title: Fragmentation characteristics and isomeric differentiation of flavonol O-rhamnosides using negative ion electrospray ionization tandem mass spectrometry.
abstract: BACKGROUND
  Flavonoids exhibit a wide range of biological activities. The differentiation and structural characterization of the flavonol O-rhamnosides and their isomers are important research topics. Electrospray ionization tandem mass spectrometry (ESI-MS(n) ) is an indispensable tool and has become an efficient method for the identification of bioactive natural products.
  
  
  METHODS
  Negative ion ESI-MS(n) was used to characterize and differentiate flavonol O-rhamnosides and their isomeric compounds. The collision energies in collision-induced dissociation were varied to optimize the structural information.
  
  
  RESULTS
  Flavonol 7-O-rhamnosides containing either a hydroxyl or a methoxyl group at the C-8 position clearly differed from their isomeric compounds, such as the flavonol 3-O-rhamnosides, in the product ion spectra of the [M-H](-) ions. The differences in the locations of the glycosyl group and OCH(3) group resulted in a significant change in the relative abundances of the Y(0)(-) and [Y(0) -H](-•) ions, and the formation of some characteristic ions, such as (1,3)A(0)(-) and [(1,3)A(0)-CH(3)](-•).
  
  
  CONCLUSIONS
  An efficient ESI-MS(n) method for the structural identification and isomeric differentiation of flavonol O-rhamnosides was developed. The differences in the glycosyl type, and the glycosylation and methoxylation positions in the structures of isomeric flavonoids, can be determined using (-)ESI-MS(n) spectra. The formation and relative abundances of [Y(0)-H](-•) and Y(0) (-) ions, as well as the comparison of some diagnostic ions, are vital in the differentiation of isomeric flavonoids. These results have practical applications in the rapid identification of flavonol O-rhamnosides present in crude bioactive extracts.
authors.affiliation: Key Laboratory of Oil and Gas Fine Chemicals, Ministry of Education & Xinjiang Uyghur Autonomous Region, College of Chemistry and Chemical Engineering, Xinjiang University, Urumqi, 830046, P.R. China. ablajan209@hotmail.com
authors.forename: Keyume
authors.initials: K
authors.lastname: Ablajan
authors.forename: Anagu
authors.initials: A
authors.lastname: Tuoheti
mesh_terms: D005419:Flavonoids / Q000032:analysis / Q000737:chemistry*; D006027:Glycosides / Q000032:analysis / Q000737:chemistry*; D007477:Ions / Q000737:chemistry; D007536:Isomerism; D010936:Plant Extracts / Q000737:chemistry; D029771:Rhodiola / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D053719:Tandem Mass Spectrometry / Q000379:methods*
chemical_list: D005419:Flavonoids; D006027:Glycosides; D007477:Ions; D010936:Plant Extracts