Abstract
Silymarin, an extract from milk thistle (Silybum marianum) fruits, is consumed in various food supplements. The metabolism of silymarin flavonolignans in mammals is complex, the exact structure of their metabolites still remains partly unclear and standards are not commercially available. This work is focused on the preparation of sulfated metabolites of silymarin flavonolignans. Sulfated flavonolignans were prepared using aryl sulfotransferase from Desulfitobacterium hafniense and p-nitrophenyl sulfate as a sulfate donor and characterized by high-resolution mass spectrometry (HRMS) and nuclear magnetic resonance (NMR). Their 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and N,N-dimethyl-p-phenylenediamine (DMPD) radical scavenging; ferric (FRAP) and Folin–Ciocalteu reagent (FCR) reducing activity; anti-lipoperoxidant potential; and effect on the nuclear erythroid 2-related factor 2 (Nrf2) signaling pathway were examined. Pure silybin A 20-O-sulfate, silybin B 20-O-sulfate, 2,3-dehydrosilybin-20-O-sulfate, 2,3-dehydrosilybin-7,20-di-O-sulfate, silychristin-19-O-sulfate, 2,3-dehydrosilychristin-19-O-sulfate, and silydianin-19-O-sulfate were prepared and fully characterized. Sulfated 2,3-dehydroderivatives were more active in FCR and FRAP assays than the parent compounds, and remaining sulfates were less active chemoprotectants. The sulfated flavonolignans obtained can be now used as authentic standards for in vivo metabolic experiments and for further research on their biological activity.
Highlights
Silymarin is an extract from the fruits of milk thistle (Silybum marianum (L.) Gaertn, Asteraceae), a medicinal plant used for various human ailments since the times of the ancient Greeks [1]
We focused on the sulfation of six flavonolignans of silymarin, namely silybin A, silybin B, 2,3-dehydrosilybin, silychristin, 2,3-dehydrosilychristin, and silydianin
We succeeded in the preparation of sulfated metabolites of silymarin flavonolignans, namely silybin A 20-O-sulfate, silybin B 20-O-sulfate, 2,3-dehydrosilybin-20-O-sulfate, 2,3-dehydrosilybin-7,20-di-O-sulfate, silychristin-19-O-sulfate, and 2,3-dehydrosilychristin-19O-sulfate
Summary
Silymarin is an extract from the fruits of milk thistle (Silybum marianum (L.) Gaertn, Asteraceae), a medicinal plant used for various human ailments since the times of the ancient Greeks [1]. Silybin is the major flavonolignan of silymarin, and literature focuses primarily on this compound mainly because of its commercial availability and relatively easy isolation [3]. Silychristin and silydianin were described more than 40 years ago [4], their biological properties were not investigated until very recently, mainly because of separation problems [5,6]. A new preparatory separation method using Sephadex LH-20 was developed, which provides multigram amounts of pure silychristin A, silydianin, and a fraction containing silybin and isosilybin [7]. The methods for the preparation of 2,3-dehydroflavonolignans were optimized and biological and biophysical properties of these compounds, such as antiradical, antilipoperoxidant, and cytoprotective, were recently described by us [5,6]
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