Structural aspects of high affinity ligands for the alpha 4 beta 2 neuronal nicotinic receptor.

Neuronal nicotinic acetylcholine receptors (nAChRs) are a heterogeneous family of related ion channels that are widely distributed throughout the central and peripheral nervous systems. They all share a common architecture of five subunit proteins that combine at the cell surface to create a ligand-gated cation permeable pore. Significant effort is currently being expended by medicinal chemistry teams to synthesize ligands that exhibit selectivity for central over peripheral nAChR subtypes. Within the CNS, multiple nAChR subtypes are recognized, and the discovery of ligands exhibiting selectivity among these subtypes offers an opportunity for the development of novel therapeutic agents. The alpha 4 beta 2 subtype is one of the most abundant nAChR subtypes within the CNS, and has been the primary focus of high affinity ligand design. Nicotine (1), and more recently, epibatidine (2) have served as structural templates for the design of the majority of active compounds. Although the diversity of nAChR ligands is growing, the structural requirements necessary for high affinity binding with the alpha 4 beta 2 receptor remain poorly understood. The putative pharmacophoric elements common to all potent alpha 4 beta 2 ligands include (1) a basic or quaternized nitrogen atom, and (2) a less basic nitrogen or a carbonyl oxygen that presumably interact with electron rich and electron deficient sites on the receptor, respectively. The family of currently known high affinity analogs consists of a diverse array of azacycles containing a basic amine. Several additional basic amine fragments have been identified, including the pyrrolizidine nucleus (exemplified by 8) and the 2-azabicyclo[2.2.1]heptane skeleton (exemplified by 9). In addition, we have found that the furo[2,3-b]pyridine heterocycle (compound 10) serves as useful bioisosteric replacement for the pyridyl substituent of nicotine. A preliminary pharmacophore model is proposed in which a reasonable superposition of the putative pharmacophoric elements of the diverse array of high affinity ligands for the alpha 4 beta 2 nAChR reported herein may be accommodated.

Discovery of a series of cyclohexylethylamine-containing protein farnesyltransferase inhibitors exhibiting potent cellular activity.

Synthesis of a library of secondary benzylic amines based on the Sebti-Hamilton type peptidomimetic farnesyltransferase (FTase) inhibitor FTI-276 (1) led to the identification of 6 as a potent enzyme inhibitor (IC(50) of 8 nM) which lacked the problematic thiol residue which had been a common theme in many of the more important FTase inhibitors reported to date. It has previously been disclosed that addition of o-tolyl substitution to FTase inhibitors of the general description 2 had a salutary effect on both FTase inhibition and inhibition of Ras prenylation in whole cells. Combination of these two observations led us to synthesize 7, a potent FTase inhibitor which displayed an IC(50) of 0.16 nM for in vitro inhibition of FTase and an EC(50) of 190 nM for inhibition of whole cell Ras prenylation. Modification of 7 by classical medicinal chemistry led to the discovery of a series of potent FTase inhibitors, culminating in the identification of 25 which exhibited an IC(50) of 0.20 nM and an EC(50) of 4.4 nM. In vivo tests in a nude mouse xenograft model of human pancreatic cancer (MiaPaCa cells) showed that oral dosing of 25 gave rise to impressive attenuation of the growth of this aggressive tumor cell line.

Structure-activity studies on a novel series of cholinergic channel activators based on a heteroaryl ether framework.

Analogs of compound 1 with a variety of azacycles and heteroaryl groups were synthesized. These analogs exhibited Ki values ranging from 0.15 to > 10,000 nM when tested in vitro for cholinergic channel receptor binding activity (displacement of [3H](-) cytisine from whole rat brain synaptic membranes).

Pyrrolidine-3-carboxylic acids as endothelin antagonists. 3. Discovery of a potent, 2-nonaryl, highly selective ETA antagonist (A-216546).

Previously we have reported the discovery of ABT-627 (1, A-147627, active enantiomer of A-127722), a 2,4-diaryl substituted pyrrolidine-3-carboxylic acid based endothelin receptor-A antagonist. This compound binds to the ETA receptor with an affinity (Ki) of 0. 034 nM and with a 2000-fold selectivity for the ETA receptor versus the ETB receptor. We have expanded our structure-activity studies in this series, in an attempt to further increase the ETA selectivity. When the p-anisyl group of 1 was replaced by an n-pentyl group, the resultant antagonist 3 exhibited substantially increased ETB/ETA activity ratio, but a decreased ETA affinity. Structure-activity studies revealed that substitution and geometry of this alkyl group, and substitution on the benzodioxolyl ring, are important in optimizing this series of highly ETA selective antagonists. In particular, the combination of a (E)-2,2-dimethyl-3-pentenyl group and a 7-methoxy-1,3-benzodioxol-5-yl group provided hydrophobic compound 10b with subnanomolar affinity for human ETA receptor subtype and with an ETB/ETA activity ratio of over 130000. Meanwhile, synthetic efforts en route to olefinic compounds led to the discovery that 2-pyridylethyl (9o) and 2-(2-oxopyrrolidinyl)ethyl (9u) replacement of the p-anisyl group of 1yielded very hydrophilic ETA antagonists with potency and selectivity equal to those of 10b. On the basis of overall superior affinity, high selectivity for the ETA receptor (Ki, 0.46 nM for ETA and 13000 nM for ETB), and good oral bioavailability (48% in rats), A-216546 (10a) was selected as a potential clinical backup for 1.

Antinociceptive effects of the novel neuronal nicotinic acetylcholine receptor agonist, ABT-594, in mice.

ABT-594 [5-((2R)-azetidinylmethoxy)-2-chloropyridine], a novel neuronal nicotinic acetylcholine receptor agonist, produced significant antinociceptive effects in mice against both acute noxious thermal stimulation--the hot-plate and cold-plate tests--and persistent visceral irritation--the abdominal constriction (writhing) assay (maximally-effective dose in each test 0.62 micromol/kg, i.p.). This effect was not stereoselective since the S-enantiomer, A-98593 [5-((2S)-azetidinylmethoxy)-2-chloropyridine], produced similar antinociceptive effects in this dose range. The effect in the hot-plate test peaked at 30 min after i.p. administration and was still present 60 min, but not 120 min, after injection. ABT-594 was orally active, but 10-fold less potent by this route than after i.p. administration. The antinociceptive effect of ABT-594 was prevented, but not reversed, by the noncompetitive neuronal nicotinic acetylcholine receptor antagonist mecamylamine (5 micromol/kg, i.p.). In contrast, the antinociceptive effect of ABT-594 was not prevented by hexamethonium (10 micromol/kg, i.p.), a neuronal nicotinic acetylcholine receptor antagonist that does not readily enter the central nervous system, nor by naltrexone (0.8 micromol/kg), an opioid receptor antagonist. Thus, initiation of antinociception by ABT-594 involves activation of central nicotinic acetylcholine receptors, but does not require activation of naltrexone-sensitive opioid receptors. The antinociceptive effects of morphine and ABT-594 in the mouse hot-plate test appeared to be additive, but ABT-594 did not potentiate the respiratory depression produced by morphine when the two compounds were coadministered. ABT-594 reduced body temperature and spontaneous exploration in the antinociceptive dose range, but did not reliably impair motor coordination in the rotarod test. Thus, it is unlikely that the antinociceptive effects result simply from impaired motor function. The compound also produced an anxiolytic-like effect in the elevated plus maze (at 0.019 and 0.062 micromol/kg, i.p.). Preliminary safety testing revealed an ED50 for overt seizure production of 1.9 micromol/kg, i.p. and an LD50 of 19.1 micromol/kg i.p. in mice, values 10 and 100 times the minimum effective antinociceptive dose of the compound. ABT-594 increased the duration of ethanol-induced hypnotic effects, tended to increase pentobarbital-induced hypnotic effects (P = 0.0502), and had no effect on pentobarbital-induced lethality. These data indicate that ABT-594 is a centrally acting neuronal nicotinic acetylcholine receptor agonist with potent antinociceptive and anxiolytic-like effects in mice.

ABT-594 [(R)-5-(2-azetidinylmethoxy)-2-chloropyridine]: a novel, orally effective analgesic acting via neuronal nicotinic acetylcholine receptors: I. In vitro characterization.

The discovery of (+/-)-epibatidine, a naturally occurring neuronal nicotinic acetylcholine receptor (nAChR) agonist with antinociceptive activity 200-fold more potent than that of morphine, has renewed interest in the potential role of nAChRs in pain processing. However, (+/-)-epibatidine has significant side-effect liabilities associated with potent activity at the ganglionic and neuromuscular junction nAChR subtypes which limit its potential as a clinical entity. ABT-594 [(R)-5-(2-azetidinylmethoxy)-2-chloropyridine] is a novel, potent cholinergic nAChR ligand with analgesic properties (see accompanying paper by Bannon et al., 1998b) that shows preferential selectivity for neuronal nAChRs and a consequently improved in vivo side-effect profile compared with (+/-)-epibatidine. ABT-594 is a potent inhibitor of the binding of [3H](-)-cytisine to alpha 4 beta 2 neuronal nAChRs (Ki = 37 pM, rat brain; Ki = 55 pM, transfected human receptor). At the alpha 1 beta 1 delta gamma neuromuscular nAChR labeled by [125I] alpha-bungarotoxin (alpha-Btx), ABT-594 has a Ki value of 10,000 nM resulting in a greater than 180,000-fold selectivity of the compound for the neuronal alpha 4 beta 2 nAChR. In contrast, (+/-)-epibatidine has Ki values of 70 pM and 2.7 nM at the alpha 4 beta 2 and alpha 1 beta 1 delta gamma nAChRs, respectively, giving a selectivity of only 38-fold. The S-enantiomer of ABT-594, A-98593 has activity at the neuronal alpha 4 beta 2 nAChR identical with ABT-594 (Ki = 34-39 pM), which demonstrates a lack of stereospecific binding similar to that reported previously for (+/-)-epibatidine. A similar lack of stereoselectivity is seen at the human alpha 7 receptor. However, A-98593 is 3-fold more potent at the neuromuscular nAChR (Ki = 3420 nM) and the brain alpha-Btx-sensitive nAChR (Ki = 4620 nM) than ABT-594. ABT-594 has weak affinity in binding assays for adrenoreceptor subtypes alpha-1B (Ki = 890 nM), alpha-2B (Ki = 597 nM) and alpha-2C (Ki = 342 nM), and it has negligible affinity (Ki > 1000 nM) for approximately 70 other receptors, enzyme and transporter binding sites. Functionally, ABT-594 is an agonist. At the transfected human alpha 4 beta 2 neuronal nAChR (K177 cells), with increased 86Rb+ efflux as a measure of cation efflux, ABT-594 had an EC50 value of 140 nM with an intrinsic activity (IA) compared with (-)-nicotine of 130%; at the nAChR subtype expressed in IMR-32 cells (sympathetic ganglion-like), an EC50 of 340 nM (IA = 126%); at the F11 dorsal root ganglion cell line (sensory ganglion-like), an EC50 of 1220 nM (IA = 71%); and via direct measurement of ion currents, an EC50 value of 56,000 nM (IA = 83%) at the human alpha 7 homooligimeric nAChR produced in oocytes. A-98593 is 2- to 3-fold more potent and displays approximately 50% greater intrinsic activity than ABT-594 in all four functional assays. In terms of potency, ABT-594 is 8- to 64-fold less active than (+/-)-epibatidine and also has less IA in these functional assays. ABT-594 (30 microM) inhibits the release of calcitonin gene-related peptide from C-fibers terminating in the dorsal horn of the spinal cord, an effect mediated via nAChRs. Pharmacologically, ABT-594 has an in vitro profile distinct from that of the prototypic nicotinic analgesic (+/-)-epibatidine, with the potential for substantially reduced side-effect liability and, as such, represents a potentially novel therapeutic approach to pain management.

ABT-594 [(R)-5-(2-azetidinylmethoxy)-2-chloropyridine]: a novel, orally effective antinociceptive agent acting via neuronal nicotinic acetylcholine receptors: II. In vivo characterization.

The antinociceptive effects of ABT-594, a novel nicotinic acetylcholine receptor (nAChR) ligand, were examined in rats in models of acute thermal (hot box) and persistent chemical (formalin test) pain. Also, the effects of ABT-594 treatment on motor function and electroencephalogram (EEG) were determined. In the hot box and formalin test (i.e., phase 1 and 2), acute treatment with ABT-594 (0.03, 0.1 and 0.3 mumol/kg i.p.) produced significant dose-dependent antinociceptive effects. In the hot box, the efficacy of ABT-594 was maintained after a repeated dosing paradigm (5 days b.i.d.i.p.). ABT-594 was fully efficacious in the formalin test when administered before formalin, and also retained significant efficacy (0.3 mumol/kg i.p.) when administered after formalin injection. The antinociceptive effects of ABT-594 in the hot box and formalin tests were attenuated by pretreatment with the nAChR antagonist, mecamylamine, and in animals treated with the nAChR antagonist chlorisondamine, given centrally (10 micrograms/rat i.c.v. 5 days before), but not in animals pretreated with the opioid receptor antagonist, naltrexone. Acute treatment with ABT-594 produced an initial decrease in open-field locomotor activity, which was absent in animals dosed repeatedly (5 days b.i.d.) with ABT-594. Also, acute treatment with ABT-594 decreased body temperature and decreased the amount of time the animals could maintain balance in an edge-balance test. These effects were no longer present in animals dosed repeatedly with ABT-594. At antinociceptive doses, ABT-594 produced activation of free running EEG in contrast to the sedative-like effects of morphine. Full antinociceptive efficacy was maintained in both the hot box and formalin tests after oral administration, whereas the effects on motoric performance were attenuated. In conclusion, these data demonstrate that ABT-594 is a potent antinociceptive agent with full efficacy in models of acute and persistent pain and that these effects are mediated predominately by an action at central neuronal nAChRs. In addition, antinociceptive effects were maintained after repeated dosing, whereas effects of ABT-594 on motor and temperature measures were attenuated in animals treated repeatedly with ABT-594. Thus, compounds acting at nAChRs may represent a novel approach for the treatment of a variety of pain states.

Identification and initial structure-activity relationships of (R)-5-(2-azetidinylmethoxy)-2-chloropyridine (ABT-594), a potent, orally active, non-opiate analgesic agent acting via neuronal nicotinic acetylcholine receptors.

New members of a previously reported series of 3-pyridyl ether compounds are disclosed as novel, potent analgesic agents acting through neuronal nicotinic acetylcholine receptors. Both (R)-2-chloro-5-(2-azetidinylmethoxy)pyridine (ABT-594, 5) and its S-enantiomer (4) show potent analgesic activity in the mouse hot-plate assay following either intraperitoneal (i.p.) or oral (p.o.) administration, as well as activity in the mouse abdominal constriction (writhing) assay, a model of persistent pain. Compared to the S-enantiomer and to the prototypical potent nicotinic analgesic agent (+/-)-epibatidine, 5 shows diminished activity in models of peripheral side effects. Structure-activity studies of analogues related to 4 and 5 suggest that the N-unsubstituted azetidine moiety and the 2-chloro substituent on the pyridine ring are important contributors to potent analgesic activity.

Structure-activity studies related to ABT-594, a potent nonopioid analgesic agent: effect of pyridine and azetidine ring substitutions on nicotinic acetylcholine receptor binding affinity and analgesic activity in mice.

Analogs of A-98593 (1) and its enantiomer ABT-594 (2) with diverse substituents on the pyridine ring were prepared and tested for affinity to nicotinic acetylcholine receptor binding sites in rat brain and for analgesic activity in the mouse hot plate assay. Numerous types of modifications were consistent with high affinity for [3H]cytisine binding sites. By contrast, only selected modifications resulted in retention of analgesic potency in the same range as 1 and 2. Analogs of 2 with one or two methyl substituents at the 3-position of the azetidine ring also were prepared and found to be substantially less active in both assays.

A-85380 [3-(2(S)-azetidinylmethoxy) pyridine]: in vitro pharmacological properties of a novel, high affinity alpha 4 beta 2 nicotinic acetylcholine receptor ligand.

The in vitro pharmacological properties of a novel cholinergic channel ligand, A-85380 [3-(2(S)-azetidinylmethoxy)pyridine], were examined using tissue preparations that express different putative nAChR subtypes. In radioligand binding studies, A-85380 is shown to be a potent and selective ligand for the human alpha 4 beta 2 nAChR subtype (Ki = 0.05 + 0.01 nM) relative to the human alpha 7 (Ki = 148 +/- 13 nM) and the muscle alpha 1 beta 1 dg subtype expressed in Torpedo electroplax (Ki = 314 +/- 12 nM). The R-enantiomer of A-85380, A-159470, displays little enantioselectivity towards the alpha 4 beta 2 and alpha 1 beta 1 delta gamma subtypes but does not display 12-fold enantioselectivity towards the alpha 7 subtype (Ki = 1275 +/- 199 nM). (+)- and(-)-Epibatidine display similar potencies at the human human alpha 4 beta 2 (Ki = 0.04 +/- 0.02 nM and 0.07 +/- 0.02 nM, respectively), human alpha 7 (Ki = 16 +/- 2 nM and 22 +/- 3 nM, respectively) and muscle alpha 1 beta 1 delta gamma g (Ki = 2.5 +/- 0.9 nM and 5.7 +/- 1.0 nM, respectively) nAChRs. Functionally, A-85380 is a potent activator of cation efflux through the human alpha 4 beta 2 (EC50 = 0.7 +/- 0.1 microM) and ganglionic (EC50 = 0.8 +/- 0.09 microM) subtypes, effects that are attenuated by pretreatment with mecamylamine (10 microM). Further, A-85380 can activate (EC50 = 8.9 +/- 1.9 microM) currents through channels formed by injection of the human alpha 7 subunit into Xenopus oocytes, effects that are attenuated by pretreatment with the alpha 7 nAChR antagonist, methyllycaconitine (10 nM). In all cases, A-85380 is more potent than (-)-nicotine but less potent than (+/-)-epibatidine. In neurotransmitter release studies, A-85380 stimulates the release of dopamine with an EC 50 value of 0.003 +/- 0.001 microM which is equipotent to (+/-)-epibatidine, and 20-fold more potent than (-)-nicotine (EC50 = 0.04 +/- 0.009 microM). Thus, A-85380 displays a profile of robust activation of a number of nAChR subtypes with substantially less affinity for [125I] alpha-BgT sites than [3H](-)-cytisine sites, suggesting that it may serve as a more selective pharmacologic probe for the alpha 4 beta 2 subtype relative to the alpha 7 and alpha 1 beta 1 delta g nAChRs than (+/-)-epibatidine.

Novel 3-Pyridyl ethers with subnanomolar affinity for central neuronal nicotinic acetylcholine receptors.

Recent evidence indicating the therapeutic potential of cholinergic channel modulators for the treatment of central nervous system (CNS) disorders as well as the diversity of brain neuronal nicotine acetylcholine receptors (nAChRs) have suggested an opportunity to develop subtype-selective nAChR ligands for the treatment of specific CNS disorders with reduced side effect liabilities. We report a novel series of 3-pyridyl ether compounds which possess subnanomolar affinity for brain nAChRs and differentially activate subtypes of neuronal nAChRs. The synthesis and structure-activity relationships for the leading members of the series are described, including A-85380 (4a), which possesses ca.50 pM affinity for rat brain [(3)H]-(-)-cytisine binding sites and 163% efficacy compared to nicotine to stimulate ion flux at human alpha4beta2 nAChR subtype, and A-84543 (2a), which exhibits 84-fold selectivity to stimulate ion flux at human alpha4beta2 nAchR subtype compared to human ganglionic type nAChRs. Computational studies indicate that a reasonable superposition of a low energy conformer of 4A with (S)-nicotine and (-)-epibatidine can be achieved.

Characterization of [3H]ABT-418: a novel cholinergic channel ligand.

ABT-418 [(S)-3-methyl-5-(1-methyl-2-pyrrolidinyl)isoxazole] is a potent and selective agonist at neuronal nicotinic acetylcholine receptors (nAChRs) with cognitive enhancing and anxiolytic activities. [3H]ABT-418 was found to bind with high affinity (KD = 2.85 +/- 0.14 nM) to membranes prepared from rat brain. Binding of [3H]ABT-418 was characterized by rapid association (T1/2 = 1.4 +/- 0.3 min) and dissociation (T1/2 = 2.9 +/- 0.4 min) half-times. The pharmacology of [3H]ABT-418 binding was consistent with an interaction with the putative alpha 4 beta 2 nAChR subtype. The nAChR agonists, (-)-nicotine, (-)-cytisine and (+/-)-epibatidine, displayed a high affinity (Ki = 0.8 +/- 0.1, 0.2 +/- 0.1 and 0.05 +/- 0.01 nM, respectively) for [3H]ABT-418 binding sites, whereas among nAChR antagonists examined, only dihydro-beta-erythroidine competed with high affinity (Ki = 32 +/- 1.5 nM). Although autoradiography studies indicate that the binding distribution of [3H]ABT-418 and (-)-[3H]cytisine are largely identical, there are some brain regions including the striatum, olivary pretectal nucleus and the superior colliculus, in which [3H]ABT-418 demonstrates significantly (P < .05) less binding. The data in the present study demonstrate that [3H]ABT-418 binds with high affinity to a population of binding sites in the rat brain that have the pharmacological characteristics of neuronal nAChRs. [3H]ABT-418 may, therefore, serve as a useful radioligand to further probe the observed differences in pharmacological properties between ABT-418 and other nicotinic agonists in vivo.

Ligands for brain cholinergic channel receptors: synthesis and in vitro characterization of novel isoxazoles and isothiazoles as bioisosteric replacements for the pyridine ring in nicotine.

Ligands which activate neuronal nicotinic acetylcholine receptors (nAChRs) represent a potential approach for the palliative treatment for the symptoms of memory loss associated with Alzheimer's disease (AD). Based upon this approach, a series of novel 3,5-disubstituted isoxazoles and isothiazoles were prepared and evaluated in vitro as cholinergic channel activators (ChCAs) of neuronal nAChRs. Many of the 3-substituted 5-(2-pyrrolidinyl)isoxazoles were found to have nanomolar binding affinities comparable to (S)-nicotine (2a) in a preparation of whole rat brain. However, in a paradigm measuring the evoked release of [3H]dopamine from a preparation of rat striatum, there were differences in the agonist potencies and efficacies of these analogues relative to 2a. The differences in agonist potency observed between compounds of comparable binding potency may be due to differences in ligand interactions with various subtypes of neuronal nAChRs.

(S)-3-methyl-5-(1-methyl-2-pyrrolidinyl)isoxazole (ABT 418): a novel cholinergic ligand with cognition-enhancing and anxiolytic activities: II. In vivo characterization.

(S)-3-methyl-5-(1-methyl-2-pyrrolidinyl)isoxazole (ABT 418), an isoxazole analog of (-)-nicotine, is a potent agonist at the alpha-4/beta-2 subtype of neuronal nicotinic acetylcholine receptor (nAChR) that exists in mammalian brain (Arneric et al., 1994). Compared to (-)-nicotine, ABT 418 has reduced potency to interact with the subunit isoforms of nAChR found in sympathetic ganglia, and it does not compete for alpha-bungarotoxin binding sites in brain or at the neuromuscular junction. ABT 418 [minimum effective dose (MED), 0.062 mumol/kg i.p.) was 10-fold more potent in improving retention of avoidance learning in normal mice than (-)-nicotine, whereas the (R)-enantiomer of ABT 418, A-81754, was inactive. The memory-enhancing effect of ABT 418 was prevented by the nAChR channel blocker, mecamylamine. In the elevated plus-maze model of anxiety, ABT 418 (MED, 0.19 mumol/kg i.p.) increased open-arm exploration in mice, as previously shown for (-)-nicotine (MED, 0.62 mumol/kg i.p.). A-81754, did not have anxiolytic-like effects in this test. Unlike the classical anxiolytic, diazepam, ABT 418 did not impair rotorod performance in the dose range where beneficial effects occurred. In rats, ABT 418 (MED, 0.002 mumol/kg i.v.) was remarkably potent in enhancing basal forebrain-elicited increases in cortical cerebral blood flow, whereas resting cerebral blood flow was unaffected. Free running cortical electroencephalography in rats was unaffected by ABT 418 at a dose of 1.9 mumol/kg i.p., whereas the same dose of (-)-nicotine caused cortical activation (decreased power in the 1-13 Hz range and increased power in the 25-50 Hz range). Whereas ABT 418 was approximately 3- to 10-fold more potent than (-)-nicotine in memory enhancement and anxiolytic test paradigms, the compound had less emetic liability in dogs as compared to (-)-nicotine, and was less potent than (-)-nicotine in eliciting hypothermia, seizures, death and reduction of locomotor activity in mice. The measured pharmacokinetic or brain disposition properties of ABT 418 in rats did not account for the observed enhancement in efficacy with reduced toxicity as compared to (-)-nicotine. The potent cognitive-enhancing and anxiolytic properties obtained for ABT 418 in animal models without eliciting significant side effects suggest that this ligand is a selective activator of cholinergic channel-mediated behaviors. Thus, ABT 418 may represent a novel, safe and effective treatment of the cognitive and emotional dysfunctions associated with Alzheimer's disease.

Synthesis and in vitro characterization of novel amino terminally modified oxotremorine derivatives for brain muscarinic receptors.

A series of novel 2-substituted acetylenic pyrrolidines and piperidines related to oxotremorine (1) were prepared and evaluated in vitro as muscarinic cholinergic agents at brain M1 and M2 receptors. One analogue, 3-(2-oxo-1-pyrrolidinyl)-1-[2(R)-pyrrolidinyl]-1-propyne hydrogen oxalate (6a), was found to be a partial agonist producing a PI hydrolysis response at cortical M1 receptors approximately 3-fold larger than that produced by 1. The intrinsic activity profile of 6a at brain muscarinic receptors is similar to those of azetidine oxo analogue 2 and dimethylamino oxo analogue. All three compounds are partial M1 agonists and full M2 agonists; however, the profile of 6a in binding studies is significantly different. While 2 and 3 exhibit large M2 selectivities ranging between 8-fold to several hundred-fold, the binding profile of 6a shows almost no subtype selectivity.