title: Oxidative ipso substitution of 2,4-difluoro-benzylphthalazines: identification of a rare stable quinone methide and subsequent GSH conjugate.
abstract: In vitro metabolite identification and GSH trapping studies in human liver microsomes were conducted to understand the bioactivation potential of compound 1 [2-(6-(4-(4-(2,4-difluorobenzyl)phthalazin-1-yl)piperazin-1-yl)pyridin-3-yl)propan-2-ol], an inhibitor of the Hedgehog pathway. The results revealed the formation of a unique, stable quinone methide metabolite (M1) via ipso substitution of a fluorine atom and subsequent formation of a GSH adduct (M2). The stability of this metabolite arises from extensive resonance-stabilized conjugation of the substituted benzylphthalazine moiety. Cytochrome P450 (P450) phenotyping studies revealed that the formation of M1 and M2 were NADPH-dependent and primarily catalyzed by CYP3A4 among the studied P450 isoforms. In summary, an unusual and stable quinone methide metabolite of compound 1 was identified, and a mechanism was proposed for its formation via an oxidative ipso substitution.
authors.affiliation: Metabolism and Pharmacokinetics, Novartis Institutes for Biomedical Research, Cambridge, MA 02139, USA. mithat.gunduz@novartis.com
authors.forename: Mithat
authors.initials: M
authors.lastname: Gunduz
authors.forename: Upendra A
authors.initials: UA
authors.lastname: Argikar
authors.forename: Amin
authors.initials: A
authors.lastname: Kamel
authors.forename: Kevin
authors.initials: K
authors.lastname: Colizza
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Bushee
authors.forename: Amanda
authors.initials: A
authors.lastname: Cirello
authors.forename: Franco
authors.initials: F
authors.lastname: Lombardo
authors.forename: Shawn
authors.initials: S
authors.lastname: Harriman
mesh_terms: D001593:Benzyl Compounds / Q000493:pharmacokinetics / Q000494:pharmacology; D051544:Cytochrome P-450 CYP3A / Q000378:metabolism; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D005978:Glutathione / Q000378:metabolism*; D053823:Hedgehog Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D006801:Humans; D045563:Indolequinones / Q000493:pharmacokinetics* / Q000494:pharmacology; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D010084:Oxidation-Reduction; D010793:Phthalazines / Q000493:pharmacokinetics* / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods
chemical_list: D001593:Benzyl Compounds; D053823:Hedgehog Proteins; D045563:Indolequinones; D010793:Phthalazines; C068040:quinone methide; D009249:NADP; D003577:Cytochrome P-450 Enzyme System; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; D005978:Glutathione