Hydroxytyrosol and Derivatives: Isolation, Synthesis, and Biological Properties

Hydroxytyrosol is a phenol found predominantly in the olive tree (Olea europea). It shows a broad spectrum of beneficial effects such as cancer chemoprevention by inducing apoptosis, cardioprotection and anti-atherogenic activity, skin photoprotection and anti-inflammatory activity. These biological properties are based on scavenging of reactive oxygen species by hydroxytyrosol, being more active than antioxidant vitamins and synthetic antioxidants. Its biological activities and beneficial effects on human health has stimulated the development of new methods of extraction and purification from olive mill wastewater, from table olive processing, or from leaves. Different procedures for the chemical and enzymatic synthesis of hydroxytyrosol have been developed from tyrosol, from 3,4-dihydroxyphenylacetic acid and its methyl ester, and from oleuropein. Some hydroxytyrosol acyl derivatives have been prepared by chemical and chemoenzimatic methods in order to increase both stability and solubility in lipophilic preparations. Mechanistic experiments on hydroxytyrosol oxidation and isolation of species formed by oxidation are also reported.