Asymmetric total synthesis and identification of tetrahydroprotoberberine derivatives as new antipsychotic agents possessing a dopamine D1, D2 and serotonin 5-HT1A multi-action profile

An effective and rapid method for the microwave-assisted preparation of the key intermediate for the total synthesis of tetrahydroprotoberberines (THPBs) including l-stepholidine (l-SPD) was developed. Thirty-one THPB derivatives with diverse substituents on A and D ring were synthesized, and their binding affinity to dopamine D₁, D₂ and serotonin 5-HT_1A and 5-HT_2A receptors were determined. Compounds 18k and 18m were identified as partial agonists at the D₁ receptor with K_i values of 50 and 6.3 nM, while both compounds act as D₂ receptor antagonists (K_i = 305 and 145 nM, respectively) and 5-HT_1A receptor full agonists (K_i = 149 and 908 nM, respectively). These two THPBs compounds exerted antipsychotic actions in animal models. Further electrophysiological studies employing single-unit recording in intact animals demonstrated that 18k-excited dopaminergic (DA) neurons are associated with its 5-HT_1A receptor agonistic activity. These results suggest that these two compounds targeted to multiple neurotransmitter receptors may present novel lead drugs with new pharmacological profiles for the treatment of schizophrenia.     

Synthesis and biological evaluation of a series of benzoxazole/benzothiazole-containing 2,3-dihydrobenzo[b][1,4]dioxine derivatives as potential antidepressants

A series of benzoxazole/benzothiazole-2,3-dihydrobenzo[b][1,4]dioxine derivatives (5a–5d and 8a–8j) was synthesized. Compounds were evaluated for binding affinities at the 5-HT_1A and 5-HT_2A receptors. Antidepressant activities of the compounds were screened using the forced swimming test (FST) and the tail suspension test (TST). The results indicated that the compounds exhibited high affinities for the 5-HT_1A and 5-HT_2A receptors and showed a marked antidepressant-like activity. Compound 8g exhibited high affinities for the 5-HT_1A (K_i = 17 nM) and 5-HT_2A (K_i = 0.71 nM) receptors; it also produced a decrease of the immobility time and exhibited potent antidepressant-like effects in the FST and TST in mice.     

The synthesis and comparative receptor binding affinities of novel,isomeric pyridoindolobenzazepine scaffolds

Compounds 7, 8, and 9, derived from the novel scaffolds 3, 5, and 6, were synthesized and evaluated in vitro. The b,c → c,d shift of the E-phenyl ring resulted in a large decrease (ca. 20- to 1000-fold) in binding to the 5-HT_2A, 5-HT_2C and H₂, receptors, and a modest decrease (ca. 10- to 20-fold) in binding to the 5-HT_5A, D₂, D₅, and α_1D, receptors. The b,c → d,e shift resulted in a large decrease in binding to the 5-HT_1D, 5-HT_2C, 5-HT₆, and H₁ receptors, a modest decrease in binding to 5-HT_1A, 5-HT_5A and D₂, D₅, α_2B, and H₂ receptors, and a large increase in affinity to the 5-HT₃, 5-HT₆, and σ₁ receptors.     

Dopamine D1 receptor and serotonin 5-HT1A receptor agonist effects of the natural product (–)-stepholidine: molecular modelling and dynamics simulations

In this study, by homology modelling and molecular dynamics (MD) simulation, models of l-stepholidine (l-SPD) activating the 5-HT_1A and D₁ receptors were constructed. In 100-ns MD simulations, the D₁ and 5-HT_1A receptors were activated by the partial agonist l-SPD, conforming with the global toggle switch activation model and the sequential activation model. The residues Y^7.53 and Y^5.58 swing significantly between different transmembrane (TM) domains after activation. Similarities between D₁ and 5-HT_1A included (1) the outward motion of TM-5; (2) the ionic lock was independent of the tilt of TM-6 and (3) there was an apparent bending of TM-6, and the ring of l-SPD formed strong π–π interactions with residue W^6.48. Differences between the two included the following: (1) in 5-HT_1A, l-SPD formed a hydrogen bond with Ala172^5.46 of TM-5, and the intracellular end of TM-5 moved outward slowly; that hydrogen bond did not form with the D₁ receptor; (2) l-SPD formed stronger interactions with D^3.32 and W^6.48 in the D₁ receptor than in the 5-HT_1A receptor and (3) the hydrogen bonding network was somewhat different in SPD-5-HT_1A and SPD-D₁ receptors. We propose the interaction between l-SPD and D^3.32 or/and W^6.48 is the original driving force during the whole activation process.     

Synthesis and biological investigation of new equatorial (β) stereoisomers of 3-aminotropane arylamides with atypical antipsychotic profile

A series of novel 3β-aminotropane derivatives containing a 2-naphthalene or a 2-quinoline moiety was synthesised and evaluated for their affinity for 5-HT_1A, 5-HT_2A and D₂ receptors. Their affinity for the receptors was in the nanomolar to micromolar range. p-Substitution (6c, 6f, 6i, 6l, 6o), as well as substitution with chlorine atoms (6g, 6h, 6i), led to a significant increase in binding affinity for D₂ receptors with compounds 6f (K_i = 0.6 nM), 6c and 6i (K_i = 0.4 nM), having the highest binding affinities. m-Substituted derivatives were the most promising ligands in terms of 5-HT_2A receptor binding affinity whereas 2-quinoline derivatives (10a, 10b) displayed the highest affinity for 5-HT_1AR and were the most selective ligands with K_i = 62.7 nM and K_i = 30.5 nM, respectively. Finally, the selected ligands 6b, 6d, 6e, 6g, 6h, 6k, 6n and 6o, with triple binding activity for the D₂, 5-HT_1A and 5-HT_2A receptors, were subjected to in vivo tests, such as those for induced hypothermia, climbing behaviour and the head twitch response, in order to determine their pharmacological profile. The tested ligands presented neither agonist nor antagonist properties for the 5-HT_1A receptors in the induced hypothermia and lower lip retraction (LLR) tests. All tested compounds displayed antagonistic activity against 5-HT_2A, with 6n and 6o being the most active. Four (6b, 6k, 6n and 6o) out of eight tested compounds could be classified as D₂ antagonists. Additionally, evaluation of metabolic stability was performed for selected ligands, and introduction of halogen atoms into the benzene ring of 6h, 6k, 6n and 6o improved their metabolic stability. The project resulted in the selection of the lead compounds 6n and 6o, which had antipsychotic profiles, combining dopamine D₂-receptor and 5-HT_2A antagonism and metabolic stability.     

Exploring the 2- and 5-positions of the pyrazolo[4,3-d]pyrimidin-7-amino scaffold to target human A1 and A2A adenosine receptors

A new series of 7-aminopyrazolo[4,3-d]pyrimidine derivatives (1–31) were synthesized to evaluate some structural modifications at the 2- and 5-positions aimed at shifting affinity towards the human (h) A_2A adenosine receptor (AR) or both hA_2A and hA₁ ARs. The most active compounds were those featured by a 2-furyl or 5-methylfuran-2-yl moiety at position 5, combined with a benzyl or a substituted-benzyl group at position 2. Several of these derivatives (22–31) displayed nanomolar affinity for the hA_2A AR (K_i = 3.62–57 nM) and slightly lower for the hA₁ ARs, thus showing different degrees (3–22 fold) of hA_2A versus hA₁ selectivity. In particular, the 2-(2-methoxybenzyl)-5-(5-methylfuran-2-yl) derivative 25 possessed the highest hA_2A and hA₁ AR affinities (K_i = 3.62 nM and 18 nM, respectively) and behaved as potent antagonist at both these receptors (cAMP assays). Its 2-(2-hydroxybenzyl) analog 26 also showed a high affinity for the hA_2A AR (K_i = 5.26 nM) and was 22-fold selective versus the hA₁ subtype. Molecular docking investigations performed at the hA_2A AR crystal structure and at a homology model of the hA₁ AR allowed us to represent the hypothetical binding mode of our derivatives and to rationalize the observed SARs.     

New dual ligands for the D2 and 5-HT1A receptors from the group of 1,8-naphthyl derivatives of LCAP

More than 300 million people are suffering from depression, one of the civilization diseases in the 21st century. Serotonin 5-HT_1AR and dopamine D₂R play an important role in the treatment and pathogenesis of depression. Moreover, in recent years, the efficacy of dual 5-HT_1A/D₂ receptors ligands has been demonstrated in the fight against depression. In this work the new bulky arylpiperazine derivatives (LCAP) were synthesized in microwave radiation field. The affinities for the selected serotonin (5-HT_1A,5-HT_2A,5-HT₆,5-HT₇) and dopamine (D₂) receptors have been evaluated in vitro. Compounds 5.3a, 5.4, 5.1c, 5.3d, 5.2a are promising dual 5-HT_1AR/D₂R ligands. The SAR analysis were additionally supported with molecular docking studies.     

Chemical puzzles in the search for new,flexible derivatives of lurasidone as antipsychotic drugs

In the pharmacotherapy of schizophrenia, there is a lack of effective drugs, and currently used agents cause a large number of side effects. The D₂, 5-HT_1A, 5-HT_2A receptors are among the most important receptor targets in the treatment of schizophrenia, but antagonism at 5-HT₆ and 5-HT₇ receptors may bring about additional improvement of cognitive functions. However, doubt exists regarding the importance of 5-HT₇R in the pharmacotherapy. In 2010, lurasidone (with high affinity for D₂, D₃, 5-HT_1A, 5-HT_2A, 5-HT₇ receptors) was approved for the treatment of schizophrenia. Due to the efficacy of the mentioned drug and doubts related to the role of 5-HT₇R, we decided to obtain compounds with an activity profile similar to that of lurasidone, but with the reduced affinity for 5-HT₇R and increased affinity for 5-HT₆R. For this purpose, we chose a flexible hexyl derivative of lurasidone (2-(6-(4-(benzo[d]isothiazol-3-yl)piperazin-1-yl)hexyl)hexahydro-1H-4,7-methanoisoindole-1,3(2H)-dione 1a) as a hit structure. After molecular modeling, we modified it, in the area of the arylpiperazine and imide group, using the moieties found in other known CNS drugs. We received the compounds in accordance with the previously developed method of ecological synthesis in the microwave radiation field. Among the obtained compounds, N-(6-(4-(benzo[d]isothiazol-3-yl)piperazin-1-yl)hexyl)naphthalene-sulfonamides 1v and 1w were distinguished as multifunctional ligands showing increased affinity for 5-HT₆R, and 2-(6-(4-(benzo[d]isothiazol-3-yl)piperazin-1-yl)hexyl)-[1,2,4]triazolo[4,3-a]pyridin-3(2H)-one 1i – a multifunctional ligand showing moderate affinity for 5-HT₆R and threefold lower for 5-HT₇R. In the paper, we discuss some of the observed dependencies regarding 5-HT₆/5-HT₇R affinity using molecular docking methods.     

Synthesis and biological study of 3-(phenylsulfonyl)thieno[2,3-e][1,2,3]triazolo[1,5-a]pyrimidines as potent and selective serotonin 5-HT6 receptor antagonists

A number of 3-(phenylsulfonyl)thieno[2,3-e][1,2,3]triazolo[1,5-a]pyrimidines were prepared and their 5-HT₆ receptor binding affinity and ability to inhibit the functional cellular responses to serotonin were evaluated. 3-[(3-Chlorophenyl)sulfonyl]-N-(tetrahydrofuran-2-ylmethyl)thieno[2,3-e][1,2,3]triazolo[1,5-a]pyrimidin-5-amine 2{5,26} appeared to be the most active in a functional assay (IC₅₀ = 29.0 nM) and 3-(phenylsulfonyl)-N-(2-thienylmethyl) thieno[2,3-e][1,2,3]triazolo[1,5-a]pyrimidin-5-amine 2{1,28} demonstrated the greatest affinity in a 5-HT₆ receptor radioligand binding assay (K_i = 1.7 nM). A screening of 5-HT_2A and 5-HT_2B receptor affinity revealed that 3-(phenylsulfonyl)thieno[2,3-e][1,2,3]triazolo[1,5-a]pyrimidines are highly selective 5-HT₆ receptor ligands.     

New 5-HT1A receptor ligands containing a N′-cyanoisonicotinamidine nucleus: Synthesis and in vitro pharmacological evaluation

N′-Cyanoisonicotinamidine derivatives, linked to an arylpiperazine moiety, were prepared to identify highly selective and potent 5-HT_1A ligands as potential pharmacological tools in studies of wide spread psychiatric disorders. The combination of structural elements (heterocyclic nucleus, alkyl chain and 4-substituted piperazine) known to be critical in order to have affinity on 5-HT_1A receptor and the proper selection of substituents led to compounds with high specificity and affinity towards serotoninergic receptors. In binding studies, several molecules showed affinity in nanomolar and subnanomolar range at 5-HT_1A and moderate to no affinity for other relevant receptors (5-HT_2A, 5-HT_2C, D₁, D₂, α₁ and α₂). N′-Cyano-N-(3-(4-(pyridin-2-yl)piperazin-1-yl)propyl)isonicotinamidine (4o) with K_i = 0.038 nM, was the most active and selective derivative for the 5-HT_1A receptor with respect to other serotoninergic, dopaminergic and adrenergic receptors.     

Synthesis and pharmacological evaluation of new arylpiperazines N-{4-[4-(aryl) piperazine-1-yl]-phenyl}-amine derivatives: Putative role of 5-HT1A receptors

In an attempt to design novel 5-HT_1A agonists/partial agonists, based on an arylpiperazine nucleus, a series of N-{4-[4-(aryl)piperazine-1-yl]-phenyl}-amine derivatives were synthesized and biologically tested. The anxiolytic effect of the compounds was investigated employing the Elevated plus Maze (EPM) task. On the basis of in vivo functional test, compound 1c (3 mg/kg) and 4c (3 mg/kg) induced significant increments in open arm entries and time on EPM as compared to Buspirone. The anxiolytic effects of compounds 1c and 4c were effectively antagonized by WAY-100635, a 5-HT_1A receptor antagonist (0.5 mg/kg). Furthermore, we have also evaluated the concentration of 5-HT in the brain tissue using HPLC with fluorescent detection. Our result showed that serotonin levels were significantly decreased by ～38% (p < 0.001) and ～32% (p < 0.001) after acute administration of compounds 1c and 4c, respectively. These findings suggest that the anxiolytic like activity of these new arylpiperazines is mediated via 5-HT_1A receptors in the brain.     

Synthesis and pharmacological characterization of novel xanthine carboxylate amides as A2A adenosine receptor ligands exhibiting bronchospasmolytic activity

The carboxylate amides of 8-phenyl-1,3-dimethylxanthine described herein represent a new series of selective ligands of the adenosine A_2A receptors exhibiting bronchospasmolytic activity. The effects of location of 8-phenyl substitutions on the adenosine receptor (AR) binding affinities of the newly synthesized xanthines have also been studied. The compounds displayed moderate to potent binding affinities toward various adenosine receptor subtypes when evaluated through radioligand binding studies. However, most of the compounds showed the maximum affinity for the A_2A subtype, some with high selectivity versus all other subtypes. Xanthine carboxylate amide 13b with a diethylaminoethylamino moiety at the para-position of the 8-phenylxanthine scaffold was identified as the most potent A_2A adenosine receptor ligand with K_i = 0.06 μM. Similarly potent and highly A_2A-selective are the isovanillin derivatives 16a and 16d. In addition, the newly synthesized xanthine derivatives showed good in vivo bronchospasmolytic activity when tested in guinea pigs.     

Synthesis and SAR of (piperazin-1-yl-phenyl)-arylsulfonamides: A novel series of atypical antipsychotic agents

(Piperazin-1-yl-phenyl)-arylsulfonamides were synthesized and identified to show high affinities for both 5-HT_2C and 5-HT₆ receptors. Among them, naphthalene-2-sulfonic acid isopropyl-[3-(4-methyl-piperazin-1-yl)-phenyl]-amide (6b) exhibits the highest affinity towards both 5-HT_2C (IC₅₀ = 4 nM) and 5-HT₆ receptors (IC₅₀ = 3 nM) with good selectivity over other serotonin (5-HT_1A, 5-HT_2A, and 5-HT₇) and dopamine (D₂–D₄) receptor subtypes. In 5-HT_2C and 5-HT₆ receptor functional assays, this compound showed considerable antagonistic activity for both receptors.     

Synthesis and structure–activity relationships of new carbonyl guanidine derivatives as novel dual 5-HT2B and 5-HT7 receptor antagonists

To identify potent dual 5-HT_2B and 5-HT₇ receptor antagonists, we synthesized a series of novel carbonyl guanidine derivatives and examined their structure–activity relationships. Among these compounds, N-(9-hydroxy-9H-fluorene-2-carbonyl)guanidine (10) had a good in vitro profile, that is, potent affinity for human 5-HT_2B and 5-HT₇ receptor subtypes (K_i = 1.8 nM and K_i = 17.6 nM, respectively) and high selectivity over 5-HT_2A, 5-HT_2C, α₁, D₂ and M₁ receptors. Compound 10 also showed a suppressing effect on 5-HT-induced dural protein extravasation in guinea pigs when orally administered.     

Development of CNS multi-receptor ligands: Modification of known D2 pharmacophores

Several known D₂ pharmacophores have been explored as templates for identifying ligands with multiple binding affinities at dopamine and serotonin receptors considered as clinically relevant receptors in the treatment of neuropsychiatric diseases. This approach has resulted in the identification of ligands that target multiple CNS receptors while avoiding others associated with deleterious effects. In particular, compounds 11, 15 and 22 may have potential for further development as antipsychotic agents as they favorably interact with the clinically relevant receptors including D₂R, 5-HT_1AR, and 5-HT₇R. We have also identified the pair of compounds 11 and 10 as high affinity D₂R ligands with and without SERT binding affinities, respectively. These differential binding profiles endow the pair with the potential for evaluating SERT contributions to antipsychotic drug activity in animal behavioral models. In addition, compound 11 has no significant affinity for 5-HT_2CR and binds only moderately to the H₁R, suggesting it may not induce weight gain or sedation when used clinically. Taken together, compound 11 displays an interesting pharmacological profile that necessitates the evaluation of its functional and in vivo effects in animal models which are currently ongoing.     

Synthesis and biological activity of 5-styryl and 5-phenethyl-substituted 2,3,4,5-tetrahydro-1H-pyrido[4,3-b]indoles

Syntheses, biological evaluation, and structure–activity relationships for a series of novel 5-styryl and 5-phenethyl analogs of dimebolin are disclosed. The novel derivatives and dimebolin share a broad spectrum of activities against therapeutically relevant targets. Among all synthesized derivatives, 2,8-dimethyl-5-[(Z)-2-phenylvinyl]-2,3,4,5-tetrahydro-1H-pyrido[4,3-b]indole and its 5-phenethyl analog are the most potent blockers of 5-HT₇, 5-HT₆, 5-HT_2C, Adrenergic α₂ and H₁ receptors. The general affinity rank order towards the studied receptors was Z-3(2) > 4(2) ? 4(3) ? dimebolin, all of them having highest affinities to 5-HT₇ receptors.     

Arylpiperazinylalkyl derivatives of 8-amino-1,3-dimethylpurine-2,6-dione as novel multitarget 5-HT/D receptor agents with potential antipsychotic activity

A series of new 7-arylpiperazinylalkyl-1,3-dimethyl-purine-2,6-dione derivatives with diversified 8-amino substituent in 8 position was synthesized and their 5-HT_1A, 5-HT_2A, 5-HT₆, 5-HT₇, and D₂ receptor affinities were determined. The binding study allowed identifying some potent 5-HT_1A/5-HT_2A/5-HT₇/D₂ ligands. The most interesting because of their multireceptor profile were 8-piperidine (30–35) and 8-dipropylamine (45–47) analogs with four and five carbon aliphatic linkers. The selected compounds 24, 31, 34, 39, 41, 43, 45, and 46 in the functional in vitro evaluation for all targeted receptors showed significant partial D₂ agonist, partial 5-HT_1A agonist, and 5-HT_2A antagonist properties. The advantageous in vitro affinity of compound 34 for 5-HT_1A and D₂ receptors has been explained by means of molecular modeling, taking into consideration its partial agonist activity towards the latter one. In behavioral studies, compounds 32 and 34 revealed antipsychotic-like properties, significantly decreasing d-amphetamine-induced hyperactivity in mice.     

Synthesis and biological evaluation of (phenylpiperazinyl-propyl)arylsulfonamides as selective 5-HT2A receptor antagonists

A novel series of 5-HT_2A ligands that contain a (phenylpiperazinyl-propyl)arylsulfonamides skeleton was synthesized. Thirty-seven N-(cycloalkylmethyl)-4-methoxy-N-(3-(4-arylpiperazin-1-yl)propyl)-arylsulfonamide and N-(4-(4-arylpiperazin-1-yl)butan-2-yl)-arylsulfonamide compounds were obtained. The binding of these compounds to the 5-HT_2A, 5-HT_2C, and 5-HT₇ receptors was evaluated. Most of the compounds showed IC₅₀ values of less than 100 nM and exhibited high selectivity for the 5-HT_2A receptor. Among the synthesized compounds, 16a and 16d showed good affinity at 5-HT_2A (IC₅₀ = 0.7 nM and 0.5 nM) and good selectivity over 5-HT_2C (50–100 times) and 5-HT₇ (1500–3000 times).     

Synthesis and pharmacological evaluation of optically pure,novel carbonyl guanidine derivatives as dual 5-HT2B and 5-HT7 receptor antagonists

A series of 9-disubstituted N-(9H-fluorene-2-carbonyl)guanidine derivatives have been discovered as potent and orally active dual 5-HT_2B and 5-HT₇ receptor antagonists. Upon screening several compounds, N-(diaminomethylene)-4′,5′-dihydro-3′H-spiro[fluorene-9,2′-furan]-2-carboxamide (17) exhibited potent affinity for both 5-HT_2B (K_i = 5.1 nM) and 5-HT₇ (K_i = 1.7 nM) receptors with high selectivity over 5-HT_2A, 5-HT_2C, α₁, D₂ and M₁ receptors. Optical resolution of the intermediate carboxylic acid 16 via the formation of diastereomeric salts using chiral alkaloids gave the optically pure compounds (R)-17 and (S)-17. Both enantiomers suppressed 5-HT-induced dural protein extravasation in guinea pigs in a dose-dependent manner and the amount of leaked protein was suppressed to near normal levels when orally administrated at 10 mg/kg. (R)-17 and (S)-17 were therefore selected as candidates for human clinical trials.     

Synthesis of cycloalkane-annelated 3-phenylsulfonyl-pyrazolo[1,5-a]pyrimidines and their evaluation as 5-HT6 receptor antagonists

Synthesis and biological evaluation of 1 (‘angular’) and 2 (‘linear’) сycloalkane-annelated 3-phenylsulfonyl-pyrazolo[1,5-a]pyrimidines as novel ligands of the 5-HT₆ receptors are disclosed. The new compounds 1 and 2 are highly selective antagonists of the receptor with sub-nanomolar affinities (K_i <1 nM). In its structure, this new chemotype lacks a basic ionizable side chain, which is considered as the characteristic feature of the 5-HT₆ receptor antagonists pharmacophore model.