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Synthesis and pharmacological studies of 4,4-disubstituted piperidines: a new class of compounds with potent analgesic properties.

A series of 4,4-disubstituted piperidines has been synthesized and evaluated for analgesic activity. Several of these analogues show analgesic potency comparable to morphine in the mouse writhing and tail-flick tests. A number of compounds exhibit high affinity for [3H]naloxone binding sites in rat brain membranes. Among the most potent derivatives are compounds 15 and 48. Although opiate-like, attempts to modify this activity with various substituents have failed to produce antagonistic properties. A few of these analogues also show marked long-lasting serotonin antagonism in the guinea pig serotonin toxicity test and the DL-5-hydroxytryptophan induced head-twitch model in the mouse.

5-Hydroxytryptophan↗

4-(Diphenylmethyl)-1-[(imino)methyl]piperidines as gastric antisecretory agents.

4-(Diphenylmethyl)-1-piperidinemethanimine (1) is a potent oral gastric antisecretory agent in rats but contains a strong anticholinergic component. Since a nonanticholinergic gastric antisecretory drug would be useful in the treatment of peptic ulcer disease, a program was initiated by us to find such an agent based on 1. Compound 1 contains structural elements common to the anticholinergics atropine and homatropine. Studies on the structure-activity relationships of these compounds and their derivatives have revealed certain modifications that diminish or abolish anticholinergic activity. The application of these modifications to the design of analogues of 1 afforded an antisecretory compound, 4-(diphenylmethyl)-1-[(octylimino)methyl]piperidine (3h, fenoctimine), which exhibited no anticholinergic activity. Fenoctimine is undergoing clinical trial as a gastric antisecretory drug.

Animals↗

Novel tetracyclic spiropiperidines. 4. Synthesis and pharmacological evaluation of spiro- and 6,7-dihydrospiro[benzo[b]pyrrolo[3,2,1-jk][1,4]benzodiazepine-2 (1H),4'-piperidine]s.

A previously described series of 1-arylspiro[indoline-3,4'-piperidine]s was reported by us to possess significant antidepressant properties. This biological activity was found to be at a maximum among those compounds bearing an ortho substituent (e.g., NH2 as in 1) in the pendant aryl ring. In order to explore further this "ortho effect", we synthesized cyclic analogues of type 3 and 4 in which the position of the o-NH2-substituted aryl group is conformationally restricted and defined. When tested for antidepressant activity by tetrabenazine ptosis prevention in mice, it was found that restriction of rotation of the pendant o-aminophenyl group in these rigid analogues resulted in a loss of antidepressant properties. However, analgesic activity was retained and even improved by this molecular constraint.

Animals↗

3-[(2-ethoxyphenoxy)methyl]piperidine derivatives. Synthesis and antidepressant activity.

The 3-[(2-ethoxyphenoxy)methyl]piperidine derivatives 3-5 were synthesized and screened as potential antidepressant agents by the reserpine interaction test in mice and the evaluation of reuptake inhibition of biogenic amines in pig brain synaptosomal fractions. In addition, their anticonvulsant activity, tested by pentyleneetrazole antagonism, and approximate acute toxicity were evaluated. In vivo and in vitro tests showed that compounds 3 and 5 possess a biological activity comparable to that of the antidepressant drug viloxazine.

Animals↗

Quantitative structure-activity relationships and eudismic analyses of the presynaptic dopaminergic activity and dopamine D2 and sigma receptor affinities of 3-(3-hydroxyphenyl)piperidines and octahydrobenzo[f]quinolines.

Data from the preceding paper were examined by QSAR and eudismic analyses. A fair parabolic relationship was found between the lipophilicity (measured by a RP-HPLC method) and the sigma-receptor affinity of 3-(3-hydroxyphenyl)piperidines (3HPP derivatives) and octahydrobenzo[f]quinolines (OHBQ derivatives). As far as the dopamine D2 receptor is concerned, the trans-7-hydroxy-OHBQ derivatives show a 10-fold higher affinity than the eutomeric S enantiomers of 3HPP derivatives, once lipophilicity has been accounted for. This difference in affinity is suggested to correspond to the energy necessary for the 3HPP derivatives to adopt the receptor-bound conformation. The R enantiomers of 3HPP derivatives display no apparent increase in D2 affinity with increasing lipophilicity, and indeed the eudismic index in this series increases with affinity (eudismic affinity quotient = 0.70), in agreement with a recent model of the binding of N-propyl-3HPP (3PPP) enantiomers to the D2 receptor. The selectivity in sigma/D2 affinities was found to depend on both lipophilicity and configuration of the ligands; thus, the selectivity is maximal for log kw values of ca. 1.7-2.1 and is much larger for the R than for the S enantiomers of 3HPP derivatives.

Phenanthrenes↗

Synthesis, pharmacological action, and receptor binding affinity of the enantiomeric 1-(1-phenyl-3-methylcyclohexyl)piperidines.

The cis and trans enantiomers of the 1-(1-methylcyclohexyl)piperidines were prepared from either 3(R)- or 3(S)-methylcyclohexanone through the Bruylents reaction or a modified azide route, respectively. Separation of the intermediate amines 5 and 6 was achieved through chromatography or selective crystallization of a fumarate salt. The cis isomer 2b had about one-third of the affinity of phencyclidine for the PCP receptor. The other isomers were less potent. There was a 40-fold difference between the binding affinity of the cis enantiomers 2a and 2b and a fourfold difference between the affinities of the trans enantiomers 1a and 1b. None of the compounds antagonized the stereotypy induced by phencyclidine in the rotorod assay in mice, after intraperitoneal introduction.

Animals↗

4-(Phenylsulfonyl)piperidines: novel, selective, and bioavailable 5-HT(2A) receptor antagonists.

On the basis of a spirocyclic ether screening lead, a series of acyclic sulfones have been identified as high-affinity, selective 5-HT(2A) receptor antagonists. Bioavailability lacking in the parent, 1-(2-(2,4-difluorophenyl)ethyl)-4-(phenylsulfonyl)piperidine (12), was introduced by using stability toward rat liver microsomes as a predictor of bioavailability. By this means, the 4-cyano- and 4-carboxamidophenylsulfonyl derivatives 26 and 31 were identified as orally bioavailable, brain-penetrant analogues suitable for evaluation in animal models. Bioavailability was also attainable by N substitution leading to the N-phenacyl derivative 35. IKr activity detected through counterscreening was reduced to insignificant levels in vivo with the latter compound.

Administration, Oral↗

Synthesis, SAR, and biological evaluation of oximino-piperidino-piperidine amides. 1. Orally bioavailable CCR5 receptor antagonists with potent anti-HIV activity.

We previously reported the discovery of 4-[(Z)-(4-bromophenyl)(ethoxyimino)methyl]-1'-[(2,4-dimethyl-3-pyridinyl)carbonyl]-4'-methyl-1,4'-bipiperidine N-oxide 1 (SCH 351125) as an orally bioavailable human CCR5 antagonist for the treatment of HIV-1 infection. Herein, we describe in detail the discovery of 1 from our initial lead compound as well as the synthesis and SAR studies directed toward optimization of substitution at the phenyl, oxime, and right-hand side amide groups in the oximino-piperidino-piperidine series. Substitutions (4-Br, 4-CF(3), 4-OCF(3), 4-SO(2)Me, and 4-Cl) at the phenyl group are well-tolerated, and small alkyl substitutions (Me, Et, (n)()Pr, (i)()Pr, and cyclopropyl methyl) at the oxime moiety are preferred for CCR5 antagonism. The 2,6-dimethylnicotinamide N-oxide moiety is the optimal choice for the right-hand side. Several compounds in this series, including compound 1, exhibited excellent antiviral activity in vitro. Compound 1, which has a favorable pharmacokinetic profile in rodents and primates, excellent oral bioavailability, and potent antiviral activity against a wide range of primary HIV-1 isolates, is a potentially promising new candidate for treatment of HIV-1 infection.

Administration, Oral↗

High affinity hydroxypiperidine analogues of 4-(2-benzhydryloxyethyl)-1-(4-fluorobenzyl)piperidine for the dopamine transporter: stereospecific interactions in vitro and in vivo.

In our effort to develop high-affinity ligands for the dopamine transporter which might find potential use as cocaine medication, a polar hydroxy substituent was introduced into the piperidine ring of one of our disubstituted lead analogues derived from 1-[2-(diphenylmethoxy)-ethyl]-4-(3-phenylpropyl)piperazine (GBR 12935). Both cis- and trans-3-hydroxy derivatives were synthesized and the racemic trans isomer, (+/-)-5, was further resolved into two enantiomers. Newly synthesized compounds were characterized for their binding affinity at the dopamine, serotonin, and norepinephrine transporter systems in rat brain. The two enantiomers (+)-5 and (-)-5 exhibited marked differential affinities at the dopamine transporter with (+)-5 being 122-fold more potent than (-)-5 in inhibiting radiolabeled cocaine analogue binding (IC(50); 0.46 vs 56.7 nM) and 9-fold more active for inhibiting dopamine uptake (IC(50); 4.05 vs 38.0 nM). Furthermore, the most active (+)-5 was 22-fold more potent at the dopamine transporter compared to the standard GBR 12909. Absolute configuration of one of the enantiomers was determined unambiguously by X-ray structural analysis. In in vivo locomotor activity studies, the enantiomer (+)-5 and the racemic (+/-)-5, but not (-)-5, exhibited stimulant activity with a long duration of effect. All three compounds, (+)-5, (-)-5, and (+/-)-5, within the dose range tested, partially (50%) but incompletely (80%) produced cocaine-like responses in mice trained to discriminate 10 mg/kg ip cocaine from vehicle. Compound (-)-5 was distinctive in this regard in that, unlike (+)-5 and (+/-)-5, it did not affect locomotor activity yet, but similar to them, was able to engender (albeit incompletely) cocaine-like responses.

Animals↗

Novel apoptosis-inducing trans-platinum piperidine derivatives: synthesis and biological characterization.

The synthesis, chemical characterization, and interaction with cells of new sterically hindered trans- and cis-diaminedichloroplatinum(II) complexes are described. The amine ligands include monofunctional piperidine (pip) and piperazine (pz). The poor solubility of trans-diaminedichloroplatinum complexes was overcome by introducing the positively charged pz ligand, which allows retaining of the classic platinum coordination sphere. In vitro evaluation in OV-1063 and C-26 tumor cells revealed that replacing one NH3 of the inactive transplatin by an aromatic planar ligand (4-picoline, 4-pic) or by an aliphatic nonplanar heterocyclic ligand (pip) or replacing both NH3 groups with a 4-pic ligand and a pip or pz ligand significantly increases the cytotoxic activity of these complexes. The unsymmetric complexes trans-[PtCl2(4-pic)(pip)] and trans-[PtCl2(4-pic)(pz)]HCl were the most cytotoxic compounds against the cisplatin-sensitive tumor cell line C-26 (IC50 = 4.5 and 5.5 microM, respectively) and the cisplatin-sensitive tumor cell line OV-1063 (IC50 = 6.5 and 7.4 microM, respectively). In contrast, replacing one NH3 of the cis isomer by an aromatic planar ligand (4-pic) or by an aliphatic amine lowered their cytotoxiciy in comparison to cisplatin. Cell penetration and Pt-DNA adduct formation were also evaluated, and it was clearly shown that both trans-[PtCl2(4-pic)(pip)] and trans-[PtCl2(4-pic)(pz)]HCl penetrate efficiently the cellular membrane of the tumor cells and platinate the cellular DNA. When comparing cellular DNA platination, positively charged trans-[PtCl2(4-pic)(pz)]HCl was 7-fold higher than both cisplatin and its neutral analogue trans-[PtCl2(4-pic)(pip)]. Moreover, in contrast to cisplatin, in the cell lines used, cell death caused by both complexes appeared to be apoptotic according to several criteria including early phosphatidylserine exposure, activation of caspases, and characteristic morphological changes. Our results suggest that these novel mixed nonclassical trans-Pt(II) complexes are biologically and mechanistically distinct from known Pt complexes and deserve evaluation of their efficacy in tumor-bearing animals.

Antineoplastic Agents↗

Generation of predictive pharmacophore models for CCR5 antagonists: study with piperidine- and piperazine-based compounds as a new class of HIV-1 entry inhibitors.

Predictive pharmacophore models were developed for a large series of piperidine- and piperazine-based CCR5 antagonists as anti-HIV-1 agents reported by Schering-Plough Research Institute in recent years. The pharmacophore models were generated using a training set consisting of 25 carefully selected antagonists based on well documented criteria. The activity spread, expressed in K(i), of training set molecules was from 0.1 to 1300 nM. The most predictive pharmacophore model (hypothesis 1), consisting of five features, namely, two hydrogen bond acceptors and three hydrophobic, had a correlation (r) of 0.920 and a root mean square of 0.879, and the cost difference between null cost and fixed cost was 44.46 bits. The model was cross-validated by randomizing the data using the CatScramble technique. The results confirmed that the pharmacophore models generated from the test set were not due to chance correlation. The best model (hypothesis 1) was validated using test set molecules (total of 78) and performed well in classifying active and inactive molecules correctly. The model was further validated by mapping onto it a diverse set of six CCR5 antagonists identified by five different pharmaceutical companies. The best model correctly predicted these compounds as being highly active. These multiple validation approaches provide confidence in the utility of the predictive pharmacophore model developed in this study as a 3D query tool in virtual screening to retrieve new chemical entities as potent CCR5 antagonists. The model can also be used in predicting biological activities of compounds prior to undertaking their costly synthesis.

Algorithms↗

A novel series of piperidin-4-yl-1,3-dihydroindol-2-ones as agonist and antagonist ligands at the nociceptin receptor.

A series of N-(4-piperidinyl)-2-indolinones were discovered as a new structural class of nociceptin receptor (NOP) ligands. Unlike other previously reported classes of NOP receptor ligands, modifications of the piperidine N substituents afforded both potent agonists and antagonists, with modest selectivities over other opioid receptors. The SAR revealed in this new series will provide important insights for the development of pharmacophores for agonist and antagonist actions at the NOP receptor.

Animals↗

Piperidine-based nocaine/modafinil hybrid ligands as highly potent monoamine transporter inhibitors: efficient drug discovery by rational lead hybridization.

Some piperidine-based nocaine/modafinil hybrid ligands have been designed, synthesized, and found to display an improved potency at all three monoamine transporters and particularly for DAT and/or NET. Some highly active and selective monoamine transporter inhibitors with low nanomolar to subnanomolar potency were identified. Ligands of this type may find important applications as positron emission tomography imaging tools and in the treatment of central nervous system disorders such as depression and sleep apnea.

Animals↗

Tricyclic pyrazoles. 3. Synthesis, biological evaluation, and molecular modeling of analogues of the cannabinoid antagonist 8-chloro-1-(2',4'-dichlorophenyl)-N-piperidin-1-yl-1,4,5,6-tetrahydrobenzo[6,7]cyclohepta[1,2-c]pyrazole-3-carboxamide.

A series of analogues of 8-chloro-1-(2',4'-dichlorophenyl)-N-piperidin-1-yl-1,4,5,6-tetrahydrobenzo[6,7]cyclohepta[1,2-c]pyrazole-3-carboxamide 4a (NESS 0327) (Ruiu, S.; Pinna, G. A.; Marchese, G.; Mussinu, J. M.; Saba, P.; Tambaro, S.; Casti, P.; Vargiu, R.; Pani, L. Synthesis and Characterization of NESS 0327: A Novel Putative Antagonist of CB1 Cannabinoid Receptor. J. Pharmacol. Exp. Ther. 2003, 306, 363-370) was synthesized and evaluated for their affinity to cannabinoid receptors. Depending on the chemical modification of the lead structure that was chosen, compounds 4b, 4c, 4i, 4l, and 4m still proved to be potent binders of the CB1 receptor. Moreover, several analogues (4c, 4d, 4e, and 4m) demonstrated superior CB2 receptor binding affinities compared to the parent ligand. Compounds 4b, 4c, 4i, and 4l displayed the most promising pharmacological profiles, having the highest selectivity for CB1 receptors with Ki(CB2) to Ki(CB1) ratios of 11,250, 2000, 3330 and 4625, respectively. Compound 4c increased the intestinal propulsion in mice and antagonized the effect induced by the CB1 receptor agonist WIN 55,212-2. Finally, molecular modeling studies were carried out on a set of tricyclic pyrazoles (2a-4a) and on rimonabant 1 (SR141716A), indicating that high CB1 receptors affinities were consistent for the tricyclic derivatives, both with a nonplanar geometry of the tricyclic cores and with a precise orientation of the substituent (chlorine) on this ring system.

Animals↗

Methyl substitution on the piperidine ring of N-[omega-(6-methoxynaphthalen-1-yl)alkyl] derivatives as a probe for selective binding and activity at the sigma(1) receptor.

The N-(6-methoxy-1,2,3,4-tetrahydronaphthalen-1-yl)propyl and N-(6-methoxynaphthalen-1-yl)propyl derivatives as well as their upper homologous butyl derivatives of various methylpiperidines were prepared. The piperidine moiety bearing monomethyl or geminal dimethyl groups was employed as a probe to explore sigma-subtype affinities and selectivities by radioligand binding assays at sigma(1) and sigma(2) receptors and the Delta(8)-Delta(7) sterol isomerase (SI) site. 4-Methyl derivative 31 was the most potent sigma(1) ligand (K(i)=0.030 nM) with a good selectivity profile (597-fold and 268-fold relative to sigma(2) receptor and SI site, respectively), whereas 3,3-dimethyl derivative 26 (K(i)=0.35 nM) was the most selective (680-fold) relative to the sigma(2) receptor. Both compounds can be proposed as tools for PET experiments. Furthermore, the naphthalene compounds 26, 28, 31, and 33 demonstrated antiproliferative activity in rat C6 glioma cells (EC(50) = 15.0 microM for 33), revealing a putative sigma(1) antagonist activity and opening a useful perspective in tumor research and therapy.

Animals↗

Tricyclic pyrazoles. 4. Synthesis and biological evaluation of analogues of the robust and selective CB2 cannabinoid ligand 1-(2',4'-dichlorophenyl)-6-methyl-N-piperidin-1-yl-1,4-dihydroindeno[1,2-c]pyrazole-3-carboxamide.

New analogues (2a-p) of the previously reported CB(2) ligands 6-methyl- and 6-chloro-1-(2',4'-dichlorophenyl)-N-piperidin-1-yl-1,4-dihydroindeno[1,2-c]pyrazole-3-carboxamides (1a,b) have been synthesized and evaluated for cannabinoid receptor affinity. One example, 1-(2',4'-dichlorophenyl)-6-methyl-N-cyclohexyilamine-1,4-dihydroindeno[1,2-c] pyrazole-3-carboxamide (2a) was shown to have single digit nanomolar affinity for cannabinoid CB(2) receptors. Furthermore, compounds 2a and 2b, as well as lead structures 1a,b, were also shown to be agonist in an in vitro model based on human promyelocytic leukemia HL-60 cells.

HL-60 Cells↗

N-heteroaryl-2-phenyl-3-(benzyloxy)piperidines: a novel class of potent orally active human NK1 antagonists.

The preparation of a series of N-heteroarylpiperidine ether-based human NK1 antagonists is described. Two of the compounds 3-[-(2S,3S)-3-(((3,5-bis(trifluoromethyl)phenyl)methyl)oxy)- 2-phenylpiperidino}methyl]-1,2,4-triazole (11) and 5-[¿(2S,3S)-3-(((3,5-bis(trifluoromethyl)-phenyl)methyl)oxy)-2- phenylpiperidino}methyl]-3-oxo-1,2,4-triazolone (12)), in particular, are orally bioavailable and exhibited significant improvements in potency, both in vitro and in vivo, over the lead (carboxamidomethyl)piperidine ether 1. Rat liver microsome studies on a selected number of compounds from this series show the triazolone heterocycle to be considerably more stable than the others. Furthermore, both 11 and 12 have been profiled in a number of assays that may be predictive of the clinical utility of substance P antagonists.

Animals↗

Targeting delavirdine/atevirdine resistant HIV-1: identification of (alkylamino)piperidine-containing bis(heteroaryl)piperazines as broad spectrum HIV-1 reverse transcriptase inhibitors.

A novel class of bis(heteroaryl)piperazine (BHAP) analogs which possesses the ability to inhibit NNRTI (non-nucleoside reverse transcriptase inhibitor) resistant recombinant HIV-1 reverse transcriptase (RT) and NNRTI resistant variants of HIV-1 has been identified via targeted screening. Further investigation of the structure-activity relationships of close congeners of these novel (alkylamino)piperidine BHAPs (AAP-BHAPs) led to the synthesis of several compounds possessing the desired phenotype (e.g., activity against recombinant RTs carrying the Y181C and P236L substitutions). Further structural modifications were required to inhibit metabolism and modulate solubility in order to obtain compounds with the desired biological profile as well as appropriate pharmaceutical properties. The AAP-BHAPs with the most suitable characteristics were compounds 7, 15, and 36.

Animals↗