Application of mass spectrometry to structural identification of flavonoidmonoglycosides isolated from shoot of lupin (Lupinus luteus L.)

Flavonoid glycosides constitute important group of plant secondary metaboli tes. This class of natural products play significant role in different phys iological processes. A new methodological approach where mass spectrometric techniques are applied to structural studies of this class of compounds is presented. Four flavonoid O-monoglycosides and one C-monoglycoside were is olated from green parts of lupin (Lupinus luteus L.). Several different mas s spectrometric techniques were applied to structural elucidation of isolat ed compounds. Desorption ionization mass spectrometry was used for registra tion of mass spectra of intact and derivatized (permethylated) flavonoid gl ycosides. In some cases electron impact mass spectra of permethylated compo unds were also recorded. Methylated samples after methanolysis and further derivatization of free hydroxyl groups (methylation or acetylation) were an alyzed with gas chromatography-mass spectrometry. Combined information draw n from the registered mass spectra enabled us to define molecular mass, str ucture of aglycones and sugars, and positions of glycosidic bonds on the ag lycon. Structures of four flavonoid monoglycosides were elucidated as follo ws: genistein 7-O-glucoside (1), genistein 4'-O-glucoside (2), 2'-hydroxyge nistein 7-O-glucoside (3), and apigenin or genistein 8-C-glycoside (5). For the fourth O-glycoside (4) only molecular mass and masses of the aglycone and sugar were estimated.