Structural characterization of flavonol di‐O‐glycosides from Farsetia aegyptia by electrospray ionization and collision‐induced dissociation mass spectrometry

Abstract

This study reports the application of mass spectrometric methods to characterize unknown flavonoids of the herb Farsetia aegyptia Turra (Crucifereae). High-performance liquid chromatography was performed in combination with UV-photodiode array detection (LC/UV-DAD) and electrospray ionization mass spectrometry (LC/ESI-MS) in both positive and negative ion modes. Collision-induced dissociation (CID) mass spectral data were obtained off-line by nanospray (nano-ESI) analysis, which provided a wealth of information and led to the structural proposal of the flavonol di-O-glycosides present in the herb extract. In addition to the mass spectral data, we also report NMR data for the major compound which allowed the completion of its structural elucidation. The Farsetia aegyptia Turra herb extract was found to contain three flavonol di-O-glycosides containing a monosaccharidic residue linked to the 3-O position and a disaccharidic residue linked to the 7-O position; the major compound was characterized as the new flavonoid, isorhamnetin 3-O-alpha-L-arabinoside 7-O-[beta-D-glucosyl-1 --> 2]-alpha(L)rhamnoside. Different types of CID spectra, i.e., low-energy [M+H]+, [M+Na]+ and [M--H]- spectra as well as high-energy [M+Na]+ spectra, were evaluated with respect to their utility to locate the O-linked saccharidic residues in flavonol di-O-glycosides and to determine the sequence in the disaccharidic part. In agreement with previously published data, the 3-O-glycosyl residue was more readily lost from the protonated molecule than the 7-O-glycosyl residue. The opposite behavior was noted for the fragmentation of the deprotonated and sodiated molecules. Radical ions were observed in the high-energy [M+Na]+ CID spectra which provided supporting information on the glycosylation positions.

Chemical composition of hydroethanolic extracts from Siparuna guianensis, medicinal plant used as anxiolytics in Amazon region

“…Compound 10, peak at 26.0 min (Table 2) (Table 2) can be rationalized by loss of an internal glucose residue (Shahat et al, 2005;Kachlicki et al, 2008). Compound 10 was tentatively characterized as quercetin-3-O-rutinoside-7-O-rhamnoside.…”

“…The different types of CID spectra were evaluated with respect to their structural information content, such as, their utility to locate the O-linked saccharide residues and to determine the sequence in the disaccharidic part. The glycan cleavage sequence in [M+H] + ions of flavonol O-glycosides started with the elimination of glycoside residue from C-3 carbon atom of flavonol (Shahat et al, 2005;Kachlicki et al, 2008). Ions of deprotonated molecules [M-H] -are usually more stable than their protonated counterparts, so higher collision energy is necessary for the fragmentation of the precursor ions.…”

“…Ions of deprotonated molecules [M-H] -are usually more stable than their protonated counterparts, so higher collision energy is necessary for the fragmentation of the precursor ions. Generally, the most abundant product ions obtained from deprotonated molecules were formed after loss of glycoside residue attached to the C-7 carbon atom of flavonol (Shahat et al, 2005;Kachlicki et al, 2008). Thus, generally, the 3-O and 7-O glycosides in flavonol 3,7-di-O-glycosides can readily be located on the basis of ESI-MS/MS, while the loss of 3-O glycoside is more abundant than that the 7-O glycoside for protonated molecules, the opposite behavior is observed for deprotonated and sodiated molecules (Shahat et al, 2005;Kachlicki et al, 2008).…”

“…Generally, the most abundant product ions obtained from deprotonated molecules were formed after loss of glycoside residue attached to the C-7 carbon atom of flavonol (Shahat et al, 2005;Kachlicki et al, 2008). Thus, generally, the 3-O and 7-O glycosides in flavonol 3,7-di-O-glycosides can readily be located on the basis of ESI-MS/MS, while the loss of 3-O glycoside is more abundant than that the 7-O glycoside for protonated molecules, the opposite behavior is observed for deprotonated and sodiated molecules (Shahat et al, 2005;Kachlicki et al, 2008). 1 R 1 =sophoroside; R 3 =OH; R 2 =R 4 =R 5 =H 2 R 1 =R 2 =glucosyl; R 3 =R 4 =R 5 =H 3 R 1 =arabinosyl; R 2 =glucosyl; R 3 =R 4 =R 5 =H 4 R 1 =glucosyl; R 2 =arabinosyl; R 3 =R 4 =R 5 =H 5 R 1 =R 4 =R 5 =H; R 2 =glucosyl; R 3 =OH 6 R 1 =sophoroside; R 2 =R 3 =R 4 =R 5 =H 7 R 1 =R 3 =R 4 =R 5 =H; R 2 =glucosyl 9 R 1 =R 2 =glucosyl; R 3 =OH; R 4 =R 5 =H 10 R 1 =R 2 =H; R 3 =OH; R 4 =rutinoside; R 5 =rhamnosyl 11 R 1 =R 2 =H; R 3 =OH; R 4 =pentosyl-pentoside; R 5 =rhamnosyl 12 R 1 =R 2 =H; R 3 =OH; R 4 =R 5 =rhamnosyl 13 R 1 =R 2 =R 3 =H; R 4 =pentosyl-pentoside; R 5 =rhamnosyl 14 R 1 =R 2 =R 3 =H; R 4 =R 5 =rhamnosyl 15 R 1 =R 2 =H; R 3 =OH; R 4 =pentosyl-rhamnoside; R 5 =rhamnosyl that compounds 10, 11 and 13 (Table 2) first lost a rhamnose (C 6 O 4 H 10 ) moiety [M-H-146]-, given the fragments at m/z 609.0 (compound 10), 565.0 (compound 11) and 549.0 (compound 13) (see Table 2) indicating the presence of 7-O-rhamnosyl group linked to hydroxyl group of aglycone (Shahat et al, 2005;Kachlicki et al, 2008).…”

“…Structural characterization of flavonoid glycosides through spectrometric methods were based on collision-induced dissociation (CID) of molecular species, such as, protonated molecules [M+H] + , deprotonated molecules [M-H] -and sodiated molecules [M+Na] + . The CID experiment can be used with soft, such as ESI-MS/MS or hard ionization, because is dependent only of the analyser (Q-TOF, ion-trap and others) and collision gas (Shahat et al, 2005;Steinmann & Ganzera, 2011).…”