title: Tandem mass spectrometric analysis and density functional theory calculations on the fragmentation behavior of two tetradecanoylingenol regioisomers from Euphorbia wallichii.
abstract: BACKGROUND
  Two structurally similar bioactive regioisomers, 3-O-tetradecanoylingenol and 20-O-tetradecanoylingenol, from Euphorbia wallichii presented quite different fragmentation behaviors. Revealing the related fragmentation pathways may improve the efficiency of characterization and identification of such type of compounds.
  
  
  METHODS
  The two regioisomers were subjected to collision-induced dissociation (CID) on Finnigan LCQ(DECA) and LTQ Orbitrap XL instruments. Based on the CID results, the possible fragmentation pathways were proposed and investigated with density functional theory (DFT) calculations.
  
  
  RESULTS
  Elimination of C(14)H(28)O(2) (tetradecanoic acid) for 3-O-tetradecanoylingenol and the sequential losses of C(4)H(8) (butylene) for 20-O-tetradecanoylingenol were observed in ESI-MS/MS, witnessed also by HR-ESI-MS/MS. The fragmentation pathways were proposed and verified by calculating the activation energy of their transition states by DFT calculations.
  
  
  CONCLUSIONS
  Based on the observations, fragmentation pathways for the two regioisomers were proposed and verified by calculating the energy of the reactants, products and the corresponding transition states using DFT. This report should have value in rapid identification of the derivatives of ingenol and other regioisomers in natural products.
authors.affiliation: Key Laboratory of Mountain Ecological Restoration and Bioresource Utilization, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu, P.R. China.
authors.forename: Bing
authors.initials: B
authors.lastname: Xia
authors.forename: Kaijie
authors.initials: K
authors.lastname: Xu
authors.forename: Xin
authors.initials: X
authors.lastname: Liu
authors.forename: Yunfeng
authors.initials: Y
authors.lastname: Chai
authors.forename: Cuirong
authors.initials: C
authors.lastname: Sun
authors.forename: Yucheng
authors.initials: Y
authors.lastname: Gu
authors.forename: Lisheng
authors.initials: L
authors.lastname: Ding
authors.forename: Yan
authors.initials: Y
authors.lastname: Zhou
mesh_terms: D004224:Diterpenes / Q000737:chemistry*; D028481:Euphorbia / Q000737:chemistry*; D008958:Models, Molecular; D010936:Plant Extracts / Q000737:chemistry*; D053719:Tandem Mass Spectrometry / Q000379:methods*
chemical_list: D004224:Diterpenes; D010936:Plant Extracts; C056099:3-O-tetradecanoylingenol