Natural and synthetic xanthone derivatives are well-known for their ability to act as antioxidants and/or enzyme inhibitors. This paper aims to present a successful synthetic methodology towards xanthenedione derivatives and the study of their aromatization to xanthones. Additionally their ability to reduce Fe(III), to scavenge DPPH radicals and to inhibit AChE was evaluated. The results demonstrated that xanthenedione derivative 5e, bearing a catechol unit, showed higher reduction capacity than BHT and similar to quercetin, strong DPPH scavenging activity (EC 50 = 3.79 ± 0.06 µM) and it was also showed to be a potent AChEI (IC 50 = 31.0 ± 0.09 µM) when compared to galantamine (IC 50 = 211.8 ± 9.5 µM).

A Novel Short-Step Synthesis of New Xanthenedione Derivatives from the Cyclization of 3-Cinnamoyl-2-styrylchromones. -Baker-Venkataraman rearrangement of the bisarylacrylate (I) under optimized conditions A) produces the desired 2-styrylchromone (II). Attempted demethylation is accompanied by further cyclization to produce the xanthone (III) bearing an exocyclic (E)-olefin. The sequence can be successfully extended to other derivatives as scaffolds of natural products. -(PINTO, D. C. G. A.; SECA, A. M. L.; LEAL, S. B.; SILVA*, A. M. S.; CAVALEIRO, J. A. S.; Synlett 2011, 14, 2005-2008, http://dx.doi.org/10.1055/s-0030-1261172 ; Dep. Chem., Univ. Aveiro, P-3810 Aveiro, Port.; Eng.) -Mais 49-132

Abstract:Novel (E)-3-aryl-4-benzylidene-8-hydroxy-3,4-dihydro-1H-xanthene-1,9(2H)-diones are prepared by the cyclization of (E,E)-3-cinnamoyl-5-hydroxy-2-styrylchromones efficiently catalyzed with boron tribromide. The (E,E)-3-cinnamoyl-5-hydroxy-2-styrylchromones are obtained from the Baker-Venkataraman rearrangement of (E,E)-2-acetyl-1,3-phenylene bis(3-phenylacrylate), which is greatly improved under microwave irradiation.

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