pirenperone pirenperone pirenperone (inn, usan, ban; developmental code names r-47456, r-50656) is a serotonin receptor antagonist described as an antipsychotic and tranquilizer which was never marketed. it is a relatively selective antagonist of the serotonin 5-ht2 receptors and has been used in scientific research to study the serotonin system. in the 1980s, the drug was found to block the effects of the lysergic acid diethylamide (lsd) in animals, and along with ketanserin, led to the elucidation of the 5-ht2a receptor as the biological mediator of the effects of serotonergic psychedelics. not to be confused with pipamperone. pirenperoneclinical dataother namesr-47456; r-50656identifiers iupac name 3-ethyl]-2-methylpyridopyrimidin-4-one cas number75444-65-4pubchem cid4847chemspider4681uniiy9fmc4513xkeggd05495chebichebi:92444chemblchembl18331comptox dashboard (epa)dtxsid9045182 echa infocard100.071.081 chemical and physical dataformulac23h24fn3o2molar mass393.462 g·mol−13d model (jsmol)interactive image smiles cc1=c(c(=o)n2c=cc=cc2=n1)ccn3ccc(cc3)c(=o)c4=cc=c(c=c4)f inchi inchi=1s/c23h24fn3o2/c1-16-20(23(29)27-12-3-2-4-21(27)25-16)11-15-26-13-9-18(10-14-26)22(28)17-5-7-19(24)8-6-17/h2-8,12,18h,9-11,13-15h2,1h3key:hxcnryxbznhdne-uhfffaoysa-n synthesis the sidechain is formed from the cyclization of 2-aminopyridine with 2-acetylbutyrolactone (2) in ppa gave 3-(2-hydroxyethyl)-2-methylpyridopyrimidin-4-one (3). halogenation replaces the hydroxy with the chloride leaving group. many syntheses do both steps in one-pot with phosphorus oxychloride. the 4-(4-fluorobenzoyl)piperidine has 12 known named uses. patent (ex xix): the alkylation between 3-(2-chloroethyl)-2-methylpyridopyrimidin-4-one (1) and 4-(4-fluorobenzoyl)piperidine hydrochloride (2) afforded pirenperone (3).