Bioactive Compounds from the Leaves of Sicilian Liquorice

Liquorice (Glycyrrhiza glabra L.) is one of the most known medicinal plants associated with the ethnobotanical traditions of many countries worldwide. However, only the roots have regarded as the active portion of this plant and the main components of which, namely the triterpene saponins glycyrrhizin, glycyrrethic acid and derivatives are considered responsible for the large number of therapeutic properties ascribed to liquorice. For this reason, liquorice roots have been the subject of many studies dealing with their biological activities as well as their phytochemical profiles. Scarce attention, however, has been given to the aerial parts of this plant, and in particular the leaves, being considered only a type of waste product. This information was used as the foundation for a multidisciplinary research project aimed at the evaluation of the phytochemical profiles of the leaves of wild liquorice collected in Sicily, in relation to the study of some biological activities of the corresponding phytocomplexes. Given the limited information on this matrix, a particular cascade extraction protocol was adopted using a sequence of solvents with increasing polarity, namely hexane, ethyl acetate, butanol and methanol. All extracts were analyzed by liquid chromatography (LC) combined with UV-vis spectrophotometry and mass spectrometry (MS). The aforesaid analyses helped identify and characterize over thirty components, the majority of which belonging to the class of polyphenols. Several flavonoids, some of which already belong to the metabolic pool of liquorice roots were determined. a Agroup of new dihydrostilbenes were discovered, representing the unique phytochemical feature of the leaves of Sicilian liquorice. Most of these polyphenols (flavonoids and dihydrostilbenes) were chromatographically purified, and their structures confirmed by a large use of spectrometric measurements, mainly nuclear magnetic resonance (NMR). Finally, the extracts and some of the pure compounds were evaluated for their antioxidant and anti-inflammatory properties, giving interesting and encouraging results.