N-[1-(2-Phenylethyl)pyrrolidin-3-yl]-1-adamantanecarboxamides as novel 5-HT2 receptor antagonists

A series of 1-adamantanecarboxamides was synthesized and examined for their potency as a selective 5-HT2 receptor antagonist. We found (S)-N-[1-[2-(4-fluorophenyl)ethyl]pyrrolidin-3-yl]-1-adamantane carboxamide hydrochloride hydrate (10-(S), Y-39241) to have a high affinity and selectivity for 5-HT2 receptors, and this potent anti-platelet effect of Y-39241 was confirmed both in vitro and in vivo.     

2-({6-[(3R)-3-amino-3-methylpiperidine-1-yl]-1,3-dimethyl-2,4-dioxo-1,2,3,4-tetrahydro-5H-pyrrolo[3,2-d]pyrimidine-5-yl}methyl)-4-fluorobenzonitrile (DSR-12727): a potent, orally active dipeptidyl peptidase IV inhibitor without mechanism-based inactivation of CYP3A

We report on the identification of 2-({6-[(3R)-3-amino-3-methylpiperidine-1-yl]-1,3-dimethyl-2,4-dioxo-1,2,3,4-tetrahydro-5H-pyrrolo[3,2-d]pyrimidine-5-yl}methyl)-4-fluorobenzonitrile (DSR-12727) (7a) as a potent and orally active DPP-4 inhibitor without mechanism-based inactivation of CYP3A. Compound 7a showed good DPP-4 inhibitory activity (IC(50)=1.1 nM), excellent selectivity against related peptidases and other off-targets, good pharmacokinetic and pharmacodynamic profile, great in vivo efficacy in Zucker-fatty rat, and no safety concerns both in vitro and in vivo.     

Synthesis, radiosynthesis and in vivo evaluation of 5-[3-(4-benzylpiperidin-1-yl)prop-1-ynyl]-1,3-dihydrobenzoimidazol-2-[(11)C]one, as a potent NR(1A)/2B subtype selective NMDA PET radiotracer

Recently, a new series of potent and highly subtype-selective 1-(heteroarylalkynyl)-4-benzylpiperidine antagonists of the NMDA receptors has been described by Pfizer Laboratories. In this series, 5-[3-(4-benzylpiperidin-1-yl)prop-1-ynyl]-1,3-dihydrobenzoimidazol-2-one (1) was identified as a selective antagonist for the NR1(A)/2B subtype, displaying IC(50) values for inhibition of the NMDA responses of 5.3 nM for this subtype (compared to NR1(A)/2A: 35 microM and NR1(A)/2C>100 microM) and was active in rat at a relatively low dosage (10mg/kg po). Derivative 1 has been synthesized in four chemical steps in good overall yield and labelled with carbon-11 at its benzoimidazolone ring using [(11)C]phosgene. The pharmacological profile of [(11)C]-1 was evaluated in vivo in rats with biodistribution studies and brain radioactivity monitored with intracerebral radiosensitive beta-microprobes. The brain uptake of [(11)C]-1 was extremely low (0.07% I.D./mL on average at 30 min) and rather uniform across the different brain structures. This in vivo brain regional distribution of [(11)C]-1 did not match with autoradiographic or binding data obtained with other NR2B subtype-selective NMDA ligands. Competition studies with ifenprodil (20 mg/kg, ip, 30 min before the radiotracer injection) failed to demonstrate specific binding of the radiotracer in the brain. In view of these results, and especially considering the low brain penetration of the radiotracer, [(11)C]-1 does not have the required properties for imaging NMDA receptors using positron emission tomography.     

Synthesis and KCNQ2 opener activity of N-(1-benzo[1,3]dioxol-5-yl-ethyl, N-[1-(2,3-dihydro-benzofuran-5-yl)-ethyl, and N-[1-(2,3-dihydro-1H-indol-5-yl)-ethyl acrylamides

Bioisosteric replacement studies led to the identification of N-(1-benzo[1,3]dioxol-5-yl-ethyl)-3-(2-chloro-phenyl)-acrylamide ((S)-3) as a highly potent KCNQ2 opener, and 3-(2,6-difluoro-phenyl)-N-[1-(2,3-dihydro-benzofuran-5-yl)-ethyl]-acrylamide ((S)-4), and N-[1-(2,3-dihydro-1H-indol-5-yl)-ethyl]-3-(2-fluoro-phenyl)-acrylamide ((S)-5) as highly efficacious KCNQ2 openers. In contrast, their respective R enantiomers showed significantly less or no appreciable KCNQ2 opener activity even at the highest concentration tested (10 microM). Because of its high potency and moderate efficacy as well as its convenient synthesis, (+/-)-3 was selected as a reference compound for analyzing efficacies of KCNQ openers in electrophysiology studies. Compounds (S)-4 and (S)-5 demonstrated significant activity in reducing neuronal hyperexcitability in rat hippocampal slices. The synthesis and the KCNQ2 opener activity of these acrylamides are described.     

Tissue distribution, autoradiography, and metabolism of 4-(2'-methoxyphenyl)-1-[2' -[N-2"-pyridinyl)-p-[(18)F]fluorobenzamido]ethyl]piperazine (p-[(18)F]MPPF), a new serotonin 5-HT(1A) antagonist for positron emission tomography: An In vivo study in rats

The in vivo behavior of 4-(2'-methoxyphenyl)-1-[2'-[N-(2"-pyridinyl)-p-[(18)F]fluorobenzamido ]ethyl]-piperazine (p-[(18)F]MPPF), a new serotonin 5-HT(1A) antagonist, was studied in awake, freely moving rats. Biodistribution studies showed that the carbon-fluorine bond was stable in vivo, that this compound was able to cross the blood-brain barrier, and that a general diffusion equilibrium could account for the availability of the tracer. The great quantity of highly polar metabolites found in plasma did not contribute to the small amounts of metabolites found in hippocampus, frontal cortex, and cerebellum. Exvivo p-[(18)F]MPPF and in vitro 8-hydroxy-2-(di-n-[(3)H]propylamino)tetralin autoradiography were compared both qualitatively and quantitatively. Qualitative evaluation proved that the same brain regions were labeled and that the p-[(18)F]MPPF labeling is (a) in total agreement with the known distribution of 5-HT(1A) receptors in rats and (b) characterized by very low nonspecific binding. Quantitative comparison demonstrated that the in vivo labeling pattern obtained with p-[(18)F]MPPF cannot be explained by differences in regional blood flow, capillary density, or permeability. The 5-HT(1A) specificity of p-[(18)F]MPPF and binding reversibility were confirmed in vivo with displacement experiments. Thus, this compound can be used to evaluate parameters characterizing 5-HT(1A) binding sites in the brain.     

Synthesis and in vivo evaluation of [O-methyl-11C] N-[3,5-dichloro-2-(methoxy)phenyl]-4-(methoxy)-3-(1-piperazinyl)benzenesulfonamide as an imaging probe for 5-HT6 receptors

The serotonin receptor 6 (5-HT(6)) is implicated in the pathophysiology of cognitive diseases, schizophrenia, anxiety and obesity and in vivo studies of this receptor would be of value for studying the pathophysiology of these disorders. Therefore, N-[3,5-dichloro-2-(methoxy)phenyl]-4-(methoxy)-3-(1-piperazinyl)benzenesulfonamide (SB399885), a selective and high affinity (pK(i)=9.11) 5-HT(6) antagonist, has been radiolabeled with carbon-11 by O-methylation of the corresponding desmethyl analogue with [(11)C]MeOTf in order to determine the suitability of [(11)C]SB399885 to quantify 5-HT(6)R in living brain using PET. Desmethyl-SB399885 was prepared, starting from 1-(2-methoxyphenyl) piperazine hydrochloride, in excellent yield. The yield obtained for radiolabeling of [(11)C]SB399885 was 30±5% (EOS) and the total synthesis time was 30min at EOB. PET studies with [(11)C]SB399885 in baboon showed fast uptake followed by rapid clearance in the brain. Highest uptake of radioactivity of [(11)C]SB399885 in baboon brain were found in temporal cortex, parahippocampal gyrus, pareital cortex, amygdala, and hippocampus. Poor brain entry and inconsistent brain uptake of [(11)C]SB399885 compared to known 5-HT(6)R distribution limits its usefulness for the in vivo quantification of 5-HT(6)R with PET.     

Synthesis and evaluation of 1-[2-(4-[11C]methoxyphenyl)phenyl]piperazine for imaging of the serotonin 5-HT7 receptor in the rat brain

1-[2-(4-Methoxyphenyl)phenyl]piperazine (4) is a potent serotonin 5-HT₇ receptor antagonist (K_i = 2.6 nM) with a low binding affinity for the 5-HT_1A receptor (K_i = 476 nM). As a potential positron emission tomography (PET) radiotracer for the 5-HT₇ receptor, [¹¹C]4 was synthesized at high radiochemical yield and specific activity, by O-[¹¹C]methylation of 2′-(piperazin-1-yl)-[1,1′-biphenyl]-4-ol (6) with [¹¹C]methyl iodide. Autoradiography revealed that [¹¹C]4 showed in vitro specific binding with 5-HT₇ in the rat brain regions, such as the thalamus which is a region with high 5-HT₇ expression. Metabolite analysis indicated that intact [¹¹C]4 in the brain exceeded 90% of the radioactive components at 15 min after the radiotracer injection, although two radiolabeled metabolites were found in the rat plasma. The PET study of rats showed moderated uptake of [¹¹C]4 in the brain (1.2 SUV), but no significant regional difference in radioactivity in the brain. Pretreatment with 5-HT₇-selective antagonist SB269970 (3) did not decrease the uptake of [¹¹C]4 in the rat brain. Further studies are warranted that focus on the development of PET ligand candidates with higher binding affinity for 5-HT₇ and higher in vivo stability in brain than 4.     

A novel,potent, and orally active VLA-4 antagonist with good aqueous solubility: trans-4-[1-[[2-(5-Fluoro-2-methylphenylamino)-7-fluoro-6-benzoxazolyl]acetyl]-(5S)-[methoxy(methyl)amino]methyl-(2S)-pyrrolidinylmethoxy]cyclohexanecarboxylic acid

We have carried out the optimization of substituents at the C-3 or the C-5 position on the pyrrolidine ring of VLA-4 antagonist 3 with 2-(phenylamino)-7-fluorobenzoxazolyl moiety for the purpose of improving in vivo efficacy while maintaining good aqueous solubility. As a result, we successfully increased in vitro activity in the presence of 3% human serum albumin and achieved an exquisite lipophilic and hydrophilic balance of compounds suitable for oral administrative regimen. The modification resulted in the identification of zwitterionic compound 7n with (5S)-[methoxy(methyl)amino]methylpyrrolidine, which significantly alleviated bronchial hyper-responsiveness to acetylcholine chloride at 12.5 mg/kg, p.o. in a murine asthma model and showed favorable aqueous solubility (JP1, 89 μg/mL; JP2, 462 μg/mL). Furthermore, this compound showed good oral bioavailability (F = 54%) in monkeys.     

Synthesis and structure-activity relationship of tetrahydropyrazolopyrimidine derivatives--a novel structural class of potent calcium-sensing receptor antagonists

A series of novel tetrahydropyrazolopyrimidine derivatives containing an adamantyl group were synthesized and evaluated as potential calcium-sensing receptor (CaSR) antagonists. After chemical modification of 9a, which was identified as a hit compound in a random screening of CaSR antagonist assay, 7,7-dimethyl derivative 16c was found to be the most active compound of this new series (IC(50)=10nM). We report the synthesis of this series and their biological activities and structure-activity relationship.     

Antagonists of the human CCR5 receptor as anti-HIV-1 agents. Part 3: a proposed pharmacophore model for 1-[N-(methyl)-N-(phenylsulfonyl)amino]-2-(phenyl)-4-[4-(substituted)piperidin-1-yl]butanes.

Structure-activity relationship studies directed toward the optimization of (2S)-2-(3-chlorophenyl)-1-[N-(methyl)-N-(phenylsulfonyl)amino]-4-[4-(substituted)piperidin-1-yl]butanes as CCR5 antagonists resulted in the synthesis of the spiro-indanone derivative 8c (IC50=5 nM). These and previous results are summarized in a proposed pharmacophore model for this class of CCR5 antagonist.     

Structure-activity relationship study towards non-peptidic positron emission tomography (PET) radiotracer for gastrin releasing peptide receptors: Development of [18F] (S)-3-(1H-indol-3-yl)-N-[1-[5-(2-fluoroethoxy)pyridin-2-yl]cyclohexylmethyl]-2-methyl-2-[3-(4-nitrophenyl)ureido]propionamide

Gastrin-releasing peptide receptors (GRP-Rs, also known as bombesin 2 receptors) are overexpressed in a variety of human cancers, including prostate cancer, and therefore they represent a promising target for in vivo imaging of tumors using positron emission tomography (PET). Structural modifications of the non-peptidic GRP-R antagonist PD-176252 ((S)-1a) led to the identification of the fluorinated analog (S)-3-(1H-indol-3-yl)-N-[1-[5-(2-fluoroethoxy)pyridin-2-yl]cyclohexylmethyl]-2-methyl-2-[3-(4-nitrophenyl)ureido]propionamide ((S)-1m) that showed high affinity and antagonistic properties for GRP-R. This antagonist was stable in rat plasma and towards microsomal oxidative metabolism in vitro. (S)-1m was successfully radiolabeled with fluorine-18 through a conventional radiochemistry procedure. [¹⁸F](S)-1m showed high affinity and displaceable interaction for GRP-Rs in PC3 cells in vitro.     

Synthesis, in vitro and in vivo evaluation of [O-methyl-11C] 2-{4-[4-(3-methoxyphenyl)piperazin-1-yl]-butyl}-4-methyl-2H-[1,2,4]-triazine-3,5-dione: a novel agonist 5-HT1A receptor PET ligand

Synthesis and in vivo evaluation of 2-{4-[4-(3-methoxyphenyl)piperazin-1-yl]-butyl}-4-methyl-2H-[1,2,4]triazine-3,5-dione (5 or MMT), a high affinity and selective serotonin 5-HT1AR agonist PET tracer, are described. GTPgammaS assay shows that MMT is an agonist with an EC50 comparable to 5-HT. Radiolabeling of 5 was achieved in 30% yield (EOS) from desmethyl-MMT (4) with >99% chemical and radiochemical purities and a specific activity >1000 Ci/mmol. PET studies in baboon show that [11C]5 penetrates the blood-brain barrier but, because of low specific binding and fast clearance of radioactivity it is not a suitable PET tracer for the in vivo quantification of 5-HT1AR.     

Lead detoxification activities and ADMET hepatotoxicities of a class of novel 5-(1-carbonyl-L-amino-acid)-2,2-dimethyl-[1,3]dithiolane-4-carboxylic acids

By linking the mercapto groups with isopropyl and introducing l-amino acid into the 5-carboxyl of DMSA a class of novel 5-(1-carbonyl-l-amino-acid)-2,2- dimethyl-[1,3]dithiolane-4-carboxylic acids were prepared. Their in vivo activities were evaluated on lead loaded mice at the dose of 0.4 mmol/kg. The results showed that the lead levels of the livers, kidneys, femurs and brains in particular could be efficiently decreased by 0.4 mmol/kg of 5-(1-carbonyl-l-amino-acid)-2,2-dimethyl-[1,3]dithiolane-4-carboxylic acids. The benefit of 5-(1-carbonyl-l-amino-acid)-2,2-dimethyl-[1,3]dithiolane-4-carboxylic acids to the detoxification of the brain lead was attributed to their transmembrane ability. Compared with the lead detoxification efficacy, they did not affect the essential metals such as Fe, Cu, Zn, and Ca of the treated mice. Silico molecular modeling predicted that 5-(1-carbonyl-l-amino-acid)-2,2-dimethyl-[1,3]dithiolane-4-carboxylic acids had no hepatotoxicity.     

Synthesis and in vivo evaluation of [18F]-4-[5-(4-methylphenyl)-3-(trifluoromethyl)-1H-pyrazol-1-yl]benzenesulfonamide as a PET imaging probe for COX-2 expression

Synthesis of [18F]4-[5-(4-methylphenyl)-3-(trifluoromethyl)-1H-pyrazol-1-yl]benzenesulfonamide ([18F]celecoxib), a selective COX-2 inhibitor, is achieved via a bromide to [18F]F- exchange reaction. Synthesis of the precursor for radiolabeling was achieved from 4'-methylacetophenone in four steps with 22% overall yield. Under non-radioactive conditions, fluorination was achieved using TBAF in DMSO at 135 degrees C in 80% yield. Synthesis of [18F]celecoxib was achieved using [18F]TBAF in DMSO at 135 degrees C in 10+/-2% yield (EOS) with >99% chemical and radiochemical purities. The specific activity was 120+/-40 mCi/micromol (EOB). [18F]celecoxib was found to be stable in ethanol, however, de[18F]fluorination (6.5%) was observed after 4 h in 10% ethanol-saline solution. Rodent PET studies show bone labeling indicating in vivo de[18F]fluorination of [18F]celecoxib. PET studies in baboon indicated a lower rate of de[18F]fluorination than rat and retention of radioactivity in brain regions consistent with the known distribution of COX-2. A radiolabeling method that can generate consistent high specific activity is needed for routine human use.     

Synthesis and pharmacological characterization of 5-phenyl-2-[2-(1-piperidinylcarbonyl)phenyl]-2,3-dihydro-1H-pyrrolo[1,2-c]imidazol-1-ones: a new class of Neuropeptide S antagonists

A new class of selective NPS antagonist was developed starting from a commercially available product identified by screening activities. Experimental NMR observations and computational experiments allowed the discovery of a new class of derivatives. 5-Phenyl-2-[2-(1-piperidinylcarbonyl)phenyl]-2,3-dihydro-1H-pyrrolo[1,2-c]imidazol-1-one represents a new lead compound in the NPS antagonist field.     

1-[4-(1H-Benzoimidazol-2-yl)-phenyl]-3-[4-(1H-benzoimidazol-2-yl)-phenyl]-urea derivatives as small molecule heparanase inhibitors

A novel class of 1-[4-(1H-benzoimidazol-2-yl)-phenyl]-3-[4-(1H-benzoimidazol-2-yl)-phenyl]-ureas are described as potent inhibitors of heparanase. Among them are 1,3-bis-[4-(1H-benzoimidazol-2-yl)-phenyl]-urea (7a) and 1,3-bis-[4-(5,6-dimethyl-1H-benzoimidazol-2-yl)-phenyl]-urea (7d), which displayed good heparanase inhibitory activity (IC(50) 0.075-0.27 microM). Compound 7a showed good efficacy in a B16 metastasis model.     

Synthesis, radiolabelling and biological characterization of (D)-7-iodo-N-(1-phosphonoethyl)-5-aminomethylquinoxaline-2,3-dione, a glycine-binding site antagonist of NMDA receptors

(D)-7-Iodo-N-(1-phosphonoethyl)-5-aminomethylquinoxaline-2,3 -dione (I-PAMQX), is a potent, in vivo active antagonist acting at the glycine binding site of the NMDA receptor complex. Radioiodinated [131I]I-PAMQX was prepared with good yields and high specific activity from its 7-bromo analogue. Biodistribution studies of [131I]I-PAMQX in mice showed a relatively slow clearance from the blood. The uptake of radioactivity was highest in the kidneys, moderate in the heart, lung, liver and bones, and low in the brain.     

6,7-Dihydro-5H-cyclopenta[d]pyrazolo[1,5-a]pyrimidines and their derivatives as novel corticotropin-releasing factor 1 receptor antagonists

To identify an orally active corticotropin-releasing factor 1 receptor antagonist, a series of 6,7-dihydro-5H-cyclopenta[d]pyrazolo[1,5-a]pyrimidines and their derivatives were designed, synthesized and evaluated. An in vitro study followed by in vivo and pharmacokinetic studies of these heterotricyclic compounds led us to the discovery of an orally active CRF1 receptor antagonist. The results of a structure-activity relationship study are presented.     

Discovery of (-)-6-[2-[4-(3-fluorophenyl)-4-hydroxy-1-piperidinyl]-1-hydroxyethyl]-3,4-dihydro-2(1H)-quinolinone--a potent NR2B-selective N-methyl D-aspartate (NMDA) antagonist for the treatment of pain

(-)-6-[2-[4-(3-Fluorophenyl)-4-hydroxy-1-piperidinyl]-1-hydroxyethyl]-3,4-dihydro-2(1H)-quinolinone was identified as an orally active NR2B-subunit selective N-methyl-d-aspartate (NMDA) receptor antagonist. It has very high selectivity for NR2B subunits containing NMDA receptors versus the HERG-channel inhibition (therapeutic index=4200 vs NR2B binding IC(50)). This compound has improved pharmacokinetic properties compared to the prototype CP-101,606.     

2-(2-[3-(pyridin-3-yloxy)phenyl]-2H-tetrazol-5-yl) pyridine: a highly potent, orally active, metabotropic glutamate subtype 5 (mGlu5) receptor antagonist

Structure-activity relationship studies on 3-(5-pyridin-2-yl-2H-tetrazol-2-yl)benzonitrile 2 led to the discovery of 2-(2-[3-(pyridin-3-yloxy)phenyl]-2H-tetrazol-5-yl)pyridine (10)-a highly potent and selective mGlu5 receptor antagonist with good brain penetration and in vivo receptor occupancy in rat and cross-species oral bioavailability.