Identification and detection of steroidal saponins of spirostane type in the date palm Phoenix dactylifera L. (Arecaceae)

Interest in the date palm, Phoenix dactylifera L., is due to its ecological role, because it creates a favorable bioclimate for oasis development and to its socio-economic importance because dates occupy a prominent place as a source of foreign currency and in human and animal food; hence, this fruit carries significant agro-food opportunities. Its chemical investigation can contribute to a better appreciation of the date palm, by the identification of new molecules of interest from its by-products. Many compounds with interesting biological activities such as flavonoids, phenol acids and derived, sugars, fatty acids, proteins, vitamins and also volatile compounds have been identified in by-products of date palm. However, the knowledge of the chemical composition of these by products is by no means complete. Hence, the studies we undertake aim at searching new natural bioactive molecules able to contribute to this Saharan plant valorisation. Our experimentation was carried out on leaflets collected in March 2008 from five date palm trees belonging to Takerbucht cultivar growing in the experimental station of the National Institute of Agronomic Research (INRA) of Adrar, in the South-west (27 degrees 54' Northern, 0 degrees 17'1 '' West) of the Algerian Sahara. The dry material (5 g) has been hydrolyzed during 40 min by hydrochloric acid (2 N) in boiling "bain-marie". The organic phase separation was obtained by three successive extractions with diethyl ether. The aqueous phase containing orange-red colored anthocyanidins has been eliminated, then the organic phase evaporated. The dry residues have been treated again by absolute methanol. The analysis of methanolic leaflets extracts was performed using a gas chromatograph Hewlett Packard 6890 coupled to a mass spectrometer Electron Impact HP 5973 type. Identification of compounds was achieved by comparing the mass spectra obtained with those of the National Institute of Standards and Technology Library (Nist98). The analytical process applied allowed the separation of complex mixtures. The chromatographic profiles by GC-MS of date palm leaflets are not very diversified. Twenty substances were detected; their total area is 99,98%. Among these compounds, eighteen were identified, adding up a 94,61% area; two could not be identified. Among the identified molecules, two are abundant; they represent an area of 33,75%. The comparison of their mass spectra and their chromatographic profiles obtained under our experimental conditions with those of the Nist98 library, allowed the identification of these substances. There are two sapogenin aglycones characterizing the steroidal saponins: the (3 beta,25R)-spirost-5-en-3-ol and (3 beta,25R)-spirost-5-en-3-ol acetate. These molecules present a C-27 spirostane-type skeleton and are commonly called diosgenin and yamogenin acetate. The yamogenin drifts from the diosgenin by isomerisation and products the yamogenin acetate by acetylating. To our knowledge, these two natural bioactive molecules are identified for the first time in the date palm, Phoenix dactylifera L. (Arecaceae). They constitute a major challenge in biological sciences, since they are increasingly used in the biomedical field because of their various biological activities and low toxicity. Their valorisation and use in the industrial field could be considered.