The synthesis and antioxidant capacities of a range of resveratrol and related phenolic glucosides

Abstract

The resveratrol analogues have attracted great attension by scientists as these compounds exhibit numerous bioactive properties due to their outstanding antioxidant capacity. However, the role of the antioxidant activity of these molecules is still not quite clear. This thesis details the development and biological evaluation of a library of resveratrol analogues in order to provide a better understanding of their pharmaceutical value. This thesis begins with an overview of an important hydroxylated stilbene (resveratrol) and its analogues present in natural plants, food and beverage. Consequently, these studies are summarised and aided in the selection of a new library of substrates to be synthesised herein and biologically evaluated. Chapter two details the successful synthesis of resveratrol glycosides from resveratrol. Pleasingly, all chemical transformations carried out herein were performed in excellent yields. In-vitro anti-oxidant studies on these substrates revealed glycosylation of resveratrol leads to a decreased antioxidant capacity. In addition, these studies suggested the para hydroxyl group on resveratrol has a higher reactivity than the meta hydroxyl group. Chapter three details the synthesis of a hydroxylated resveratrol (piceatannol) and many of its glycosides. Almost all of the targeted compounds were prepared by applying a modified strategy designed for resveratrol glycosides in high efficiency. The anti-oxidant assays suggested that piceatannol is a more powerful antioxidant than resveratrol. The assays also revealed that the antioxidant activity of piceatannol glycosides is quite dependent on the glycosylation position. Chapter four then details the preparation of several common resveratrol dimers. The individual products were obtained via a one step oxidation of resveratrol followed by acetylation of the products, separation, and base hydrolysis. In addition, successful isomerisation of some of the trans-dimers into their cis forms was achieved in this study. With a simple protocol now in place to synthesise such resveratrol dimers, it paves the way for future work on the synthesis of glucosylated dimers of resveratrol. Such compounds would be expected to have a diverse range of antioxidant properties and other related bioactivities and are worthy of further exploration. Finally, Chapter five contains the associated experimental procedures and characterisation data for all synthesised resveratrol and piceatannol analogues along with a range of oligomers.