Synthesis of new 4-[2-(4-methyl(amino)sulfonylphenyl)-5-trifluoromethyl-2H-pyrazol-3-yl]-1,2,3,6-tetrahydropyridines: a search for novel nitric oxide donor anti-inflammatory agents

A group of 4-[2-(4-methyl(amino)sulfonylphenyl)-5-trifluoromethyl-2H-pyrazol-3-yl]-1,2,3,6-tetrahydropyridines possessing a variety of substituents (Me, CO2Et, H, N=O) attached to the 1,2,3,6-tetrahydropyridyl N(1)-nitrogen atom were synthesized and evaluated as anti-inflammatory agents. Structure-activity relationship data showed that the N-methyl-1,2,3,6-tetrahydropyridyl moiety is a suitable bioisosteric replacement for the tolyl moiety in celecoxib. The most potent compound 4-[5-(1-methyl-1,2,3,6-tetrahydropyridin-4-yl)-3-trifluoromethylpyrazol-1-yl]benzenesulfonamide (ED(50)=61.2 mg/kg po) exhibited an anti-inflammatory activity between that of the reference drugs celecoxib (ED(50)=10.8 mg/kg po) and aspirin (ED(50)=128.7 mg/kg po). The synthesis of model hybrid nitric oxide donor N-diazen-1-ium-1,2-diolate derivatives of 4-[2-(4-methyl(amino)sulfonylphenyl)-5-trifluoromethyl-2H-pyrazol-3-yl]-1,2,3,6-tetrahydropyridines requires further investigation since the reaction of 1,2,3,6-tetrahydropyridines with nitric oxide furnished the undesired N-nitroso-1,2,3,6-tetrahydrohydropyridyl product rather than the desired N-diazen-1-ium-1,2-diolate-1,2,3,6-tetrahydropyridyl product.     

Synthesis and biological evaluation of MAO-A selective 1,4-disubstituted-1,2,3,6-tetrahydropyridinyl substrates

Many mammalian tissues express both the A and B forms of monoamine oxidase (MAO), flavoenzymes that catalyze the oxidative deamination of a variety of endogenous and exogenous amines and the ring alpha-carbon oxidative bioactivation of neurotoxic 1,4-disubstituted-1,2,3,6-tetrahydropyridinyl derivatives. Substrates selective for MAO-A that display good kinetic and spectroscopic properties would be of value for developing quantitative assays for MAO-A in tissues that express both the A and B forms of the enzyme. This paper describes the synthesis of several 1-substituted-4-(1-methylpyrrol-2-yl)-1,2,3,6-tetrahydropyridinyl derivatives. Kinetic parameters and MAO-A selectivity indicate that 1-allyl- and 1-propyl-4-(1-methylpyrrol-2-yl)-1,2,3,6-tetrahydropyridine should be good candidates to develop a robust spectrophotometric-based assay that is selective for MAO-A.     

2-Alkyl-3-(1,2,3,6-tetrahydropyridin-4-yl)-1H-indoles as novel 5-HT6 receptor agonists

A series of 2-alkyl-3-(1,2,3,6-tetrahydropyridin-4-yl)-1H-indoles were synthesized and evaluated for their 5-HT6 activity. The most potent agonist in this series was 5-chloro-2-methyl-3-(1,2,3,6-tetrahydropyridin-4-yl)-1H-indole with an IC50=7.4 nM in 3H-LSD binding and an EC50=1.0 nM in a functional assay measuring production of cyclic AMP.     

N1-arylsulfonyl-3-(1,2,3,6-tetrahydropyridin-4-yl)-1H-indole derivatives are potent and selective 5-HT6 receptor antagonists

A series of N(1)-arylsulfonyl-3-(1,2,3,6-tetrahydropyridin-4-yl)indole derivatives was designed and synthesized. These compounds were shown to have high affinity for the 5-HT(6) receptor. Two analogs, 4-[3-(1,2,3,6-tetrahydropyridin-4-yl)-1H-indole-1-sulfonyl]-phenylamine 15g and 4-[3-(1,2,3,6-tetrahydropyridin-4-yl)-5-methoxy-1H-indole-1-sulfonyl]-phenylamine 15y, had 0.4 and 3.0 nM affinity, respectively, and antagonized the production of adenylate cyclase at sub-nanomolar concentrations.     

Reaction of benzophenone triplet with aliphatic amines. What a potent neurotoxin can tell us about the reaction mechanism

A photochemical model study of benzophenone triplet ((3)BP) with the MAO-B substrate 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine [MPTP (1)] and two of it's derivatives, 1-cyclopropyl-4-phenyl-1,2,3,6-tetrahydropyridine (2) and (±)-[trans-2-phenylcyclopropyl-4-phenyl-1,2,3,6-tetrahydropyridine (3) were performed. Literature precedent and calculations reported herein suggest that the barrier to ring opening for aminyl radical cations derived from N-cyclopropyl derivatives of tertiary amines (such as MPTP) will be low. The LFP results reported herein demonstrate that pathways for the reaction of (3)BP with 1, 2, and 3 are very similar. In each instance, disappearance of (3)BP is accompanied solely by appearance of bands corresponding to the diphenylhydroxylmethyl radical and neutral radical derived from MPTP and it's two derivatives 2 and 3. These results suggest that the reaction between benzophenone triplet and tertiary aliphatic amines proceed via a simple hydrogen atom transfer reaction. Additionally these model examinations provide evidence that oxidations of N-cyclopropyl derivatives of MPTP catalyzed by MAO-B may not be consistent with a pure SET pathway.     

Moderate chemical modifications of WAY-100635 improve the selectivity for 5-HT1A versus D4 receptors

The selectivity for 5-HT(1A) versus D(4) receptors is significantly increased when the basic side chain of WAY-100635 is replaced by a 4-phenylpiperazine (3e) or a 4-phenyl-1,2,3,6-tetrahydropyridine moiety (3i). The 4-phenyl-1,2,3,6-tetrahydropyridine compounds (3i-l) have a higher affinity for 5-HT(1A) receptors than do the corresponding unsubstituted phenylpiperazine analogues (3e-h). Compounds 3e and 3i appear to be selective for 5-HT(1A) receptors over other relevant receptors and still behave as neutral antagonists.     

Synthesis and structure-affinity relationships of 4-(5-Aryl-1,2,3,6-tetrahydropyridino)pyrimidine derivatives as corticotropin-releasing factor(1) receptor antagonists

Recently, various non-peptide corticotropin-releasing factor(1) (CRF(1)) receptor antagonists have been reported. Structure-affinity relationships (SARs) of non-peptide CRF(1) antagonists suggest that such antagonists can be constructed of three units: a hydrophobic unit (Up-Area), a proton accepting unit (Central-Area), and an aromatic unit (Down-Area). We previously presented 4-aryl-1,2,3,6-tetrahydropyridinopyrimidine derivatives including potent CRF receptor ligands 1a and 1b and proposed that the 4-aryl-1,2,3,6-tetrahydropyridino moiety might be useful as a substituent in the Up-Area. Our interest shifted to 5-aryl-1,2,3,6-tetrahydropyridinopyrimidine derivatives 2, among which compound 2m (CRA0165) had highest affinity for CRF(1) receptors (IC(50)=11nM). We report here the design, synthesis and SARs of derivatives 2.     

Rat liver microsomal enzyme catalyzed oxidation of 4-phenyl-trans-1-(2-phenylcyclopropyl)-1,2,3,6-tetrahydropyridine.

As part of our ongoing studies to characterize the catalytic pathway(s) for the monoamine oxidase and cytochrome P450 catalyzed oxidations of 1,4-disubstituted 1,2,3,6-tetrahydropyridinyl derivatives, we have examined the metabolic fate of 4-phenyl-trans-1-(2-phenylcyclopropyl)-1,2,3,6-tetrahydropyridine in NADPH supplemented rat liver microsomes. Three metabolic pathways have been identified: (1) allylic ring alpha-carbon oxidation to yield the dihydropyridinium species, (2) nitrogen oxidation to yield the N-oxide and (3) N-dealkylation to yield 4-phenyl-1,2,3,6-tetrahydropyridine and cinnamaldehyde. A possible mechanism to account for the formation of cinnamaldehye involves an initial single electron transfer from the nitrogen lone pair to the iron oxo system Fe(+3)(O) to form the corresponding cyclopropylaminyl radical cation that will be processed further to the final products. The reaction pathway leading to the dihydropyridinium metabolite may also proceed via the same radical cation intermediate but direct experimental evidence to this effect remains to be obtained.     

Evaluation of the Biological Activity of Several Analogs of the Dopaminergic Neurotoxin 1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine

Several analogs of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) were synthesized and screened for their capacity to be oxidized by monoamine oxidase (MAO-A or MAO-B) and their capacity to produce nigrostriatal dopaminergic neurotoxicity in mice. All of the compounds were relatively weak substrates for MAO-A but many of the compounds were found to be good substrates for MAO-B. Only three of the compounds, in addition to MPTP itself, were found to be neurotoxic. These were 1-methyl-4-cyclohexyl-1,2,3,6-tetrahydropyridine, 1-methyl-4-(2'-methylphenyl)-1,2,3,6-tetrahydropyridine and 1-methyl-4-(3'-methoxyphenyl)-1,2,3,6-tetrahydropyridine. All three of these neurotoxic compounds were found to be substrates for MAO-B; in contrast no compound was found to be neurotoxic that was not oxidized by MAO-B. The capacity of the compounds studied to be oxidized by MAO-B appears to be an important aspect of the neurotoxic process.     

3-(2-pyrrolidin-1-ylethyl)-5-(1,2,3,6-tetrahydropyridin-4-yl)-1H-indole derivatives as high affinity human 5-HT(1B/1D) ligands

A series of 3-(2-pyrrolidin-1-ylethyl)-5-(1,2,3,6-tetrahydropyridin-4-yl)-1H-indole derivatives (2) has been prepared using parallel synthesis techniques, and their structure-activity relationships studied. High affinity human 5-HT(1B/1D) (h5-HT(1B/1D)) ligands have been identified.     

Synthesis, SAR studies, and evaluation of 1,4-benzoxazepine derivatives as selective 5-HT1A receptor agonists with neuroprotective effect: Discovery of Piclozotan

A new series of 1,4-benzoxazepine derivatives was designed, synthesized, and evaluated for binding to 5-HT1A receptor and cerebral anti-ischemic effect. A lot of compounds exhibited nanomolar affinity for 5-HT1A receptor with good selectivity over both dopamine D2 and alpha1-adrenergic receptors. Among these compounds, 3-chloro-4-[4-[4-(2-pyridinyl)-1,2,3,6-tetrahydropyridin-1-yl]butyl]-1, 4-benzoxazepin-5(4H)-one (50: SUN N4057 (Piclozotan) as 2HCl salt) showed remarkable neuroprotective activity in a transient middle cerebral artery occlusion (t-MCAO) model.     

(R)-3-(N-methylpyrrolidin-2-ylmethyl)-5-(1,2,3,6-tetrahydropyridin-4-yl)-1H-indole derivatives as high affinity h5-HT1B/1D ligands

A series of (R)-3-(N-methylpyrrolidin-2-ylmethyl)-5-(1,2,3,6-tetrahydropyridin-4-yl)-1H-indole derivatives (2) have been prepared using parallel synthesis, and their structure-activity relationship studied. High affinity human 5-HT(1B/1D) (h5-HT(1B/1D)) ligands have been identified.     

New 5-HT1A receptor agonists possessing 1,4-benzoxazepine scaffold exhibit highly potent anti-ischemic effects

A series of new 3-substituted-4-(4-aminobutyl)-1,4-benzoxazepin-5(4H)-one derivatives (1-5) which showed a very high affinity for 5-HT1A receptor with good selectivity over dopamine D2 receptor was synthesized. Among these compounds, 3-chloro-4-[4-[4-(2-pyridinyl)-1,2,3,6-tetrahydropyridin-1-yl]butyl]-1,4-benzoxazepin-5(4H)-one (5: SUN N4057) exhibited remarkable neuroprotective activity in a transient middle cerebral artery occlusion (t-MCAO) model.     

Synthesis and MAO-B substrate properties of 1-methyl-4-heteroaryl-1,2,3,6-tetrahydropyridines

The parkinsonian inducing drug 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is bioactivated in a reaction catalyzed by the flavoenzyme monoamine oxidase B (MAO-B) to form the corresponding dihydropyridinium and subsequently pyridinium metabolites. As part of our ongoing studies to characterize the structural features responsible for this unexpected biotransformation, we have examined the MAO-B substrate properties of a variety of MPTP analogues bearing various heteroaryl groups at the 4-position of the tetrahydropyridinyl ring. The newly synthesized analogues are 4-(1-methylimidazol-2-yl)-, 4-(3-methylfuran-2-yl)-, 4-(3-methylthien-2-yl)-, 4-(3,4-dimethylpyrrol-1-yl)-, 4-(3-methylpyrrol-2-yl)-, and 4-(1,3-dimethylpyrrol-2-yl)-1-methyl-1,2,3,6-tetrahydropyridine. Except for the 4-(1-methylimidazol-2-yl) analogue, all compounds displayed good to excellent substrate properties. The 1-methyl-4-(3-methylfuran-2-yl) analogue is the most active member of this series with a kcat/Km value greater than 8,500 min(-1)mM(-1). The results of these studies are discussed in terms of catalytic pathways proposed for MAO-B.     

Analysis of γ-Aminobutyric AcidA Receptor Subunits in the Mouse Cochlea by Means of the Polymerase Chain Reaction

Abstract: Unlike 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), which produces consistent decreases in levels of striatal dopamine (DA) with considerably smaller and more variable effects on mouse brain levels of serotonin (5-HT) and norepinephrine (NE), a novel amine-substituted MPTP analogue, 1-methyl-4-(2'-aminophenyl)-1,2,3,6-tetrahydropyridine (2'-NH₂-MPTP), administered in a standard mouse dosing paradigm for MPTP (20 mg/kg X 4) did not affect striatal DA but led to marked reductions (60–70%) in levels of 5-HT, 5-hydroxyindoleacetic acid (5-HIAA), and NE measured in frontal cortex and hippocampus 1 week after treatment. Another 2'-substituted MPTP analogue, 1-methyl-4-(2'-methylphenyl)-1,2,3,6-tetrahydropyridine, affected cortical and hippocampal 5-HT, 5-HIAA, and NE only minimally, while markedly reducing the DA content in striatum (90%), thus indicating that the substituent (-NH₂ versus -CH₃) at the 2'position is important for the differential effects of these MPTP analogues. In a replication study with a 3-week end point, hippocampal and cortical 5-HT, 5-HIAA, and NE levels remained depressed with no indication of recovery. These results suggest that 2'-NH₂-MPTP may be a novel, regionally selective neurotoxin for serotonergic and norad-renergic nerve terminals.     

Chemical modification of aryl-1,2,3,6-tetrahydropyridinopyrimidine derivative to discover corticotropin-releasing factor(1) receptor antagonists: aryl-1,2,3,6-tetrahydropyridino-purine, -3H-1,2,3-triazolo[4,5-d)pyrimidine, -purin-8-one, and -7H-pyrrolo[2,3-d]pyrimidine derivatives

Structure-affinity relationships (SARs) of non-peptide CRF(1) antagonists suggest that such antagonists can be constructed of three units: a hydrophobic unit (Up-Area), a proton accepting unit (Central-Area), and an aromatic unit (Down-Area). Recently, various non-peptide corticotropin-releasing factor(1) (CRF(1)) receptor antagonists obtained by modification of the Central-Area have been reported. In contrast, we modified the Up-Area and presented 4- or 5-aryl-1,2,3,6-tetrahydropyridinopyrimidine derivatives including potent CRF receptor ligands 1a-c, and proposed that the 4- or 5-aryl-1,2,3,6-tetrahydropyridino moiety might be useful as a substituent in the Up-Area. Our interest shifted to the chemical modification in which the pyrimidine ring of 1a-c was replaced by other heterocycles, purine ring of 2, 3H-1,2,3-triazolo[4,5-d]pyrimidine ring of 3, purin-8-one ring of 4 and 7H-pyrrolo[2,3-d]pyrimidine ring of 5. Among them, 5-aryl-1,2,3,6-tetrahydropyridinopurine compound 6j (CRA0186) had the highest affinity for CRF(1) receptors (IC(50)=20nM). We report here the synthesis and SARs of derivatives 6-9.     

Chemically induced Parkinson's disease. II: Intermediates in the oxidation and reduction reactions of the 1-methyl-4-phenyl-2,3-dihydropyridinium ion and its deprotonated form

The one-electron reduction product of 1-methyl-4-phenyl-2,3-dihydropyridinium ion has been generated by pulse radiolysis and its absorption spectrum recorded. This radical was found to decay by second-order kinetics (2k = 9.5 x 10(8) M-1 s-1) to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine and 1-methyl-4-phenyl-2,3-dihydropyridinium ion. Reactions of the above radical species and that formed by one-electron reduction of 1-methyl-4-phenylpyridinium ion, which can also be generated by one-electron oxidation of 1-methyl-4-phenyl-1,2-dihydropyridine, with a number of molecules of biochemical interest have been studied. The one-electron reduction product of oxidised nicotinamide adenine dinucleotide efficiently reduced 1-methyl-4-phenyl-2,3-dihydropyridinium ion (k = 2.2 x 10(9) M-1 s-1). The relevance of these results in relation to redox cycling, a possible mechanism for 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine neurotoxicity, is discussed.     

Dicationic dithiocarbamate carbapenems with anti-MRSA activity.

A new class of 1 beta-methylcarbapenems bearing a doubly quaternarized 1,4-diazabicyclooctane (DABCO) substituted dithiocarbamate moiety at the C-2 side chain was prepared, and the biological profiles of the compounds, including in vitro and in vivo anti-MRSA activity and DHP-I susceptibility, were evaluated to identify a carbapenem derivative that was superior to BO-3482 (1). As a result, we discovered a 1 beta-methyl-2-[4-(4-carbamoylmethyl-1,4-diazabicyclo[2,2,2]octanediium-1-yl)methyl-1,2,3,6-tetrahydropyridinylthiocarbonylthio]carbapenem, 14a showing greater than 2-fold better anti-MRSA activity in a mouse infection model and 3-fold better DHP-I susceptibility as compared with BO-3482 (1).     

1 -Methyl-4-Phenyl- 1,2,3,6-Tetrahydropyridine: Correspondence of Its Binding Sites to Monoamine Oxidase in Rat Brain, and Inhibition of Dopamine Oxidative Deamination In Vivo and In Vitro

A saturable, specific, high-affinity binding site for [3H]1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine was found in rat brain homogenates. The CNS regional distribution, the subcellular fractionation, and the displacement by pargyline, clorgyline, and deprenyl suggest that this binding site may correspond to monoamine oxidase. 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine inhibited the oxidative deamination of dopamine, both in vivo and in vitro. Striatal levels of 3,4-dihydroxyphenylacetic acid were significantly reduced shortly after intravenous administration, and returned to normal values after a few hours. The in vitro formation of 3,4-dihydroxyphenylacetic acid from dopamine was inhibited by concentrations of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine comparable to those of pargyline.     

1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine- and 1-Methyl-4-(2''-Ethylphenyl)-1,2,3,6-Tetrahydropyridine-Induced Toxicity in PC 12 Cells: Role of Monoamine Oxidase A

The toxicity of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), 1-methyl-4-(2'-ethylphenyl)-1,2,3,6-tetrahydropyridine (2'Et-MPTP), and their corresponding pyridinium species was studied in the rat pheochromocytoma PC12 cell line. MPTP and its analogues are known to be metabolized by monoamine oxidase (MAO) to dihydropyridinium intermediates which are further transformed, either enzymatically or spontaneously, into pyridinium species. MAO activity in PC12 cells is almost exclusively of the A form, and 2'Et-MPTP is a good substrate for both MAO-A and MAO-B. In contrast, MPTP is a poor substrate for MAO-A, but a good substrate for MAO-B. 2'Et-MPTP caused considerably more cell death than MPTP in the PC12 cells. However, 1-methyl-4-(2'-ethylphenyl)pyridinium and 1-methyl-4-phenylpyridinium, the corresponding pyridinium species formed from 2'Et-MPTP and MPTP, respectively, were equipotent as toxins. The toxic effects of the tetrahydropyridines and their corresponding pyridiniums were both concentration- and time-dependent. Measurements of the levels of the pyridinium species formed and the remaining tetrahydropyridine in the media indicated that 2'Et-MPTP was converted about five to seven times more readily into its toxic pyridinium species than was MPTP. There was, moreover, an excellent correlation between amount of pyridinium formed and cell death. There was also a parallel between the capacity of clorgyline and pargyline, irreversible MAO inhibitors, to decrease the formation of the pyridinium species and their capacity to protect against the toxic actions of the tetrahydropyridines. These data are consistent with the concept that the MAO-A-dependent formation of the pyridinium species from the tetrahydropyridine is a prerequisite for toxicity in PC12 cells.