Sulfated Metabolites of Luteolin, Myricetin, and Ampelopsin: Chemoenzymatic Preparation and Biophysical Properties

Abstract

Authentic standards of food flavonoids are important for human metabolic studies. Their isolation from biological material is impracticable; however, they can be prepared in vitro. Twelve sulfated metabolites of luteolin, myricetin and ampelopsin were obtained with arylsulfotransferase from Desulfitobacterium hafniense and fully characterized by HPLC, MS and NMR. The compounds were tested for their ability to scavenge DPPH (1,1-diphenyl-2-picrylhydrazyl), ABTS (2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulphonic acid)) and DMPD+ (N,N-dimethyl-p-phenylenediamine) radicals, to reduce ferric ions and Folin-Ciocalteau reagent, and to inhibit tert-butyl hydroperoxide induced lipid peroxidation of rat liver microsomes. The activity differed considerably even between monosulfate isomers. The parent compounds and myricetin-3′-O-sulfate were the most active while other compounds displayed significantly lower activity, particularly the luteolin sulfates. No mutagenic activity of parent compounds and their main metabolites was observed, only myricetin showed minor pro-mutagenicity. The prepared sulfated metabolites are now available as authentic standards for future in vitro and in vivo metabolic studies.