Synthesis of new 1,8-dihydroxy-9h-xanthen-9-ones

XXVth European Colloquium on Heterocyclic Chemistry, Reading, UK, 13 – 17 Agosto de 2012.Xanthones have a rather restricted occurrence among higher plants, being found almost exclusively in Guttiferae and Gentianaceae. Xanthones are sometimes found as polyhydroxylated derivatives, exhibiting valuable biological activities [1], but more often bearing a variety of substituents. Xanthones are well known for their interesting phytochemical properties, which make them attractive to the pharmaceutical industry. Natural and synthetic derivatives have been described as exhibiting several important biological properties, such as anti-tumor [2], anti-inflammatory [3], antioxidant [4] and anticoagulant/antiplatelet activities [5]. Owing to our continuing interest in the synthesis of novel oxygen heterocycles we have recently developed an unique synthetic procedure towards the synthesis of new (E)-3-aryl-4-benzylidene-8-hydroxy-3,4-dihydro-1H-xanthene-1,9(2H)-diones (2) [6]. In the sequence of that work and pursuing our objective to synthesize xanthone derivatives with potential biological activities, we set up a program aiming the transformation of xanthenediones (2) into new 1,8-dihydroxy-9H-xanthen-9-one derivatives (3). The experimental procedure and the structural characterization (1D and 2D NMR) of the new compounds will be presented and discussed.Thanks are due to the University of Aveiro, Fundação para a Ciência e a Tecnologia (FCT) and FEDER for funding the Organic Chemistry Research Unit (project PEst-C/QUI/UI0062/2011). We are also grateful to the Portuguese National NMR Network (RNRMN) supported with funds from FCT