Amination of Flavonoids Possessing a Pyrogallol Group in Cell Culture Medium at 37°C

A class of flavonoid aminated derivatives that had been consistently overlooked in literature was shown to be formed as artefacts in cell culture medium. In this study, 34 flavonoids from different subclasses were incubated in Dulbecco's modified Eagle's Medium (DMEM) at 37°C for 2 h to identify the reaction mechanism behind aminated derivatives formation from flavonoids. Baicalein, scutellarein, dihydromyricetin, (−)-gallocatechin (GC), (−)-epigallocatechin (EGC), (−)-GC gallate, and (−)-EGC gallate were found to yield corresponding nitrogenous derivatives in both DMEM and amino acid solution. The nitrogen source of these seven flavonoid -aminated derivatives was revealed to be amino acids in DMEM. The pyrogallol group of the flavonoids was a key structural motif, being first oxidized into quinone and then further reacting with amino acids (Strecker degradation) to yield aminated flavonoids and corresponding aldehydes. A slightly alkaline environment accelerated the amination of flavonoids, possibly via the formation of flavonoid quinone. These results provide the mechanistic evidence for the in vitro generation of flavonoid -aminated derivatives, yet to be tested using in vivo assays.