2 deoxyadenosine da

High performance liquid chromatography (HPLC)-grade standards for 20(S)-ginsenoside Rg3 and 20(R)-ginsenoside Rg3 were purchased from Shanghai Yuanye Biotechnology Co., Ltd. (Shanghai, China) and dissolved at a concentration of 50 mg/ml in dimethyl sulfoxide as a stock solution (stored at −20°C). This solution was then further diluted in cell culture medium to prepare the working concentrations (0, 7.81, 15.63, 31.25, 62.5, 125, 250 and 500 µg/ml). 5-methyl-2′-deoxycytidine (5-MedC) was purchased from United States Biological (Salem, MA, USA), and 2′-deoxyguanosine (dG), thymidine (T), 2′-deoxycytidine (dC) and 2′-deoxyadenosine (dA) were obtained from Sigma-Aldrich; Merck Millipore (Darmstadt, Germany). Sodium acetate, ammonium formate and acetonitrile were supplied by Beijing Chemical Works (Beijing, China). MNase, nuclease P1 and alkaline phosphatase were purchased from Takara Bio, Inc. (Otsu, Japan).

N-acetylcysteine, calf thymus DNA (sodium salt, Type I), nuclease P1, micrococcal nuclease, spleen phosphodiesterase, NADPH, 2′-deoxyguanosine (dG), and 2′-deoxyadenosine (dA) were purchased from Sigma-Aldrich (St. Louis, MO, USA). Dimethylformamide, acetonitrile, potassium carbonate, chloroform, diethyl ether, and phosphate buffered saline were obtained from Fisher Scientific (Pittsburg, PA, USA). AX 1-X8 anion exchange resin was purchased from Bio-Rad (Hercules, CA, USA). All solvents used were high performance liquid chromatography (HPLC) grade.
Dehydromonocrotaline was synthesized by dehydrogenation of monocrotaline in chloroform with o-chloranil, as previously described [19 (link)]. DHP was obtained from the metabolism of riddelliine by rat liver microsomes [27 ]. DHP-dG-1, DHP-dG-2, DHP-dG-3, DHP-dG-4, DHP-dA-1, DHP-dA-2, DHP-dA-3, and DHP-dA-4 adducts were synthesized as previously described [10 (link),19 (link)]. Isotopically labeled DHP-[¹⁵N₅]dG and DHP-[¹⁵N₅, ¹³C₁₀] dA adducts, used as internal standards for quantitation of DHP-dG and DHP-dA adducts by liquid chromatographytandem mass spectrometry (LC/MS/MS), were synthesized as described previously [8 (link),10 (link)].
Male human liver microsomes and male Fischer 344 rat liver microsomes were purchased from Bioreclamation IVT (Baltimore, MD, USA). DNA concentrations were determined spectrophotometrically.