A novel and selective 5-HT2 receptor agonist with ocular hypotensive activity: (S)-(+)-1-(2-aminopropyl)-8,9-dihydropyrano[3,2-e]indole

Serotonin 5-HT2 receptor agonists have recently been shown to be effective in lowering intraocular pressure in nonhuman primates and represent a potential new class of antiglaucoma agents. As part of an effort to identify new selective agonists at this receptor, we have found that (S)-(+)-1-(2-aminopropyl)-8,9-dihydropyrano[3,2-e]indole (AL-37350A, 11) has high affinity and selectivity (>1000-fold) for the 5-HT(2) receptor relative to other 5-HT receptors. More specifically, 11 is a potent agonist at the 5-HT2A receptor (EC50 = 28.6 nM, E(max) = 103%) that is comparable to serotonin. Evaluation of 11 in conscious ocular hypertensive cynomolgus monkeys showed this compound to be efficacious in reducing intraocular pressure (13.1 mmHg, -37%). Thus, 11 is a potent full agonist with selectivity for the 5-HT2 receptor and is anticipated to serve as a useful tool in exploring the role of the 5-HT2 receptor and its effector system in controlling intraocular pressure.     

Thieno[3,2-b]- and thieno[2,3-b]pyrrole bioisosteric analogues of the hallucinogen and serotonin agonist N,N-dimethyltryptamine

The synthesis and biological activity of 6-[2-(N, N-dimethylamino)ethyl]-4H-thieno[3,2-b]pyrrole (3a) and 4-[2-(N, N-dimethylamino)ethyl]-6H-thieno[2,3-b]pyrrole (3b), thienopyrroles as potential bioisosteres of N,N-dimethyltryptamine (1a), are reported. Hallucinogen-like activity was evaluated in the two-lever drug discrimination paradigm using LSD- and DOI-trained rats. Neither 3a nor 3b substituted for LSD or DOI up to doses of 50 micromol/kg. By comparison, 1a fully substituted in LSD-trained rats. However, 3a and 3b fully substituted for the 5-HT1A agonist LY293284 ((-)-(4R)-6-acetyl-4-(di-n-propylamino)-1,3,4, 5-tetrahydrobenz[c,d]indole). Both 3a and 3b induced a brief "serotonin syndrome" and salivation, an indication of 5-HT1A receptor activation. At the cloned human 5-HT2A receptor 3b had about twice the affinity of 3a. At the cloned human 5-HT2B and 5-HT2C receptors, however, 3a had about twice the affinity of 3b. Therefore, thiophene lacks equivalence as a replacement for the phenyl ring in the indole nucleus of tryptamines that bind to 5-HT2 receptor subtypes and possess LSD-like behavioral effects. Whereas both of the thienopyrroles had lower affinity than the corresponding 1a at 5-HT2 receptors, 3a and 3b had significantly greater affinity than 1a at the 5-HT1A receptor. Thus, thienopyrrole does appear to serve as a potent bioisostere for the indole nucleus in compounds that bind to the serotonin 5-HT1A receptor. These differences in biological activity suggest that serotonin receptor isoforms are very sensitive to subtle changes in the electronic character of the aromatic systems of indole compounds.     

Selective, centrally acting serotonin 5-HT2 antagonists. 2. Substituted 3-(4-fluorophenyl)-1H-indoles.

A series of 3-(4-fluorophenyl)-1H-indoles substituted in the 1-position with 4-piperidinyl, 1,2,3,6-tetrahydro-4-pyridinyl, and 4-piperazinyl was synthesized. By variation of the substituents in the benzene part of the indole nucleus in 1-[2-[4-[3-4-fluorophenyl)-1H-indol-1-yl]-1-piperidinyl]-ethyl]-2- imidazolidinones, the highest 5-HT2 receptor affinity and selectivity with respect to dopamine D2 receptors and alpha 1 adrenoceptors were obtained by 5-methyl substitution. Different substituents were introduced in the 1-position of the piperidine ring in the 5-methyl-substituted derivative. Thus replacement of the 2-(2-imidazolidinon-1-yl)ethyl side chain with a 2-(1,3-dimethyl-1-ureido)ethyl or methyl substituent resulted in unchanged affinity and selectivity for 5-HT2 receptors. Replacement with a 2-[3-(2-propyl)-2-imidazolidinon-1-yl]ethyl side chain reduced binding to alpha 1 adrenoceptors with a factor of four, while affinities for 5-HT2 and D2 receptors were retained, compared to the 3-unsubstituted imidazolidinone. Indoles substituted in the 1-position with 4-piperazinyl had generally weaker affinity for both 5-HT2 and D2 receptors compared to corresponding 4-piperidinyl- and 1,2,3,6-tetrahydro-4-pyridinyl-substituted indoles. Introduction of a methyl group in the 2-position of the 5-methyl-substituted indole resulted in further increase of selectivity for the 5-HT2 receptor. Compounds with potent receptor binding also potently inhibited the quipazine-induced head twitch syndrome in rats. The compounds were equally active after oral and subcutaneous administration and showed a long duration of action (> 24 h). In general, the derivatives were found to be considerably more potent at 24 h than at 2 h after the administration. The compounds within this series were prepared as analogues of the previously described 1-(4-fluorophenyl)-3-(4-piperidyl)-1H-indoles by interchange of the C-3 carbon atom and the nitrogen atom in the indole nucleus. The pharmacological results indicate that this isosteric replacement results in higher selectivity for 5-HT2 receptors compared to the former series. The 1-[2-[4-[2,5-dimethyl-3-(4-fluorophenyl)-1H-indol-1-yl]-1- piperidinyl]ethyl]-2-imidazolidinone has high affinity for 5-HT2 receptors (IC50 = 3.4 nM) and extremely low affinity for both dopamine D2 receptors (IC50 = 6900 nM) and alpha 1 adrenoceptors (IC50 = 2300 nM).     

New 3-[4-(3-substituted phenyl)piperazin-1-yl]-1-(benzo[b]thiophen-3-yl)propanol derivatives with dual action at 5-HT1A serotonin receptors and serotonin transporter as a new class of antidepressants

In this paper a series of new 3-[4-(3-substituted phenyl)piperazin-1-yl]-1-(benzo[b]thiophen-3-yl)propanol derivatives is presented as a new class of antidepressant drugs with dual activity at 5-HT1A serotonin receptors and serotonin transporter. The 5-HT1A receptor and 5-HT transporter binding affinities of hydroxylic compounds 4 a-e have been determined. The new compounds present nanomolar affinity for both activities, and 1-(benzo[b]thiophen-3-yl)-3-[4-(3-methoxyphenyl)piperazin-1-yl]propan-1-ol (4d) shows values (nM) of Ki = 86 for 5-HT1A receptors and Ki = 76 for the serotonin transporter, respectively.     

Synthesis and SAR of adatanserin: novel adamantyl aryl- and heteroarylpiperazines with dual serotonin 5-HT(1A) and 5-HT(2) activity as potential anxiolytic and antidepressant agents

Several novel functionalized adamantyl aryl- and heteroarylpiperazine derivatives were prepared and examined in various receptor binding and behavioral tests to determine their serotonin receptor activities. Many compounds demonstrated modest to high affinity for 5-HT(1A) receptors, with compounds 9, 13, 23, 33, 34, and 43 being the most potent at this site. Compound 1, 2-[4-(2-pyrimidinyl)-1-piperazinyl]ethyl adamantyl-1-carboxylate, demonstrated relatively high affinity for 5-HT(1A) receptors (K(i) = 8 nM) and acceptable selectivity versus D(2) receptors (K(i) = 708 mM); however, it lacked in vivo activity in serotonergic behavioral models. In contrast, compounds 9 (WY-50,324, SEB-324, adatanserin), adamantyl-1-carboxylic acid 2-[4-(2-pyrimidinyl)-1-piperazinyl]ethylamide, and 13, adamantyl-1-carboxylic acid 2-[4-(2-methoxyphenyl)-1-piperazinyl]ethylamide, demonstrated high affinity for 5-HT(1A) binding sites (K(i) = 1 nM for both) and moderate affinity for 5-HT(2) receptors (K(i) = 73 and 75 nM, respectively). Both compounds also demonstrated partial 5-HT(1A) agonist activity in vivo in rat serotonin syndrome and 5-HT(2) antagonist activity in quipazine- and DOI-induced head shake paradigms. The selective 5-HT(1A) partial agonist and 5-HT(2) antagonist activity of 9 was accompanied by significant anxiolytic activity in an animal conflict model. On the basis of this profile, compound 9 entered development as a combined anxiolytic and antidepressant agent.     

Design and synthesis of long-chain arylpiperazines with mixed affinity for serotonin transporter (SERT) and 5-HT(1A) receptor

A new generation of antidepressant agents could be represented by compounds with mixed activity as serotonin transporter (SERT) inhibitors and 5-HT(1A) receptor antagonists. We report here on the synthesis and evaluation of SERT and 5-HT(1A) receptor affinity of long-chain arylpiperazines obtained either by modifying 6-nitroquipazine into a long-chain arylpiperazine or by inserting a modified 6-nitroquipazine moiety or other structures endowed with SERT affinity into a long-chain arylpiperazine with 5-HT(1A) affinity. Among the compounds studied, 2-[4-(2-methoxyphenyl)piperazin-1-yl]-N-(6-nitro-2-quinolyl)ethylamine (21) and 1-(5-bromo-1,2,3,4-tetrahydronaphthalen-1-yl)-3-[4-(2-methoxyphenyl)-piperazin-1-yl]-1-propanone (24) showed good affinity values for SERT and 5-HT(1A) receptors (SERT: K(i) (inhibition constant)=71.8 and 62.8 nM; 5-HT(1A)K(i)=14.2 and 0.82 nM, respectively).     

Synthesis, in vitro and in vivo 5-HT1A/5-HT2A serotonin receptor activity of new hybrid 1,2,3,4-tetrahydro-gamma-carbolines with 1-(2-methoxyphenyl)piperazine moiety

A series of 15 new 2-H- and 2-substituted 5-[omega-[4-(2-methoxyphenyl)-piperazinyl]-alkyl]-1,2,3,4-tetrahydro-gamma-carboline derivatives were prepared, and their affinity for 5-HT1A and 5-HT2A serotonin receptors was determined. Most of those hybrid compounds were found to bind with high affinity to 5-HT1A sites (Ki < 50 nM; 2d, 3a, 3b, 3d, 3e, 4b, 4d, 4e) and moreover two of them (4d, 4e) were mixed 5-HT1A/5-HT2A ligands. The results of a lower lip retraction test in rats indicated that the 2-acetyl derivative with a dimethylene spacer (2d) had features of a postsynaptic 5-HT1A receptor agonist, whereas its analogues with longer chains (3d and 4d) behaved like antagonists. Both 5-HT2A receptor ligands (4d, 4e) at high doses inhibited the (+/-)-DOI-induced head twitches in mice and were classified as weak antagonists of those receptors.     

N-Arylsulfonylindole derivatives as serotonin 5-HT(6) receptor ligands.

A series of N(1)-arylsulfonyltryptamines were found to be potent ligands of the human serotonin 5-HT(6) receptor with the 5-methoxy-1-benzenesulfonyl analogue (19) having the highest affinity. Additionally, it was discovered that a group such as 3-(3-methoxybenzyl)-1,2,4-oxadiazol-5-yl in the 2-position of the indole ring (43) can replace the arylsulfonyl substituent in the 1-position with no loss of affinity. This suggested that the binding conformation of the aminoethyl side chain at this receptor was toward the 4-position of the indole ring and was supported by the fact that the 4-(aminoethyl)indoles (45) also displayed high affinity, as did the conformationally rigid 1,3,4,5-tetrahydrobenz[c,d]indole (49). Molecular modeling showed that 19, 43, and 45 all had low-energy conformers that overlaid well onto 49. Both 19 and 49 had good selectivity over other serotonin receptors tested, with 49 also showing excellent selectivity over all dopamine receptors. In a functional adenylate cyclase stimulation assay, 19 and 49 had no agonist activity, whereas 45 behaved as a partial agonist. Finally, it was shown that 19 had good activity in the 5-HT(2A) centrally mediated mescaline-induced head twitch assay, which implies that it is brain-penetrant.     

Benzofuran bioisosteres of hallucinogenic tryptamines.

The benzofuran analogues of the hallucinogens 5-methoxy-N,N-dimethyltryptamine and 5-methoxy-alpha-methyltryptamine were synthesized and evaluated for affinity at the serotonin 5-HT2 and 5-HT1A receptors in rat brain homogenate, labeled with [125I]-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane ([125I]DOI) and [3H]-8-hydroxy-2-(N,N-di-n-propylamino)tetralin ([3H]-8-OH-DPAT), respectively. At the 5-HT2 receptor, the benzofurans had slightly decreased affinities, approximately one-third and one-sixth those of the indoles, for the primary amines and the tertiary amines, respectively. The benzofurans also had lower affinity at the 5-HT1A receptor, but decreased only about 20-30% from that of the indole isosteres. Thus, the 5-HT1A receptor is less discriminating with respect to preference for an indole versus a benzofuran, although all of the compounds did have higher affinities for the 5-HT2 receptor than for the 5-HT1A receptor. It is suggested that benzofurans may be useful in the design of serotonin receptor ligands.     

Synthesis and 5-hydroxytryptamine antagonist activity of 2-[[2-(dimethylamino)ethyl]thio]-3-phenylquinoline and its analogues

A series of 2-[(2-aminoethyl)thio]quinolines substituted at the 3-position with alkyl, aryl, or heteroaryl groups has been prepared in the search for novel and selective 5-HT2 antagonists. The affinity of the compounds for 5-HT1 receptor sites was measured by their ability to displace [3H]-5-HT from rat brain synaptosomes whereas the affinity for 5-HT2 receptor sites was measured by their ability to displace [3H]spiperone from synaptosomes prepared from rat brain cortex. The 5-HT2 antagonist properties of the compounds were measured in vivo by their antagonism of 5-hydroxytryptophan-induced head twitches in the mouse and by their antagonism of hyperthermia induced by fenfluramine (N-ethyl-alpha-methyl-m-(trifluoromethyl)phenethylamine hydrochloride) in the rat. The structure-activity relationships in this series are discussed and the properties of 2-[[2-(dimethylamino)ethyl]thio]-3-phenylquinoline hydrochloride (70) are highlighted.     

Selective, centrally acting serotonin 5-HT2 antagonists. 1. 2- and 6-substituted 1-phenyl-3-(4-piperidinyl)-1H-indoles.

A series of 1-[2-[4-(1H-indol-3-yl)-1-piperidinyl]ethyl]-2-imidazolidinones has been synthesized. The 1-position of the indole is substituted with phenyl groups and in the 2- or 6-positions are additional substituents. An analogous series with the imidazolidinone ring opened to corresponding urea derivatives was also prepared. High potency and selectivity for 5-HT2 receptors (as compared with D2 and alpha 1 receptor affinities) were obtained with medium-large substituents such as 6-chloro, 6-methyl, and 6-trifluoromethyl or a 2-methyl substituent. Larger 6-substituents such as isopropyl considerably reduced activity, while the smaller 6-fluoro substituent afforded unselective compounds. Selective 5-HT2 antagonists were found by combining 6-substitution with both unsubstituted 1-phenyl and substituted 1-phenyl groups (2-F, 4-F, 4-Cl). However, 3-substitution of the phenyl group markedly reduced 5-HT2 receptor affinity, especially with a 3-trifluoromethyl substituent. Introduction of a 3-(2-propyl) substituent in the imidazolidinone ring reduced binding to alpha 1 adrenoceptors with a factor of 3-8. Practically no influence on 5-HT2 and D2 receptor affinities were found by the presence of this substituent compared to the 3-unsubstituted derivatives. Compounds with potent receptor binding also potently inhibited the quipazine-induced head twitch syndrome in rats. The compounds were equally active after oral and subcutaneous administration and they had a long duration of action (> 24 h). Especially urea derivatives were found to be considerably more potent at 24 h than at 2 h after subcutaneous administration. Some of the compounds potently inhibited isolation-induced aggression in mice, an effect which, however, did not correlate to 5-HT2 receptor-mediated activities. On the basis of these structure-activity studies 1-[2-[4-[6-chloro-1-(4-fluorophenyl)-1H-indol-3-yl]-1- piperidinyl]ethyl]-3-(2-propyl)-2-imidazolidinone (Lu 26-042, compound 4c) was selected for further pharmacological and toxicological investigations.     

Selectivity of serotonergic drugs for multiple brain serotonin receptors. Role of [3H]-4-bromo-2,5-dimethoxyphenylisopropylamine ([3H]DOB), a 5-HT2 agonist radioligand

The affinities of putative serotonin receptor agonists and antagonists for 5-HT1A, 5-HT1B, 5-HT1C, and 5-HT2 receptors were assayed using radioligand binding assays. The 5-HT1 sites were labeled with the agonist radioligands [3H]-8-hydroxy-2-(di-n-propylamino)-tetralin [3H]-8-OH-DPAT, [3H]-5-HT, and [3H]mesulergine. The 5-HT2 receptor was labeled with the antagonist radioligand [3H]ketanserin or the agonist radioligand [3H]-4-bromo-2,5-dimethoxyphenylisopropylamine ([3H]DOB). The apparent 5-HT1 receptor selectivity of agonist compounds was found to be 50- to 100-fold higher when the 5-HT2 receptor affinity was determined using the antagonist radioligand [3H]ketanserin than when the agonist radioligand [3H]DOB was used. Quipazine, a putative specific 5-HT2 agonist, appeared to be only 3-fold more potent at 5-HT2 than at 5-HT1A receptors when [3H]ketanserin was used as the 5-HT2 radioligand. When [3H]DOB was used as the 5-HT2 radioligand, quipazine was determined to be 100-fold more potent at 5-HT2 receptors than at 5-HT1A receptors. 1-(3-trifluoromethylphenyl)piperazine (TFMPP), a putative specific 5-HT1B receptor agonist was apparently 10-fold more potent at 5-HT1B receptors than at 5-HT2 receptors when [3H]ketanserin was used as the 5-HT2 radioligand. When [3H]DOB was used as the 5-HT2 radioligand, TFMPP was found to be equipotent at 5-HT1B and 5-HT2 receptors. Using the 5-HT2 antagonist radioligand [3H]ketanserin, a similar pattern of underestimating 5-HT2 receptor selectivity and/or overestimating 5-HT1A or 5-HT1B receptor selectivity was observed for a series of serotonin receptor agonists. Antagonist receptor selectivity was not affected significantly by the nature of the 5-HT2 receptor assay used. These data indicate that, by using an antagonist radioligand to label 5-HT2 receptors and agonist radioligands to label 5-HT1 receptors, the 5-HT1 receptor selectivity may be overestimated. This may be an especially severe problem in serotonin drug development as drugs that interact potently with 5-HT2 receptors have been reported to be psychoactive and/or hallucinogenic.     

Binding of beta-carbolines and related agents at serotonin (5-HT(2) and 5-HT(1A)), dopamine (D(2)) and benzodiazepine receptors

A large series of beta-carbolines was examined for their ability to bind at [3H]agonist-labeled 5-HT(2A) serotonin receptors. Selected beta-carbolines were also examined at 5-HT(2C) serotonin receptors, 5-HT(1A) serotonin receptors, dopamine D(2) receptors, and benzodiazepine receptors. Indolealkylamines and phenylisopropylamines were also evaluated in some of these binding assays. The beta-carbolines were found to bind with modest affinity at 5-HT(2A) receptors, and affinity was highly dependent upon the presence of ring substituents and ring saturation. The beta-carbolines displayed little to no affinity for 5-HT(1A) serotonin receptors, dopamine D(2) receptors and, with the exception of beta-CCM, for benzodiazepine receptors. Examples of beta-carbolines, indolealkylamines (i.e. N,N-dimethyltryptamine analogs), and phenylisopropylamines have been previously shown to produce common stimulus effects in animals trained to discriminate the phenylisopropylamine hallucinogen DOM (i.e. 1-(2, 5-dimethoxy-4-methylphenyl)-2-aminopropane) from vehicle. Although the only common receptor population that might account for this action is 5-HT(2A), on the basis of a lack of enhanced affinity for agonist-labeled 5-HT(2A) receptors, as well as on their lack of agonist action in the PI hydrolysis assay, it is difficult to conclude that the beta-carbolines behave in a manner consistent with that of other classical hallucinogens.     

2-[4-[3-(4-aryl/heteroaryl-1-piperazinyl)propoxy]phenyl]-2H- benzotriazoles and their N-oxides as ligands for serotonin and dopamine receptors.

A small set of 2-{4-[3-(4-aryl/heteroaryl-piperazinyl)propoxy]phenyl}-2H-benzo tri azoles and corresponding N-oxides were prepared. The synthesized compounds were able to bind on some serotonin (5-HT1A, 5-HT2A) and dopamine (D2, D3) receptors, while displaying poor or no affinity for 5-HT1B, 5-HT2C, 5-HT3, and 5-HT4 subtypes. The strong contribution of the N-oxide function for the binding on 5-HT1A, D2 and D3 receptors is noteworthy. For 2-{4-[3-[4-(2-methoxyphenyl)-1-piperazinyl]propoxy]phenyl}-2H-benzotr iazole- 1-oxide (4b), the binding constants (Ki) were 11.9 (5-HT1A) and 10.5 nM (D3). In a general pharmacological screening, the 2-{4-[3-(4-phenyl-1-piperazinyl)propoxy]phenyl}-2H-benzotriazole (3a) exhibited only very weak activities, with the exception of protecting mice from cyanide-induced hypoxia.     

Novel potent 5-HT(1F) receptor agonists: structure-activity studies of a series of substituted N-[3-(1-methyl-4-piperidinyl)-1H-pyrrolo[3,2-b]pyridin-5-yl]amides

Compound 1a (LY334370), a selective 5-HT(1F) receptor agonist (SSOFRA), inhibited dural inflammation in the neurogenic plasma protein extravasation model of migraine and demonstrated clinical efficacy for the acute treatment of migraine. Although 1a was greater than 100-fold selective over both the 5-HT(1B) and 5-HT(1D) receptors, it exhibited appreciable 5-HT(1A) receptor affinity. Described here is the synthesis and evaluation of a series of pyrrolo[2,3-c]pyridine and pyrrolo[3,2-b]pyridine (2a and 3a) as well as pyrrolo[3,2-d]pyrimidine (4a) analogues of 1a, compounds prepared in an effort to identify SSOFRAs with improved selectivity over other 5-HT(1) receptor subtypes. The pyrrolo[3,2-b]pyridine analogue 3a showed high 5-HT(1F) receptor affinity but offered no improvement in selectivity compared to 1a. However, the C-5 acetamide derivative, 3b, was greater than 100-fold selective over the 5-HT(1A), 5-HT(1B), and 5-HT(1D) receptors. SAR studies of this series determined that alkylamides in particular exhibited high selectivity for the 5-HT(1F) receptor. Replacement at C-5 with other substituents decreased affinity or selectivity. These SAR studies identified SSOFRAs that demonstrated oral activity in the neurogenic plasma protein extravasation model, a model indicative of antimigraine activity.     

Synthesis and pharmacological characterization of a series of geometrically constrained 5-HT(2A/2C) receptor ligands

In studies of the SAR of phenethylamine-type serotonin 5-HT(2A) receptor agonists, substituted conformationally constrained tetrahydronaphthofurans were designed to investigate the optimal conformation of the 2-aminoethyl moiety. These compounds were tested using in vitro assays for affinity at 5-HT(1A), 5-HT(2A), and 5-HT(2C) receptors. The benzofuran-containing analogues, 6a and 6b, had significantly higher affinity for the 5-HT receptors tested than did the benzodihydrofuran-containing compounds, 4a, 4b, 5a, and 5b. The most potent compound (8-bromo-6-methoxy-4,5-dihydro-3H-naphtho[1,8-bc]furan-5-yl)aminomethane, 6b, had K(i) values for displacement of [(125)I]-DOI from 5-HT(2A) and 5-HT(2C) cloned rat receptors of 2.6 and 1.1 nM, respectively. Despite their high affinity, the compounds of this naphthofuran series lacked high intrinsic activity at the 5-HT(2A) receptor as measured using the phosphoinositide hydrolysis assay. The most potent compound in vitro, 6b, was tested in the two-lever drug discrimination assay in rats trained to discriminate LSD from saline, and failed to substitute, a result typical for compounds with low intrinsic activity. Thus, although conformational constraint has led to high-affinity 5-HT(2A) ligands with partial agonist activity, all of the spatial and steric properties of the ligand necessary for full receptor activation have not yet been identified.     

New serotonin 5-HT(2A), 5-HT(2B), and 5-HT(2C) receptor antagonists: synthesis, pharmacology, 3D-QSAR, and molecular modeling of (aminoalkyl)benzo and heterocycloalkanones.

A series of 52 conformationally constrained butyrophenones have been synthesized and pharmacologically tested as antagonists at 5-HT(2A), 5-HT(2B), and 5-HT(2C) serotonin receptors, useful for dissecting the role of each 5-HT(2) subtype in pathophysiology. These compounds were also a consistent set for the identification of structural features relevant to receptor recognition and subtype discrimination. Six compounds were found highly active (pK(i) > 8.76) and selective at the 5-HT(2A) receptor vs 5-HT(2B) and/or 5-HT(2C) receptors. Piperidine fragments confer high affinity at the 5-HT(2A) receptor subtype, with benzofuranone- and thiotetralonepiperidine as the most selective derivatives over 5-HT(2C) and 5-HT(2B) receptors, respectively; K(i) (2A/2C) and/or K(B) (2A/2B) ratios greater than 100 were obtained. Compounds showing a more pronounced selectivity at 5-HT(2A)/5-HT(2C) than at 5-HT(2A)/5-HT(2B) bear 6-fluorobenzisoxazolyl- and p-fluorobenzoylpiperidine moieties containing one methylene bridging the basic piperidine to the alkanone moiety. An ethylene bridge between the alkanone and the amino moieties led to ligands with higher affinities for the 5-HT(2B) receptor. Significant selectivity at the 5-HT(2B) receptor vs 5-HT(2C) was observed with 1-1[(1-oxo-1,2,3,4-tetrahydro-3-naphthyl)methyl]-4-[3-(p-fluorobenzoyl)propyl]piperazine (more than 100-fold higher). Although piperidine fragments also confer higher affinity at 5-HT(2C) receptors, only piperazine-containing ligands were selective over 5-HT(2A). Moderate selectivity was observed at 5-HT(2C) vs 5-HT(2B) (10-fold) with some compounds bearing a 4-[3-(6-fluorobenzisoxazolyl)]piperidine moiety in its structure. Molecular determinants for antagonists acting at 5-HT(2A) receptors were identified by 3D-QSAR (GRID-GOLPE) studies. Docking simulations at 5-HT(2A) and 5-HT(2C) receptors suggest a binding site for the studied type of antagonists (between transmembrane helices 2, 3, and 7) different to that of the natural agonist serotonin (between 3, 5, and 6).     

2-Substituted tryptamines: agents with selectivity for 5-HT(6) serotonin receptors

Several 2-alkyl-5-methoxytryptamine analogues were designed and prepared as potential 5-HT(6) serotonin agonists. It was found that 5-HT(6) receptors accommodate small alkyl substituents at the indole 2-position and that the resulting compounds can bind with affinities comparable to that of serotonin. In particular, 2-ethyl-5-methoxy-N, N-dimethyltryptamine (8) binds with high affinity at human 5-HT(6) receptors (K(i) = 16 nM) relative to 5-HT (K(i) = 75 nM) and was a full agonist, at least as potent (8: K(act) = 3.6 nM) as serotonin (K(act) = 5.0 nM), in activating adenylate cyclase. Compound 8 displays modest affinity for several other populations of 5-HT receptors, notably h5-HT(1A) (K(i) = 170 nM), h5-HT(1D) (K(i) = 290 nM), and h5-HT(7) (K(i) = 300 nM) receptors, but is otherwise quite selective. Compound 8 represents the first and most selective 5-HT(6) agonist reported to date. Replacing the 2-ethyl substituent with a phenyl group results in a compound that retains 5-HT(6) receptor affinity (i.e., 10: K(i) = 20 nM) but lacks agonist character. 2-Substituted tryptamines, then, might allow entry to a novel class of 5-HT(6) agonists and antagonists.     

New 3-[4-(2,3-dihydro-14-benzodioxin-5-yl)piperazin-1-yl]-1-(5-substituted benzo[b]thiophen-3-yl)propanol derivatives with dual action at 5-HT(1A) serotonin receptors and serotonin transporter as a new class of antidepressants

Compounds derived from 2,3-dihydro-(1,4-benzodioxin-5-yl)piperazine and benzo[b]thiophene with different substituents in 5 position (H, F, NO2, NH2, CH3 and OH) have been synthesized in order to obtain new dual antidepressant drugs. The final compounds were evaluated for in vitro 5-HT(1A) receptor affinity and serotonin reuptake inhibition by radioligand assays. Compounds 1-(5-nitrobenzo[b]thiophen-3-yl)-3-[4-(2,3-dihydro-1,4-benzodioxin-5-yl)piperazin-1-yl]propan-1-ol (4c) (Ki = 6.8 for 5-HT(1A) receptor and Ki = 14 for 5-HT transporter) and 1-(5-hydroxybenzo[b]thiophen-3-yl)-3-[4-(2,3-dihydro-1,4-benzodioxin-5-yl)piperazin-1-yl] propan-1-ol (4f) (Ki = 6.2 for 5-HT(1A) receptor and Ki = 18.2 for 5-HT transporter) showed the best results for both activities.     

Analogues of the 5-HT1A serotonin antagonist 1-(2-methoxyphenyl)-4-[4-(2-phthalimido)butyl]piperazine with reduced alpha 1-adrenergic affinity.

1-(2-Methoxyphenyl)-4-[4-(2-phthalimido)butyl]piperazine (NAN-190; 1a) is a putative postsynaptic 5-HT1A serotonin antagonist. This high affinity ligand (Ki = 0.6 nM), although selective for 5-HT1A versus other 5-HT receptors, binds with nearly equal affinity at alpha 1-adrenergic receptors (Ki = 0.8 nm). Structure-affinity relationship studies were conducted in order to achieve an improved selectivity. Replacement of the phthalimide moiety by substituted benzamides led to retention of 5-HT1A affinity but to no improvement in selectivity, whereas replacement by alkyl amides proved beneficial, leading to an improvement in affinity and selectivity. Branching alpha to the amide carbonyl group and increased bulkiness of the alkyl moiety further improved 5-HT1A affinity and selectivity. 4-[4-(1-Adamantanecarboxamido)butyl]-1- (2-methoxyphenyl)piperazine (2j) was found to bind at 5-HT1A sites with high affinity (Ki = 0.4 nM) and with a 160-fold selectivity over alpha 1-adrenergic sites. Preliminary studies show that this agent retains antagonist activity as determined in a 5-HT1A-coupled adenylyl cyclase assay. Further functional studies are warranted to fully characterize this agent.