Xanthone dimers: a compound family which is both common and privileged

Xanthone dimers are a widespread, structurally-diverse family of natural products frequently found in plants, fungi and lichens. They feature an intriguing variety of linkages between the component xanthones (benzannulated chromanones). These synthetically elusive secondary metabolites are of great interest due to their broad array of bioactivities, which has led to the xanthones being designated as 'privileged structures'. We seek herein to give an overview of all reliably-described xanthone dimers, their structures, occurrence, and the bioactivities established to date. The possible biosynthetic pathways leading to members of this family are also discussed in light of our current knowledge.