Browsing by Author "Brito, Cristela"
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- New syntheses of novel arylxanthonesPublication . Rocha, Dejnisa; Esteves, Cátia; Pinto, Diana; Santos, Clementina M.M.; Brito, Cristela; Silva, Artur; Cavaleiro, JoséXanthones represent an outstanding class of oxyg~1_1ated heterocycles widespread in nature, commonly distributed in several higher plant families, such as Gentianaceae, Guttiferae and Polygalaceae and in a few families of fungi and lichens [1]. Both natural and synthetic derivatives often endowed with interesting pharmacological properties (e.g. anti-inflammatory, antitumour and antioxidant activities [1,2]. Naturally-occurring xanthones present different types .of substituents (e.g. hydroxyl, methoxyl and prenyl groups, among others) in different positions of their scaffold leading to a large variety of analogues [2]. The presence of an aryl ring attached to the xanthone core has only been reported in some synthetic derivatives [3 ,4]. We have dedicated our previous work to the development of novel methodologies for the synthesis of xanthones bearing a 2,3-diaryl substitution pattern [4]. Herein, we report the latest advances in the synthesis of novel 5-arylbenzo[ c ]xanthones 2 and 1- aryl-9H-xanthen-9-ones 4 [5]. 5-Arylbenzo[c]xanthones 2 are obtained by the Heck reaction of 3-bromoflavones 1 with styrene derivatives, leading to (E)-3-styrylflavones, followed by an one-pot photoinduced electrocyclisation and in situ oxidation of cycloadducts. The condensation of 2-methylchromone 3 with cinammaldehydes leaded to (E,E)-2-(4-arylbuta-1,3-dien-1-yl)-4H-chromen-4-ones, which after an one-pot electrocyclization and in situ oxidation of cycloadducts gave the desired 1-aryl-9Hxanthen- 9-ones 4.
- Recent developments in the synthesis of 1-aryl-9H-xanthen-9-onesPublication . Esteves, Cátia; Santos, Clementina M.M.; Brito, Cristela; Silva, Artur; Cavaleiro, José
- Structure determination of some oxygen and nitrogen heterocyclic compounds by NMRPublication . Seixas, Raquel; Esteves, Cátia; Brito, Cristela; Leal, Stephanie; Pinto, Diana; Santos, Clementina M.M.; Seca, Ana; Silva, Artur; Cavaleiro, JoséOxygen heterocyclic compounds are widely distributed in Nature, being chromone and xanthone derivatives some examples. For instance, the xanthone ring system is a structural motif prevalent in higher plants such as those of Guttiferae and Gentianaceae families.1 Both natural and synthetic derivatives often endowed with interesting pharmacological properties, such as anti-inflammatory,2 antitumour3 and antioxidant activities.4 Chromones and chromone derivatives play an important role in the normal human diet, due to their significant anti-inflammatory,5 anti-cancer,6 and antioxidant activities.5 Nitrogen heterocyclic compounds are also widely distributed in Nature, being 4-quinolones a large group that can be found, mainly, in plants of the Rutaceae family.7 However, a great number of the well-known derivatives are of synthetic origin and have been designed to be used as drugs, mainly for the treatment of tuberculosis.8 In view of these important properties, we have dedicated our investigation in the establishment of new synthetic methods for these types of compounds9 and also for the assessment of their biological properties.10 Naturally, we devote special attention to the structural characterization, mainly by NMR experiments, not only to confirm the product structure but also to unequivocally establish their stereochemistry. The aim of this communication is to report some of our studies on the structural characterization of heterocyclic compounds by NMR spectroscopy.
- Synthesis of Novel 1-Aryl-9H-xanthen-9-onesPublication . Esteves, Cátia; Santos, Clementina M.M.; Brito, Cristela; Silva, Artur; Cavaleiro, JoséA novel route for the synthesis of 1-aryl-9H-xanthen-9-ones is reported. This methodology involves the condensation of 2-methylchromone with cinammaldehydes leading to (E,E)-2-(4-arylbuta-1,3-dien-1-yl)-4H-chromen-4-ones. The final step was the electrocyclization and oxidation reactions of the latter compounds, in an one-pot synthesis, giving the desired 1-aryl-9H-xanthen-9-ones.