Profiling isoflavone conjugates in root extracts of lupine species with LC/ESI/MSn systems

Abstract

Extracts obtained from roots of three lupine species (Lupinus albus, L. angustifolius, L. luteus) were analysed using LC/UV and LC/ESI/MS(n). The experiments were performed using two mass spectrometric systems, equipped with the triple quadrupole or ion trap analysers. Thirteen to twenty isomeric isoflavone conjugates were identified in roots of the investigated lupine species. These were di- and monoglycosides of genistein and 2'-hydroxygenistein with different patterns of glycosylation, both at oxygen and carbon atoms; some glycosides were acylated with malonic acid. It was not possible to establish the glycosylation sites of the aglycone only on the basis of the registered mass spectra; however, it was possible to differentiate C- and O-glucosides of isoflavones. Only comparison of retention times with those of standard compounds permitted to indicate the correct glycosylation pattern. In the case of diglycosides, the glycosylation pattern (O-diglucoside or O-glucosylglucoside) was distinguishable on the basis of the relative intensities of daughter ions in the mass spectra of protonated molecular ions. It was not possible to elucidate the site of malonylation on the sugar moiety from mass spectra, however, protonated molecules [M + H](+) of isoflavone glucosides with different placement of the malonyl group on the sugar ring were recognized in the extracts. In addition to the isoflavone glycosides, some flavone or flavonol glycosides were identified in the samples on the basis of collision-induced daughter ion spectra of the aglycone ions. A comparison of results obtained with the triple quadrupole and ion trap analysers was done in the course of the investigations.