Mass spectral characterization of C-glycosidic flavonoids isolated from a medicinal plant (Passiflora incarnata)

The four major C-glycosidic flavonoids isolated from Passiflora incarnata were identified as schaftoside, isoschaftoside, isovetexin-2'-O-glucopyranoside and isoorientin-2'-O-glucopyranoside on the basis of mass spectral and 13C NMR data. The daughter ion spectra of M + H]+ ions of schaftoside and isoschaftoside showed differences for the M + H - 104]+ ions, which could be rationalized by hydrogen bonding effects. In the negative-ion mode, pronounced differences were found for the M - H - 90]- and M - H - 120]- ions, formed by prevalent fragmentation in the C-6-linked sugar moiety. With respect to isovitexin-2'-O-beta-glucopyranoside and isoorientin-2'-O-beta-glucopyranoside, the daughter ion spectra of both the M + H]+ and M - H]- ions provided evidence for a 1----2 linkage in the diglucosidic moiety. Support for C-6 glucosylation was obtained by recording the daughter ion spectra of M - H - 162]- ions, which were in good agreement with that obtained for M - H]- ions of isovitexin.