title: Study of the reaction products of flavonols with 2,2-diphenyl-1-picrylhydrazyl using liquid chromatography coupled with negative electrospray ionization tandem mass spectrometry.
abstract: The products obtained after the reaction between flavonols and the stable free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH(*)) in both methanol and acetonitrile were characterized using liquid chromatography coupled with negative electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) and NMR spectroscopy. The flavonols studied were quercetin, kaempferol and myricetin. In methanol, two reaction products of oxidized quercetin were identified using LC/ESI-MS/MS and NMR. Quercetin was oxidized through a transfer of two H-atoms to DPPH(*) and subsequently incorporated either two CH(3)OH molecules or one CH(3)OH- and one H(2)O molecule giving the products 2-(3,4-dihydroxyphenyl)-3,5,7-trihydroxy-2,3-dimethoxy-2,3-dihydrochromen-4-one and 2-(3,4-dihydroxyphenyl)-3,3,5,7-tetrahydroxy-2-methoxy-2,3-dihydrochromen-4-one, respectively. LC/ESI-MS/MS analysis revealed that in methanol, kaempferol and myricetin also gave rise to methoxylated oxidation products similar to that identified for quercetin. Kaempferol, in addition, also exhibited products where a kaempferol radical, obtained by a transfer of one H-atom to DPPH(*), reacted with CH(3)OH through the addition of CH(3)O(*), yielding two isomeric products. When the reaction took place in acetonitrile, LC/ESI-MS/MS analysis showed that both quercetin and myricetin formed stable isomeric quinone products obtained by a transfer of two H-atoms to DPPH(*). In contrast, kaempferol formed two isomeric products where a kaempferol radical reacted with H(2)O through the addition of OH(*), i.e. similar to the reaction of kaempferol radicals with CH(3)OH.
authors.affiliation: Department of Chemistry, Biotechnology and Food Science, Agricultural University of Norway, N-1432 As, Norway. erland.hvattum@amersham.com
authors.forename: Erlend
authors.initials: E
authors.lastname: Hvattum
authors.forename: Yngve
authors.initials: Y
authors.lastname: Stenstrøm
authors.forename: Dag
authors.initials: D
authors.lastname: Ekeberg
mesh_terms: D001713:Biphenyl Compounds; D047309:Flavones / Q000737:chemistry* / Q000302:isolation & purification; D006834:Hydrazines; D007202:Indicators and Reagents; D015394:Molecular Structure; D010851:Picrates; D010944:Plants / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods
chemical_list: D001713:Biphenyl Compounds; D047309:Flavones; D006834:Hydrazines; D007202:Indicators and Reagents; D010851:Picrates; C004931:1,1-diphenyl-2-picrylhydrazyl