Senecionine

Intermedine (Im), senecionine (Sc), and senkirkine (Sk) were purchased from PhytoLab (Vestenbergsgreuth, Germany) the purity being specified as 97, 100, and 97%. Lasiocarpine (Lc) was obtained from Cfm Oskar Tropitzsch (Marktredwitz, Germany) with 98% purity. Methanol (MeOH, LC–MS grade) was purchased from Merck KGaA (Darmstadt, Germany). All other chemicals and co-factors were purchased from Carl Roth (Karlsruhe, Germany) or Sigma-Aldrich (Steinheim, Germany) at the highest purity available.

The structurally different PAs echimidine (94% purity), heliotrine (91% purity), lasiocarpine (98% purity), senecionine (99% purity), and senkirkine (98% purity) were purchased from PhytoLab (Verstenbergsgreuth, Germany). Platyphylline (95% purity) was purchased from BOC Sciences (New York, USA). PAs were dissolved in 0.15 M NaCl. Due to the poorer solubility, senecionine was first dissolved in 0.2 M hydrochloric acid, then the pH was adjusted to 6–7 and afterwards NaCl was added to a final concentration of 0.15 M.

Methanol (MeOH) (MS grade), formic acid (FA) (MS grade) and PTFE membrane filter (0.2 μm) were purchased from Sigma-Aldrich (Darmstadt, Germany). Cellulose acetate filters (0.22 µm) were purchased from Frisenette (Knebel, Denmark). Analytical standards of ptaquiloside and caudatoside were prepared from bracken plant material by the method described by Kisielius et al. (2020b) . Analytical standards of gramine, sparteine and caffeine were purchased from Sigma-Aldrich (Darmstadt, Germany), and jacobine, jacobine N-oxide, senecionine, and senecionine N-oxide were purchased from Phytolab (Vestenbergsgreuth, Germany). MilliQ water (resistivity 18.2 Mohm × cm, TOC less than 1 µg L^-1) was produced in-house with a type I ultrapure water purification system from ELGA-Veolia LabWater (High Wycombe, UK).

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).