New spiro-piperidines as 5-HT2B receptor antagonists

A functional screening highlighted a series of spiro-piperidines as 5-HT2B receptor antagonists. Preliminary structure-activity relationship has been explored driving to potent antagonists (IC50 = 1 nM) and indicating directions for further explorations.     

Quinazolindione derivatives as potent 5-HT3A receptor antagonists

5-HT_3A receptor antagonists have been used mainly for the treatment of nausea and vomiting. These days, the antagonists are of special interest due to their therapeutic potential to treat other diseases such as depression, psychotic disorder, drug abuse, and irritable bowel syndrome. To discover novel 5-HT_3A receptor antagonists, we screened our in-house small molecule library, resulting in identifying the quinazolindione derivatives as potent 5-HT_3A receptor antagonists. For the purpose of structure–activity relationship study, 24 quinazolindione analogues were biologically evaluated against 5-HT_3A receptor. Among those, KKHT10612 shows the best antagonistic effect against 5-HT_3A receptor with an IC₅₀ value of 0.8 μM which is comparable with that of the reference compound, MDL72222, and selectivity over T-type calcium channel as well.     

Discovery and pharmacological profile of new hydrophilic 5-HT4 receptor antagonists

The synthesis and pharmacological data of some new and potent hydrophilic 5-HT₄ receptor antagonists are described. Propanediol derivative 25 was identified as a potent antagonist with low affinity for the hERG potassium channel and promising pharmacokinetics.     

Discovery of 3-aryl-5-acylpiperazinyl-pyrazoles as antagonists to the NK3 receptor

A series of 3-aryl-5-acylpiperazinyl-pyrazoles (e.g., 3a-b) initially identified through a high-throughput screening campaign using the aequorin Ca²⁺ bioluminescence assay as novel, potent small molecule antagonists of the G protein-coupled human tachykinin NK₃ receptor (hNK3-R) is described. Preliminary profiling revealed poor plasma and metabolic stability for these structures in rodents. Further optimization efforts resulted in analogs with improved potency, stability, and pharmacokinetic properties as well as good brain permeability, for example, compounds 26 and 42. Unexpected cytotoxicity was observed in such N-Me pyrazole structures as compounds 41-42.     

Discovery of 3-aryl-3-methyl-1H-quinoline-2,4-diones as a new class of selective 5-HT6 receptor antagonists

A 5,7-dichloro-3-phenyl-3-methyl-quinoline-2,4-dione (11a) has been identified in a random screen as a lead for 5-HT(6) antagonist. During the lead optimization process, several analogs were synthesized and their biological activities were investigated. Within this series, several compounds display high binding affinity and selectivity for the 5-HT(6) receptor. In particular, 3-(4-hydroxyphenyl)-3-methyl-quinoline-2,4-dione (12f) exhibits high affinity (K(i)=12.3 nM) for 5-HT(6) receptor with good selectivity over other serotonin and dopamine (D(1)-D(4)) receptor subtypes. In a functional adenylyl cyclase stimulation assay, this compound exhibited considerable antagonistic activity (IC(50)=0.61 microM).     

SAR studies of novel 5-substituted 2-arylindoles as nonpeptidyl GnRH receptor antagonists

The discovery of the potency-enhancing effect of 5-substitutions on the novel 2-arylindoles as nonpeptidyl GnRH receptor antagonists led to the identification of several analogues with high affinities on the GnRH receptor. The syntheses and SARs of these 5-substituted-2-arylindole analogues are reported.     

Preparation of piperazine derivatives as 5-HT7 receptor antagonists

Twenty-four compounds of 4-methoxy-N-[3-(4-substituted phenyl-piperazine-1-yl)propyl] benzene sulfonamides and N-[3-(4-substituted phenyl-piperazine-1-yl)propyl] naphthyl sulfonamides were prepared and evaluated as 5-HT(7) receptor antagonists. Most of the compounds showed the IC(50) values of 12-580nM. Four methyl branched analogues were also obtained, but the activity for methyl branched analogues was almost same as its straight chain congeners. Among the synthesized compounds, 3c showed a good activity on 5-HT(7) receptors and a good selectivity on 5-HT(1a), 5-HT(2a), 5-HT(2c), and 5-HT(6) receptors.     

Synthesis and pharmacological characterization of a new benzoxazole derivative as a potent 5-HT3 receptor agonist

N-(2-Benzoxazol-2-yl-ethyl)-guanidine hydrochloride (10) was synthesized and pharmacologically tested. This compound showed high affinity for the 5-HT(3) receptor (K(i)=0.77 nM) and potently triggered the von Bezold-Jarisch reflex (BJR) in rats with an ED(50)=0.52 microg/kg iv and intrinsic activity next to 1 (i.a.=0.94). This stimulant effect was abolished by pretreatment with the 5-HT(3) receptor antagonist granisetron and was subject to a rapid and pronounced tachyphylaxis, due to desensitization of the peripheric cardiac 5-HT(3) receptor. Consequently, 10 acts as an in vivo 5-HT(3) antagonist inhibiting the BJR responses evoked by submaximal doses of 5-HT with an ID(50)=5.8 microg/kg iv.     

Synthesis and SAR of 3- and 4-substituted quinolin-2-ones: discovery of mixed 5-HT(1B)/5-HT(2A) receptor antagonists

Quinolin-2-ones bearing a heteroaryl-piperazine linked by a two carbon chain at the 3- or 4-position were synthesised and evaluated as mixed 5-HT(1B)/5-HT(2A) receptor antagonists. Potent mixed antagonists were obtained with thieno[3,2-c]pyridine derivatives. In this series, compound 2.1 (SL 65.0472) proved to be functional antagonist at both the 5-HT(2A) receptor (rat in vivo 5-HT-induced hypertension model) and the 5-HT(1B) receptor (dog in vitro saphenous vein assay).     

Quinoxalin-2-carboxamides: synthesis and pharmacological evaluation as serotonin type-3 (5-HT3) receptor antagonists

A series of quinoxalin-2-carboxamides were designed as per the pharmacophoric requirements of 5-HT(3) receptor antagonists and synthesized by condensing the carboxylic group of quinoxalin-2-carboxylic acid with various amines in the presence of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 1-hydroxybenzotriazole. The structures of the synthesized compounds were confirmed by physical and spectroscopic data. The carboxamides were evaluated for their 5-HT(3) receptor antagonisms in longitudinal muscle-myenteric plexus preparation from guinea pig ileum against 5-HT(3) agonist, 2-methy-5-HT. All the synthesized compounds showed 5-HT(3) receptor antagonism, (4-benzylpiperazin-1-yl)(quinoxalin-2-yl)methanone was the most potent compound among this series.     

Quinoxalin-2-carboxamides: synthesis and pharmacological evaluation as serotonin type-3 (5-HT3) receptor antagonists

A series of quinoxalin-2-carboxamides were designed as per the pharmacophoric requirements of 5-HT₃ receptor antagonists and synthesized by condensing the carboxylic group of quinoxalin-2-carboxylic acid with various amines in the presence of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 1-hydroxybenzotriazole. The structures of the synthesized compounds were confirmed by physical and spectroscopic data. The carboxamides were evaluated for their 5-HT₃ receptor antagonisms in longitudinal muscle-myenteric plexus preparation from guinea pig ileum against 5-HT₃ agonist, 2-methy-5-HT. All the synthesized compounds showed 5-HT₃ receptor antagonism, (4-benzylpiperazin-1-yl)(quinoxalin-2-yl)methanone was the most potent compound among this series.     

Microwave assisted synthesis of 2-(4-substituted piperazin-1-yl)-1,8-naphthyridine-3-carbonitrile as a new class of serotonin 5-HT3 receptor antagonists

A series of novel 2-(4-substituted piperazin-1-yl)-1,8-naphthyridine-3-carbonitrile 6 were prepared by microwave irradiation and conventional heating. The intermediate, 2-oxo-1,2-dihydro-1,8-naphthyridine-3-carbonitrile 3, was prepared from 2-aminonicotinaldehyde 1 and ethyl cyanoacetate 2 in the presence of piperidine under solvent free condition. The synthesized compounds were evaluated for 5-HT3 antagonisms in longitudinal muscle-myenteric plexus (LMMP) preparation from Guinea pig ileum against 5-HT3 agonist, 2-methyl-5-HT. Among the compounds tested, 2-(4-allylpiperazin-1-yl)-1,8-naphthyridine-3-carbonitrile 6d showed most favorable 5-HT3 receptor antagonism in the Guinea pig ileum.     

Indoloxypropanolamine analogues as 5-HT(1A) receptor antagonists

Analogues of pindolol, 1-(1H-indol-4-yloxy)-3-isopropylamino-propan-2-ol, were synthesized and evaluated as 5-HT(1A) receptor antagonists. The structural features required for optimal binding to the 5-HT1A receptor are as follows: S-2-propanol linker, 4-indoloxy substituent, and a large lipophilic cyclic amine substituent.     

Bicyclic heteroarylpiperazines as selective brain penetrant 5-HT6 receptor antagonists

Starting from the potent and selective but poorly brain penetrant 5-HT6 receptor antagonist SB-271046, a successful strategy for improving brain penetration was adopted involving conformational constraint with concomitant reduction in hydrogen bond count. This provided a series of bicyclic heteroarylpiperazines with high 5-HT6 receptor affinity. 5-Chloroindole 699929 combined high 5-HT6 receptor affinity with excellent brain penetration and also had good oral bioavailability in both rat and dog.     

Discovery of new anti-depressants from structurally novel 5-HT3 receptor antagonists: design, synthesis and pharmacological evaluation of 3-ethoxyquinoxalin-2-carboxamides

A novel series of 3-ethoxyquinoxalin-2-carboxamides were designed as per the pharmacophoric requirements of 5-HT₃ receptor antagonist using ligand-based approach. The desired carboxamides were synthesized from the key intermediate, 3-ethoxyquinoxalin-2-carboxylic acid by coupling with appropriate amines in the presence of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC·HCl) and 1-hydroxybenzotriazole (HOBt). The 5-HT₃ receptor antagonism was evaluated in longitudinal muscle myenteric plexus preparation from guinea pig ileum against 5-HT₃ agonist, 2-methy-5-HT, which was expressed in the form of pA₂ values. Compound 6h (3-ethoxyquinoxalin-2-yl)(4-methylpiperazin-1-yl)methanone was found to be the most active compound, which expressed a pA₂ value of 7.7. In forced swim test, the compounds with higher pA₂ value exhibited good anti-depressant-like activity and compounds with lower pA₂ value failed to show activity as compared to the vehicle-treated group.     

Discovery and SAR of 5-aminooctahydrocyclopentapyrrole-3a-carboxamides as potent CCR2 antagonists

SAR study of 5-aminooctahydrocyclopentapyrrole-3a-carboxamide scaffold led to identification of several CCR2 antagonists with potent activity in both binding and functional assays. Their cardiovascular safety and pharmacokinetic properties were also evaluated.     

Neuropathic pain-alleviating effects of pyrazole-conjugated arylsulfonamides as 5-HT6 receptor antagonists

A novel series of arylsulfonylaminomethyl-3-(1-phenyl-5-isopropyl)pyrazoles was evaluated for serotonin receptor subtype 6 (5-HT₆R) antagonistic effects in vitro. We also investigated their neuropathic pain-alleviating effects in vivo using a rat spinal nerve ligation (SNL) model. Bicyclic aromatic sulfonamino groups, such as naphthalene and quinolin-substituted derivatives, showed good 5-HT₆ inhibitory activity in vitro. Among them, selected compounds, 12 and 13, having 8-quinoylsulfonamino groups, showed potent neuropathic pain-alleviating effects in the rat model.     

Discovery of novel pyridyl carboxamides as potent CCR5 antagonists and optimization of their pharmacokinetic profile in rats

A novel series of pyridyl carboxamide-based CCR5 inhibitors was designed, synthesized, and demonstrated to be highly potent against HIV-1 infection in both HOS and PBL assays. Attempts to evaluate this series of compounds in a rat PK model revealed its instability in rat plasma. A hypothesis for this liability was proposed, and strategies to overcome this issue were pursued, leading to discovery of highly potent 40 and 41, which featured dramatically improved rat PK profiles.     

3,4-Dihydro-2H-benzo[1,4]oxazine derivatives as 5-HT6 receptor antagonists

A series of novel 3,4-dihydro-2H-benzo[1,4]oxazine derivatives has been designed and synthesized as 5-HT(6) receptor antagonists. Many of the compounds displayed subnanomolar affinities for the 5-HT(6) receptor and good brain penetration in rats. The relationship of structure and lipophilicity to hERG inhibition of this series of compounds is discussed.     

3-Amino-1-alkyl-cyclopentane carboxamides as small molecule antagonists of the human and murine CC chemokine receptor 2

A series of low molecular weight antagonists of both the human and murine CC chemokine receptor 2, containing a 1-alkyl-3-(3-methyl-4-spiroindenylpiperidine)-substituted cyclopentanecarboxamide, is described. A SAR study of the C(1) substituent revealed that short, branched alkyl groups such as isopropyl, isobutyl, or cyclopropyl are optimal for both human and murine CCR2 binding activity.