Antioxidant capacity and fragmentation features of C‐glycoside isoflavones by high‐resolution electrospray ionization tandem mass spectrometry using collision‐induced and high‐energy collisional dissociation techniques

Abstract

The rapid annotation and identification by mass spectrometry techniques of flavonoids remains a challenge, due to their structural diversity and the limited availability of reference standards. This study applies a workflow to characterize two isoflavonoids, the orobol-C-glycosides analogs, using high-energy collisional dissociation (HCD)-and collision-induced dissociation (CID)-type fragmentation patterns, and also to evaluate the antioxidant effects of these compounds by ferric reducing antioxidant power (FRAP), 2,2 0 -azino-bis(3-ethylbenzothiazolin acid) 6-sulfonic acid (ABTS), and 2,2-diphenyl-1-picrylhydrazyl (DPPH) methods. By the CID-type fragmentation, in positive mode and at all high-resolution mass spectrometry (HRMS) multiple stage, there were shown differences in the annotation of the compounds, mainly concerning some ratios of relative abundance. At CID-MS 2 20 eV, the compounds could be efficiently characterized, because they present distinct base peaks [M + H] + and [M + H-H 2 O] + for the orobol-8-C-and orobol-6-C-glycoside, respectively. Similarly, by the HCD-type fragmentation, in HRMS 2 stage, differences between orobol analogs in both mode of ionization were observed. However, the HR HCD-MS 2 at 80 eV, in positive mode, generated more ions and each isomer presented different base peaks ions, [0,2X] + for the orobol-8-C-glycoside and [0,3X] + for the orobol-6-Cglycoside. By the DPPH, the 8-C-derivative showed a very close value compared with the standard rutin and, in the ABTS method, a higher radical-scavenging activity. In both methods, the EC 50 of orobol-8-C-glycoside was almost twice better compared with orobol-6-C-glycoside. In FRAP, both C-glycosides showed a good capacity as Fe +3 reducing agents. We could realize that combined MS techniques, highlighting the positive mode of ionization, can be used to evaluate the isoflavones analogs being useful to differentiate between the isomeric flavones; therefore, these data are important to mass spectrometry dereplication studies become more efficient.