Synthesis and biological investigation of new equatorial (β) stereoisomers of 3-aminotropane arylamides with atypical antipsychotic profile

A series of novel 3β-aminotropane derivatives containing a 2-naphthalene or a 2-quinoline moiety was synthesised and evaluated for their affinity for 5-HT_1A, 5-HT_2A and D₂ receptors. Their affinity for the receptors was in the nanomolar to micromolar range. p-Substitution (6c, 6f, 6i, 6l, 6o), as well as substitution with chlorine atoms (6g, 6h, 6i), led to a significant increase in binding affinity for D₂ receptors with compounds 6f (K_i = 0.6 nM), 6c and 6i (K_i = 0.4 nM), having the highest binding affinities. m-Substituted derivatives were the most promising ligands in terms of 5-HT_2A receptor binding affinity whereas 2-quinoline derivatives (10a, 10b) displayed the highest affinity for 5-HT_1AR and were the most selective ligands with K_i = 62.7 nM and K_i = 30.5 nM, respectively. Finally, the selected ligands 6b, 6d, 6e, 6g, 6h, 6k, 6n and 6o, with triple binding activity for the D₂, 5-HT_1A and 5-HT_2A receptors, were subjected to in vivo tests, such as those for induced hypothermia, climbing behaviour and the head twitch response, in order to determine their pharmacological profile. The tested ligands presented neither agonist nor antagonist properties for the 5-HT_1A receptors in the induced hypothermia and lower lip retraction (LLR) tests. All tested compounds displayed antagonistic activity against 5-HT_2A, with 6n and 6o being the most active. Four (6b, 6k, 6n and 6o) out of eight tested compounds could be classified as D₂ antagonists. Additionally, evaluation of metabolic stability was performed for selected ligands, and introduction of halogen atoms into the benzene ring of 6h, 6k, 6n and 6o improved their metabolic stability. The project resulted in the selection of the lead compounds 6n and 6o, which had antipsychotic profiles, combining dopamine D₂-receptor and 5-HT_2A antagonism and metabolic stability.     

Asymmetric total synthesis and identification of tetrahydroprotoberberine derivatives as new antipsychotic agents possessing a dopamine D1, D2 and serotonin 5-HT1A multi-action profile

An effective and rapid method for the microwave-assisted preparation of the key intermediate for the total synthesis of tetrahydroprotoberberines (THPBs) including l-stepholidine (l-SPD) was developed. Thirty-one THPB derivatives with diverse substituents on A and D ring were synthesized, and their binding affinity to dopamine D₁, D₂ and serotonin 5-HT_1A and 5-HT_2A receptors were determined. Compounds 18k and 18m were identified as partial agonists at the D₁ receptor with K_i values of 50 and 6.3 nM, while both compounds act as D₂ receptor antagonists (K_i = 305 and 145 nM, respectively) and 5-HT_1A receptor full agonists (K_i = 149 and 908 nM, respectively). These two THPBs compounds exerted antipsychotic actions in animal models. Further electrophysiological studies employing single-unit recording in intact animals demonstrated that 18k-excited dopaminergic (DA) neurons are associated with its 5-HT_1A receptor agonistic activity. These results suggest that these two compounds targeted to multiple neurotransmitter receptors may present novel lead drugs with new pharmacological profiles for the treatment of schizophrenia.     

New 5-HT1A receptor ligands containing a N′-cyanoisonicotinamidine nucleus: Synthesis and in vitro pharmacological evaluation

N′-Cyanoisonicotinamidine derivatives, linked to an arylpiperazine moiety, were prepared to identify highly selective and potent 5-HT_1A ligands as potential pharmacological tools in studies of wide spread psychiatric disorders. The combination of structural elements (heterocyclic nucleus, alkyl chain and 4-substituted piperazine) known to be critical in order to have affinity on 5-HT_1A receptor and the proper selection of substituents led to compounds with high specificity and affinity towards serotoninergic receptors. In binding studies, several molecules showed affinity in nanomolar and subnanomolar range at 5-HT_1A and moderate to no affinity for other relevant receptors (5-HT_2A, 5-HT_2C, D₁, D₂, α₁ and α₂). N′-Cyano-N-(3-(4-(pyridin-2-yl)piperazin-1-yl)propyl)isonicotinamidine (4o) with K_i = 0.038 nM, was the most active and selective derivative for the 5-HT_1A receptor with respect to other serotoninergic, dopaminergic and adrenergic receptors.     

Synthesis and SAR of (piperazin-1-yl-phenyl)-arylsulfonamides: A novel series of atypical antipsychotic agents

(Piperazin-1-yl-phenyl)-arylsulfonamides were synthesized and identified to show high affinities for both 5-HT_2C and 5-HT₆ receptors. Among them, naphthalene-2-sulfonic acid isopropyl-[3-(4-methyl-piperazin-1-yl)-phenyl]-amide (6b) exhibits the highest affinity towards both 5-HT_2C (IC₅₀ = 4 nM) and 5-HT₆ receptors (IC₅₀ = 3 nM) with good selectivity over other serotonin (5-HT_1A, 5-HT_2A, and 5-HT₇) and dopamine (D₂–D₄) receptor subtypes. In 5-HT_2C and 5-HT₆ receptor functional assays, this compound showed considerable antagonistic activity for both receptors.     

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.     

Synthesis and biological evaluation of a series of benzoxazole/benzothiazole-containing 2,3-dihydrobenzo[b][1,4]dioxine derivatives as potential antidepressants

A series of benzoxazole/benzothiazole-2,3-dihydrobenzo[b][1,4]dioxine derivatives (5a–5d and 8a–8j) was synthesized. Compounds were evaluated for binding affinities at the 5-HT_1A and 5-HT_2A receptors. Antidepressant activities of the compounds were screened using the forced swimming test (FST) and the tail suspension test (TST). The results indicated that the compounds exhibited high affinities for the 5-HT_1A and 5-HT_2A receptors and showed a marked antidepressant-like activity. Compound 8g exhibited high affinities for the 5-HT_1A (K_i = 17 nM) and 5-HT_2A (K_i = 0.71 nM) receptors; it also produced a decrease of the immobility time and exhibited potent antidepressant-like effects in the FST and TST in mice.     

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.     

Synthesis and evaluation of pharmacological properties of some new xanthone derivatives with piperazine moiety

A series of new xanthone derivatives with piperazine moiety [1–7] was synthesized and evaluated for their pharmacological properties. They were subject to binding assays for α₁ and β₁ adrenergic as well as 5-HT_1A, 5-HT₆ and 5-HT_7b serotoninergic receptors. Five of the tested compounds were also evaluated for their anticonvulsant properties. The compound 3a 3-methoxy-5-{[4-(2-methoxyphenyl)piperazin-1-yl]methyl}-9H-xanthen-9-one hydrochloride exhibited significantly higher affinity for serotoninergic 5-HT_1A receptors (K_i = 24 nM) than other substances. In terms of anticonvulsant activity, 6-methoxy-2-{[4-(benzyl)piperazin-1-yl]methyl}-9H-xanthen-9-one (5) proved best properties. Its ED₅₀ determined in maximal electroshock (MES) seizure assay was 105 mg/kg b.w. (rats, p.o.). Combining of xanthone with piperazine moiety resulted in obtaining of compounds with increased bioavailability after oral administration.     

Synthesis and biological activity of 5-styryl and 5-phenethyl-substituted 2,3,4,5-tetrahydro-1H-pyrido[4,3-b]indoles

Syntheses, biological evaluation, and structure–activity relationships for a series of novel 5-styryl and 5-phenethyl analogs of dimebolin are disclosed. The novel derivatives and dimebolin share a broad spectrum of activities against therapeutically relevant targets. Among all synthesized derivatives, 2,8-dimethyl-5-[(Z)-2-phenylvinyl]-2,3,4,5-tetrahydro-1H-pyrido[4,3-b]indole and its 5-phenethyl analog are the most potent blockers of 5-HT₇, 5-HT₆, 5-HT_2C, Adrenergic α₂ and H₁ receptors. The general affinity rank order towards the studied receptors was Z-3(2) > 4(2) ? 4(3) ? dimebolin, all of them having highest affinities to 5-HT₇ receptors.     

Design,synthesis and evaluation of benzo[a]thieno[3,2-g]quinolizines as novel l-SPD derivatives possessing dopamine D1, D2 and serotonin 5-HT1A multiple action profiles

A novel scaffold derived from l-SPD with a substituted thiophene group in the D ring were designed, synthesized, and evaluated for their binding affinities at dopamine (D₁, D₂ and D₃) and serotonin (5-HT_1A and 5-HT_2A) receptors. Most of the tetracyclic compounds exhibited higher affinities for D₂ and 5-HT_1A receptors than l-SPD, while compound 23e showed the highest K_i value of 7.54 nM at D₂ receptor which was 14 times more potent than l-SPD. Additionally, compounds 23d and 23e were more potent than l-SPD at D₃ receptor. According to the functional assays, 23d and 23e were demonstrated as full antagonists at D₁ and D₂ receptors and full agonists at 5-HT_1A receptor. Since the combination of D₂ antagonism and 5-HT_1A agonism is considered effective in treating both the positive and negative symptoms of schizophrenia, these novel compounds are implicated as potential therapeutic agents.     

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.     

9-Aminomethyl-9,10-dihydroanthracene (AMDA) analogs as structural probes for steric tolerance in 5-HT2A and H1 receptor binding sites

Synthesis, radioligand binding and molecular modeling studies of several 9-aminomethyl-9,10-dihydroanthracene (AMDA) analogs were carried out to determine the extent of the steric tolerance associated with expansion of the tricyclic ring system and amine substitution at 5-HT_2A and H₁ receptors. A mixture of (7,12-dihydrotetraphene-12-yl)methanamine and (6,11-dihydrotetracene-11-yl)methanamine in a 75–25% ratio was found to have an apparent K_i of 10 nM at the 5-HT_2A receptor. A substantial binding affinity for (7,12-dihydrotetraphene-3-methoxy-12-yl)methanamine at the 5-HT_2A receptor (K_i = 21 nM) was also observed. Interestingly, this compound was found to have 100-fold selectivity for 5-HT_2A over the H₁ receptor (K_i = 2500 nM). N-Phenylalkyl-AMDA derivatives, in which the length of the alkyl chain varied from methylene to n-butylene, were found to have only weak affinity for both 5-HT_2A and H₁ receptors (K_i = 223 to 964 nM). Our results show that large rigid annulated AMDA analogs can be sterically accommodated within the proposed 5-HT_2A binding site.     

Synthesis and biological evaluation of (phenylpiperazinyl-propyl)arylsulfonamides as selective 5-HT2A receptor antagonists

A novel series of 5-HT_2A ligands that contain a (phenylpiperazinyl-propyl)arylsulfonamides skeleton was synthesized. Thirty-seven N-(cycloalkylmethyl)-4-methoxy-N-(3-(4-arylpiperazin-1-yl)propyl)-arylsulfonamide and N-(4-(4-arylpiperazin-1-yl)butan-2-yl)-arylsulfonamide compounds were obtained. The binding of these compounds to the 5-HT_2A, 5-HT_2C, and 5-HT₇ receptors was evaluated. Most of the compounds showed IC₅₀ values of less than 100 nM and exhibited high selectivity for the 5-HT_2A receptor. Among the synthesized compounds, 16a and 16d showed good affinity at 5-HT_2A (IC₅₀ = 0.7 nM and 0.5 nM) and good selectivity over 5-HT_2C (50–100 times) and 5-HT₇ (1500–3000 times).     

Synthesis and pharmacological evaluation of new arylpiperazines N-{4-[4-(aryl) piperazine-1-yl]-phenyl}-amine derivatives: Putative role of 5-HT1A receptors

In an attempt to design novel 5-HT_1A agonists/partial agonists, based on an arylpiperazine nucleus, a series of N-{4-[4-(aryl)piperazine-1-yl]-phenyl}-amine derivatives were synthesized and biologically tested. The anxiolytic effect of the compounds was investigated employing the Elevated plus Maze (EPM) task. On the basis of in vivo functional test, compound 1c (3 mg/kg) and 4c (3 mg/kg) induced significant increments in open arm entries and time on EPM as compared to Buspirone. The anxiolytic effects of compounds 1c and 4c were effectively antagonized by WAY-100635, a 5-HT_1A receptor antagonist (0.5 mg/kg). Furthermore, we have also evaluated the concentration of 5-HT in the brain tissue using HPLC with fluorescent detection. Our result showed that serotonin levels were significantly decreased by ～38% (p < 0.001) and ～32% (p < 0.001) after acute administration of compounds 1c and 4c, respectively. These findings suggest that the anxiolytic like activity of these new arylpiperazines is mediated via 5-HT_1A receptors in the brain.     

Synthesis and pharmacological evaluation of aminopyrimidine series of 5-HT1A partial agonists

Aminopyrimidine 2 (4-(1-(2-(1H-indol-3-yl)ethyl)piperidin-3-yl)-N-cyclopropylpyrimidin-2-amine) emerged from a high throughput screen as a novel 5-HT_1A agonist. This compound showed moderate potency for 5-HT_1A in binding and functional assays, as well as moderate metabolic stability. Implementation of a strategy for improving metabolic stability by lowering the lipophilicity (c Log D) led to identification of methyl ether 31 (4-(1-(2-(1H-indol-3-yl)ethyl)piperidin-3-yl)-N-(2-methoxyethyl)pyrimidin-2-amine) as a substantially improved compound within the series.     

Discovery of novel α1-adrenoceptor ligands based on the antipsychotic sertindole suitable for labeling as PET ligands

The synthesis and in vitro preclinical profile of a series of 5-heteroaryl substituted analogs of the antipsychotic drug sertindole are presented. Compounds 1-(4-fluorophenyl)-3-(1-methylpiperidin-4-yl)-5-(pyrimidin-5-yl)-1H-indole (Lu AA27122, 3i) and 1-(4-fluorophenyl)-5-(1-methyl-1H-1,2,4-triazol-3-yl)-3-(1-methylpiperidin-4-yl)-1H-indole (3l) were identified as high affinity α_1A-adrenoceptor ligands with K_i values of 0.52 and 0.16 nM, respectively, and with a >100-fold selectivity versus dopamine D₂ receptors. Compound 3i showed almost equal affinity for α_1B- (K_i = 1.9 nM) and α_1D-adrenoceptors (K_i = 2.5 nM) as for α_1A, as well as moderate affinity for 5-HT_1B (K_i = 13 nM) and 5-HT₆ (K_i = 16 nM) receptors, whereas 3l showed >40-fold selectivity toward all other targets tested. Based on in vitro assays for assessment of permeability rates and extent, it is predicted that both compounds enter the brain of rats, non-human primates, as well as humans, and as such are good candidates to be carried forward for further evaluation as positron emission tomography (PET) ligands.     

Discovery of a new series of 5-HT1A receptor agonists

Starting from compounds previously identified as α₁-adrenoceptor antagonists that were also found to bind to the 5-HT_1A receptor, in an attempt to separate the two activities, a new series of 5-HT_1A receptor agonists was identified and shown to have high potency and/or high selectivity. Of these, compound 13, which combines high selectivity (5-HT_1A/α₁ = 151) and good agonist potency (pD₂ = 7.82; E_max = 76), was found to be the most interesting.     

Synthesis and in vivo evaluation of [18F]2-(4-(4-(2-(2-fluoroethoxy)phenyl)piperazin-1-yl)butyl)-4-methyl-1,2,4-triazine-3,5(2H,4H)-dione ([18F]FECUMI-101) as an imaging probe for 5-HT1A receptor agonist in nonhuman primates

The 5-HT_1AR partial agonist PET radiotracer, [¹¹C]CUMI-101, has advantages over an antagonist radiotracer as it binds preferentially to the high affinity state of the receptor and thereby provides more functionally meaningful information. The major drawback of C-11 tracers is the lack of cyclotron facility in many health care centers thereby limiting widespread clinical or research use. We identified the fluoroethyl derivative, 2-(4-(4-(2-(2-fluoroethoxy)phenyl)piperazin-1-yl)butyl)-4-methyl-1,2,4-triazine-3,5(2H,4H)dione (FECUMI-101) (K_i = 0.1 nM; E_max = 77%; EC₅₀ = 0.65 nM) as a partial agonist 5-HT_1AR ligand of the parent ligand CUMI-101. FECUMI-101 is radiolabeled with F-18 by O-fluoroethylation of the corresponding desmethyl analogue (1) with [¹⁸F]fluoroethyltosylate in DMSO in the presence of 1.6 equiv of K₂CO₃ in 45 ± 5% yield (EOS). PET shows [¹⁸F]FECUMI-101 binds specifically to 5-HT_1AR enriched brain regions of baboon. The specificity of [¹⁸F]FECUMI-101 binding to 5-HT_1AR was confirmed by challenge studies with the known 5-HT_1AR ligand WAY100635. These findings indicate that [¹⁸F]FECUMI-101 can be a viable agonist ligand for the in vivo quantification of high affinity 5-HT_1AR with PET.     

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.     

Synthesis and evaluation of 1-[2-(4-[11C]methoxyphenyl)phenyl]piperazine for imaging of the serotonin 5-HT7 receptor in the rat brain

1-[2-(4-Methoxyphenyl)phenyl]piperazine (4) is a potent serotonin 5-HT₇ receptor antagonist (K_i = 2.6 nM) with a low binding affinity for the 5-HT_1A receptor (K_i = 476 nM). As a potential positron emission tomography (PET) radiotracer for the 5-HT₇ receptor, [¹¹C]4 was synthesized at high radiochemical yield and specific activity, by O-[¹¹C]methylation of 2′-(piperazin-1-yl)-[1,1′-biphenyl]-4-ol (6) with [¹¹C]methyl iodide. Autoradiography revealed that [¹¹C]4 showed in vitro specific binding with 5-HT₇ in the rat brain regions, such as the thalamus which is a region with high 5-HT₇ expression. Metabolite analysis indicated that intact [¹¹C]4 in the brain exceeded 90% of the radioactive components at 15 min after the radiotracer injection, although two radiolabeled metabolites were found in the rat plasma. The PET study of rats showed moderated uptake of [¹¹C]4 in the brain (1.2 SUV), but no significant regional difference in radioactivity in the brain. Pretreatment with 5-HT₇-selective antagonist SB269970 (3) did not decrease the uptake of [¹¹C]4 in the rat brain. Further studies are warranted that focus on the development of PET ligand candidates with higher binding affinity for 5-HT₇ and higher in vivo stability in brain than 4.