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Digital archive of theses discussed at the University of Pisa


Thesis etd-01212019-185744

Thesis type
Tesi di dottorato di ricerca
email address
Thesis title
Chemical and biological investigations of six plants from North Africa and South America
Academic discipline
Course of study
tutor Prof.ssa Braca, Alessandra
controrelatore Prof. Martinelli, Adriano
controrelatore Prof.ssa Modesti, Alessandra
controrelatore Prof.ssa Passerini, Nadia
controrelatore Prof.ssa Karioti, Anastasia
  • antiangiogenic activity
  • Aphanamixis polystachya
  • Cedrela odorata
  • Euphorbiaceae
  • Galium tunetanum
  • Guarea guidonia
  • Hsp90
  • Joannesia princeps
  • Lamiaceae
  • Meliaceae
  • Rubiaceae
  • Stachys ocymastrum
Graduation session start date
The main subject of this PhD project is the isolation and structural characterization of active constituents from plant sources. In this context, a series of experimental steps, focused in the chemical and biological study of six species belonging to different families, collected in northern Africa and South America, was proposed. The studied plants were mainly selected for their potential in yielding new secondary metabolites, including: Aphanamixis polystachya (Wall.) R. N. Parker (Meliaceae), Cedrela odorata L. (Meliaceae), Guarea guidonia (L.) Sleumer (Meliaceae), Galium tunetanum Lam. (Rubiaceae), Stachys ocymastrum (L.) Briq. (Lamiaceae), and Joannesia princeps Vell. (Euphorbiaceae).
The isolation of the main plant chemical constituents was achieved by extractive and chromatographic processes, including flash silica gel or Sephadex LH-20 column chromatography, High-Performance Centrifugal Partition Chromatography (HPCPC), and High-Performance Liquid Chromatography (HPLC). The structural elucidation of the isolated secondary metabolites was carried out by 1D and 2D NMR spectroscopic techniques, and by mass spectrometry analyses.
Chromatographic processes performed with the respective plant materials afforded the isolation of 93 compounds belonging to different classes of secondary metabolites, including mainly limonoids, iridoid glycosides, lignans, phenylpropanoid glycosides, ionones, phenolic compounds, tannins, and flavonoids, which structural elucidation was carried out by 1D and 2D NMR spectroscopic techniques, and by mass spectrometry analyses. Among all obtained compounds, 17 resulted to be new natural products.
Surface Plasmon Resonance (SPR) experiments were carried out on all limonoids isolated from the Meliaceae species in order to assess their ability to interact with the chaperone protein Hsp90, affording the identification of seven active compounds, including two andirobin, two limonol, one nomilin, one mexicanolide, and one ring A2,B,D-seco limonoid derivatives.
The anti-angiogenic effects of the iridoids isolated from G. tunetanum Lam. and S. ocymastrum (L.) Briq. were evaluated in the chick chorioallantoic membrane (CAM) and zebrafish embryo assays. The results of these studies highlighted that asperuloside, geniposidic acid, and iridoid V1 isolated from G. tunetanum Lam. were the most active compounds, being able to reduce CAM microvessel formation with inhibitions of 67%, 59%, and 54%, respectively, as compared to the control, showing a similar trend of percentage inhibition of blood vessel formation in the zebrafish embryo test. Regarding iridoids isolated from Stachys ocymastrum (L.) Briq., 6β-hydroxyipolamiide, ipolamiide, and ipolamiidoside showed a weak angiogenesis inhibitory effect in zebrafish embryo models at a dose of 2 µM, displaying capacity to reduce blood vessel formation of 35%, 34%, and 31%, respectively, as compared to the control. In the CAM assay, the same compounds did not show any angiogenesis inhibitory effect at a dose of 2 µM.
Finally, the phytochemical study of the chemical constituents of J. princeps Vell. leaves afforded the isolation of twenty-eight known secondary metabolites, which could be grouped into: gallic acid derivatives, gallotannins, flavonoids, including C-glycosyl flavones, galloylated C-glycosyl flavones, and flavonol O-glycosides, α-ionones, glycosylated monoterpenes, lignan, and other phenolic derivatives. All these compounds were isolated from this species and from the genus Joannesia for the first time. Some of them were found to be chemotaxonomic markers of the family Euphorbiaceae and allowed to highlight some chemotaxonomic considerations.