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Attempts to extend the hydrated imidazoline ring expansion (HIRE) strategy to a series of diarene-fused [1,4]diazepinones (earlier applied successfully to bis-pyrido substrate nevirapine) did not result in ring expansion but, rather, led to 2-aminoethyl side chain expulsion. This seeming setback (setting the limitations to the HIRE methodology substrate scope) led to the discovery of selective dopamine D2 ligands with elements of structure–activity relationships.

Di(het)areno-fused 1,4,7-(oxa)thiadiazecanes were synthesized by the reduction of the corresponding ten-membered lactams obtained, in turn, via the ‘hydrated imidazoline ring expansion’ (HIRE) methodology. Two of them displayed micromolar agonistic activity towards trace amine-associated receptor 1 (TAAR1) and no affinity towards a panel of dopamine (D2) and serotonin (5-HT1A, 5-HT2A and 5-HT7) receptors. These findings validate compounds of this chemotype as scaffolds for the design of selective aminergic receptor modulators.

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., Graphical Abstract

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.

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.

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.

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.

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.

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.

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.

The 5-HT

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.

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.

A series of new quinoline- and isoquinoline-sulfonamide analogs of aripiprazole was synthesized to explore the influence of two structural features - replacement of ether/amide moiety with sulfonamide one, and localization of a sulfonamide group in the azine moiety. In contrast to aripiprazole, compound 33 (N-(3-(4-(2,3-dichlorophenyl)piperazin-1-yl)propyl)quinoline-7-sulfonamide) and 39 (N-(4-(4-(2,3-dichlorophenyl)piperazin-1-yl)butyl)isoquinoline-3-sulfonamide) displaying multireceptor 5-HT(1A)/5-HT(2A)/5-HT(7)/D(2)/D(3) profile, and behaving as 5-HT(1A) agonists, D(2) partial agonists, and 5-HT(2A)/5-HT(7) antagonists, produced significant antidepressant activity in FST in mice. On the other hand, their 4-isoquinolinyl analog 40 (N-(4-(4-(2,3-dichlorophenyl)piperazin-1-yl)butyl)isoquinoline-4-sulfonamide), with similar receptor binding and functional profile, additionally displayed remarkable antipsychotic properties in the MK-801-induced hyperlocomotor activity in mice.

Background SB 269970, a 5-HT 7 receptor antagonist may produce a faster antidepressant-like effect in animal models, than do antidepressant drugs, e.g., imipramine. The present work was aimed at examining the effect of single and repeated (14 days) administration of SB 269970 on the 5-HT 7 receptor in the hippocampus. Methods The reactivity of 5-HT 7 receptors was determined using 5-carboxamidotryptamine (5-CT), which increased the bursting frequency of spontaneous epileptiform activity in hippocampal slices. Additionally, the effects of SB 269970 administration on the affinity and density of 5-HT 7 receptors were investigated using [ 3 H]-SB 269970 and the influence of SB 269970 and imipramine on mRNA expression levels of Gα s and Gα 12 mRNA were studied using RT-qPCR. Results Acute and repeated treatment with SB 269970 led to attenuation of the excitatory effects of activation of 5-HT 7 receptors. Neither single nor repeated administration of SB 269970 changed the mean affinity of 5-HT 7 receptors for [ 3 H]-SB 269970. Repeated, but not single, administration of SB 269970 decreased the maximum density of [ 3 H]-SB 269970 binding sites. While administration of imipramine did not change the expression of mRNAs for Gα s and Gα 12 proteins after both single and repeated administration of SB 269970, a reduction in Gα s and Gα 12 mRNA expression levels was evident. Conclusions These findings indicate that even single administration of SB269970 induces functional desensitization of the 5-HT 7 receptor system, which precedes changes in the receptor density. This mechanism may be responsible for the rapid antidepressant-like effect of the 5-HT 7 antagonist in animal models.

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.

The synthesis and evaluation as 5-HT1A and 5-HT7 serotonin receptor ligands of the two sets of O-substituted hydroxybenzamides, structurally related to 2-{3-[4-(2-methoxyphenyl)piperazin-1-yl]propoxy}benzamide (1), (Ki 5-HT1A = 21 nM, 5-HT7 = 234 nM) are reported. To affect the affinity for 5-HT1A and 5-HT7 receptors, an amide moiety (2, 3, 4, 5, 6) and a hydrocarbon chain length (7, 8, 9, 10) were modified. The serotonergic activity of compounds 2, 3, 4, 5, 6, 7, 8, 9, 10 was generally higher in the case of 5-HT1A receptors compared with 5-HT7 ones; the most active 5-HT1A ligands being meta-isomer 2 (Ki = 7 nM) and both analogs of 1 with the longest spacer, i.e., penta- and hexa-methylene derivatives 9 and 10 (Ki = 4 and 3 nM, respectively). The observed biological properties of compounds 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 were elucidated using molecular modeling procedures. J. Heterocyclic Chem., (2010).

The addition reaction of lithium reagents to the 4 position of 2-chloropyrimidine or 2-chloroquinazoline followed by oxidation of the resultant dihydro intermediate product is a powerful tool for the synthesis of 4-substituted 2-chloropyrimidines or 2-chloroquinazolines. 4-Vinyl derivatives undergo a conjugate nucleophilic addition across the vinyl group. A nucleophilic displacement of chloride in 4substituted 2-chloropyrimidines or 2-chloroquinazolines by treatment with 4-methylpiperazine provides compounds that are antagonists of the serotonin 5-HT2A receptor.

The 1-arylpiperazine series of N-substituted 1,3-benzoxazine-2,4-diones as well as O- and N-substituted salicylamides with an n-propyl chain were synthesized in order to explore the effect of cyclic and acyclic salicylamide moieties on their binding affinity for 5-HT1A, 5-HT2A and 5-HT7 receptor sites. Target compounds 1 and 2 were prepared by a two-step procedure, i.e. by alkylation of 1,3-benzoxazine-2,4-dione or salicylamide with 1,3-dibromopropane and next by condensation of 3-bromopropyl intermediates with arylpiperazines; syntheses of 3-bromopropyl intermediates were performed in solvent-free conditions. Compounds 3 were prepared by hydrolysis of 1. In respect of salicylamide moieties, binding affinities for 5-HT1A and 5-HT7 receptors increase according to the rank of derivatives 3 < 1 < 2, for the same arylpiperazines. Regarding 5-HT2A receptors, increased activity of ligands was changed in reverse order to the affinity for 5-HT1A, i.e. 2 < 1 < 3. 5-HT1A and 5-HT7 receptor binding constants were the highest for the 2-methoxyphenyl ligand 2c, while the 3-chlorophenyl ligand 3b was most active for 5-HT2A receptors.

New, flexible (7, 9, 11 and 13) and rigid (8, 10, 12 and 14) imides with a 1-(m-trifluorophenyl)piperazine fragment and a tetramethylene or a 1e,4e-cyclohexylene spacer, respectively, showed very high affinity (K(i)=0.3-34 nM) and agonistic in vivo activity for 5-HT(1A) receptors. Flexible new compounds and the previously described 5 also bound to 5-HT(7) receptors (K(i)=21-134 nM). Selected glutarimide derivatives, that is, the most potent postsynaptic 5-HT(1A) receptor agonist rigid compound 8 and its flexible analogue 7, as well as the previously described full agonist-rigid compound 6 and the partial agonist-its flexible counterpart 5 exhibited moderate affinity for alpha(1)-adrenoceptors (K(i)=85 - 268 nM), but were practically devoid of any affinity for dopamine D(2) sites. Those glutarimides demonstrated anxiolytic- (5 and 7) and antidepressant-like (5, 6 and 8) activity in the four-plate and the swim tests in mice, respectively; at the same time, however, they inhibited the locomotor activity of mice. The antidepressant-like effect of 8 was significantly stronger than that induced by imipramine used as a reference antidepressant.

On the basis of our earlier studies with the serotonin receptor ligands in the group of 1,3-dimethyl-3,7-dihydropurine-2,6-dione derivatives, a series of new arylpiperazinylalkyl and tetrahydroisoquinolinylalkyl analogs of 8-alkoxy-1,3-dimethyl-3,7-dihydropurine-2,6-dione (10-25) and 1,3-dimethyl-7,9-dihydro-3H-purine-2,6,8-trione (26-30) were synthesized and their 5-HT(1A), 5-HT(2A), and 5-HT(7) receptor affinities were determined. The new compounds 17, 18, 20, and 21 were found to be highly active 5-HT(1A) receptor ligands (K(i)=11-19nM) with diversified affinity for 5-HT(2A) receptors (K(i)=15-253nM). Compounds 12, 13, 15, and 19 were moderately potent 5-HT(2A) ligands (K(i)=23-57nM), whereas 17, 18, 24, and 25 showed distinct affinity for 5-HT(7) receptors (K(i)=51-83nM). Purine-2,6,8-triones showed weak affinities for 5-HT(1A) and 5-HT(7) receptors; among them, 27 and 29 were classified as 5-HT(2A) receptor ligands. The selected compounds 17 and 21 were pharmacologically evaluated to determine their functional activities at pre-(hypothermia in mice) and post-(lower lip retraction in rats) synaptic 5-HT(1A) receptors. Compound 17 showed features of a potential agonist of pre- and post-synaptic 5-HT(1A) receptors, whereas 21 was classified as a potential, weak partial agonist of postsynaptic sites. Last of all, the most interesting compound 17 tested in behavioral models showed potential anxiolytic and antidepressant activities.

Syntheses of the N-substituted butyl derivatives of 1,8-naphthalimide (1-8), containing various arylpiperazines, tetrahydroisoquinoline and methylhomopiperazine moieties attached at 4-position of the butyl chain have been described. Biological activities were evaluated in vitro for their ability to bind to serotonin 5-HT1A and 5-HT7 receptors. Due to the structural similarity of derivatives 1-8 to psychotropic agents, the pharmacological properties of target compounds were predicted using PASS program.

Novel arylpiperazines with N-acylated amino acids, selected on the basis of a preliminary screening of two libraries previously synthesized on SynPhase Lanterns, were prepared in solution and their affinity for 5-HT(1A), 5-HT(2A), and D(2) receptors was evaluated. The compounds bearing (3-acylamino)pyrrolidine-2,5-dione (19-26) and N-acylprolinamide (29-34) moieties showed high affinity for 5-HT(1A) (K(i)=3-47 nM), high-to-low for 5-HT(2A) (K(i)=4.2-990 nM), and low for D(2) receptors (K(i)=0.77-21.19 microM). All the new o-methoxy derivatives of (3-acylamino)pyrrolidine-2,5-diones tested in vivo revealed agonistic activity at postsynaptic 5-HT(1A) receptors, while m-chloro derivatives were classified as antagonists of these sites; similar relations were observed for o-methoxy (29) and m-chlorophenylpiperazine derivatives of N-acylprolinamides. The reported results show that the amino acid-derived terminal fragment modified the in vivo functional profile. Finally, the selected compounds 19 and 20, a 5-HT(1A) partial agonist and a full agonist, respectively, and 26, a mixed 5-HT(1A)/5-HT(2A) antagonist, were evaluated in preclinical animal models of depression and anxiety. The project allowed selecting the lead compound 20 which exhibited an anxiolytic-like effect in the four-plate test in mice and revealed distinct antidepressant-like effects in the forced swimming and tail suspension tests in mice.

A library consisting of 60 arylpiperazines modified with N-acylated amino acids was prepared on BAL linker SynPhase™ Lanterns and evaluated in vitro for 5-HT 1A receptor affinity. Biological screening, followed by a simple Fujita–Ban analysis, enabled the description of structure–activity relationships and allowed the selection of some potent, high-affinity ligands for in vivo pharmacological investigations.

A solid-phase synthesis of the 64-member library of novel sulfonamide and carboxamide proline derivatives, focused on the 5-HT7 receptor antagonist SB-258741, was described. The final compounds were obtained in good yields and high purity upon cleavage from SynPhase Lanterns, functionalized by a BAL linker. The library representatives were screened for 5-HT7, 5-HT1A and D2 receptors to explore the impact of a tertiary amine moiety, the length of an alkylene spacer and the aryl fragment on the receptor affinity. The preliminary biological results provided data for further investigation aimed at a search for 5-HT7 receptor agents, and permitted the identification of several compounds with significant 5-HT1A receptor affinity.

Starting with the structure of potent 5-HT 1A ligands, that is, MM77 [1-(2-methoxyphenyl)-4-(4-succinimidobutyl)piperazine, 4 ] and its constrained version 5 (MP349), previously obtained in our laboratory, a series of their direct analogues with differently substituted aromatic ring (R = H, m -Cl, m -CF 3 , m -OCH 3 , p -OCH 3 ) were synthesized. The flexible and the corresponding 1e,4e-disubstituted cyclohexane derivatives were designed in order to investigate the influence of rigidification on 5-HT 1A affinity, selectivity for 5-HT 2A , 5-HT 7 , D 1 , and D 2 binding sites and functional profile at pre- and postsynaptic 5-HT 1A receptors. The new compounds 19 – 25 were found to be highly active 5-HT 1A receptor ligands ( K i = 4–44 nM) whereas their affinity for other receptors was: either significantly decreased after rigidification (5-HT 7 ), or controlled by substituents in the aromatic ring (α 1 ), or influenced by both those structural modifications (5-HT 2A ), or very low (D 2 , K i = 5.3–31 μM). Since a distinct disfavor towards rigid compounds was observed for 5-HT 7 receptors only, it seems that the bioactive conformation of chain derivatives at those sites should differ from the extended one. Several in vivo models were used to asses functional activity of 19 – 25 at pre- (hypothermia in mice) and postsynaptic 5-HT 1A receptors (lower lip retraction in rats and serotonin syndrome in reserpinized rats). Unlike the parent antagonists 4 and 5 , all the new derivatives tested were classified as partial agonists with different potency, however, similar effects were observed within pairs (flexible and rigid) of the analogues. The obtained results indicated that substitution in the aromatic ring, but not spacer rigidification, controls the 5-HT 1A functional activity of the investigated compounds. Moreover, an o -methoxy substituent in the structure of 5 seems to be necessary for its full antagonistic properties. Of all the new compounds studied, trans -4-(4-succinimidocyclohexyl)-1-(3-trifluoromethylphenyl)piperazine 24 was the most potent 5-HT 1A receptor ligand in vitro ( K i = 4 nM) and in vivo, with at least 100-fold selectivity for the other receptors tested.

Two sets of new o-methoxyphenylpiperazine (MPP; series a) and 1,2,3,4-tetrahydroisoquinoline (THIQ; series b) derivatives, containing various imide moieties derived from NAN190, were synthesized and evaluated in vitro for their ability to bind to the serotonin 5-HT(1A) and 5-HT(2A) receptors. All new derivatives from series a demonstrated high 5-HT(1A) affinities, whereas THIQ analogues were much less active. With respect to 5-HT(2A) receptors, three MPP derivatives presented moderate activity but the rest of the investigated compounds were practically inactive. The influence of changes in terminus geometry on 5-HT(1A) receptor affinity was analyzed in regard to model compounds NAN190and MM199.

Noncovalent complexes consisting of two protonated amines and a chloride anion were observed under electrospray ionization mass spectrometry (ESI-MS) conditions. The observed phenomenon was investigated for the hydrochlorides of buspirone, a well-known anxiolytic drug, and 23 other arylpiperazine derivatives that had been developed as serotonin 5-HT 1 A receptor ligands. Due to the major role of ionic interactions in a vacuum, it was proposed that the detected complexes were formed by NH + ...Cl - ...NH + bridges. It was found that complexation depended on structural features of the analyzed compounds. For derivatives with a shorter linker (three methylene groups) containing a terminal cyclic amide fragment, complex ions were not observed. It was postulated that, in the latter case, steric hindrance due to a terminal group could disturb ionic bridge formation. Since both the observed complexation and ligand-binding processes are driven by noncovalent forces, and a qualitative relationship between them was found (compounds with a 4-carbon chain always display higher affinity for 5-HT 1 A receptors than do their 3-carbon analogues), such ESI-MS studies may yield valuable information on ligand-receptor interactions.

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

New 1-arylpiperazine (series d-f) and 1,2,3,4-tetrahydroisoquinoline (series g) derivatives of 1,4-benzoxazin-3(4H)-one 1, 1,2-benzoxazolin-3-one 2, and 1,3-benzoxazolin-2,4-dione 3 with an n-butyl chain were synthesized in order to explore the effect of spacer elongation on their binding affinity and in vivo functional activity at 5-HT 1A and 5-HT 2A receptors in comparison with trimethylene analogues (a, bc). 5-HT 1A receptor binding constants of derivatives 1d-g, 2d-f, and 3d-f were very high (K i = 1.25-54 nM), and 5-HT 2A affinities were maintained at a similar, high level (K i = 27-85 nM) for series d and e, and moderate (K i = 246-495 nM) for series f. In respect of a spacer, the obtained results showed either no effect or a slight increase in the 5-HT 1A /5-HT 2A affinity in case of derivatives of 1 and 2, respectively. A striking effect was observed for derivatives 3d and 3f, whose 5-HT 1A affinity was reinforced by two orders of magnitude with a simultaneous decrease in 5-HT 2A binding constants in comparison with trimethylene analogues. As shown by X-ray crystallography, this phenomenon may be attributed to the position of non-carbonyl oxygen atom in the amide moiety. In vivo studies demonstrated that compounds 1e-g, 2d-f, and 3f behaved like typical postsynaptic 5-HT 1A receptor antagonists, whereas 3d and 3e might be qualified as their potential partial agonists. Moreover, 1e, 2e, and 3e demonstrated 5-HT 2A receptor antagonistic properties. Of the tested compounds, two derivatives showed some very outstanding properties: 3e may be regarded as a potential anxiolytic and/or antidepressant agent, while 3f as a new potent 5-HT 1A antagonist.

5HT 1A and 5HT 2A receptor affinities of several γ-(3'-chloro- or 2'-methoxyphenyl)-piperazinopropyl derivatives of pyrimido[2,1- f ]purines or 1,3-diazepino[2,1- f ]purines are reported. Some behavioral models demonstrated that 1,3-dimethyl-9-{3-[4-(2'-methoxyphenyl)-1-piperazinyl]propyl}-2,4-dioxo-1,3,6,7,8,9-hexahydropyrimido[2,1- f ]purine 5b and 1,3-dimethyl-9-{3-[4-(2'-methoxyphenyl)-1-piperazinyl]propyl}-2,4,8-trioxo-1,3-dihydro-9H-pyrimido[2,1- f ]purine 8b , may be classified as partial agonist and a full agonist, respectively of pre- and post-synaptic 5HT 1A receptors.

Three series of new N-substituted 1,2,3,4-tetrahydroisoquinolines with 2-, 3-, and 4-membered alkyl chains (a, b, and c, respectively) were synthesized, and the effect of some structural modifications on their 5-HT1A receptor affinities and functional properties was discussed. It was found that the volume of the terminal amide substituent was a crucial parameter which determined 5-HT1A receptor affinities of the tested compounds, while the in vivo activity seemed to depend on both the R-volume and the length of a hydrocarbon chain. It was demonstrated that the most active ligands behaved like agonists or partial agonists at postsynaptic 5-HT1A receptors.

A series ol 1-{ω-(4-aryl-1-piperazinyl)alkyl]indolin-2(1H)-one derivatives 2-14 was synthesized in order to obtain ligands with a dual 5-HT 1A /5-HT 2A activity. The majority of those compounds (2-5, 7, 10-13) exhibited a high 5-HT 1A (K i =2-44 nM) and/or 5-HT 2A affinity (K i = 51 and 39 for 5 and 7, respectively). Induction of lower lip retraction (LLR) and behavioral syndrome and inhibition of these erects evoked by 8-hydroxy-2-(di-n-propyl-amino)tetralin (8-OH-DPAT) were used for determination the agonistic and antagonistic activity, respectively, at 5-HT 1A receptors. The 5-HT 2A antagonistic activity was assessed by the blocking effect on the head twitches induced by (±)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) in mice. Two of the tested compounds, 1-{3-[4-(3-chlorophenyl)-1-piperazinyl]propyl}-6-fluoroindolin-2(1H)-one (5) and 1-{3-[4-(2-methoxyphenyl)-1-piperazinyl]propyl indolin-2(1H)-one (7), demonstrated a high 5-HT 1A /5-HT 2A affinity and an in vivo antagonistic activity towards both receptor subtypes.

The title pyrimidines 7–12 are potent 5-HT2A receptor ligands with fairly strong behavioral antagonistic activity. A comparison of the structural and binding properties within the entire group of these and other pyrimidines demonstrates two different modes of the bioactive complex formation.

Summary New N -methylpiperazino-substituted quinazolines 8 and 9 , phthalazine 13 , and quinoline 19 have been synthesized. The receptor binding profiles (α 1 , 5-HT 1A , 5-HT 2A ) of these compounds and their analogs ( 7–22 ) have been determined. It has been demonstrated that orientation of a local dipole moment of the heteroaromatic ring system affects both the α 1 and 5-HT 2A affinity of the investigated class of ligands. Distortion of the coplanar unfused heteroaromatic ring system results in a decreased 5-HT 2A affinity. 4-(4-Methylpiperazino)-2-(2-thienyl)quinoline 18 is the most active and selective α 1 ligand ( K i = 4.9 nM) with a much lower affinity for 5-HT 1A ( K i = 3420 nM) and 5-HT 2A ( K i = 211 nM) receptors.

A new analog of buspirone (1), i.e., 8-[4-[2-(1,2,3,4-tetrahydroisoquinolinyl)]butyl]-8-azaspiro- [4.5]decane-7,9-dione (6a), was synthesized. In was demonstrated that buspirone and its analog 6a were equipotent 5-HT(1A) ligands. Several behavioral models showed that 6a had essentially the same functional profile at 5-HT(1A) receptors as buspirone. The obtained results permit a conclusion that the basic nitrogen atom and terminal, bulky cycloimide moiety, but not the 2-pyrimidinyl group, of buspirone are directly involved in the formation of the bioactive complex with 5-Ht1A receptors.

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.

Background Our previous studies in a group of arylpiperazine derivatives of 1,3-dimethyl-3,7-dihydro-purine-2,6-diones, aimed at chemical diversification of the purine-2,6-dione by introduction of hydrophobic substituent in a 7- or 8- position or elongation of the linker length between arylpiperazine and purine core, allowed a selection of potent 5-HT 1A , 5-HT 2A and 5-HT 7 receptor ligands displaying anxiolytic and antidepressant properties. Continuing our research in this field, in the present studies we designed a new series of 8-aminoalkylamino ( 15–35 ) and 8-arylpiperazinylpropoxy ( 36–42 ) derivatives of 7-substituted 1,3-dimethyl-3,7-dihydropurine- 2,6-dione as potential 5-HT 1A , 5-HT 2A and 5-HT 7 receptor ligands with potential psychotropic activity. Methods Radioligand binding assays were employed for determining the affinity and the selectivity profile of the synthesized compounds for native 5-HT 1A , 5-HT 2A , and cloned 5-HT 6 and 5-HT 7 receptors. The functional activity of the selected compounds at 5-HT 1A and 5-HT 2A receptors was tested in the commonly used in vivo models. Antidepressant and anxiolytic properties were evaluated in the forced swim (FST) and the four-plate test (FPT) in mice, respectively. Results Among the evaluated series, selected 7-benzyl-8-((4-(4-(3-chlorophenyl)piperazin-1-yl)butyl)amino)-1,3-dimethyl- 1 H -purine-2,6(3 H ,7 H )-dione (21), a mixed 5-HT 1A /5-HT 2A /5-HT 7 receptor ligand, produced an antidepressant-like effect in FST, and exerted anxiolytic-like activity in FPT. Another pharmacologically evaluated compound 42 (a mixed 5-HT 1A /5-HT 7 ligand) slightly, but non-significantly attenuated the immobility time of mice in FST and was devoid of activity in FPT. Conclusions Study revealed advantage of mixed 5-HT 1A /5-HT 2A /5-HT 7 receptor ligands over 5-HT 1A /5-HT 7 agents to display antidepressant- and anxiolytic-like activity. Modification of arylalkyl/allyl substituent in position 7 of purine-2,6-dione opens possibility for designing new 5-HT ligands with preserved π electron system and lower molecular weight.

The 5-HT 1A receptor affinities and ionization constants of a set of 1-arylpiperazine (4) 1,2,3,4-tetrahydroisoquinoline (6), and -quinoline (7) containing N-(ω-arylalkyl) or N-(E)-cinnamyl substituents as well as two morpholine derivatives (8a, 8b) were determined. It was shown that some tetrahydroisoquinoline (6c, 6d) and morpholine (8a) derivatives were 5-HT 1A ligands equipotentto 1-phenylpiperazine (4a) and 1,2,3,4,4a,5-hexahydropyrazino[1,2-a]indole (5). On the basis of molecular modelling studies it was also demonstrated that 6c, 6d and 8a mimicked very well the reference structures of 4a and its rigid analog 5. Another, more complex 1,2,3,4-tetrahydroisoquinoline derivative 3, which served as a model compound to confirm the previously reported 5-HT 1A binding mode of derivatives 1a-d and 2, had the highest 5-HT 1A affinity (K i = 6.7 ± 0.5 nM) of all the investigated compounds

A series of new quinoline- and isoquinoline-sulfonamide analogs of aripiprazole was synthesized to explore the influence of two structural features - replacement of ether/amide moiety with sulfonamide one, and localization of a sulfonamide group in the azine moiety. In contrast to aripiprazole, compound 33 (N-(3-(4-(2,3-dichlorophenyl)piperazin-1-yl)propyl)quinoline-7-sulfonamide) and 39 (N-(4-(4-(2,3-dichlorophenyl)piperazin-1-yl)butyl)isoquinoline-3-sulfonamide) displaying multireceptor 5-HT(1A)/5-HT(2A)/5-HT(7)/D(2)/D(3) profile, and behaving as 5-HT(1A) agonists, D(2) partial agonists, and 5-HT(2A)/5-HT(7) antagonists, produced significant antidepressant activity in FST in mice. On the other hand, their 4-isoquinolinyl analog 40 (N-(4-(4-(2,3-dichlorophenyl)piperazin-1-yl)butyl)isoquinoline-4-sulfonamide), with similar receptor binding and functional profile, additionally displayed remarkable antipsychotic properties in the MK-801-induced hyperlocomotor activity in mice.

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.

The compounds (Ia), (IIb), and (IIc) are 5-HT1A receptor ligands with nanomolar affinity (Ki = 7, 4 and 3 nM, respectively) and reasonable selectivity for 5-HT1A receptors.

The 5-HT 1A receptor affinities and ionization constants of a set of 1-arylpiperazine (4) 1,2,3,4-tetrahydroisoquinoline (6), and -quinoline (7) containing N-(ω-arylalkyl) or N-(E)-cinnamyl substituents as well as two morpholine derivatives (8a, 8b) were determined. It was shown that some tetrahydroisoquinoline (6c, 6d) and morpholine (8a) derivatives were 5-HT 1A ligands equipotentto 1-phenylpiperazine (4a) and 1,2,3,4,4a,5-hexahydropyrazino[1,2-a]indole (5). On the basis of molecular modelling studies it was also demonstrated that 6c, 6d and 8a mimicked very well the reference structures of 4a and its rigid analog 5. Another, more complex 1,2,3,4-tetrahydroisoquinoline derivative 3, which served as a model compound to confirm the previously reported 5-HT 1A binding mode of derivatives 1a-d and 2, had the highest 5-HT 1A affinity (K i = 6.7 ± 0.5 nM) of all the investigated compounds

A series of new 4,6-di(heteroaryl)pyrimidines containing an N-methylpiperazino group (6-13) or an ethylenediamine chain (15-20) in position 2 were synthesized and their 5-HT 1A and 5-HT 2A receptor affinities were determined. It was shown that the substituent effects on the 5-HT 2A affinity are additive and could be described quantitatively. In a behavioral model is was also demonstrated that 6-11 are 5-HT 2A receptors antagonists. The molecular modelling results suggested that the distances between the basic nitrogen atom and the two aromatic centers (d 1 = 5.2-8.4 A, d 2 = 5.7-8.5 A, and d 3 = 4.6-7.3 A) define the molecular topography of the 5-HT 2A receptor antagonists under study.

A series of new 3-(ω-aminoalkyl)-5,5-disubstituted hydantoins, containing 1-phenylpiperazine, 1-(o-methoxyphenyl)piperazine or 1,2,3,4-tetrahydroisoquinoline fragments, were synthesized by standard alkylation procedures and their 5-HT 2A receptor affinities were determined. It has been shown that the investigated derivatives are recognized by 5-HT 1A and 5-HT 2A receptors due to the presence of a 1-arylpiperazine fragment; however, the terminal hydantoin moiety plays an important role in stabilization of the receptor-ligand complex. It has also been found that the two 1-phenylpiperazine derivatives 32 and 36 are new, selective 5-HT 2A receptor ligands (K i = 34 and 37 nM, respectively), whereas the derivative of 1-(o-methoxyphenyl)piperazine (38) is a new, highly potent 5-HT 1A receptor ligand (K i = 0.51 nM) with a moderate affinity for 5-HT 2A receptors (K i = 213 nM).