Metabolic stabilization of benzylidene ketal M(2) muscarinic receptor antagonists via halonaphthoic acid substitution.

The potential toxicological liabilities of the M(2) muscarinic antagonist 1 were addressed by replacing the methylenedioxyphenyl moiety with a p-methoxyphenyl group, resulting in M(2) selective compounds such as 3. Several halogenated naphthamide derivatives of 3 were studied in order to improve the pharmacokinetic profile via blockage of oxidative metabolism. Compound 4 demonstrated excellent M(2) affinity and selectivity, human microsomal stability, and oral bioavailability in rodents and primates.

Muscarinic agonists and antagonists in the treatment of Alzheimer's disease.

Alzheimer's disease (AD) is a neurodegenerative disease characterized by cognitive impairment and personality changes. The development of drugs for the treatment of the cognitive deficits of AD has focused on agents which counteract loss in cholinergic activity. Although symptoms of AD have been successfully treated with acetylcholinesterase inhibitors (tacrine, donepezil. rivastigmine, galanthamine), limited success has been achieved with direct M1 agonists, probably due to their lack of selectivity versus other muscarinic receptor subtypes. Muscarinic M2 antagonists have been reported to increase synaptic levels of acetylcholine after oral administration to rats (e.g. BIBN-99, SCH-57790), but their selectivity versus other muscarinic receptor subtypes is modest. Exploration of a series of piperidinylpiperidines has yielded the potent and selective M2 antagonist SCH-217443. This antagonist has excellent bioavailability in rats and dogs and shows activity in a rat model of cognition.

Facilitation of acetylcholine release and improvement in cognition by a selective M2 muscarinic antagonist, SCH 72788.

Current treatment of Alzheimer's Disease (AD) requires acetylcholinesterase inhibition to increase acetylcholine (ACh) concentrations in the synaptic cleft. Another mechanism by which ACh levels can be increased is blockade of presynaptic M2 muscarinic autoreceptors that regulate ACh release. An antagonist designed for this purpose must be highly selective for M2 receptors to avoid blocking postsynaptic M1 receptors, which mediate the cognitive effects of ACh. Structure-activity studies of substituted methylpiperadines led to the synthesis of 4-[4-[1(S)-[4-[(1,3-benzodioxol-5-yl)sulfonyl]phenyl]ethyl]-3(R)-methyl-1-piperazinyl]-4-methyl-1-(propylsulfonyl)piperidine. This compound, SCH 72788, binds to cloned human M2 receptors expressed in CHO cells with an affinity of 0.5 nM, and its affinity at M1 receptors is 84-fold lower. SCH 72788 is a functional M2 antagonist that competitively inhibits the ability of the agonist oxotremorine-M to inhibit adenylyl cyclase activity. In an in vivo microdialysis paradigm, SCH 72788 increases ACh release from the striatum of conscious rats. The compound is also active in a rodent model of cognition, the young rat passive avoidance response paradigm. The effects of SCH 72788 suggest that M2 receptor antagonists may be useful for treating the cognitive decline observed in AD and other dementias.

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.

Design and synthesis of piperidinyl piperidine analogues as potent and selective M2 muscarinic receptor antagonists.

Identification of a number of highly potent M2 receptor antagonists with >100-fold selectivity against the M1 and M3 receptor subtypes is described. In the rat microdialysis assay, this series of compounds showed pronounced enhancement of brain acetylcholine release after oral administration.

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.

Diphenylsulfone muscarinic antagonists: piperidine derivatives with high M2 selectivity and improved potency.

Piperidine analogues of our previously described piperazine muscarinic antagonists are described. Piperidine analogues show a distinct structure-activity relationship (SAR) that differs from comparable piperazines. Compounds with high selectivity and improved potency for the M2 receptor have been identified. The lead compound, 12b, increases acetylcholine release in vivo. Compounds of this class may be useful for the treatment of cognitive disorders such as Alzheimer's disease (AD).

Benzylidene ketal derivatives as M2 muscarinic receptor antagonists.

Benzylidene ketal derivatives were investigated as selective M2 receptor antagonists for the treatment of Alzheimer's disease. Compound 10 was discovered to have subnanomolar M2 receptor affinity and 100-fold selectivity against other muscarinic receptors. Also, 10 demonstrated in vivo efficacy in rodent models of muscarinic activity and cognition.

Design, synthesis, and structure-activity relationship studies of himbacine derived muscarinic receptor antagonists.

A parallel synthesis of racemic himbacine analogs was carried out by N-alkylation of various commercially available cyclic amine derivatives with the alkylating agent 4 which bears the tricyclic unit of himbacine. Several of these analogs have potency comparable to that of himbacine, albeit lacking the desired selectivity. Structure-activity relationship studies support the existence of a hydrophobic pocket in the receptor where the piperidine ring of dihydrohimbacine binds.

SCH 57790: a novel M2 receptor selective antagonist.

As a decrease in cholinergic neurons has been observed in Alzheimer's Disease (AD), therapeutic approaches to AD include inhibition of acetylcholinesterase to increase acetylcholine levels. Evidence suggests that acetylcholine release in the CNS is modulated by negative feedback via presynaptic M2 receptors, blockade of which should provide another means of increasing acetylcholine release. Structure-activity studies of [4-(phenylsulfonyl)phenyl]methylpiperazines led to the synthesis of 4-cyclohexyl-alpha-[4-[[4-methoxyphenyl]sulfinyl]-phenyl]-1-piperazin eacetonitrile. This compound, SCH 57790, binds to cloned human M2 receptors expressed in CHO cells with an affinity of 2.78 nM; the affinity at M1 receptors is 40-fold lower. SCH 57790 is an antagonist at M2 receptors expressed in CHO cells, as the compound blocks the inhibition of adenylyl cyclase activity mediated by the muscarinic agonist oxotremorine. This compound should be useful in assessing the potential of M2 receptor blockade for enhancement of cognition.

Determination of plasma and brain concentrations of SCH 39166 and their correlation to conditioned avoidance behavior in rats.

Plasma and brain concentrations of the dopamine D1 receptor antagonist, SCH 39166, were measured and compared to behavioral activity in the conditioned avoidance response paradigm (CAR). SCH 39166 was administered at two behaviorally active doses (1 mg/kg, SC and 10 mg/kg, PO) and the time course for CAR activity was compared with the plasma and brain concentrations of unconjugated SCH 39166. Conjugation and N-demethylation of SCH 39166 after oral administration were also determined and first pass metabolism examined. Results from these studies demonstrated a similar time-dependent disappearance of unconjugated SCH 39166 from both the plasma and brain, independent of route of administration. Brain concentrations of SCH 39166 were approximately 5-fold higher than corresponding plasma concentrations, regardless of route. However, plasma and brain concentrations of unconjugated SCH 39166 were higher after SC administration of 1.0 mg/kg, than after PO administration of 10 mg/kg, suggesting a substantial first pass metabolism of SCH 39166. In addition, total (conjugated and unconjugated) plasma concentrations of SCH 39166 were at least 10-fold higher than unconjugated concentrations of SCH 39166 after PO administration of 10 mg/kg, demonstrating that a high proportion of drug was conjugated. Metabolism to the N-desmethyl analog, SCH 40853, was observed after PO administration of 10 mg/kg SCH 39166 and a high proportion of conjugation of the desmethyl analog was also seen. Finally, plasma concentrations of unconjugated SCH 39166 exhibited a high positive correlation (r = 0.934, P < 0.001) with brain concentrations of unconjugated SCH 39166.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of a rat liver glucuronosyltransferase that glucuronidates the selective D1 antagonist, SCH 23390, and other benzazepines.

SCH 23390 is a novel benzazepine that selectively blocks dopamine receptors of the D1 subtype. Glucuronidation of this selective D1 antagonist was studied in vitro using rat liver microsomes. Methods to separate SCH 23390 glucuronide from SCH 23390 were developed which utilized either HPLC techniques or solvent extraction of SCH 23390 with 3-heptanone. Formation of a SCH 23390 glucuronide was confirmed upon incubation of SCH 23390 and UDPGA with naive rat liver microsomes. Liver enzyme activity for SCH 23390 glucuronidation was also enhanced after addition of the detergents, Lubrol or Triton X-100, to the naive liver microsomes. Kinetic analyses indicated an apparent Vmax and Km for UDPGA as 120.9 pmol/mg protein/min and 0.63 mM, and an apparent Vmax and Km for SCH 23390 as 282.4 pmol/mg protein/min and 0.41 microM. Further characterization of the liver enzyme responsible for the glucuronidation of SCH 23390 revealed a stereoselective substrate preference similar to that seen with the D1 dopamine receptor. Substrate inhibition studies indicated that SCH 23390, haloperidol, apomorphine, and alpha-naphthol demonstrated the highest affinity for the glucuronosyltransferase enzyme. However, (-)-sulpiride, raclopride, and endogenous substrates such as dopamine, serotonin, epinephrine, and norepinephrine demonstrated low affinity for the liver enzyme. These studies describe a rat liver glucuronosyltransferase with a unique substrate specificity toward selected dopaminergic agents. Finally, induction profiles revealed that neither phenobarbital (100 mg/kg, ip, for 3 days), beta-naphthoflavone (100 mg/kg, ip, for 4 days), nor 3-methylcholanthrene (80 mg/kg, ip, for 4 days) enhanced liver glucuronosyltransferase activity for SCH 23390 glucuronidation.

Characterization of the binding of 3H-SCH 23390, a selective D-1 receptor antagonist ligand, in rat striatum.

A novel benzazepine, SCH 23390, has recently been described as a very potent and selective dopamine D-1 receptor antagonist based on its potent inhibition of dopamine sensitive adenylate cyclase and its selective displacement of 3H-piflutixol from rat striatal receptor sites. In the present study, the in vitro binding of 3H-SCH 23390 to specific striatal receptor sites has been characterized. Binding was saturable and stereospecific, and the results of both saturation and competition studies are consistent with the binding of 3H-SCH 23390 to a single striatal site. A KD of 0.53 nM was obtained through Scatchard analysis. Relative potencies of a variety of neuroleptics in competing with 3H-SCH 23390 and also 3H-spiperone support an interpretation that the single site to which 3H-SCH 23390 binds is the D-1 dopamine receptor. Also, the binding capacity of 3H-SCH 23390 (69 pmoles/gm wet weight) is in agreement with published values for the binding capacities of 3H-piflutixol and 3H-flupentixol. These data, coupled with the low level of non-specific binding encountered with this radioligand (4-8% of total binding at normally employed ligand concentration of 0.3 nM), its high specific activity and its negligible binding to plastic and glass surfaces make it ideally suited for studying interactions with this receptor.