Sulfide analogues as potent and selective M(2) muscarinic receptor antagonists

We have discovered highly potent, selective sulfide M(2) receptor antagonists with low molecular weight and different structural features compared with our phase I clinical candidate Sch 211803. Analogue 30 showed superior M(2) receptor selectivity profile over Sch 211803. More importantly, this study provided new leads for the discovery of M(2) receptor antagonists as potential drug candidates.     

Indanyl piperazines as melatonergic MT2 selective agents

Optimization of a benzyl piperazine pharmacophore produced N-acyl-4-indanyl-piperazines that bind with high affinity to melatonergic MT(2) receptors. (R)-4-(2,3-dihydro-6-methoxy-1H-inden-1-yl)-N-ethyl-1-piperazine-carboxamide fumarate (13) is a water soluble, selective MT(2) agonist, which produces advances in circadian phase in rats at doses of 1-56 mg/kg that are no different from those of melatonin at 1 mg/kg. Unlike melatonin, 13 produced only weak contractile effects in rat tail artery.     

2-(Arylmethyl)-3-substituted quinuclidines as selective alpha 7 nicotinic receptor ligands

A series of 2-(arylmethyl)-3-substituted quinuclidines was developed as alpha7 neuronal nicotinic acetylcholine receptor (nAChR) agonists based on a putative pharmacophore model. The series is highly selective for the alpha7 over other nAChRs (e.g., the alpha4beta2 of the CNS, and the muscle and ganglionic subtypes) and is functionally tunable at alpha7. One member of the series, (+)-N-(1-azabicyclo[2.2.2]oct-3-yl)benzo[b]furan-2-carboxamide (+)-8l), has potent agonistic activity for the alpha7 nAChR (EC(50)=33nM, I(max)=1.0), at concentrations below those that result in desensitization.     

Diphenyl sulfoxides as selective antagonists of the muscarinic M2 receptor

Structure activity studies on [4-(phenylsulfonyl)phenyl]methylpiperazine led to the discovery of 4-cyclohexyl-alpha-[4-[[4-methoxyphenyl(S)-sufinyl]phenyl]-1-pi perazineacetonitrile, 1, an M2 selective muscarinic antagonist. Affinity at the cloned human M2 receptor was 2.7 nM; the M1/M2 selectivity is 40-fold.     

Substituted phenoxypropyl-(R)-2-methylpyrrolidine aminomethyl ketones as histamine-3 receptor inverse agonists

Optimization of a series of aminomethyl ketone diamine H(3)R antagonists to reduce the brain exposure by lowering the pKa, led to molecules with improved pharmacokinetic properties. Compounds 9, 19, and 25 had high affinity for human H(3)R and demonstrated in vivo H(3)R functional activity in the rat dipsogenia model. Compound 9 displayed modest wake-promoting activity in the rat EEG/EMG model.     

Design and pharmacology of quinuclidine derivatives as M2-selective muscarinic receptor ligands

In our search for M2-selective muscarinic receptor antagonists, we synthesized 1,3-disubstituted indenes. The effects of different basic moieties with regard to binding and selectivity towards the five distinct muscarinic receptor subtypes were investigated. The results show that the quinuclidine series afforded the most promising compounds in terms of both receptor affinity and M2-subtype selectivity.     

Synthesis and biological evaluation of (2S)- and (2R)-2-(3'-phosphonobicyclo[1.1.1]pentyl)glycines as novel group III selective metabotropic glutamate receptor ligands

The synthesis of (2S)- and (2R)-2-(3'-phosphonobicyclo[1.1.1]pentyl)glycine isomers (10 and 11), characterized by the bioisosteric replacement of the distal carboxylic group of 2-(3'-carboxybicyclo[1.1.1]pent-1-yl)glycine by the phosphonate moiety, was accomplished by a stereoselective Ugi condensation. The two isomers were tested for their activity against an array of metabotropic glutamate receptors, and the S-isomer (10) turned out to be a moderately potent and selective mGluR4 agonist.     

Substituted piperazines as novel dipeptidyl peptidase IV inhibitors

Incorporation of a fluorophenyl beta-amino amide moiety into piperazine screening lead 2 has resulted in the discovery of a structurally novel series of potent and selective DP-IV inhibitors. Simplification of the molecule and incorporation of multiple fluorine atoms on the phenyl ring has provided low molecular weight analogs such as compound 32, which is a 19nM DP-IV inhibitor with >4000-fold selectivity over QPP.     

Benzoyl 2-methyl indoles as selective PPARgamma modulators

Routine screening for human PPAR ligands yielded compounds 1 and 2, both of which were sub-micromolar hPPARgamma agonists. Synthetic modifications of these leads led to a series of potent substituted 3-benzyl-2-methyl indoles, a subset of which were noted to be selective PPARgamma modulators (SPPARgammaMs). SPPARgammaM 24 displayed robust anti-diabetic activity with an improved therapeutic window in comparison to a PPARgamma full agonist in a rodent efficacy model.     

Stereoselectivity of (R)- and (S)-hexahydro-difenidol binding to neuroblastoma M1, cardiac M2, pancreatic M3, and striatum M4 muscarinic receptors

(R)-Hexahydro-difenidol has a higher affinity for M1 receptors in NB-OK 1 cells, pancreas M3 and striatum M4 receptors (pKi 7.9 to 8.3) than for cardiac M2 receptors (pKi 7.0). (S)-Hexahydro-difenidol, by contrast, is nonselective (pKi 5.8 to 6.1). Our goal in the present study was to evaluate the importance of the hydrophobic phenyl, and cyclohexyl rings of hexahydro-difenidol for the stereoselectivity and receptor selectivity of hexahydro-difenidol binding to the four muscarinic receptors. Our results indicated that replacement of the phenyl ring of hexahydro-difenidol by a cyclohexyl group (----dicyclidol) and of the cyclohexyl ring by a phenyl moiety (----difenidol) induced a large (4- to 80-fold) decrease in binding affinity for all muscarinic receptors. Difenidol had a significant preference for M1, M3, and M4 over M2 receptors; dicyclidol, by contrast, had a greater affinity for M1 and M4 than for M2 and M3 receptors. The binding free energy decrease due to replacement of the phenyl and the cyclohexyl groups of (R)-hexahydro-difenidol by, respectively, a cyclohexyl and a phenyl moiety was almost additive in the case of M4 (striatum) binding sites. In the case of the cardiac M2, pancreatic M3, or NB-OK 1 M1 receptors the respective binding free energies were not completely additive. These results suggest that the four (R)-hexahydro-difenidol "binding moieties" (phenyl, cyclohexyl, hydroxy, and protonated amino group) cannot simultaneously form optimal interactions with the M1, M2, and M3 muscarinic receptors.(ABSTRACT TRUNCATED AT 250 WORDS)     

2-(4,5-Dihydroimidazol-2-yl)benzimidazoles as highly selective imidazoline I2/adrenergic alpha2 receptor ligands

2-(4,5-Dihydroimidazol-2-yl)benzimidazoles have been identified as selective imidazoline I2/alpha2-adrenoceptor ligands. 4-Methyl (2) and 4-chloro (4) derivatives display I2 affinity at nanomolar concentration (Ki=4.4 and 17.7 nM, respectively) and high I2/alpha2 selectivity ratio=4226 and 5649, respectively. An evidence has been obtained that pKa value influences considerably the I2/alpha2-selectivity ratio of this class of imidazoline I2 receptor ligands.     

(2R)-2-methylchromane-2-carboxylic acids: discovery of selective PPARalpha agonists as hypolipidemic agents

A SAR study was conducted on chromane-2-carboxylic acid toward selective PPARalpha agonisim. As a result, highly potent, and selective PPARalpha agonists were discovered. The optimized compound 43 exhibited robust lowering of total cholesterol levels in hamster and dog animal models.     

Trafficking of M(2) muscarinic acetylcholine receptors

Internalization is an important mechanism regulating the agonist-dependent responses of G-protein-coupled receptors. The internalization of the M(2) muscarinic cholinergic receptors (mAChR) in HEK293 cells has been demonstrated to occur by an unknown mechanism that is independent of arrestins and dynamin. In this study we examined various aspects of the trafficking of the M(2) mAChR in HEK293 cells to characterize this unknown pathway of internalization. Internalization of the M(2) mAChR was rapid and extensive, but prolonged incubation with agonist did not lead to appreciable down-regulation (a decrease in total receptor number) of the receptors. Recovery of M(2) mAChRs to the cell surface following agonist-mediated internalization was a very slow process that contained protein synthesis-dependent and -independent components. The protein synthesis-dependent component of the recovery of receptors to the cell surface did not appear to reflect a requirement for synthesis of new receptors, as no changes in total receptor number were observed either in the presence or absence of cycloheximide. Phosphorylation of the M(2) mAChR did not appear to influence the rate or extent of the recovery of receptors to the cell surface, as the recovery of a phosphorylation-deficient mutant M(2) mAChR, the N,C(Ala-8) mutant, was similar to the recovery of the wild type M(2) mAChR. Finally, the constitutive, nonagonist-dependent internalization and recycling of the M(2) mAChR was very slow and also contained protein synthesis-dependent and -independent components, suggesting that a similar pathway controls the recovery from agonist-dependent and -independent internalization. Overall, these data demonstrated a variety of previously unappreciated facets involved in the regulation of M(2) mAChRs.     

Synthesis and structure-activity relationships of M(2)-selective muscarinic receptor ligands in the 1-[4-(4-arylsulfonyl)-phenylmethyl]-4-(4-piperidinyl)-piperazine family

The synthesis and muscarinic binding properties of compounds based on the 1-[4-(4-arylsulfonyl)phenylmethyl]-4-(1-aroyl-4-piperidinyl)-piperazine skeleton are described. For compounds, substituted with appropriately configured methyl groups at the benzylic center and at the piperazine 2-position, high levels of selective, M(2) subtype affinity could be obtained, particularly when the terminal N-aroyl residue was ortho-substituted.     

Muscarinic M(3) receptor antagonists with (2R)-2-[(1R)-3,3-difluorocyclopentyl]-2-hydroxyphenylacetamide Structures. Part 2

Optimization of the amine part of our original muscarinic M(3) receptor antagonist 1 was performed to identify M(3) receptor antagonists that are superior to 1. Compounds carrying a variety of diamine moieties without hydrophobic substituent on the nitrogen atom were screened against the binding affinity for the M(3) receptor and the selectivity for M(3) over the M(1) and M(2) receptors. This process led to a 4-aminopiperidinamide (2l) with a K(i) value of 5.1 nM and with a selectivity of the M(3) receptor that was 46-fold greater than that of the M(2) receptor. Further derivatization of 2l by inserting a spacer group or by incorporating alkyl group(s) into the amine part resulted in the identification of an 4-(aminoethyl)piperidinamide 2l-b with a K(i) value of 3.7 nM for the M(3) receptor and a selectivity for the M(3) receptor that was 170-fold greater than that of the M(2) receptor.     

Recombinant expression of a selective blocker of M(1) muscarinic receptors

Mamba venoms contain peptides with high selectivity for muscarinic receptors. Due to the limited availability of the M(1) muscarinic receptor-selective MT7 or m1-toxin 1, the peptide was expressed in Sf9 cells using a synthetic cDNA and purified. The isolated peptide had over four orders of magnitude higher affinity for the M(1) compared to M(2)-M(5) muscarinic receptors. The peptide strongly inhibited Ca(2+) mobilisation through recombinant and endogenously expressed M(1) receptors, having no effect on the function of the other subtypes. The MT7 peptide provides a unique tool for identification and functional characterisation of M(1) receptors in cells and tissues.     

Substituted 3-(2-benzoxazyl)-benzimidazol-2-(1H)-ones: a new class of GABA(A) brain receptor ligands

A novel class of potent benzodiazepine receptor (BZR) ligands has been designed and synthesized aided by molecular modeling of known benzodiazepine ligands such as CGS-8216 and the use of known pharmacophore models.     

Design and synthesis of ether analogues as potent and selective M2 muscarinic receptor antagonists

Novel, selective M2 muscarinic antagonists, which replace the metabolically labile styrenyl moiety of the prototypical M2 antagonist 1 with an ether linkage, were synthesized. A detailed SAR study in this class of compounds has yielded highly active compounds that showed M2 Ki values of < 1.0 nM and >100-fold selectivity against M1, M3, and M5 receptors.     

Synthesis of 3-phenylnaphthalenic derivatives as new selective MT(2) melatoninergic ligands

A series of naphthalenic analogues of melatonin were prepared and evaluated as melatonin receptor MT(2) selective ligands. Activity and MT(2) selectivity can be modulated with suitable variations of the C-3 phenyl and the acyl group on the C-1 side chain. Surprisingly, in contrast with what had been previously described in other series (2-benzylindoles, 2-benzylbenzofurans and 3-phenyltetralins), the presence of a C-3 phenyl with a functional group on the meta position seems to be primordial for MT(2) affinity and selectivity. Indeed, N-[2-(3-(3-hydroxymethylphenyl)-7-methoxynaphth-1-yl)ethyl]acetamide (21) is one of the best MT(2) selective ligands described until now and behaves as an antagonist.     

Pharmacokinetic simulations of SPECT quantitation of the M2 muscarinic neuroreceptor subtype in disease states using radioiodinated (R,R)-4IQNB.

Alzheimer's disease (AD) involves selective loss of muscarinic M2, but not M1, subtype neuroreceptors in the posterior parietal cortex of the human brain. Emission tomographic study of the loss of M2 receptors in AD is limited by the fact that there is currently no available M2-selective radioligand which can penetrate the blood-brain barrier. However, by taking advantage of the different pharmacokinetic properties of (R,R)-[123I]IQNB for the M1 and M2 subtypes, it may be possible to estimate losses in M2. It has previously been hypothesized that the difference between an early study and a late study should provide information on the M2 receptor population. In order to test this hypothesis, we present here the results of pharmacokinetic simulations of the in vivo localization of (R,R)-[123I]IQNB in brain regions containing various proportions of M1 and M2 subtypes. These results permit us to conclude that SPECT imaging of (R,R)-[123I]IQNB localization can potentially be used to quantitate changes in the M2 subtype in a disease state within a brain region for which the ratio M2/M1 is sufficiently high in normal individuals.