title: Electrospray ionization tandem mass spectrometry analysis of isopimarane diterpenes from Velloziaceae.
abstract: BACKGROUND
  The study of natural products by electrospray ionization tandem mass spectrometry (ESI-MS/MS) is an important strategy for the characterization of the major fragmentation reactions which can then help to determine the composition of complex mixtures. Application of ESI-MS/MS to a series of isopimarane diterpenes from Velloziaceae allowed the rationalization of their fragmentation mechanisms.
  
  
  METHODS
  Velloziaceae diterpenes were isolated by silica gel column chromatography and investigated by ESI-MS/MS analysis. The fragmentation studies were performed on a quadrupole-time-of-flight instrument using N2 as the collision gas. To help rationalize the fragmentation pathways observed, the geometry and sites of reactivity of the diterpenes were obtained by theoretical calculations using the B3LYP/6-31 + G(d,p) model. Fragmentation mechanisms were proposed on the basis of the calculated protonation sites and product ions energies using density functional theory (DFT) methods.
  
  
  RESULTS
  The presence of hydroxyl and carbonyl groups on the terpene core influences the protonation site observed. One compound showed a radical cation as the base peak. MS/MS spectra exhibit water elimination as the major fragmentation pathway (via two ways), either when protonation takes place on the oxygen atom, or through elimination after activation from hydrogen migration. After the elimination of water, the formation of an endocyclic double bond induces a sequential retro-Diels-Alder (RDA) reaction as the major fragmentation step.
  
  
  CONCLUSIONS
  A thorough rational analysis of the fragmentation mechanisms of protonated Velloziaceae diterpenes was used to propose the dissociation mechanisms in ESI-MS/MS. The presence of esters in the side chain also influenced the intensity or occurrence of the observed protonated or cationized molecules in ESI-MS. These results will aid the identification of analogues in sample extracts in future metabolomics studies.
authors.affiliation: Departamento de Química Orgânica, Instituto de Química, Universidade Federal do Rio de Janeiro, Cidade Universitária, CT, Bloco A, sala 626A, CEP 21941-909, Rio de Janeiro, RJ, Brazil.
authors.forename: Angelo
authors.initials: A
authors.lastname: da Cunha Pinto
authors.affiliation: Departamento de Química, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, 14040-901, Ribeirão Preto, SP, Brazil.
authors.forename: Ricardo
authors.initials: R
authors.lastname: Vessecchi
authors.affiliation: Instituto Federal de Educação, Ciência e Tecnologia. Campus Nilópolis, R. LúcioTaváres, 1045, CEP 26530-060, Centro, Nilópolis, RJ, Brazil.
authors.forename: Carmelita Gomes
authors.initials: CG
authors.lastname: da Silva
authors.affiliation: Departamento de Química Orgânica, Instituto de Química, Universidade Federal do Rio de Janeiro, Cidade Universitária, CT, Bloco A, sala 626A, CEP 21941-909, Rio de Janeiro, RJ, Brazil.
authors.forename: Ana Carolina Lourenço
authors.initials: AC
authors.lastname: Amorim
authors.affiliation: Departamento de Química Orgânica, Instituto de Química, Universidade Federal do Rio de Janeiro, Cidade Universitária, CT, Bloco A, sala 626A, CEP 21941-909, Rio de Janeiro, RJ, Brazil.
authors.forename: Helvécio Martins
authors.initials: HM
authors.lastname: dos Santos Júnior
authors.affiliation: Departamento de Química Orgânica, Instituto de Química, Universidade Federal do Rio de Janeiro, Cidade Universitária, CT, Bloco A, sala 626A, CEP 21941-909, Rio de Janeiro, RJ, Brazil.
authors.forename: Michelle Jakeline Cunha
authors.initials: MJ
authors.lastname: Rezende
authors.affiliation: School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 1TS, UK.
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Gates
authors.affiliation: Departamento de Química Orgânica, Instituto de Química, Universidade Federal do Rio de Janeiro, Cidade Universitária, CT, Bloco A, sala 626A, CEP 21941-909, Rio de Janeiro, RJ, Brazil.
authors.forename: Claudia Moraes
authors.initials: CM
authors.lastname: Rezende
authors.affiliation: Núcleo de Pesquisas em Produtos Naturais e Sintéticos (NPPNS) - Faculdade de Ciências Farmacêuticas de Ribeirão Preto, Universidade de São Paulo, Av. do Café, s/n, CEP 14040-903, Ribeirão Preto, SP, Brazil.
authors.forename: Norberto Peporine
authors.initials: NP
authors.lastname: Lopes
mesh_terms: D045784:Abietanes / Q000032:analysis* / Q000737:chemistry*; D019684:Magnoliopsida / Q000737:chemistry*; D008958:Models, Molecular; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D053719:Tandem Mass Spectrometry / Q000379:methods*
chemical_list: D045784:Abietanes