Differentiation of flavonol glucoside and galactoside isomers combining chemical isopropylidenation with liquid chromatography–mass spectrometry analysis

• Published in: Journal of Chromatography A 2016-05, Vol.1447, p.64-71
• Main Authors: de Souza, Lauro M., Dartora, Nessana, Scoparo, Camila T., Gorin, Philip A.J., Iacomini, Marcello, Sassaki, Guilherme L.
• Format: Article
• Language: English
• Subjects: Chromatography; Flavonols; Galactosides; Glucosides; Glycoside isomers; Isomers; Isopropylidene; Mass spectrometry; Maytenus ilicifolia; Molecular weight; Multiple-stage mass spectrometry; Spectroscopy; UHPLC–MS
• ISSN: 0021-9673
• DOI: 10.1016/j.chroma.2016.03.069

•A method for glycan analysis based on multiple stage mass spectrometry was developed.•Chemical modification was used to distinguish between isomers.•Isomeric monosaccharides were fragmented producing a distinct fingerprint-MS profile. Flavonol glycosides are important components of leaves from vascular plants. A lot of isomers of these compounds are produced by plants, making their analysis very difficult and causing many structural misinterpretations. Galactosides and glucosides as mono- or oligosaccharides yield many diastereoisomers, hindering the analysis by mass spectrometry. In order to enable the mass spectrometric distinctions of these isomers, in this work we combine an isopropylidene based chemical derivatization with liquid chromatography with multiple-stage mass spectrometry (LC–MSn) analysis. The isomers of flavonol triglycosides, after the reaction, yielded products with different molecular weight, therefore, they were no longer isomers, allowing their identification by MS1 analysis. However, to the 4 isomers of flavonol diglycosides, only one yielded, after isopropylidenation, a product with different molecular weight. To the other 3 species, the incorporation of 2 isopropylidene groups retained them in the isomeric form. For such species, chromatographic separation and MSn detection targeting the lithium adducts of 3,4-O-isopropylidene-galactosyl or 4,6-O-isopropylidene-glucosyl residues (m/z 209.099) provided specific MS profile.