Flavonoid triglycosides from Astragalus armatus

Astragalus armatus Willd. is an endemic shrub of the Northern Africa (Algeria, Morocco, Tunisia), is distributed in the pre-Saharian zone and is associated with the desertification in arid areas due to overgrazing [1]. In Tunisia it is used as tonic, stimulant and in cases of anaemia [2]. From the aerial parts of A. armatus a new acylated flavonoid triglycoside, isorhamnetin-3-O-(4'''-p-hydroxybenzoyl)-α-apiofuranosyl-(1→2)[α-rhamnopyranosyl-(1→6)]-β-galactopyranoside (1), and one new flavonoid triglycoside, tamarixetin-3-O-α-apiofuranosyl-(1→2)[α-rhamnopyranosyl-(1→6)]-β-glucopyranoside (2), have been isolated together with six known flavonoids: isorhamnetin-3-O-α-apiofuranosyl-(1→2)[α-rhamnopyranosyl-(1→6)]-β-galactopyranoside, kaempferol-3-O-α-rhamnopyranosyl-(1→2) [α-rhamnopyranosyl-(1→6)]-β-glucopyranoside, kaempferol-3-O-α-rhamnopyranosyl-(1→2)[α-rhamnopyranosyl-(1→6)]-β-galactopyranoside, isorhamnetin-3-O-α-rhamnopyranosyl-(1→2)[α-rhamnopyranosyl-(1→6)]-β-galactopyranoside, nikotiflorin and narcissin. The structures of the isolated compounds were established by means of 2D NMR, HPLC-DAD-MS, HR-MS, and UV spectral analyses. Pivotal role in the structure elucidation and in particular in the determination of the sugar sequence, played ROESY and HSQC-TOCSY experiments.

Figure 1: Structures of the new naturally occurring compounds

Acknowledgement: The authors are grateful to ANDRS and DG-RSDT (MESRS, Algeria) for financial support and to Prof. Gérard De Bélair (Faculty of Sciences, University Badji-Mokhtar-Annaba) for the identification of the plant material and to Dr. Elena Michelucci (Mass Spectrometry Center, University of Florence – CISM) for recording the HRESI mass spectra. The authors would like to thank Stefano Rocchi for technical assistance

References: 1. Hirche A et al. (2010) Environ Monit Assess DOI 10.1007/s10661–010–1744–5

2. Bouaziz et al. (2009) Afr J Biotechnol 8: 7017–7027.