TI: Determination of flavone, flavonol, and flavanone
aglycones by negative ion liquid chromatography electrospray ion trap mass
spectrometry.
AU: Fabre,-N; Rustan,-I; de-Hoffmann,-E; Quetin-Leclercq,-J
AD: Laboratoire de Pharmacognosie, Universite Catholique de Louvain,
Brussels, Belgium.
SO: J-Am-Soc-Mass-Spectrom. 2001 Jun; 12(6): 707-15
PY: 2001
AB: Eleven naturally occurring flavonoid aglycones, belonging
to the representative flavone, flavonol, and flavanone types were separated
by high performance liquid chromatography and analyzed on-line with negative
ion electrospray ionization tandem mass spectrometry (ESI-MS/MS). In order
to resolve the MS/MS spectra obtained, each compound was reinvestigated
by direct loop injections using an ion trap mass spectrometer. The MSn
spectra obtained allowed us to propose plausible schemes for their fragmentation
supported by the analysis of five complementary synthetic flavonoid aglycones.
The negative ion ESI-MS/MS behavior of the different aglycones investigated
in this study revealed interesting differences when compared with the previously
described patterns obtained using various ionization techniques in positive
ion. Thus, concerning the retro Diels-Alder (RDA) fragmentation pathways,
several structurally informative anions appeared highly specific of the
negative ion mode. In addition, a new lactone-type structure, instead of
a ketene, was proposed for a classic RDA diagnostic ion. We also observed
unusual CO, CO2, and C3O2 losses which appear to be characteristic of the
negative ion mode. All these results and these unusual neutral losses show
that the negative ion mode was a powerful complementary tool of the positive
ion mode for the structural characterization of flavonoid aglycones by
ESI-MS/MS.