title: Metabolism of a serotonin-4 receptor partial agonist 4-{4-[4-tetrahydrofuran-3-yloxy)-benzo[d]isoxazol-3-yloxymethyl]-piperidin-1-ylmethyl}-tetrahydropyran-4-ol (TBPT): identification of an unusual pharmacologically active cyclized oxazolidine metabolite in human.
abstract: 4-{4-[4-Tetrahydrofuran-3-yloxy)-benzo[d]isoxazol-3-yloxymethyl]-piperidin-1-ylmethyl}-tetrahydropyran-4-ol (PF-4995274, TBPT) is a new agent that is a partial agonist of the human serotonin-4 (5-HT4) receptor and is under investigation for neurological disorders. Metabolism of TBPT was examined in vitro in human liver microsomes and human hepatocytes. Metabolites were also identified in the plasma of healthy human subjects in a phase 1 clinical study. Human-derived metabolite profiles were compared with corresponding profiles obtained in laboratory animal species. There were two major routes of metabolism in vitro: N-dealkylation of the methyltetrahydropyran moiety (M1) and hydroxylation at the seven position of the benzisoxazole moiety (M4). These were also observed in human plasma; however, in that matrix, the major metabolite was an unusual cyclized oxazolidine entity (M2). M2 was proposed to be formed via generation of an intermediate 4° iminium ion on the piperidine ring followed by spontaneous cyclization by attack of the β-hydroxyl substituent of the tetrahydropyran ring to form a cyclized oxazolidine product. An authentic standard of the metabolite was generated using a methylene-blue-sensitized photochemical oxidation reaction as well as microbial transformation. Further investigation of this metabolite showed that it also possessed 5-HT4 agonism activity similar to the parent. The metabolite was 150-fold more highly protein bound in human plasma than TBPT, which is consistent with its presence as a major circulating metabolite while being only a minor metabolite in in vitro systems. Overall, this illustrates the importance of understanding the complex dispositional properties of a pharmacologically active metabolite.
authors.affiliation: Pfizer Inc., Groton, Connecticut 06340, USA.
authors.forename: Aarti
authors.initials: A
authors.lastname: Sawant-Basak
authors.forename: Karen J
authors.initials: KJ
authors.lastname: Coffman
authors.forename: Gregory S
authors.initials: GS
authors.lastname: Walker
authors.forename: Tim F
authors.initials: TF
authors.lastname: Ryder
authors.forename: Elaine
authors.initials: E
authors.lastname: Tseng
authors.forename: Emily
authors.initials: E
authors.lastname: Miller
authors.forename: Carlos
authors.initials: C
authors.lastname: Lee
authors.forename: Michelle A
authors.initials: MA
authors.lastname: Vanase-Frawley
authors.forename: John W
authors.initials: JW
authors.lastname: Wong
authors.forename: Michael A
authors.initials: MA
authors.lastname: Brodney
authors.forename: Tracey
authors.initials: T
authors.lastname: Rapp
authors.forename: R Scott
authors.initials: RS
authors.lastname: Obach
mesh_terms: D000818:Animals; D001798:Blood Proteins / Q000378:metabolism; D001921:Brain / Q000378:metabolism; D003500:Cyclization; D003640:Dealkylation; D004285:Dogs; D005260:Female; D005663:Furans / Q000737:chemistry / Q000378:metabolism* / Q000493:pharmacokinetics / Q000494:pharmacology; D022781:Hepatocytes / Q000378:metabolism*; D006801:Humans; D006900:Hydroxylation; D008297:Male; D008862:Microsomes, Liver / Q000378:metabolism*; D010080:Oxazoles / Q000737:chemistry / Q000378:metabolism / Q000493:pharmacokinetics / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D044422:Receptors, Serotonin, 5-HT4 / Q000378:metabolism; D058828:Serotonin 5-HT4 Receptor Agonists / Q000737:chemistry / Q000378:metabolism* / Q000493:pharmacokinetics / Q000494:pharmacology
chemical_list: D001798:Blood Proteins; D005663:Furans; D010080:Oxazoles; D058828:Serotonin 5-HT4 Receptor Agonists; C064210:oxazolidine; D044422:Receptors, Serotonin, 5-HT4; C018674:tetrahydrofuran
keywords: hepatic metabolism; mass spectrometry; metabolism; microsomes; protein binding