Synthesis of Prenylated Xanthones: An Overview

Xanthones or 9H-xanthen-9-ones (dibenzo-γ-pyrones) comprise an important class of oxygenated heterocycles, with prenylated derivatives being the most abundant group. The prenylated xanthones are found to possess a wide range of important biological and pharmacological activities. As a consequence of this, synthetic strategies leading to new and more complex molecules have been widely explored in the past years. In our literature survey, from January 1963 to March 2009, a total of 93 synthetic prenylated xanthones were described and 24 of them were firstly obtained from natural sources. Thus, the main purpose of this review is to report synthetic methods to obtain prenylated xanthones, such as simple prenylation, Claisen rearrangement and/or cyclization. We also discuss the application of new methodologies to the synthesis of prenylated derivatives, such as microwave assisted organic synthesis, heterogeneous catalysis with Montmorillonite K10 Clay as catalyst and the combination of heterogeneous catalysis with microwave irradiation. Furthermore, different approaches and methodologies used to synthesize bioactive natural prenylated xanthones, like α-mangostin, are also discussed. Finally, biological activities of prenylated xanthones are also briefly referred.