**4. Conclusions**

Hydroxytyrosol is a phenolic compound that can be isolated from olive oil mill wastewaters. The remarkable biological properties of this compound, mainly due to its strong antioxidant activity, has stimulated the synthesis of a series of derivatives, some of them are also naturally-occurring in the olive tree. Among these derivatives hydroxytyrosyl esters and ethers are of great interest, as some of them show strong antioxidant activity and improved bioavailability.
