Design and Synthesis of New Quinazolin-4-one Derivatives with Negative mGlu7 Receptor Modulation Activity and Antipsychotic-Like Properties.

Following the glutamatergic theory of schizophrenia and based on our previous study regarding the antipsychotic-like activity of mGlu7 NAMs, we synthesized a new compound library containing 103 members, which were examined for NAM mGlu7 activity in the T-REx 293 cell line expressing a recombinant human mGlu7 receptor. Out of the twenty-two scaffolds examined, active compounds were found only within the quinazolinone chemotype. 2-(2-Chlorophenyl)-6-(2,3-dimethoxyphenyl)-3-methylquinazolin-4(3H)-one (A9-7, ALX-171, mGlu7 IC50 = 6.14 µM) was selective over other group III mGlu receptors (mGlu4 and mGlu8), exhibited satisfactory drug-like properties in preliminary DMPK profiling, and was further tested in animal models of antipsychotic-like activity, assessing the positive, negative, and cognitive symptoms. ALX-171 reversed DOI-induced head twitches and MK-801-induced disruptions of social interactions or cognition in the novel object recognition test and spatial delayed alternation test. On the other hand, the efficacy of the compound was not observed in the MK-801-induced hyperactivity test or prepulse inhibition. In summary, the observed antipsychotic activity profile of ALX-171 justifies the further development of the group of quinazolin-4-one derivatives in the search for a new drug candidate for schizophrenia treatment.

New 1,2,4-oxadiazole derivatives with positive mGlu4 receptor modulation activity and antipsychotic-like properties.

Considering the allosteric regulation of mGlu receptors for potential therapeutic applications, we developed a group of 1,2,4-oxadiazole derivatives that displayed mGlu4 receptor positive allosteric modulatory activity (EC50 = 282-656 nM). Selectivity screening revealed that they were devoid of activity at mGlu1, mGlu2 and mGlu5 receptors, but modulated mGlu7 and mGlu8 receptors, thus were classified as group III-preferring mGlu receptor agents. None of the compounds was active towards hERG channels or in the mini-AMES test. The most potent in vitro mGlu4 PAM derivative 52 (N-(3-chloro-4-(5-(2-chlorophenyl)-1,2,4-oxadiazol-3-yl)phenyl)picolinamide) was readily absorbed after i.p. administration (male Albino Swiss mice) and reached a maximum brain concentration of 949.76 ng/mL. Five modulators (34, 37, 52, 60 and 62) demonstrated significant anxiolytic- and antipsychotic-like properties in the SIH and DOI-induced head twitch test, respectively. Promising data were obtained, especially for N-(4-(5-(2-chlorophenyl)-1,2,4-oxadiazol-3-yl)-3-methylphenyl)picolinamide (62), whose effects in the DOI-induced head twitch test were comparable to those of clozapine and better than those reported for the selective mGlu4 PAM ADX88178.

Synthesis of Novel Pyrido[1,2-c]pyrimidine Derivatives with 6-Fluoro-3-(4-piperidynyl)-1,2-benzisoxazole Moiety as Potential SSRI and 5-HT1A Receptor Ligands.

Two series of novel 4-aryl-2H-pyrido[1,2-c]pyrimidine (6a-i) and 4-aryl-5,6,7,8-tetrahydropyrido[1,2-c]pyrimidine (7a-i) derivatives were synthesized. The chemical structures of the new compounds were confirmed by 1H and 13C NMR spectroscopy and ESI-HRMS spectrometry. The affinities of all compounds for the 5-HT1A receptor and serotonin transporter protein (SERT) were determined by in vitro radioligand binding assays. The test compounds demonstrated very high binding affinities for the 5-HT1A receptor of all derivatives in the series (6a-i and 7a-i) and generally low binding affinities for the SERT protein, with the exception of compounds 6a and 7g. Extended affinity tests for the receptors D2, 5-HT2A, 5-HT6 and 5-HT7 were conducted with regard to selected compounds (6a, 7g, 6d and 7i). All four compounds demonstrated very high affinities for the D2 and 5-HT2A receptors. Compounds 6a and 7g also had high affinities for 5-HT7, while 6d and 7i held moderate affinities for this receptor. Compounds 6a and 7g were also tested in vivo to identify their functional activity profiles with regard to the 5-HT1A receptor, with 6a demonstrating the activity profile of a presynaptic agonist. Metabolic stability tests were also conducted for 6a and 6d.

Design, Sustainable Synthesis and Biological Evaluation of a Novel Dual α2A/5-HT7 Receptor Antagonist with Antidepressant-Like Properties.

The complex pathophysiology of depression, together with the limits of currently available antidepressants, has resulted in the continuous quest for alternative therapeutic strategies. Numerous findings suggest that pharmacological blockade of α2-adrenoceptor might be beneficial for the treatment of depressive symptoms by increasing both norepinephrine and serotonin levels in certain brain areas. Moreover, the antidepressant properties of 5-HT7 receptor antagonists have been widely demonstrated in a large set of animal models. Considering the potential therapeutic advantages in targeting both α2-adrenoceptors and 5-HT7 receptors, we designed a small series of arylsulfonamide derivatives of (dihydrobenzofuranoxy)ethyl piperidines as dually active ligands. Following green chemistry principles, the designed compounds were synthesized entirely using a sustainable mechanochemical approach. The identified compound 8 behaved as a potent α2A/5-HT7 receptor antagonist and displayed moderate-to-high selectivity over α1-adrenoceptor subtypes and selected serotonin and dopaminergic receptors. Finally, compound 8 improved performance of mice in the forced swim test, displaying similar potency to the reference drug mirtazapine.

N-Skatyltryptamines-Dual 5-HT6R/D2R Ligands with Antipsychotic and Procognitive Potential.

A series of N-skatyltryptamines was synthesized and their affinities for serotonin and dopamine receptors were determined. Compounds exhibited activity toward 5-HT1A, 5-HT2A, 5-HT6, and D2 receptors. Substitution patterns resulting in affinity/activity switches were identified and studied using homology modeling. Chosen hits were screened to determine their metabolism, permeability, hepatotoxicity, and CYP inhibition. Several D2 receptor antagonists with additional 5-HT6R antagonist and agonist properties were identified. The former combination resembled known antipsychotic agents, while the latter was particularly interesting due to the fact that it has not been studied before. Selective 5-HT6R antagonists have been shown previously to produce procognitive and promnesic effects in several rodent models. Administration of 5-HT6R agonists was more ambiguous-in naive animals, it did not alter memory or produce slight amnesic effects, while in rodent models of memory impairment, they ameliorated the condition just like antagonists. Using the identified hit compounds 15 and 18, we tried to sort out the difference between ligands exhibiting the D2R antagonist function combined with 5-HT6R agonism, and mixed D2/5-HT6R antagonists in murine models of psychosis.

Towards metabolically stable 5-HT7 receptor ligands: a study on 1-arylpiperazine derivatives and related isosters.

Serotonin 7 (5-hydroxytryptamine7 or 5-HT7) is the most recently identified serotonin receptor. It is involved in mood disorders and is studied as a target for antidepressants. Here, we report on the structural manipulation of the 5-HT7 receptor ligand 4-[2-(3-methoxyphenyl)ethyl]-1-(2-methoxyphenyl)piperazine (1a) aimed at obtaining 5-HT7 receptor ligands endowed with good in vitro metabolic stability. A set of N-[3-methoxyphenyl)ethyl-substituted] 1-arylpiperazine, 4-arylpiperidine and 1-aryl-4-aminopiperidine was synthesized and tested in radioligand binding assays at human cloned 5-HT7 and 5-HT1A receptors. In vitro metabolic stability of the target compounds was assessed after incubation with rat hepatic S9 microsomal fraction. Among the new compounds, 1-(2-biphenyl)-4-[2-(3-methoxyphenyl)ethyl]piperazine (1d) and 4-(2-biphenyl)-1-[2-(3-methoxyphenyl)ethyl]piperidine (2d) showed a good compromise between affinity at 5-HT7 receptor (K i = 7.5 nM and 13 nM, respectively) and in vitro metabolic stability (26 and 65 % recovery of parent compound, respectively) but were poorly selective over 5-HT1A receptor.

New arylpiperazines with flexible versus partly constrained linker as serotonin 5-HT(1A)/5-HT(7) receptor ligands.

A series of new long-chain arylpiperazine (LCAP) derivatives with flexible and partly constrained alkyl linker were synthesized and investigated in vitro as potential serotonin 5-HT(1A) and 5-HT(7) receptor ligands. The compounds were prepared by a two-step procedure using naphthalimide and 2H-1,3-benzoxazine-2,4(3H)-dione as imides, and 1-(2-methoxyphenyl)piperazine (o-OMe-PhP) and 1,2,3,4-tetrahydroisoquinoline (THIQ) as amine pharmacophores. Modifications of the spacer structure included introduction of flexible penta- and hexamethylene chains as well as partly constrained m- and p-xylyl moieties. In general, the new compounds were more active at the 5-HT(1A) than at the 5-HT(7) receptor, and the o-OMe-PhP derivatives displayed higher affinities than their respective THIQ analogs. The spacer modifications had little effect on the observed in vitro activities. Within the o-OMe-PhP series, except for a small binding reduction for ligands containing the m-xylyl moiety, there was no substantial change in the compounds' potency at both receptors, while for the THIQ derivatives a clear structure-activity relationship was visible only for the interaction of the compounds with the 5-HT(7) receptor, which strongly favored flexible analogs.

Quinoline- and isoquinoline-sulfonamide derivatives of LCAP as potent CNS multi-receptor-5-HT1A/5-HT2A/5-HT7 and D2/D3/D4-agents: the synthesis and pharmacological evaluation.

Two series of arylpiperazinyl-alkyl quinoline-, isoquinoline-, naphthalene-sulfonamides with flexible (13-26) and semi-rigid (33-36) alkylene spacer were synthesized and evaluated for 5-HT(1A), 5-HT(2A), 5-HT(6), 5-HT(7) and selected compounds for D(2), D(3), D(4) receptors. The compounds with a mixed 5-HT and D receptors profile 16 (N-{4-[4-(3-chlorophenyl)-piperazin-1-yl]-butyl}-3-quinolinesulfonamide) and 36 (4-(4-{2-[4-(4-chloro-phenyl)-piperazin-1-yl]-ethyl}-piperidine-1-sulfonyl)-isoquinoline), displaying antagonistic activity at 5-HT(7), 5-HT(2A), D(2) postsynaptic sites, produced antidepressant-like effects in the forced swim test in mice and showed significant anxiolytic activity in the plus-maze test in rats. The lead compound 36, a multi-receptor 5-HT(2A)/5-HT(7)/D(2)/D(3)/D(4) agent, also displayed significant antipsychotic properties in the MK-801-induced hyperlocomotor activity in mice.

Design, Synthesis, and Characterization of a Novel Fluoroprobe for Live Human Islet Cell Imaging of Serotonin 5-HT1A Receptor.

Mounting evidence suggests that the serotonin system serves in signal transmission to regulate insulin secretion in pancreatic islets of Langerhans. Among the 5-HT receptor subtype found in pancreatic islets, serotonin receptor 1A (5-HT1A ) demonstrates a unique ability to inhibit ß-cell insulin secretion. We report the design, synthesis, and characterization of two novel fluorescent probes for the 5-HT1A receptor. The compounds were prepared by conjugating the scaffold of the 5-HT1A receptor agonist 8-OH-DPAT with two fluorophores suitable for live-cell imaging. Compound 5a {5-(dimethylamino)-N-[5-[(8-hydroxy-1,2,3,4-tetrahydronaphthalen-2-yl)(propyl)amino]pentyl]naphtalen-1-sulfonammide} showed high affinity for the 5-HT1A receptor (Ki =1.8 nM). Fluoroprobe 5a was able to label the 5-HT1A receptor in pancreatic islet cell cultures in a selective manner, as the fluorescence emission was significantly attenuated by co-administration of the 5-HT1A receptor antagonist WAY-100635. Thus, fluoroprobe 5a showed useful properties to further characterize this unique receptor's role.

Arene- and quinoline-sulfonamides as novel 5-HT7 receptor ligands.

Novel arene- and quinolinesulfonamides were synthesized using different solutions and a solid-support methodology, and were evaluated for their affinity for 5-HT(1A), 5-HT(2A), 5-HT(6), and 5-HT(7) receptors. Compound 54 (N-Ethyl-N-[4-(1,2,3,4,4a,5,6,7,8,8a-decahydroisoquinolin-2-yl)butyl]-8-quinolinesulfonamide) was identified as potent 5-HT(7) antagonist (K(i)=13 nM, K(B)=140 nM) with good selectivity over 5-HT(1A), 5-HT(2A), 5-HT(6) receptors. In the FST in mice, it reduced immobility in a manner similar to the selective 5-HT(7) antagonist SB-269970.

Tuning the activity of known drugs via the introduction of halogen atoms, a case study of SERT ligands - Fluoxetine and fluvoxamine.

The selective serotonin reuptake inhibitors (SSRIs), acting at the serotonin transporter (SERT), are one of the most widely prescribed antidepressant medications. All five approved SSRIs possess either fluorine or chlorine atoms, and there is a limited number of reports describing their analogs with heavier halogens, i.e., bromine and iodine. To elucidate the role of halogen atoms in the binding of SSRIs to SERT, we designed a series of 22 fluoxetine and fluvoxamine analogs substituted with fluorine, chlorine, bromine, and iodine atoms, differently arranged on the phenyl ring. The obtained biological activity data, supported by a thorough in silico binding mode analysis, allowed the identification of two partners for halogen bond interactions: the backbone carbonyl oxygen atoms of E493 and T497. Additionally, compounds with heavier halogen atoms were found to bind with the SERT via a distinctly different binding mode, a result not presented elsewhere. The subsequent analysis of the prepared XSAR sets showed that E493 and T497 participated in the largest number of formed halogen bonds. The XSAR library analysis led to the synthesis of two of the most active compounds (3,4-diCl-fluoxetine 42, SERT Ki = 5 nM and 3,4-diCl-fluvoxamine 46, SERT Ki = 9 nM, fluoxetine SERT Ki = 31 nM, fluvoxamine SERT Ki = 458 nM). We present an example of the successful use of a rational methodology to analyze binding and design more active compounds by halogen atom introduction. 'XSAR library analysis', a new tool in medicinal chemistry, was instrumental in identifying optimal halogen atom substitution.

Sulfonamides with the N-alkyl-N'-dialkylguanidine moiety as 5-HT7 receptor ligands.

A series of arylsulfonamides containing guanidine incorporated in the structure of secondary amines (piperidine, piperazine) was synthesized on SynPhase Lanterns and evaluated for 5-HT(1A), 5-HT(2A), and 5-HT(7) receptors. The results demonstrated that N-alkyl-N'-dialkylguanidines displayed good 5-HT(7)/5-HT(1A) selectivity and may be regarded as promising structural core for development of 5-HT(7) ligands.

Fluorinated indole-imidazole conjugates: Selective orally bioavailable 5-HT7 receptor low-basicity agonists, potential neuropathic painkillers.

The 5-HT7 receptor has recently gained much attention due to its involvement in multiple physiological functions and diseases. The insufficient quality of the available molecular probes prompted design of fluorinated 3-(1-alkyl-1H-imidazol-5-yl)-1H-indoles as a new generation of selective 5-HT7 receptor agonists. A potent and drug-like agonist, 3-(1-ethyl-1H-imidazol-5-yl)-5-iodo-4-fluoro-1H-indole (AGH-192, 35, Ki 5-HT7R = 4 nM), was identified by optimizing the halogen bond formation with Ser5.42 as the supposed partner. The compound was characterized by excellent water solubility, high selectivity over related CNS targets, high metabolic stability, oral bioavailability and low cytotoxicity. Rapid absorption into the blood, medium half-life and a high peak concentration in the brain Cmax = 1069 ng/g were found after i.p. (2.5 mg/kg) administration in mice. AGH-192 may thus serve as the long-sought tool compound in the study of 5-HT7 receptor function, as well as a potential analgesic, indicated by the antinociceptive effect observed in a mouse model of neuropathic pain.

Allosteric Inhibition of Serotonin 5-HT7 Receptors by Zinc Ions.

The allosteric regulation of G protein-coupled receptors (GPCRs) is a well-known phenomenon, but there are only a few examples of allosteric modulation within the metabotropic serotonergic receptor family. Recently, we described zinc non-competitive interactions toward agonist binding at serotonin 5-HT1A receptors, in which biphasic effects, involving potentiation at sub-micromolar concentrations (10 µM) and inhibition at sub-millimolar concentrations (500 µM) of Zn2+ in radioligand binding assays, were consistent with both the agonist and antagonist-like effects of zinc ions observed in in vivo studies. Here, we showed new data demonstrating zinc allosteric inhibition of both agonist and antagonist binding at human recombinant 5-HT7 receptors stably expressed in HEK293 cells as observed by radioligand binding studies as well as zinc neutral antagonism displayed by the concentration of 10 µM in the functional LANCE assay. The allosteric nature of the effect of Zn on 5-HT7 receptors was confirmed (1) in saturation studies in which zinc inhibited the binding of potent orthosteric 5-HT7 receptor radioligands, the agonist [3H]5-CT, and the two antagonists [3H]SB-269970 and [3H]mesulergine, showing ceiling effect and differences in the magnitude of negative cooperativity (α = 0.15, 0.06, and 0.25, respectively); (2) in competition experiments in which 500 µM of zinc inhibited all radioligand displacements by non-labeled orthosteric ligands (5-CT, SB-269970, and clozapine), and the most significant reduction in affinity was observed for the 5-CT agonist (4.9-16.7-fold) compared with both antagonists (1.4-3.9-fold); and (3) in kinetic experiments in which 500 µM zinc increased the dissociation rate constants for [3H]5-CT and [3H]mesulergine but not for [3H]SB-269970. Additionally, in the functional LANCE test using the constitutively active HEK293 cell line expressing the 5-HT7 receptor, 10 µM zinc had features of neutral antagonism and increased the EC50 value of the 5-CT agonist by a factor of 3.2. Overall, these results showed that zinc can act as a negative allosteric inhibitor of 5-HT7 receptors. Given that the inhibiting effects of low concentrations of zinc in the functional assay represent the most likely direction of zinc activity under physiological conditions, among numerous zinc-regulated proteins, the 5-HT7 receptor can be considered a serotonergic target for zinc modulation in the CNS.

Synthesis and 5-HT1A/5-HT2A receptor activity of N-(4-arylpiperazin-1-yl)alkyl derivatives of 2-azaspiro([4.4]nonane and [4.5]decane-1,3-dione.

Two series of N-[(4-arylpiperazin-1-yl)-alkyl]-2-azaspiro[4.4]nonane (5-10) and [4.5]decane-1,3-dione (11-16) derivatives were synthesized and their serotonin 5-HT1A and 5-HT2A receptor affinities were determined. Compounds with the methylene spacer (5-7 and 11-13) exhibited low 5-HT1A/5-HT2A receptor affinity, in contrast to their ethylene analogues regarded as potent 5-HT1A ligands, especially those containing a cyclohexane moiety (14-16; Ki = 5.1, 2.7 and 4.3 nM, respectively) in the 3-position of the pyrrolidine-2,5-dione ring. Moreover, derivatives with 3-chloro substituent (10 and 14) showed distinct affinity for 5-HT2A receptors. The functional activity of compounds 10, 14, 15 and 16 was tested in vivo in the commonly used animal models. In those experiments, the tested compounds showed features of agonists of pre- and postsynaptic (14), agonists of presynaptic and antagonists of postsynaptic (10, 15), or agonists of postsynaptic (16) 5-HT1A receptors. Additionally, 10 and 16 exhibited properties of potential 5-HT2A receptor antagonists. The above results suggested a crucial role of the spacer between the amide fragment and 4-arylpiperazine moiety, as well as of the size of the cycloalkyl ring at the 3-position of pyrrolidine-2,5-dione ring in functional 5-HT1A/5-HT2A properties.

Concentration-Dependent Dual Mode of Zn Action at Serotonin 5-HT1A Receptors: In Vitro and In Vivo Studies.

Recent data has indicated that Zn can modulate serotonergic function through the 5-HT1A receptor (5-HT1AR); however, the exact mechanisms are unknown. In the present studies, radioligand binding assays and behavioural approaches were used to characterize the pharmacological profile of Zn at 5-HT1ARs in more detail. The influence of Zn on agonist binding to 5-HT1ARs stably expressed in HEK293 cells was investigated by in vitro radioligand binding methods using the agonist [3H]-8-OH-DPAT. The in vivo effects of Zn were compared with those of 8-OH-DPAT in hypothermia, lower lip retraction (LLR), 5-HT behavioural syndrome and the forced swim (FST) tests. In the in vitro studies, biphasic effects, which involved allosteric potentiation of agonist binding at sub-micromolar Zn concentrations and inhibition at sub-millimolar Zn concentrations, were found. The in vivo studies showed that Zn did not induce LLR or elements of 5-HT behavioural syndrome but blocked such effects induced by 8-OH-DPAT. Zn decreased body temperature in rats and mice; however, Zn failed to induce hypothermia in the 5-HT1A autoreceptor knockout mice. In the FST, Zn potentiated the effect of 8-OH-DPAT. However, in the FST performed with the 5-HT1A autoreceptor knockout mice, the anti-immobility effect of Zn was partially blocked. Both the binding and behavioural studies suggest a concentration-dependent dual mechanism of Zn action at 5-HT1ARs, with potentiation at low dose and inhibition at high dose. Moreover, the in vivo studies indicate that Zn can modulate both presynaptic and postsynaptic 5-HT1ARs; however, Zn's effects at presynaptic receptors seem to be more potent.

Synthesis and 5-HT(1A), 5-HT(2A) receptor activity of new beta-tetralonohydantoins.

A series of new 3-[4-(4-arylpiperazinyl)-butyl]-beta-tetralonohydantoins (8a-13a) were synthesized. The compounds exhibited high affinity for 5-HT(1A) receptors (K(i)=6 to 55 nM) combined with moderate-to-high 5-HT(2A) receptor affinities (K(i)=45 to 213 nM). The results of in vivo studies indicated that of the compounds tested, 3-[4-(4-phenylpiperazinyl)-butyl-beta-tetralonohydantoin (8a) showed features of full (pre- and postsynaptic) 5-HT(1A) receptor agonists, whereas compounds 9a-13a behaved like antagonists of postsynaptic 5-HT(1A) receptors; additionally, compound 13a produced an effect characteristic of presynaptic 5-HT(1A) receptor agonists. Moreover, compounds 8a and 10a-13a exhibited properties of 5-HT(2A) receptor antagonists. Due to the most interesting 5-HT(1A)/5-HT(2A) functional profile compounds 8a and 13a were further tested for their potential psychotropic activity. In fact, compound 8a (but not 13a) showed diazepam-like anxiolytic activity and behaved like a weak antidepressant.

In-vivo effects of the 1,2,4-piperazine derivatives MM5 and MC1, putative 5-HT agonists, on dopamine and serotonin release in rat prefrontal cortex.

Two 1,2,4-substituted derivatives of piperazine were tested for their effect on dopamine and serotonin (5-HT) release in rat prefrontal cortex. Both compounds, 1-[4-(4-chinolin-2-yl-piperazin-1yl)-butyl]piperidin-2-on (MM5) and 1-[4-(2-methyl-4-chinolin-2-yl-piperazin-1-yl)-butyl]-8-azaspiro [4.5]decano-7,9-dion (MC1), produced hypothermia in mice and showed affinity for 5-HT1A receptors in-vitro. Like the selective 5-HT1A agonist 8-OH-DPAT (0.1 mg kg(-1)), MM5 given peripherally (30 mg kg(-1)) decreased the extracellular 5-HT level in rat prefrontal cortex, while MC1 suppressed 5-HT release at a higher dose (40 mg kg(-1)), but not at a lower one (30 mg kg(-1)). The effect of both compounds on 5-HT release was abolished by WAY 100635 (0.3 mg kg(-1)). MC1 (30 and 40 mg kg(-1)), but not MM5, raised cortical dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC) and extracellular homovanillic acid (HVA) levels. The effect of MC1 on dopamine release was reversed by neither WAY 100635 nor the non-selective 5-HT2 antagonist ritanserin (2 mg kg(-1)). However, ritanserin prevented the effect of the higher dose of MC1 on 5-HT release. The results of this study suggest that MM5 exhibits the profile of a 5-HT1A agonist devoid of dopaminergic activity. MC1 seems to possess moderate agonist activity at 5-HT1A and 5-HT2A receptors, while acting on 5-HT release in the rat prefrontal cortex. However, the facilitation of dopamine release by this compound does not seem to be related to its affinity for 5-HT1A and 5-HT2A receptors.

Synthesis and 5-HT1A/5-HT2A activity of some butyl analogs in the group of phenylpiperazine alkyl pyrimido[2,1-f]theophyllines.

New arylpiperazines with a four-methylene spacer containing a terminal pyrimido[2,1-f] theophylline fragment were synthesized, and their 5-HT1A and 5-HT2A receptor affinities were determined. All these compounds displayed a high affinity for 5-HT1A receptors (Ki=0.5-21.5 nM), and low affinity for 5-HT2A ones. The results of in vivo experiments showed that compounds revealed potential agonistic activity at presynaptic 5-HT1A receptors, whereas their functional activity at postsynaptic 5-HT1A sites was diversified. In fact, compounds and behaved like partial agonists, antagonists or agonists of postsynaptic 5-HT1A receptors, respectively. The pharmacological properties of the tested compounds were discussed in comparison with those of the three methylene-analogs described earlier.

New arylpiperazine 5-HT(1A) receptor ligands containing the pyrimido[2,1-f]purine fragment: synthesis, in vitro, and in vivo pharmacological evaluation.

New 1H,3H-pyrimido[2,1-f]purine-2,4-dione derivatives of arylpiperazine (11-22) were prepared and evaluated in vitro for their affinity for 5-HT(1A), 5-HT(2A), alpha(1), and D(2) receptors. The tested compounds showed high affinity for 5-HT(1A) and alpha(1) receptors (K(i) = 1.1-87 and 10-62 nM, respectively) and moderate to low affinity for 5-HT(2A) (K(i) = 56-881 nM) and D(2) receptors (K(i) = 94-1245 nM). Compounds 14, 15, 18, 19, and 21, mostly 3'-chlorophenylpiperazine derivatives, can be classified as mixed 5-HT(1A)/5-HT(2A)/alpha(1) ligands. Compound 13, which showed the highest 5-HT(1A) receptor affinity (K(i) = 1.1 nM), was 50-fold selective in relation to alpha(1) adrenoceptors and at least 250-fold over 5-HT(2A) and D(2) sites. On the basis of in vivo functional tests, 8-phenylpiperazinoethylamino (11), 8-(2'-methoxyphenylpiperazino)ethylamino (13), and 8-phenylpiperazinopropylamino (14) derivatives of 1,3-dimethyl-1H,3H-pyrimido[2,1-f]purine-2,4-dione were identified as potent pre- and postsynaptic 5-HT(1A) receptor antagonists. 1,3-Dimethyl-7-bromo-8-(phenylpiperazinopropylamino)-1H,3H-pyrimido[2,1-f]purine-2,4-dione (20) behaved like an agonist of presynaptic and as a partial agonist of postsynaptic 5-HT(1A) receptors and resembled ipsapirone in terms of functional intrinsic activity. It revealed marked anxiolytic-like activity in the Vogel test in rats, comparable to that of the reference drug diazepam, and exhibited antidepressant-like activity in the Porsolt test in rats. The sedative effect of 20, evaluated in the open field test in rats, appeared at doses twice as high as those inducing a minimal anxiolytic-like effect and was similar to the effects of diazepam.