Description
Pirenzepine is available as dihydrochloride
monohydrate, soluble in water.
Because of its unfavorable balance between
weak antisecretory and frequent anticholinergic
adverse effects (dry mouth, blurred vision),
pirenzepine is considered obsolete .
Manufacturing Process
48.4 g of 5,11-dihydro-6H-pyrido[2,3-b][1,4]benzo-diazepin-6-one were refluxed in 900 ml of absolute dioxane for 15 minutes. Thereafter, over a period of 45 minutes, 28 ml of chloroacetyl chloride and 52 ml of triethylamine were simultaneously added dropwise to the mixture. The mixture was refluxed for eight hours and then vacuum-filtered after having cooled. The filtrate was evaporated in vacuum. The crystalline residue was recrystallized from acetonitrile in the presence of activated charcoal. MP: 212°-213°C (with decomposition). Yield: 85% of theory.
A mixture of 67.5 g of 11-chloroacetyl-5,11-dihydro-6H-pyrido[2,3b][1,4]benzodiazepin-6-one, 183 ml of N-methylpiperazine and 1.37 liters of absolute benzene was refluxed for 18 hours. Thereafter, the crystalline precipitate was vacuum filtered off, dissolved in aqueous 20% hydrochloric acid, the solution was evaporated in vacuum, the crystalline residue wasdissolved in 250 ml of water while heating, the solution was admixed with 150 ml of isopropanol and active charcoal, filtered, and 2.5 liters of isopropanol were added to the filtrate. After cooling, the precipitate was vacuum filtered off, yielding 70% of theory of the 5,11-dihydro-11-[(4'-methyl-1'-piperazinyl)acetyl]-6H-pyrido[2,3-b][1,4]benzodiazepin-6-one dihydrochloride, M.P. 257259°C (decomp.).
The free base of pirenzepine, obtained from the dihydrochloride by making an aqueous solution thereof alkaline with dilute sodium hydroxide and extracting it with chloroform, had MP: 226°-228°C after recrystallization from methanol/ether.
Enzyme inhibitor
This hygroscopic antiulcerative (FWfree-base = 351.41 g/mol; CAS 28797-61- 7) is a gastric acid inhibitor and selective M1 muscarinic receptor antagonist, and the antisecretory properties of pirenzepine on gastric acid and pepsin secretion may be attributed to this antagonistic activity on muscarinic M1 receptors.
