title: Characterization of 2,3-diarylxanthones by electrospray mass spectrometry: gas-phase chemistry versus known antioxidant activity properties.
abstract: BACKGROUND
  Xanthones (XH) are a class of heterocyclic compounds widely distributed in nature that hold numerous noteworthy biological and antioxidant activities. Therefore, it is of utmost importance to achieve relevant detailed structural information to understand and assist prediction of their biological properties. The potential relationship between radical-mediated xanthone chemistry in the gas phase and their promising antioxidant activities has not been previously explored.
  
  
  METHODS
  Protonated xanthones XH1-9 were generated in the gas phase by electrospray ionization (ESI) and the main fragmentation pathways of the protonated XH1-9 formed due to collision-induced dissociation (CID) were investigated.
  
  
  RESULTS
  In the CID-MS/MS spectra of [M+H](+) ions of XH1, XH2 and XH4 the product ions formed due to H2 O elimination corresponding to the base peak of the spectra. For the remaining six xanthones (XH3, XH5-9), showing the most promising biological profile, the product ion produced with the highest relative abundance (RA) corresponded to the one formed through concomitant loss of H2 O plus CO. Indicative of an inexistent or lower biological activity is the combined loss of CO plus O unique to the CID-MS/MS spectra of XH1, XH2, XH4, and XH5. The product ion formed by loss of 64 Da (concomitant loss of two molecules of H2 O plus CO) is only observed for xanthones containing a catechol unit (XH3 and XH6-9). This product ion has the highest RA for the most potent scavenger of reactive oxygen and nitrogen species XH9 that contains two of these catechol moieties.
  
  
  CONCLUSIONS
  A strong relationship between some of the biological activities of the studied 2,3-diarylxanthones and their ESI-MS/MS fragmentation spectra was found. The multivariate statistical analysis results suggest that the selected MS features are related to the important biological features. Copyright © 2016 John Wiley & Sons, Ltd.
authors.affiliation: Organic Chemistry Group, QOPNA, Department of Chemistry, University of Aveiro, 3810-193, Aveiro, Portugal. esilva@ff.up.pt.
authors.forename: Eduarda M P
authors.initials: EM
authors.lastname: Silva
authors.affiliation: Mass Spectrometry Centre, QOPNA, Department of Chemistry, University of Aveiro, 3810-193, Aveiro, Portugal.
authors.forename: Cristina M R F
authors.initials: CM
authors.lastname: Barros
authors.affiliation: Organic Chemistry Group, QOPNA, Department of Chemistry, University of Aveiro, 3810-193, Aveiro, Portugal.|Department of Vegetal Production and Technology, Polytechnic Institute of Bragança, School of Agriculture, 5301-855, Bragança, Portugal.
authors.forename: Clementina M M
authors.initials: CM
authors.lastname: Santos
authors.affiliation: Organic Chemistry Group, QOPNA, Department of Chemistry, University of Aveiro, 3810-193, Aveiro, Portugal.
authors.forename: António S
authors.initials: AS
authors.lastname: Barros
authors.affiliation: Mass Spectrometry Centre, QOPNA, Department of Chemistry, University of Aveiro, 3810-193, Aveiro, Portugal.
authors.forename: M Rosário M
authors.initials: MR
authors.lastname: Domingues
authors.affiliation: Organic Chemistry Group, QOPNA, Department of Chemistry, University of Aveiro, 3810-193, Aveiro, Portugal. artur.silva@ua.pt.
authors.forename: Artur M S
authors.initials: AM
authors.lastname: Silva
mesh_terms: D015394:Molecular Structure; D044367:Phase Transition; D021241:Spectrometry, Mass, Electrospray Ionization; D044004:Xanthones / Q000737:chemistry*
chemical_list: D044004:Xanthones; C009689:xanthone