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.

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.

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.