Browsing by Author "Leal, Stephanie B."
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- A new strategy for the synthesis of 3-cinnamoyl-2-styrylchromones and their transformation into new xanthenodiones derivativesPublication . Pinto, Diana C. G. A.; Seca, Ana M. L.; Leal, Stephanie B.; Silva, Artur M. S.; Cavaleiro, José A. S.Chromones are a class of oxygen heterocyclic compounds widely distributed in Nature. 2-Styrylchromones are, however, a small and rare naturally occurring chromones; only three derivatives have been isolated, two from the marine blue green algae Chrysophaeum taylori1 and one from the rhizomes of Imperata cylindrical. Even so, 2-styrylchromone derivatives are associated with noticeable biological activities. Our group has also been interested in the synthesis and biological evaluation of 3-aroylflavones and found that 3’,4’,5,7-tetrahydroxy-3-(3,4-dihydroxybenzoyl)flavone is a potential antioxidant agent. As part of our continuing work on the synthesis and antioxidant evaluations of polyhydroxy-2-styrylchromones,4 we set up a program aiming the synthesis of 3-cinnamoyl-2-styrylchromone (2) bearing hydroxyl groups, features considered essential to be good antioxidant and anti-inflammatory agents.
- New syntheses of potential biologically active xanthones and benzoxanthonesPublication . Rocha, Djenisa H. A.; Leal, Stephanie B.; Seca, Ana M. L.; Pinto, Diana C. G. A.; Silva, Artur M. S.The synthesis of xanthones, adequately functionalized for a specific application, is a challenging task. In this presentation, will be disclosed our recent studies with this unique family of compounds, namely the one-pot photoinduced electrocyclisation of (E)-3-styrylflavones 1 and in situ oxidation of cycloadducts to give 5-phenyl-7H-benzo[c]xanthen-7-one derivatives 2,3a and aromatization studies of (E)-3-aryl-4-benzylidene-8-hydroxy-3,4-dihydro-1H-xanthene-1,9(2H)-diones 33b into 4-benzyl-1,8-dihydroxy-3-phenyl-9H-xanthen-9-one derivatives 4.
- New xanthenodione: synthesis and antioxidant activity evaluationPublication . Leal, Stephanie B.; Pinto, Diana C. G. A.; Seca, Ana M. L.; Silva, Artur M. S.; Cavaleiro, José A. S.Due to the continuing interest of the research group in the synthesis of novel oxygen heterocycles we have recently developed a unique synthetic route towards new xanthenodiones 5 (scheme 1).[6] The application of this methodology in the cyclization of chromone derivatives 4b,c bearing methoxyl groups not only promote the cyclization to xanthenedione derivatives but also promote the demethylation leading to the 4-(benzylidene)-8-hydroxy-3-phenyl-3,4-dihydro-1H-xanthene-1,9(2H)-diones 5b,c . This interesting result prompted us to investigate the antioxidant potential of 4-(benzylidene)-8-hydroxy-3-phenyl-3,4-dihydro-1H-xanthene-1,9(2H)-diones 5a-c .
- A Novel Short-Step Synthesis of New Xanthenedione Derivatives from the Cyclization of 3-Cinnamoyl-2-styrylchromonesPublication . Pinto, Diana C. G. A.; Seca, Ana M. L.; Leal, Stephanie B.; Silva, Artur M. S.; Cavaleiro, José A. S.Novel (E)-3-aryl-4-benzylidene-8-hydroxy-3,4-dihydro-1 H-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.
- Synthesis and antioxidant activity of new xanthone-type compoundsPublication . Leal, Stephanie B.; Pinto, Diana C. G. A.; Seca, Ana M. L.; Silva, Artur M. S.; Cavaleiro, José A. S.Owing to our continuing interest in the synthesis of novel oxygen heterocycles we have recently developed a unique synthetic procedure towards the synthesis of new xanthenodiones (2)[5] and extend the work to their aromatization into xanthones (3). Our aim was also to obtain new derivatives with potential biological activities, therefore their ability to scavenge the DPPH radical and to reduce iron(III) were also evaluated. In the present communication we will present and discussed our last results on the synthetic and potential application of xanthones (3).
- Synthesis of new 1,8-dihydroxy-9h-xanthen-9-onesPublication . Leal, Stephanie B.; Seca, Ana M. L.; Pinto, Diana C. G. A.; Silva, Artur M. S.; Cavaleiro, José A. S.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.
- Xanthenedione derivatives, new promising acetylcholinesterase inhibitor agentsPublication . Seca, Ana M. L.; Leal, Stephanie B.; Pinto, Diana C. G. A.; Barreto, Maria do Carmo; Silva, Artur M. S.Acetylcholinesterase inhibitors (AChEIs) are employed in medicine mostly for correcting the effects of insufficient levels of acetylcholine [1]. Xanthones are a class of secondary metabolites associated with important pharmacological properties, being some of its derivatives AChEIs [2]. Xanthenedione derivatives are not widely spread in nature but their synthesis and bioactivities evaluation is still a hot topic. Following our interest in the synthesis of biologically active compounds, several xanthene-1,9(2H)-diones (2a-2f) were synthesized by simple and efficient methodologies from (E,E)-3-cinnamoyl-5-hydroxy-2-styrylchromones (Scheme 1) [3] and their acetylcholinesterase activity evaluated by a modification of the Ellman's method [4]. The results (Table 1) showed that variations in the substitution and hydroxylation pattern seem to be important for their activity, being the xanthenedione bearing a catechol unit the most potent AChEI, even more active than galantamine, an AChEI alkaloid used clinically in early stages of Alzheimer's disease. SAR studies showed that the presence of hydroxyl 3-aryl and 4-benzylidene moieties is essential for the activity. Furthermore xanthenedione 2c showed a combination of partially competitive and non-competitive inhibition, while xanthenedione 2e shows an almost pure competitive type inhibition. The most active xanthenediones 2e and 2c present zero violations of Lipinski's 'rule of five' and xanthenedione 2c combine higher AChE activity with good oral bioavailability properties (TPSA < 140 Å2). The results suggest that they may be excellent templates for drugs to be used in the prevention and treatment of neurodegenerative diseases.
- Xanthenedione derivatives, new promising antioxidant and acetylcholinesterase inhibitor agentsPublication . Seca, Ana M. L.; Leal, Stephanie B.; Pinto, Diana C. G. A.; Barreto, Maria do Carmo; Silva, Artur M. S.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 (EC50 = 3.79 ± 0.06 μM) and it was also showed to be a potent AChEI (IC50 = 31.0 ± 0.09 μM) when compared to galantamine (IC50 = 211.8 ± 9.5 μM).