Liquid chromatographic/electrospray ionization mass spectrometric identification of the oxidation end-products of metformin in aqueous solutions.
Metformin is an antihyperglycemic drug that exhibits some antioxidant properties. HO*-induced oxidation of metformin was studied in aqueous solution, in both aerated and deaerated conditions. Gamma radiolysis of water was used to generate HO* free radicals, capable of initiating one-electron oxidation of metformin. Oxidation end-products were identified by direct infusion mass spectrometry (MS) and high-performance liquid chromatography/mass spectrometry (HPLC/MSn): for every product, structure elucidation was based on its mass (simple mass spectra confirmed by HPLC/MS). In addition, fragmentation spectra (MS2, MS3 and MS4) and the determination of deuterium-hydrogen exchange sites provided valuable information allowing the complete identification of some of the end-products. At low radiation dose, four products were identified as primary ones, since they result from the direct attack of HO* radicals on metformin. These primary oxidation end-products were identified respectively as hydroperoxide of metformin, covalent dimer of metformin, methylbiguanide and 2-amino-4-imino-5-methyl-1,3,5-triazine. At high radiation dose, seven other products were identified as secondary ones, resulting from the HO*-induced oxidation of the primary end-products. A reaction scheme was postulated for the interpretation of the results.
Collin
F
F
Laboratoire de Chimie Physique, CNRS UMR 8601, Université Paris 5, 75270, France. fabrice.collin@univ-paris5.fr
Khoury
H
H
Bonnefont-Rousselot
D
D
Thérond
P
P
Legrand
A
A
Jore
D
D
Gardès-Albert
M
M
D000975:Antioxidants / Q000032:analysis / Q000737:chemistry; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D017665:Hydroxyl Radical / Q000737:chemistry; D007004:Hypoglycemic Agents / Q000032:analysis* / Q000737:chemistry; D008687:Metformin / Q000032:analysis* / Q000737:chemistry; D010084:Oxidation-Reduction; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D014867:Water / Q000737:chemistry
D000975:Antioxidants; D007004:Hypoglycemic Agents; D014867:Water; D017665:Hydroxyl Radical; D008687:Metformin