Studies towards the synthesis of polyhydroxyxanthones with potential antioxidant activity
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abstract
Xanthones are a class of aromatic oxygen-containing compounds commonly occurring in a few higher plant families such as the Guttiferae and Gentianaceae.1 The significance of these compounds is due to the important biological functions they play in Nature, but also because certain derivatives have been used as drugs, biocides or food additives. In this broad spectrum of biological applications special mention deserves the antioxidant activity being exemplified for several derivatives by their action as free radical scavengers, inhibitors of lipid peroxidation and metal chelators.2 Considering the promising studies in this area we are interested in the design of new and effective radical scavengers using a xanthone scaffold.
In this context, a large number of hydroxy-2,3-diaryl-9H-xanthen-9-ones 1a-i have been synthesized by two different approaches, starting from 3-bromo-2-methyl-4H-chromen-4-one 2 and from (E)-3-bromo-2-styryl-4H-chromen-4-ones 3a-c.3 The former method involves Heck reactions of bromo derivative 2 and styrenes 4a-c, leading to (E)-2-methyl-3-styryl-4H-chromen-4-ones 5a-c; these condensed with benzaldehyde give (E,E)-2,3-distyryl-4H-chromen-4-ones 6a-c, which led to the desired 2,3-diaryl-9H-xanthen-9-ones 7a-c in refluxing 1,2,4-trichlorobenzene. An alternative and more general method involves the Heck reaction of (E)-3-bromo-2-styryl-4H-chromen-4-ones 3a-c as aryl halides and styrenes 4a-c as alkenes. This method was extended to 3-bromochromones bearing methoxy-substituents in their A ring.
