Polygala is the largest genus of Polygalaceae, comprising about 350 species (one third of the entire family), including trees, shrubs and herbs distributed throughout the world (1). In Italy, this genus is composed only of herbaceous plants, with a significant number of specific and subspecific taxa endemic to the country (2). Among them, there is Polygala flavescens DC., the only Italian species with yellow flowers, whose geographical distribution is ranging from Liguria to Basilicata, across Italian peninsula. Very recently, three subspecies were recognised within P. flavescens, based on qualitative morphological characters (3): P. flavescens subsp. flavescens (covering most of the geographic range of the species), P. flavescens subsp. maremmana (Fiori) Arrigoni (with range limited to the coastal portion of Tuscany), and P. flavescens subsp. pisaurensis (Caldesi) Arrigoni (with range limited to the coastal portion of Emilia-Romagna and Marche). The latter taxon was considered as a distinct species, for a long time (4). In order to contribute to the systematics and correct taxonomic setting of these taxa, a chemotaxonomic study was carried out. To this aim, we selected five different populations: three of P. flavescens subsp. flavescens (i.e. the species with the largest range), collected in Tuscany (PFF-T), Molise (PFF-M) and Abruzzo (PFF-A); P. flavescens subsp. maremmana collected at Monte Argentario (PFM), and P. flavescens subsp. pisaurensis collected at Fano (PFP), i.e. the areas from which they were originally described (loci classici). Aerial parts were dried, defatted with n-hexane, and extracted at room temperature with methanol. Each MeOH extract was partitioned between n-BuOH and H2O and the n-BuOH soluble fraction was subjected to LC-PDA-ESIMS and LC-PDA-ESIMS/MS analyses, in order to compare the chromatographic profile and provide wider information concerning the secondary metabolites contents. A preliminary qualitative analysis showed that all plants displayed an identical flavonoid and oligosaccharide pattern, while the profile of saponins showed little differences among the five populations. Then, a more in-depth chemical study was carried out on the selected population PFF-T collected in the highest amount. PFF-T n-BuOH extract was so separated by Sephadex LH-20 followed by CPC and RP-HPLC. Flavonoids and oligosaccharide esters, including some new compounds, were purified and fully characterized by spectroscopic techniques such as 1D and 2D-NMR, and mass spectrometry. Results were in agreements with those reported in the literature for other Polygala species, being flavonoids, oligosaccharides, and saponins widely distributed in the genus (5, 6). In addition, also the volatile profile of fresh flowers was compared among populations, by means of Head Space-Solid Phase Micro Extraction (HS-SPME) technique (7). The captured volatile organic compounds were then characterized by GC-MS and a Multivariate Statistical Analysis was carried out. According to the SPME emission pattern, the most similar ones resulted PFF-M and PFP that formed a cluster in the HCA dendrogram. Another cluster was provided by the three remaining ones, with PFF-A and PFM more similar each other than PFF-T. The PCA confirmed this behavior. The solitary placement of PFF-T is due to its high production of cis-α-ambrinol and the exclusive emission of caryophyllene oxide and dendrolasin.

A systematic and chemical study of Polygala flavescens (Polygalaceae), endemic to Italy

DE LEO, MARINELLA;BRACA, ALESSANDRA;FLAMINI, GUIDO;PERUZZI, LORENZO
2016-01-01

Abstract

Polygala is the largest genus of Polygalaceae, comprising about 350 species (one third of the entire family), including trees, shrubs and herbs distributed throughout the world (1). In Italy, this genus is composed only of herbaceous plants, with a significant number of specific and subspecific taxa endemic to the country (2). Among them, there is Polygala flavescens DC., the only Italian species with yellow flowers, whose geographical distribution is ranging from Liguria to Basilicata, across Italian peninsula. Very recently, three subspecies were recognised within P. flavescens, based on qualitative morphological characters (3): P. flavescens subsp. flavescens (covering most of the geographic range of the species), P. flavescens subsp. maremmana (Fiori) Arrigoni (with range limited to the coastal portion of Tuscany), and P. flavescens subsp. pisaurensis (Caldesi) Arrigoni (with range limited to the coastal portion of Emilia-Romagna and Marche). The latter taxon was considered as a distinct species, for a long time (4). In order to contribute to the systematics and correct taxonomic setting of these taxa, a chemotaxonomic study was carried out. To this aim, we selected five different populations: three of P. flavescens subsp. flavescens (i.e. the species with the largest range), collected in Tuscany (PFF-T), Molise (PFF-M) and Abruzzo (PFF-A); P. flavescens subsp. maremmana collected at Monte Argentario (PFM), and P. flavescens subsp. pisaurensis collected at Fano (PFP), i.e. the areas from which they were originally described (loci classici). Aerial parts were dried, defatted with n-hexane, and extracted at room temperature with methanol. Each MeOH extract was partitioned between n-BuOH and H2O and the n-BuOH soluble fraction was subjected to LC-PDA-ESIMS and LC-PDA-ESIMS/MS analyses, in order to compare the chromatographic profile and provide wider information concerning the secondary metabolites contents. A preliminary qualitative analysis showed that all plants displayed an identical flavonoid and oligosaccharide pattern, while the profile of saponins showed little differences among the five populations. Then, a more in-depth chemical study was carried out on the selected population PFF-T collected in the highest amount. PFF-T n-BuOH extract was so separated by Sephadex LH-20 followed by CPC and RP-HPLC. Flavonoids and oligosaccharide esters, including some new compounds, were purified and fully characterized by spectroscopic techniques such as 1D and 2D-NMR, and mass spectrometry. Results were in agreements with those reported in the literature for other Polygala species, being flavonoids, oligosaccharides, and saponins widely distributed in the genus (5, 6). In addition, also the volatile profile of fresh flowers was compared among populations, by means of Head Space-Solid Phase Micro Extraction (HS-SPME) technique (7). The captured volatile organic compounds were then characterized by GC-MS and a Multivariate Statistical Analysis was carried out. According to the SPME emission pattern, the most similar ones resulted PFF-M and PFP that formed a cluster in the HCA dendrogram. Another cluster was provided by the three remaining ones, with PFF-A and PFM more similar each other than PFF-T. The PCA confirmed this behavior. The solitary placement of PFF-T is due to its high production of cis-α-ambrinol and the exclusive emission of caryophyllene oxide and dendrolasin.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11568/827401
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