G. H. N. Towers, J. E. Page and J. B. Hudson. Natural products from both plants and fungi exhibit light-mediated or photodynamic biological activity against viruses, microorganisms, cells and insects. We review new aspects of the photochemistry and photobiology of natural products, including their potential as therapeutic agents, with a focus on publications from 1991 to 1996. Natural compounds with antioxidative properties which have been reported from plant, microbial or animal sources are reviewed. Antioxidants have been found within most natural substance classes.
Flavonoids are by far the most comprehensively investigated natural products.
Reactivity towards various radicals has been studied under many experimental conditions and structure-activity relationships have been established. Tannins, coumarins and, more recently, xanthones have also been investigated in some detail. Studies on alkaloids have concentrated so far mostly on benzylisoquinoline alkaloids. At the same time, particular interest have been provided by some plant species or genera normally consumed as food or spices. Curcuminoids isolated from various Curcuma have shown potent antioxidant properties.