Electrospray mass spectrometry with consecutive fragmentation steps (ESI-MSn) as a tool for rapid and sensitive analysis of ginsenosides and their galactosyl derivatives

The ginsenosides Rb-1 (3) and Rg(1) (4) isolated from Panax ginseng were en zymatically modified with galactosyltransferase to furnish new derivatives carrying galactose units in one or both sugar chains at position C(20) and/ or C(3) or C(6) of the protopanaxadiol and protopanaxatriol aglycones 1 and 2, respectively. To determine the linkage position(s) of the introduced ga lactose unit(s), an electrospray-ionization MS analysis with consecutive fr agmentation steps (ESI-MSn) was carried out using an ion-trap mass spectrom eter (Figs. 2 and 3). It was shown that both sugar moieties, located at dif ferent positions of the protopanaxadiol and protopanaxatriol aglycone, can be easily differentiated and analyzed in the subsequent fragmentation steps . Collision-induced dissociation (CID) of the Na+-ionized molecule (MS2) le ads to cleavage of the most labile O-C(20) glycosidic bond, liberating the C(20) oligosaccharide fragment ion that can be analyzed in a subsequent fra gmentation step (MS3). MS3 of the C(20) monodeglycosylated ginsenoside lead s to cleavage of the second sugar moiety, allowing structure analysis of th is fragment ion (MS4). By this method, the linkages of the monosaccharides and branching positions can be rapidly determined using only a few mu l of a 10(-5) M sample solution.