Characterization of iridoids by fast atom bombardment mass spectrometry followed by collision-induced dissociation of [M+Li](+) ions

Fast atom bombardment mass spectra of a series of naturally occurring and s ynthetically modified iridoid glycosides were studied using lithium cationi zation and collision-induced dissociation of the resulting [M + Li](+) ions . Lithium cationization leads to the unambiguous determination of the molec ular masses of these compounds. Collision-induced dissociation of the lithi ated molecular ions give valuable structural information regarding the natu re of the substituent on both the aglycone and the sugar moieties, The char acteristic fragmentation pathways identified are (1) elimination of neutral molecules comprising the substituents on either the aglycone or sugar moie ties, (2) formation of Lithiated aglycone and their fragment ions, (3) form ation of lithiated sugar and their fragment ions, (4) fragmentation corresp onding to the cleavage of the aglycone or sugar ring and (5) fragmentation characteristic of the substituents present in either the aglycone or sugar parts of the molecule. Elimination of two acyloxy radicals from the lithiat ed molecular ion is a characteristic fragmentation in the case of acyloxy d erivatives. Copyright (C) 2000 John Wiley & Sons, Ltd.