Dc. Vansetten et al., MULTIPLE-STAGE TANDEM MASS-SPECTROMETRY FOR STRUCTURAL CHARACTERIZATION OF SAPONINS, Analytical chemistry (Washington), 70(20), 1998, pp. 4401-4409
Nanoelectrospray ion trap multiple-stage tandem mass spectrometry was
applied to characterize saponins present in HPLC fractions from Quil A
, a commercially available bark extract. An analytical strategy was de
veloped based on recognition of carbohydrate sequence ions as well as
glycosidic ring-cross ions formed by gamma-hydrogen rearrangements and
successive retro-Diels-Alder fragmentations. These ions could be used
for the determination of several glycosidic linkages, ring sizes, and
positions of acyl groups. The presence of an acyl group on a monosacc
haride residue facilitated the determination of the substitution patte
rn, due to the induction of ring-cross fragmentation. Deuteriomethylat
ion resulted in a more extended set of ring-cross ions, thus allowing
determination of additional glycosidic linkages. An analysis typically
consumed 200 ng of sample and a total of 1-4 h for measurement and in
terpretation. The applied method is attractive as a pre-NMR analysis,
especially because it resulted rapidly in an overall idea of the struc
ture even when starting from scratch. The multiple-stage tandem approa
ch enabled structural determination of saponins to a more detailed lev
el than achievable with current single-stage tandem mass spectrometry.