Xanthones are privileged scaffolds in medicinal chemistry - but are they over-privileged?

The xanthone core underpins a staggering diversity of bioactive molecules. Xanthones, of either natural or of synthetic origin, have been found to be active in virtually every class of major disease state known. This plethora of activities includes anti-algal, anti-allergic, anti-bacterial, anti-cancer, anti-fungal, anti-HIV, anti-inflammatory, anti-mutagenic, anti-leukemia, anti-malarial, anti-nociception, anti-oxidant, anti-Parkinson's, anti-protozoal, anti-tubercular, anti-viral, anthelmintic, enzyme inhibition, hepatoprotection, nerve-growth factor inducing activity, neurogenic inflammation and vasorelaxant activity, neuroprotective and novel cytotoxicity, amongst many others. The structural characteristics which allow these compounds to bind to target biomolecules are multiple and include: (1) a planar, or predominantly planar (unsaturated xanthones) tricyclic core; (2) the ubiquitous feature of a carbonyl functionality on the central ring; (3) the presence of a biaryl-ether, further modifying the electronics of this system; (4) the frequent presence of phenolic hydroxyl group(s); (5) the further annulation of the core tricyclic system, or (6) its elaboration with a vast variety of substituents