Descrição
Oxygen 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.
; Esteves, Cátia 
