Elimination of 118 Da: a characteristic fragmentation in the tandem mass spectra of 11(15 --> 1)-abeo-taxanes

The mechanism of the elimination of 118 Da from 11(15-->1)-abeo-taxanes was elucidated with the help of the tandem mass spectra of M + NH(4)](+) and M + Li](+) ions and the corresponding D-exchanged species. The fragmentation is triggered by the initial loss of the C-10 substituent. Evidence was also obtained for the stepwise elimination of acetone and acetic acid. Acetone is eliminated from the C-1 hydroxyisopropyl group and acetic acid from either the C-9 or C-7 acetoxy groups. The presence of an additional acetoxy group at C-13 leads to the direct elimination of 118 Da from M + NH(4)](+) and M + Li](+) ions involving the C-13 acetoxy group.