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.     

Synthesis and biological activity of novel tert-amylphenoxyalkyl (homo)piperidine derivatives as histamine H3R ligands

As a continuation of our search for novel histamine H₃ receptor ligands a series of twenty new tert-amyl phenoxyalkylamine derivatives (2–21) was synthesized. Compounds of four to eight carbon atoms spacer alkyl chain were evaluated on their binding properties at human histamine H₃ receptor (hH₃R). The highest affinities were observed for pentyl derivatives 6–8 (K_i = 8.8–23.4 nM range) and among them piperidine derivative 6 with K_i = 8.8 nM. Structures 6, 7 were also classified as antagonists in cAMP accumulation assay (with EC₅₀ = 157 and 164 nM, respectively). Moreover, new compounds were also evaluated for anticonvulsant activity in Antiepileptic Screening Program (ASP) at National Institute of Neurological Disorders and Stroke (USA). Seven compounds (2–4, 9, 11, 12 and 20) showed anticonvulsant activity at maximal electroshock (MES) test in the dose of 30 mg/kg at 0.5 h. In the subcutaneous pentetrazole (scMET) test compound 4 showed protection at 100 and 300 mg/kg dose at mice, however compounds showed high neurotoxicity in rotarod test at used doses. Also, molecular modeling studies were undertaken, to explain affinity of compounds at hH₃R (taking into the consideration X-ray analysis of compound 18). In order to estimate “drug-likeness” of selected compounds in silico and experimental evaluation of lipophilicity, metabolic stability and cytotoxicity was performed.     

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.     

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 biological evaluation of novel 3,4-diaryl lactam derivatives as triple reuptake inhibitors

A series of 3,4-diarylpyrrolidin-2-one was designed, prepared and evaluated as triple reuptake inhibitors for antidepressant. Most compounds exhibited comparable in vitro efficacy as norepinephrine and dopamine transporter reuptake inhibitors. Especially, 2i showed better potency than GBR-12909 (IC₅₀ = 14 nM) which was used as reference compound for dopamine transporter. In addition, 2a and 2b showed inhibition (5.17 μM–85.6 nM) for three transporters.     

Synthesis and antidepressant effect of novel aralkyl piperazine and piperidine derivatives targeting SSRI/5-HT1A/5-HT7

A series of novel aralkyl piperazine and piperidine derivatives were synthesized, and evaluated for their serotonin reuptake inhibitory and 5-HT_1A/5-HT₇ receptors affinities activity. Antidepressant activities in vivo of the selective compound were screened using the forced swimming test (FST) and tail suspension test (TST). The results indicated that compound 19a exhibited high affinities for the 5-HT_1A/5-HT₇ receptors (5-HT_1A, K_i = 12 nM; 5-HT₇, K_i = 3.2 nM) coupled with potent serotonin reuptake inhibition (IC₅₀ = 14 nM) and showed a marked antidepressant-like effect in the FST and TST models.     

Synthesis and antidepressant-like activity of novel alkoxy-piperidine derivatives targeting SSRI/5-HT1A/5-HT7

A series of novel alkoxy-piperidine derivatives were synthesized and evaluated for their serotonin reuptake inhibitory and binding affinities for 5-HT_1A/5-HT₇ receptors. In vivo antidepressant activities of the selective compounds were explored using the forced swimming test (FST) and tail suspension test (TST) in mice. The results showed that compounds 7a (reuptake inhibition (RUI), IC₅₀ = 177 nM; 5-HT_1A, K_i = 12 nM; 5-HT₇, K_i = 25 nM) and 15g (RUI, IC₅₀ = 85 nM; 5-HT_1A, K_i = 17 nM; 5-HT₇, K_i = 35 nM) were potential antidepressant agents in animal behavioral models with high 5-HT_1A/5-HT₇ receptor affinities and moderate serotonin reuptake inhibition, and good metabolic stability in vitro.     

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 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.     

Synthesis,anticancer, and docking studies of salicyl-hydrazone analogues: A novel series of small potent tropomyosin receptor kinase A inhibitors

A series of novel salicyl-hydrazone analogues were synthesized and evaluated for their in vitro cytotoxic activities in five human cancer cell lines, namely, lung cancer (A549), ovarian cancer (SK-OV-3), skin cancer (SK-MEL-2), colon cancer (HCT15) and pancreatic cancer (MIA-PaCa-2) cells, and for their in vitro tropomyosin receptor kinase A (TrkA) inhibitory activities. Each of the compounds showed significant cytotoxicity against all cancer cells. Compound 3i was found to be most potent against all cancer cell lines with IC₅₀ values of 2.46 (A549), 0.87 (SK-OV-3), 1.43 (SK-MEL-2), 0.89 (HCT15), and 0.48 μM (MIA-PaCa-2), followed by compound 3l. Cytotoxicity of 3i was similar to that of doxorubicin (0.87 μM) against HCT15 cells. Compounds 3i and 3l also showed highest TrkA inhibitory activities with IC₅₀ values of 0.231 and 0.380 μM, respectively. A SAR study of the series revealed that compounds with hydroxyl groups showed better cytotoxicity and TrkA inhibitory potency (in the following order 2,4-OH > 2,3,4-OH > 3,4-OH > 4-OH) than compounds possessing electron donating or withdrawing groups on the benzylidenephenyl ring. Docking studies of compounds 3i and 3l conducted on the crystal structure of TrkA receptor (a promising target for anticancer agents) showed both had a high docking score and similar order of experimental TrkA inhibitory activities. The formation of several hydrogen bonds involving N and O containing moieties contributed most significantly to ligand binding and stabilization at the active site of the receptor. In addition, ligand-receptor complexes were further stabilized by π-cation, π-anion, amide-π stacked, and van der Waal’s interactions. Conformational analyses showed ligand molecules adopted similar conformations at the receptor active site during interactions, but that the low energy optimized conformations of compounds 3i and 3l differed.     

3-Aryl-3-arylmethoxyazetidines. A new class of high affinity ligands for monoamine transporters

A series of 3-aryl-3-arylmethoxy-azetidines were synthesized and evaluated for binding affinities at dopamine and serotonin transporters. The 3-aryl-3-arylmethoxyazetidines were generally SERT selective with the dichloro substituted congener 7c (K_i = 1.0 nM) and the tetrachloro substituted derivative 7i (K_i = 1.3 nM) possessing low nanomolar affinity for the SERT. The 3-(3,4-dichlorophenyl-3-phenylmethoxyazetidine (7g) exhibited moderate affinity at both DAT and SERT transporters and suggests that substitution of the aryl rings can be used to tune the mononamine transporter affinity.     

Study of antileishmanial activity of 2-aminobenzoyl amino acid hydrazides and their quinazoline derivatives

A new small library of 2-aminobenzoyl amino acid hydrazide derivatives and quinazolinones derivatives was synthesized and fully characterized by IR, NMR, and elemental analysis. The activity of the prepared compounds on the growth of Leishmania aethiopica promastigotes was evaluated. 2-Benzoyl amino acid hydrazide showed higher inhibitory effect than the quinazoline counterpart. The in vitro antipromastigote activity demonstrated that compounds 2a, 2b, 2f and 4a had IC₅₀ better than standard drug miltefosine and comparable activity to amphotericin B deoxycholate, which indicates their high antileishmanial activity against Leishmania. aethiopica. Among the prepared compounds; 2-amino-N-(6-hydrazinyl-6-oxohexyl)benzamide 2f (IC₅₀ = 0.051 μM) has the best activity, 154 folds more active than reference standard drug miltefosine (IC₅₀ = 7.832 μM), and half fold the activity of amphotericin B (IC₅₀ = 0.035 μM). In addition, this compound was safe and well tolerated by experimental animals orally up to 250 mg/kg and parenterally up to 100 mg/kg.     

Design,synthesis and herbicidal activity study of aryl 2,6-disubstituted sulfonylureas as potent acetohydroxyacid synthase inhibitors

A series of sulfonylurea derivatives containing a 2,6-disubstituted aryl moiety were designed, synthesized and evaluated for their herbicidal activities. Most of these compounds showed excellent inhibitory rates against both monocotyledonous and dicotyledonous weeds, especially 10a, 10h and 10i. They exhibited equivalent or superior herbicidal efficiency than commercial chlorsulfuron at the dosage of 15 g/ha and the preliminary SAR was summarized. In order to illuminate the molecular mechanism of several potent compounds, their apparent inhibition constant (K_i^app) of Arabidopsis thaliana acetohydroxyacid synthase (AHAS) were determined and the results confirmed that these compounds were all potent AHAS inhibitors. 10i have a K_i^app of 11.5 nM, which is about 4 times as potent as chlorsulfuron (52.4 nM).     

Synthesis and evaluation of anticonvulsant properties of new N-Mannich bases derived from pyrrolidine-2,5-dione and its 3-methyl-, 3-isopropyl,and 3-benzhydryl analogs

The aim of this paper was to describe the synthesis of a library of 28 new 1,3-substituted pyrrolidine-2,5-dione as potential anticonvulsant agents. The anticonvulsant activity was evaluated using three acute models of seizures in mice (MES-maximal electroshock, scPTZ-subcutaneous pentylenetetrazole, and 6 Hz-psychomotor seizure tests). The neurotoxicity was determined by rotarod test. The most promising compound was found to be N-[{morpholin-1-yl}-methyl]-3-benzhydryl-pyrrolidine-2,5-dione (15), as it was active in the MES (ED₅₀ = 41.0 mg/kg), scPTZ (ED₅₀ = 101.6 kg/mg), and 6 Hz (ED₅₀ = 45.42 mg/kg) tests. This compound displayed more beneficial protection index (PI) than antiepileptic drugs such as ethosuximide, lacosamide and valproic acid. In vitro studies for compound 15 were conducted and provided information that its possible mechanism of action is related to blocking of the neuronal voltage-sensitive sodium (site 2) and L-type calcium channels.     

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.     

Synthesis of substituted diphenyl sulfones and their structure–activity relationship with the antagonism of 5-НТ6 receptors

Substituted diphenyl sulfones (10a–n) were synthesised, and the structures were confirmed by NMR, LC–MS and X-ray crystallography. Their antagonistic activities towards 5-HT₆ receptor were assessed in a cell-based functional assay. Diphenyl sulfone 10a, in spite of being the smallest and simplest known sulfonyl-containing 5-HT₆R antagonist, showed a strong potency (K_i = 1.6 μM). Its derivative with a methylamine substituent, 10g (N-methyl-2-(phenylsulfonyl)aniline), was ～66-times as active as diphenyl sulfone (K_i = 24.3 nM). Addition of a piperazinyl moiety in the para-position relative to the sulfonyl group in compound 10m (N-methyl-2-(phenylsulfonyl)-5-piperazin-1-ylaniline) led to a further 150-fold increase in potency (K_i = 0.16 nM) to block the serotonin-induced response of HEK-293 cells that were stably transfected with the human recombinant 5-HT₆ receptor.     

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.     

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.     

Design,synthesis and antifungal activity of novel fenfuram-diarylamine hybrids

Ten novel fenfuram-diarylamine hybrids were designed and synthesized. And their antifungal activities against four phytopathogenic fungi have been evaluated in vitro and most of the compounds demonstrated a significant antifungal activities against Rhizoctonia solani and Sclerotinia sclerotiorum. Compound 5e exhibited the most potent antifungal activity against R. solani with an EC₅₀ value of 0.037 mg/L, far superior to the commercially available fungicide boscalid (EC₅₀ = 1.71 mg/L) and lead fungicide fenfuram (EC₅₀ = 6.18 mg/L). Furthermore, scanning electron microscopy images showed that the mycelia on treated media grew abnormally with tenuous, wizened and overlapping colonies compared to the negative control. Molecular docking studies revealed that compound 5e featured a higher affinity for succinate dehydrogenase (SDH) than fenfuram. Furthermore, it was shown that the 3-chlorophenyl group in compound 5e formed a CH-π interaction with B/Trp-206 and a Cl-π interaction with D/Tyr-128, rendering compound 5e more active than fenfuram against SDH.     

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.