have a range of 5-HT_2C receptor affinities and selectivities over the closely related 5-HT_2A receptor. Extrapolation of simple SAR, derived from this set of compounds, to the more active but synthetically more complex 1-(3-pyridyl-carbamoyl)indoline series allowed us to target optimal substitution patterns and identify potent and selective 5-HT_2C/2B antagonists.     

Synthesis and structure–activity relationships of new carbonyl guanidine derivatives as novel dual 5-HT2B and 5-HT7 receptor antagonists. Part 2

We previously reported that the novel dual 5-HT_2B and 5-HT₇ receptor antagonist N-(9-hydroxy-9H-fluorene-2-carbonyl)guanidine (4) exerted a suppressing effect on 5-HT-induced dural protein extravasation in guinea pigs. To develop a synthetic strategy, we performed docking studies of lead compound 4 bound to 5-HT_2B and 5-HT₇ receptors, and observed that the carbonyl guanidine group forms a tight interaction network with an active center Asp (D135:5-HT_2B, D162:5-HT₇), Tyr (Y370:5-HT_2B, Y374:5-HT₇) and aromatic residue (W131:5-HT_2B, F158:5-HT₇). Based on molecular modeling results, we optimized the substituents at the 5- to 8-position and 9-position of the fluorene ring and identified N-(diaminomethylene)-9-hydroxy-9-methyl-9H-fluorene-2-carboxamide (24a) exhibits potent affinity for 5-HT_2B (K_i = 4.3 nM) and 5-HT₇ receptor (K_i = 4.3 nM) with high selectivity over 5-HT_2A, 5-HT_2C, α₁, D₂ and M₁ receptors. Compound 24a reversed the hypothermic effect of 5-carboxamidotryptamine (5-CT) in mice and also showed a suppressing effect on 5-HT-induced dural protein extravasation in guinea pigs when orally administered at 30 mg/kg. Compound 24a is therefore a promising candidate for a novel class of anti-migraine agent without any adverse effects.     

N-Alkylated arylsulfonamides of (aryloxy)ethyl piperidines: 5-HT7 receptor selectivity versus multireceptor profile

The N-alkylation of the sulfonamide moiety, in a group of arylsulfonamide derivatives of (aryloxy)ethyl piperidines, may be considered as a strategy for the design of selective 5-HT₇ receptor ligands or multifunctional agents to extend a polypharmacological approach to the treatment of complex diseases. The study allowed for the identification of 31 (1-methyl-N-{1-[2-(2-(t-butyl)phenoxy)ethyl]piperidin-4-yl}-N-cyclopropylmethyl-1H-pyrazole-4-sulfonamide), a potent and selective 5-HT₇ receptor antagonist and 33 (1-methyl-N-{1-[2-(biphenyl-2-yloxy)ethyl]piperidin-4-yl}-N-cyclopropylmethyl-1H-pyrazole-4-sulfonamide), as multimodal 5-HT/dopamine receptor ligand, as 5-HT_2A/5-HT₇/D₂ receptor antagonists. Both selected compounds were evaluated in vivo in a forced swim test (FST) in mice and in a novel object recognition (NOR) task in rats, demonstrating distinct antidepressant-like and pro-cognitive properties (MED = 1.25 mg/kg and 1 mg/kg, ip, respectively). These findings warrant further studies to explore the therapeutic potential of N-alkylated arylsulfonamides for the treatment of CNS disorders.     

Sequence and Functional Analysis of Cloned Guinea Pig and Rat Serotonin 5-HT1D Receptors: Common Pharmacological Features Within the 5-HT1D Receptor Subfamily

Abstract: This study was undertaken to investigate the pharmacology of cloned guinea pig and rat 5-hydroxytryptamine (serotonin; 5-HT)_1D receptor sites. Guinea pig, rat, and mouse 5-HT_1D receptor genes were cloned, and their amino acid sequences were compared with those of the human, dog, and rabbit. The overall amino acid sequence identity between these 5-HT_1D receptors is high and varies between 86 and 99%. The sequence homology is slightly more divergent (13–27%) in the N-terminal extracellular region of these 5-HT_1D receptors. Guinea pig and rat 5-HT_1D receptors, stably and separately expressed in rat C6 glial cells, are negatively coupled to cyclic AMP formation upon stimulation with agonists, as previously found for cloned human 5-HT_1D receptor sites. The cyclic AMP data show some common pharmacological features for the 5-HT_1D receptors of guinea pig, rat, and human: an almost similar rank order of potency for the investigated 5-HT_1D receptor agonists, stereoselectivity for the binding affinity and agonist potency of R(+)-8-hydroxy-2-(di-n-propylamino)tetralin, and equal 5-HT_1D receptor-mediated antagonist potency for methiothepin and the 5-HT₂ receptor antagonists ritanserin and ketanserin. In conclusion, the pharmacology of the cloned 5-HT_1D receptor subtype seems, unlike the 5-HT_1B receptor subtype, conserved among various mammal species such as the human, guinea pig, and rat.     

Design,synthesis and pharmacological evaluation of 4-(piperazin-1-yl methyl)-N1-arylsulfonyl indole derivatives as 5-HT6 receptor ligands

4-(Piperazin-1-yl methyl)-N₁-arylsulfonyl indole derivatives were designed and synthesized as 5-HT₆ receptor (5-HT₆R) ligands. The lead compound 6a, from this series shows potent in vitro binding affinity, good PK profile, no CYP liabilities and activity in animal models of cognition.     

Identification of fluorinated (R)-(−)-aporphine derivatives as potent and selective ligands at serotonin 5-HT2C receptor

A series of novel aporphine derivatives were synthesized for initial screening at the 5-HT₂ receptor subtypes. Among them, Compounds 11a and 11b were identified as potent 5-HT_2C hit ligands with high selectivity over other 5-HT₂ receptor subtypes. Molecular docking study revealed that compounds 11a and 11b formed two key interactions with the binding site of 5-HT_2C receptor, including a salt-bridge to D3.32 and a H-bond interaction with N6.55.     

In vitro structure–activity relationships of aplysinopsin analogs and their in vivo evaluation in the chick anxiety–depression model

Aplysinopsins are tryptophan-derived natural products that have been isolated from a variety of marine organisms and have been shown to possess a range of biological activities. In vitro receptor binding assays showed that of the 12 serotonin receptor subtypes, analogues showed a high affinity for the 5-HT_2B and 5-HT_2C receptor subtypes, with selectivity for 5-HT_2B over 5-HT_2C. While no conclusions could be drawn about the number and position of N-methylations, bromination at C-4 and C-5 of the indole ring resulted in greater binding affinities, with K_i’s as low as 35 nM. This data, combined with previous knowledge of the CNS activity of aplysinopsin analogs, suggested that these compounds may have potential as leads for antidepressant drugs. Compounds 3c, 3u, and 3x were evaluated in the chick anxiety–depression model to assess their in vivo efficacy. Compound 3c showed a modest antidepressant effect at a dose of 30 nM/kg in the animal model.     

2-Amino-6-chloro-3,4-dihydroquinazoline: A novel 5-HT3 receptor antagonist with antidepressant character

2-Amino-6-chloro-3,4-dihydroquinazoline HCl (A6CDQ, 4) binds at 5-HT₃ serotonin receptors and displays antidepressant-like action in the mouse tail suspension test (TST). Empirically, 4 was demonstrated to be a 5-HT₃ receptor antagonist (two-electrode voltage clamp recordings using frog oocytes; IC₅₀ = 0.26 μM), and one that should readily penetrate the blood–brain barrier (log P = 1.86). 5-HT₃ receptor antagonists represent a potential approach to the development of new antidepressants, and 4 is an example of a structurally novel 5-HT₃ receptor antagonist that is active in a preclinical antidepressant model (i.e., the mouse TST).     

Synthesis and structure–activity relationship of novel lactam-fused chroman derivatives having dual affinity at the 5-HT1A receptor and the serotonin transporter

The structure–activity relationship (SAR) for three series of lactam-fused chroman derivatives possessing 3-amino substituents was evaluated. Many compounds exhibited affinities for both the 5-HT_1A receptor and the 5-HT transporter. Compounds 45 and 53 demonstrated 5-HT_1A antagonist activities in the in vitro cAMP turnover model.     

Tricyclic dihydroquinazolinones as novel 5-HT2C selective and orally efficacious anti-obesity agents

Agonists of the 5-HT_2C receptor have been shown to suppress appetite and reduce body weight in animal models as well as in humans. However, agonism of the related 5-HT_2B receptor has been associated with valvular heart disease. Synthesis and biological evaluation of a series of novel and highly selective dihydroquinazolinone-derived 5-HT_2C agonists with no detectable agonism of the 5-HT_2B receptor is described. Among these, compounds (+)-2a and (+)-3c were identified as potent and highly selective agonists which exhibited weight loss in a rat model upon oral dosing.     

Design,synthesis and evaluation of activity and pharmacokinetic profile of new derivatives of xanthone and piperazine in the central nervous system

Searching for CNS active cyclic amines derivatives containing heterocyclic xanthone core we designed and synthesized a set of fourteen novel 2- or 4-methylxanthone substituted by alkyl- or aryl-piperazine moieties. The compounds were evaluated in vivo for their potential antidepressant-like activity (in the forced swim test) and anxiolytic-like activity (four-plate test) and their inhibitory effect against rat 5-HT₂ receptor was checked. The pharmacokinetic analysis of active compounds done by a non-compartmental approach have shown a rapid absorption of all studied molecules from intraperitoneal cavity and good penetration the blood-brain barrier after i.p. administration with brain to plasma ratios varied from 2.8 to 31.6. Genotoxicity and biotransformation of active compounds were studied. Compound 19 interactions with major classes of GPCRs, uptake systems and ion channels were tested and results indicated that it binds to 5-HT_2A, 5-HT_2B receptors and sodium channels.