Echimidine n oxide

Analytical standards of all pyrrolizidine alkaloids and their N-oxide were purchased from Phytolab (Vestenbergsgreuth, Germany): Echimidine (Em), Echimidine-N-oxide (EmNO), Echinatine (En), Echinatine-N-oxide (EnNO), Erucifoline-N-oxide (ErNO), Europine (Eu), Europine-N-oxide (EuNO), Heliosupine (Hs), Heliosupine-N-oxide (HsNO), Heliotrine (Ht), Heliotrine-N-oxide (HtNO), Indicine (Id), Indicine-N-oxide (IdNO), Integerrimine (Ir), Integerrimine-N-oxide (IrNO), Intermedine (Im), Intermedine-N-oxide (ImNO), Lasiocarpine (Lc), Lycopsamine (Ly), Lycopsamine-N-oxide (LyNO), Retrorsine (Rt), Retrorsine-N-oxide (RtNO), Rinderine (Rn), Rinderine-N-oxide (RnNO), Senecionine (Sn), Senecionine-N-oxide (SnNO), Seneciphylline (Sp), Seneciphylline-N-oxide (SpNO), Senecivernine (Sv), Senecivernine-N-oxide (SvNO), Senkirkine (Sk), Spartioidine (St), Spartioidine-N-oxide (StNO), Usaramine (Us) and Usaramine-N-oxide (UsNO). Methanol (LC-MS grade) was from VWR Chemicals (Rosny-sous-Bois-cedex, France), sulphuric acid (96%) and acetonitrile (LC-MS grade) were from Carlo Erba Reagents (Val de Reuil Cedex, France), formic acid was from Carlo Erba Reagents (Milan, Italy) and ammonium formate (analytical grade) was from Sigma-Aldrich (St. Louis, MO, USA). Ultrapure water used throughout the experiments was produced by an EvoQua Water Technologies system (Diessechem, Milan, Italy).

Lasiocarpine (Las) and lasiocarpine N-oxide were ordered from Cfm Oskar Tropitzsch (Marktredwitz, Germany). Lycopsamine (Lyc), Lycopsamine N-oxide, europine (Eur), europine N-oxide, senecionine (Sen), senecionine N-oxide, echimidine (Ech), echimidine N-oxide, intermedine, intermedine N-oxide, jacobine, jacobine N-oxide, heliosupine, heliosupine N-oxide, retrorsine N-oxide, retronecine, and senkirkine were obtained from Phytolab (Vestenbergsgreuth, Germany). Retrorsine (Ret) was delivered by AppliChem (Darmstadt, Germany). Methanol (MeOH, LC–MS grade) and water (H₂O, LC–MS grade) were purchased from Merck KGA (Darmstadt, Germany). 7,9-Diglutathionyl-6,7-dihydro-1-hydroymethyl-5H-pyrrolizidine was obtained from ASCA (Berlin, Germany). Potassium cyanide (KCN), isotopically labeled potassium cyanide (KCX, K¹³C¹⁵N), glutathione and isotopically labeled glutathione (GSX, ¹³C₂¹⁵N-GSH), and all other chemicals and co-factors were purchased from Sigma-Aldrich (Steinheim, Germany). All chemicals were obtained in analytical grade, if available. Human liver microsomes (mixed gender from 50 donors; protein concentration 20 mg/mL; cytochrome P450 content 310 pmol/mg protein) and rat liver microsomes (male Sprague–Dawley rats; protein concentration 20 mg/mL; cytochrome P450 content 700 pmol/mg protein) were obtained from Corning (Corning, USA).

Reference substances for 25 PA and PANO were purchased from Phytolab, Vestenbergsgreuth, Germany (echimidine, echimidine N-oxide, europine, europine N-oxide, erucifoline, erucifoline N-oxide, heliotrine, heliotrine N-oxide, intermedine, intermedine N-oxide, jacobine, jacobine N-oxide, lasiocarpine, lasiocarpine N-oxide, lycopsamine, lycopsamine N-oxide, monocrotaline, monocrotaline N-oxide, retrorsine, retrorsine N-oxide, senecionine, senecionine N-oxide, seneciphylline, seneciphylline N-oxide, and senkirkine). Stock solutions (c = 1.0 mg/mL) of each PA/PANO were prepared either with acetonitrile or acetonitrile/water (50/50, v/v), depending on the solubility, and stored at 4 °C in the dark. A PA/PANO mix solution (c = 1.0 µg/mL of each analyte) was used to prepare calibration standards and for the validation experiments. Water, acetonitrile and methanol were used in LC–MS grade (Th. Geyer, Renningen, Germany). Ammonia solution (32%) was purchased from Th. Geyer as well. Formic acid and ammonium formate used as eluent additive (LC–MS/MS grade) were from Sigma Aldrich (Deisenhofen, Germany).