Electrospray ionization tandem mass spectrometric analysis of ent-6,7-seco-kaurane diterpenoids from the Isodon species

Electrospray ionization tandem mass spectrometry (ESI-MSn) using an ion trap instrument and accurate mass measurement on a quadrupole time-of-flight (Q-TOF) mass spectrometer has aided the structural characterization and differentiation of the enmein and spiro-lactone types of ent-6,7-seco-kaurane diterpenoids from Isodon species. The mass spectral fragmentation data from both techniques was compared to obtain the mass spectrometric fragmentation pathways of the ent-6,7-seco-kaurane diterpenoids with high confidence. The analysis revealed that losses of CH2O and CO2 are the predominant process for the enmein type of ent-kauranes in negative ion mode, and the loss Of CO2 is typical for the spiro-lactone type in positive ion mode. In addition, compounds of the spiro-lactone type with a conserved core structure but different substituent groups, such as acetyl, hydroxyl, and aldehyde moiety, resulted in diagnostic product ions by means of successive losses of AcOH, H2O, and CO, respectively. The fragmentation knowledge will facilitate the analysis and identification of the ent-6,7-seco-kauranes in future plant research. Copyright (C) 2008 John Wiley & Sons, Ltd.