Mass Spectrometric Approaches in Profiling and Monitoring Bioreactivity of Polyphenols in Medicinal Plants

Abstract

Flavonoids are one of the most abundant secondary metabolites (SM) in the nature. They possess a wide range of the biological activity. This work comprises of two chapters, in which the application of mass spectrometry (MS) in fields of phytochemistry and secondary metabolites bioactivity were emphasized. The first chapter covered the advantages of the hyphenated techniques of LC-MS in profiling flavonoids in some known medicinal plants; Bupleurum marginatum, Camellia sinensis, Citrus jambhiri, and Scutellaria immaculata, as well as Scutellaria ramosisima. LC-MS proved to be a par excellence technique providing many attractive features in the profiling of medicinal plant extracts and in the identification of new bioactive polyphenols. The second chapter covered the applications of ESI-MS in monitoring non-covalent interactions between some polyphenols with different peptides. flavonoid glycosides show an ability to build non-covalent complexes with angiotensin (I) through ionic bonds. The stability of the formed complexes is dependent on the number of sugar residues contributing in the structure of the flavonoid glycoside. On the other hand, flavonoid aglycones exhibit disability to form stable complexes with angiotensin(I). Co-planarity of flavonoid aglycones makes them relatively inflexible and less complaint in forming ionic bonds with biomolecules. One exception is taxifolin, whereas the missing π system at C2-C3 of ring C grants taxifolin more flexibility in comparison to other studied glycones. Moreover, the quantity of the interacted molecules of the tested flavonoid glycoside will increase, as the number of lysine residues in the targeted peptide increases. Complexes such as 2:1, 3:1 and even 8:1 polyphenol:peptide have been detected. The polyphenol:peptide ratio increases proportionally with the number of the phenolic groups incorporated with the chemical structure of the tested flavonoid, e.g.; EGCG˃ rutin˃ hyperoside˃ scutellarin. On the other hand, flavonoid aglycones can interact with the backbone amides forming hydrogen bonds, whereas flavonoid glycosides cannot build hydrogen bonds with the backbone amides of insulin. Nevertheless, spiraeoside; 4'-O-glucoside of quercetin, can form hydrogen bonds. Cleavage of the sugar bridge at 4' position occurs spontaneously, and the related aglycone; i.e. quercetin, will be free to undergo the non-covalent interaction.