title: Isolation and structure determination of oxidative degradation products of atorvastatin.
abstract: Methods were developed for the preparation and isolation of four oxidative degradation products of atorvastatin. ATV-FX1 was prepared in the alkaline acetonitrile solution of atorvastatin with the addition of hydrogen peroxide. The exposition of aqueous acetonitrile solution of atorvastatin to sunlight for several hours followed by the alkalization of the solution with potassium hydroxide to pH 8-9 gave ATV-FXA. By the acidification of the solution with phosphoric acid to pH 3 ATV-FXA1 and FXA2 were prepared. The isolation of oxidative degradation products was carried out on a reversed-phase chromatographic column Luna prep C18(2) 10 microm applying several separation steps. The liquid chromatography coupled with a mass spectrometer (LC-MS), high resolution MS (HR-MS), 1D and 2D NMR spectroscopy methods were applied for the structure elucidation. All degradants are due to the oxidation of the pyrrole ring. The most probable reaction mechanism is intermediate endoperoxide formation with subsequent rearrangement and nucleophilic attack by the 5-hydroxy group of the heptanoic fragment. ATV-FX1 is 4-[1b-(4-Fluoro-phenyl)-6-hydroxy-6-isopropyl-1a-phenyl-6a-phenylcarbamoyl-hexahydro-1,2-dioxa-5a-aza-cyclopropa[a]inden-3-yl]-3-(R)-hydroxy-butyric acid and has a molecular mass increased by two oxygen atoms with regard to atorvastatin. ATV-FXA is the regioisomeric compound, 4-[6-(4-Fluoro-phenyl)-6-hydroxy-1b-isopropyl-6a-phenyl-1a-phenylcarbamoyl-hexahydro-1,2-dioxa-5a-aza-cyclopropa[a]inden-3-yl]-3-(R)-hydroxy-butyric acid. Its descendants ATV-FXA1 and FXA2 appeared without the atorvastatin heptanoic fragment and are 3-(4-Fluoro-benzoyl)-2-isobutyryl-3-phenyl-oxirane-2-carboxylic acid phenylamide and 4-(4-Fluoro-phenyl)-2,4-dihydroxy-2-isopropyl-5-phenyl-3,6-dioxa-bicyclo[3.1.0]hexane-1-carboxylic acid phenylamide, respectively. Quantitative NMR spectroscopy was employed for the assay determination of isolated oxidative degradation products. The results obtained were used for the determination of the UV response factors relative to atorvastatin.
authors.affiliation: Lek Pharmaceuticals d.d., Verovskova 57, SI-1526 Ljubljana, Slovenia.
authors.forename: Matjaz
authors.initials: M
authors.lastname: Kracun
authors.forename: Andrej
authors.initials: A
authors.lastname: Kocijan
authors.forename: Andrej
authors.initials: A
authors.lastname: Bastarda
authors.forename: Rok
authors.initials: R
authors.lastname: Grahek
authors.forename: Janez
authors.initials: J
authors.lastname: Plavec
authors.forename: Darko
authors.initials: D
authors.lastname: Kocjan
mesh_terms: D000097:Acetonitriles / Q000737:chemistry; D000069059:Atorvastatin; D002626:Chemistry, Pharmaceutical / Q000379:methods; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D002853:Chromatography, Liquid / Q000379:methods; D004355:Drug Stability; D006538:Heptanoic Acids / Q000032:analysis* / Q000737:chemistry*; D006861:Hydrogen Peroxide / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D006878:Hydroxides / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry / Q000379:methods; D010100:Oxygen / Q000737:chemistry*; D010756:Phosphoric Acids / Q000737:chemistry; D017680:Potassium Compounds / Q000737:chemistry; D011758:Pyrroles / Q000032:analysis* / Q000737:chemistry*; D014466:Ultraviolet Rays
chemical_list: D000097:Acetonitriles; D006538:Heptanoic Acids; D006878:Hydroxides; D010756:Phosphoric Acids; D017680:Potassium Compounds; D011758:Pyrroles; D000069059:Atorvastatin; D006861:Hydrogen Peroxide; C030242:phosphoric acid; D010100:Oxygen; C029943:potassium hydroxide; C032159:acetonitrile