Molecular Structural Features and Tandem Mass Spectral Characteristics of Flavonoids From the Analysis of the LIPID...

Flavonoids comprise an important class of phytochemicals that have not only been proven to be good antioxidants, but also have been shown to have anticancer and neuroprotective activities, of late. Therefore, these compounds find immense applications in food, pharmaceutical and nutraceutical industries. Though these are prevalently of plant origin, some recent evidences reveal their occurrence in bacteria and fungi as well. Thus, identification and characterization of flavonoids is essential, for which tandem mass spectrometry (MS/MS) plays a significant role, whereby diagnostic fragment ions observed from MS/MS experiments are useful in lucidly distinguishing one subclass from another. In order to understand the extent of diversity of flavonoids, we surveyed the database of LIPID MAPS consortium (www.lipidmaps.org), wherein we found more than 6000 flavonoids within the molecular mass range, 200-800 Daltons (Da). To simplify the complexity of such a large dataset, we classified these compounds based on intact molecular mass as well as degree of glycosylation. In doing so, we found ∼3400 aglycones and ~2700 glycosides (glycosylated flavonoids). The number of O-glycosylated flavonoids are greater than the C-glycosylated flavonoids. Further, we highlight the utility of MS/MS, by reviewing some key fragmentation pathways that aid in discriminating subtle variations in the flavonoids' molecular structures, thereby facilitating to identify different subclass types. Altogether, this review clarifies that the LIPID MAPS database is not just solely limited for analyzing well-known lipids such as fatty acyls, glycerolipids, etc., but also is absolutely suitable for investigating 'flavonoids' as well, including mass spectral data analysis.