Abstract
A selective acylation protocol using cerium chloride (CeCl3) as catalyst was applied to functionalize silybinin (1), a natural antioxidant flavonolignan from milk thistle fruit, in order to increase its solubility in lipophilic media while retaining its strong antioxidant activity. The selective esterification of 1 at the position 3-OH with a palmitate acyl chain leading to the formation of the 3-O-palmitoyl-silybin (2) was confirmed by both mass spectroscopy (MS) and nuclear magnetic resonance (NMR) analyses. The antioxidant activity of 1 was at least retained and even increased with the CUPRAC assay designed to estimate the antioxidant activity of both hydrophilic and lipophilic compounds. Finally, the 3-O-palmitoylation of 1, resulting in the formation of 2, also increased its anti-lipoperoxidant activity (i.e., inhibition of conjugated diene production) in two different lipophilic media (bulk oil and o/w emulsion) subjected to accelerated storage test.
Highlights
Lipids are essential constituents of food and cosmetic preparations but are predisposed to oxidation that constitute the major source of quality deterioration of these products and could result in important health issues for the consumers [1]
We evaluated the anti-lipoperoxidation activities (inhibition of conjugated diene hydroperoxides (CD) formation) of 2 in two different lipophilic media subjected during six days to the Schaal oven test (Table 3)
Our results showed that the lipophilic 2 was more efficient to inhibit Conjugated Diene Hydroperoxides (CD) formation in o/w emulsion whereas its more polar counterpart 1 was more efficient in bulk oil
Summary
Lipids are essential constituents of food and cosmetic preparations but are predisposed to oxidation that constitute the major source of quality deterioration of these products and could result in important health issues for the consumers [1]. Its effective antioxidant action have been described and molecular mechanism elucidated [6,12] From these results, it can be assumed that (1) could be a serious candidate to stabilize lipophilic media against oxidative deterioration for food and cosmetic applications. Natural 1 is composed of two stereoisomers: silybin A (2R, 3R, 10R, 11R) and silybin B (2R, 3R, 10S, 11S) and is poorly soluble in water and in lipids [12] For this purpose, there are several examples of semisynthetic modifications to increase its bioavailability or solubility in lipophilic media while retaining its biological activity. Derivatives can be made to increase the solubility in hydrophobic media, like silybin 7-O- and 23-O-acyl-derivatives of various acyl chain lengths [12] These compounds were tested for their antioxidant through inhibition of lipid peroxidation and 2,2-diphenyl-1-picrylhydrazyl (DPPH)-scavenging assays. The present study aimed at branching selectively at the position 3-OH of 1 an acyl C16 and evaluating the antioxidant activity of the generated 3-O-palmitoyl-silybin (2) in lipophilic media such as bulk oil and o/w emulsion
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