Acute flesinoxan treatment produces a different effect on rat brain serotonin synthesis than chronic treatment: An α-methyl-l-tryptophan autoradiographic study

5-HT_1A receptor agonists display anxiolytic and anti-depressant properties in clinical studies. In this study, we used the α-[¹⁴C]methyl-l-tryptophan (α-MTrp) autoradiographic method to evaluate the effects of the 5-HT_1A agonist, flesinoxan, on regional 5-HT synthesis in the rat brain, following acute or a 14-day continuous treatment. In the first series of experiments, flesinoxan (5 mg/kg; i.p.) was administered 40 min before the α-MTrp. It resulted in a significant increase of the arterial blood oxygen partial pressure (pO₂) and a reduction of the regional rate of 5-HT synthesis throughout the brain, with the exception of a few regions (medial geniculate body and thalamus). In the second series of experiments, flesinoxan (5 mg/kg day) was administered for 14 days, using an osmotic minipump implanted subcutaneously. When compared to rats treated with saline, there was an overall significant (p < 0.05) reduction in the synthesis (one-sample two-tailed t-test). However, there was no significant influence on the 5-HT synthesis rate in the dorsal and median raphe nuclei and the majority of their projection areas. A significant (p < 0.05) reduction was observed in the nucleus raphe magnus, medial caudate, ventral thalamus, amygdala, ventral tegmental area, medial forebrain bundle, nucleus accumbens, medial anterior olfactory nucleus and superior olive. The unaltered 5-HT synthesis rates in a large majority of regions following the 14-day treatment of flesinoxan may reflect the normalization (implies to not be different from salne treated control) of synthesis due to a desensitization of 5-HT_1A autoreceptors on the cell body of 5-HT neurons as well as at postsynaptic sites, which is known to occur following long-term treatment with 5-HT_1A agonists. It is of some importance to note that the normalization of the synthesis occurred in the majority of the brain limbic structures, the brain areas implicated in affective disorders and the corresponding successful treatments, as well as in the cortical regions, which are implicated in mood. However, there were some terminal regions (e.g., accumbens, anterior olfactory, lateral thalamus, raphe magnus and obscurus) in which the chronic flesinoxan treatment resulted in a significant reduction of synthesis, suggesting that there was not a full desensitization across the brain of the receptors controlling 5-HT synthesis.     

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.     

Short-term effects of 3,4-methylen-dioxy-metamphetamine (MDMA) on 5-HT1A receptors in the rat hippocampus

The first effects of 3,4-methylen-dioxy-metamphetamine (MDMA, “ecstasy”), on serotonin 1A (5-HT_1A) receptors in rat hippocampus were determined by means of [³H]-8-hydroxy-dipropylamino-tetralin ([³H]-8-OH-DPAT) and 5′guanosine-(γ-[³⁵S]-thio)triphosphate ([³⁵S]-GTPγS) binding as well as inhibition of forskolin (FK)-stimulated adenylyl cyclase (AC) activity. The study was completed by [³⁵S]-GTPγS functional autoradiography experiments carried out in frontal sections of rat brain, including the hippocampal region. Results showed that MDMA was either able to displace [³H]-8-OH-DPAT binding (K_i ≅ 500 nM) or to reduce the number of specific sites (B_max) without affecting K_d. The drug also failed to change the [³⁵S]-GTPγS binding or to inhibit AC velocity, underlying its behavior as a non-competitive 5-HT_1A receptor antagonist. Further, MDMA (1 or 100 μM), partially antagonized either [³⁵S]-GTPγS binding stimulation of the agonists 5CT and 8-OH-DPAT or the AC inhibition induced by 5CT and DP-5CT. However, in contrast to binding studies, in AC assays the amphetamine displayed an effect also on EC₅₀, always being less potent than the reference antagonist WAY100,635. In functional autoradiography, MDMA behaved either as a partial 5-HT_1A antagonist in limbic areas or, added alone, as an agonist, increasing the coupling signal presumably through 5-HT release from synapses. Interestingly, the selective 5-HT re-uptake inhibitor (SSRI) fluoxetine had no effect on MDMA [³⁵S]-GTPγS binding activation. This latter finding indicates that the amphetamine can release 5-HT via alternative mechanisms to 5-HT transporter binding, probably via membrane synaptic receptors or vesicular transporters. The release of other transmitters is not excluded. Therefore, our results encourage at extending the study of MDMA biochemical profiles, in the attempt to elucidate those amphetamine-induced pathways with a potential for neurotoxicity or psycho-stimulant activity.     

Flesinoxan challenge suggests that chronic treatment with paroxetine in rats does not desensitize receptors controlling 5-HT synthesis

It has been proposed that the desensitization of 5-HT_1A (5-hydroxytryptamine; serotonin) receptors following chronic therapy with selective serotonin reuptake inhibitors (SSRIs) is necessary for their therapeutic efficacy. Stimulation of the 5-HT_1A receptors decreases serotonin (5-HT) synthesis and release, but it is not clear if the receptors are fully desensitized following chronic SSRI treatment. The main objective of this study was evaluation of ability of 5-HT_1A receptors to modulate 5-HT synthesis after 14-day paroxetine treatment. 5-HT_1A receptor sensitivity following chronic administration of the SSRI paroxetine was assessed by the ability of an acute challenge with the 5-HT_1A agonist, flesinoxan, to modulate 5-HT synthesis in the rat brain. The rates of 5-HT synthesis were measured using the α-[¹⁴C]methyl-l-tryptophan autoradiographic method. The rats were treated for 2 weeks with paroxetine (10 mg/(kg day), s.c., delivered by osmotic minipump). After this treatment, the rats received an acute challenge with flesinoxan (5 mg/kg, i.p.), while the control rats were injected with the vehicle. Forty minutes following the flesinoxan injection, the tracer, α-[¹⁴C]methyl-l-tryptophan, was injected over 2 min. 5-HT synthesis rates were calculated from autoradiographically measured tissue tracer concentrations and plasma time–activity curves. The results demonstrated that the acute flesinoxan challenge produced a significant decrease in 5-HT synthesis rates throughout the rat brain. The greatest decrease was observed in the ventral hippocampus, somatosensory cortex and the ascending serotonergic cell bodies. In comparison with data reported on an acute challenge with flesinoxan in naïve rats (rats without any other treatment), the results presented here suggest a greater effect of flesinoxan on synthesis reduction in rats chronically treated with paroxetine. The results also suggest that the 5-HT receptors were not fully desensitized by paroxetine treatment, and that the stimulation of 5-HT_1A receptors with an agonist is still capable of reducing 5-HT synthesis.     

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.     

Both acute and subchronic treatments with pindolol,a 5-HT1A and β1 and β2 adrenoceptor antagonist,elevate regional serotonin synthesis in the rat brain: An autoradiographic study

Antidepressant treatments, including those that increase serotonin (5-HT) neurotransmission, require several weeks or months until the onset of the therapeutic effect in depressed patients. The negative feedback on 5-HT transmission exhibited by the 5-HT_1A and 5-HT_1B autoreceptors has been postulated as a possible delaying factor. The aim of the present study was to assess the effect of the acute and subchronic treatment with pindolol, a 5-HT_1A/1B, β₁ and β₂ adrenoceptor antagonist, on 5-HT synthesis, one of the key parameters of 5-HT neurotransmission. Male Sprague–Dawley (SPD) rats (180–220 g) were treated with pindolol or an adequate volume of saline, administered either acutely (15 mg/kg i.p.; SPD-AC-SAL, SPD-AC-TR) or subchronically (15 mg/kg day i.p. for 7 days; SPD-SUBCHR-SAL, SPD-SUBCHR-TR). Thirty minutes following the single i.p. injection (acute experiment) or at the 8th day following the commencement of the subchronic treatment (subchronic experiment), 5-HT synthesis was measured using α-[¹⁴C]methyl-l-tryptophan autoradiography. The analysis of variance (ANOVA), followed by the Benjamini–Hochberg correction for multiple comparisons, revealed: (1) a significant increase of 5-HT synthesis in the SPD-AC-TR rats, relative to the SPD-AC-SAL rats in all brain regions examined except the substantia nigra – pars reticularis, dorsal subiculum, inferior olive, raphe magnus and raphe obscurus and (2) a significant increase of 5-HT synthesis in the SPD-SUBCHR-TR rats, relative to the SPD-SUBCHR-SAL rats in all brain regions except the median raphe, hypothalamus and raphe pontine. On the basis of these results, we hypothesized that the antagonism of the 5-HT_1A/1B receptors prevents the negative feedback mediated by these receptors on 5-HT synthesis, resulting in a persistent increase of 5-HT synthesis. The results accord with clinical reports on the utility of pindolol in the augmentation of antidepressant treatment.     

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 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.     

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 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.     

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.     

3-(Arylsulfonyl)-1-(azacyclyl)-1H-indoles are 5-HT6 receptor modulators

Novel 3-(arylsulfonyl)-1-(azacyclyl)-1H-indoles 6 were synthesized as potential 5-HT₆ receptor ligands, based on constraining a basic side chain as either a piperidine or a pyrrolidine. Many of these compounds had good 5-HT₆ binding affinity with K_i values <10 nM. Depending on substitution, both agonists (e.g., 6o: EC₅₀ = 60 nM, E_max = 70%) and antagonists (6y: IC₅₀ = 17 nM, I_max = 86%) were identified in a 5-HT₆ adenylyl cyclase assay.     

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.     

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 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 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.     

Binding of STW 5 (Iberogast®) and its components to intestinal 5-HT,muscarinic M3, and opioid receptors

Clinical studies with the fixed herbal combination product STW 5 (Iberogast^®) have indicated an efficacy comparable to metoclopramide (5-HT₃ antagonist) and cisapride (5-HT₄ agonist) in functional gastro-intestinal diseases like functional dyspepsia (FD) and irritable bowel syndrome (IBS). Since serotonin (5-HT₃ and 5-HT₄) and muscarinic M₃ receptors are known to play a central role in the etiology of FD and IBS, the extracts contained in STW 5 and several of their phytochemical components were studied in vitro for binding affinities to these receptors of the intestine. STW 5 inhibited the binding of ³H-GR113808 and ³H-4-DAMP to 5-HT₄ and M₃ receptors, respectively, about 10 times more potently than the binding of ³H-GR65630 to 5-HT₃ receptors. IC₅₀ values for STW 5 did correspond to extract dilutions of 1:1000 (M₃ binding) and 1:2000 (5-HT₄ binding). In addition, STW 5 also potently inhibited the binding to opioid receptors with an IC₅₀ value of 1:2000. Of the nine herbal extracts contained in STW 5, the fresh plant extract of bitter candy tuft (Iberis amara) selectively inhibited binding to M₃ receptors, while ethanolic extracts of celandine herb and chamomile flower were selective to 5-HT₄, and liquorice root to 5-HT₃ receptors. Binding affinities to human recombinant 5-HT₃, 5-HT₄ and M₃ receptors were qualitatively similar to those of the corresponding intestinal receptors. The benzylisoquinoline alkaloid berberine had significant inhibitory action on 5-HT₄ and M₃ binding, showing IC₅₀ values of 40 ng/ml (100 nM) and 200 ng/ml (500 nM), respectively, but is present in the extract of celandine herb only in traces, so that also for the celandine extract a cooperative effect of several phytochemical constituents can be assumed. These in vitro data indicate that 5-HT₄ (to a lesser degree 5-HT₃), muscarinic M₃, and opioid receptors represent target sites for the treatment of FD and IBS with STW 5 (Iberogast^®).     

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.     

Novel highly potent serotonin 5-HT7 receptor ligands: Structural modifications to improve pharmacokinetic properties

Here we report the synthesis, pharmacological and pharmacokinetic evaluation of a pilot set of compounds structurally related to the potent and selective 5-HT₇ ligand LP-211. Among the studied compounds, N-pyridin-3-ylmethyl-3-[4-[2-(4-methoxyphenyl)phenyl]piperazin-1-yl]ethoxy]propanamide (4b) showed high affinity for 5-HT₇ receptors (K_i = 23.8 nM), selectivity over 5-HT_1A receptors (>50-fold), in vitro metabolic stability (82%) and weak interaction with P-glycoprotein (BA/AB = 3.3). Compound 4b was injected ip in mice to preliminarily evaluate its distribution between blood and brain.     

N-Tetrahydrothiochromenoisoxazole-1-carboxamides as selective antagonists of cloned human 5-HT2B

The serendipitous discovery of N-cyclohexyl-8-fluoro-3,3a,4,9b-tetrahydro-1H-thiochromeno[4,3-c]isoxazole-1-carboxamide as a selective human serotonin 5-HT_2B antagonist with K_i of 42 ± 5 nM is reported herein. A subsequent functional assay indicated little agonist activity compared to 5-HT itself.