A tandem mass spectrometric investigation of the low-energy collision-activated fragmentation of neo-clerodane diterpenes

Mass spectrometric fragmentation data of neo-clerodane diterpenes are almost inexistent but they can prove helpful for the qualitative and quantitative analysis of these compounds as well as for the identification of unknown compounds belonging to this class of plant secondary metabolites. [M-H]-ions of nine neo-clerodane diterpenes (1-9), recently isolated from Teucrium chamaedrys, were generated by electrospray ionization and were fragmented in the collision cell of a Triple Quadrupole (TQ) and of a Quadrupole Ion Trap (QIT) mass spectrometer. The deprotonated neo-clerodane glucosides, chamaedryoside A and B (1, 2), readily lost the sugar residue to give, as their main fragmentation channel, the neo-clerodane ions, I and II, which were structurally characterized by TQ and QIT MS. The collision-activated dissociation (CAD) mass spectra of I and II and of deprotonated neo-clerodanes 3-9 allowed us to reach some general conclusions on the fragmentation pathways of this class of compounds. For example, teuflin and its OH derivatives, teucrin A, teuflidin and 6-β-hydroxyteucridin, showed a characteristic fragmentation pattern involving the loss of 94 Da and 124 Da from the lactone moiety, whereas a loss of 44 Da was observed for teucrin E, and of 58 Da for teucrin F and G. In addition, several compound-specific fragmentations were observed and can be proposed for the identification of individual compounds. The systematic approach allowed us to hypothesize the mechanisms of the most important collision-activated dissociation/isomerization channels. © 2010 John Wiley & Sons, Ltd.