Oleanane glycosides from Astragalus tauricolus: Isolation and structural elucidation based on a preliminary liquid chromatography-electrospray ionization tandem mass spectrometry profiling

As a part of our ongoing research for bioactive compounds from Turkish Astragalus species, the investigation of Astragalus tauricolus has been carried out. An approach based on HPLC-ESIMSn experiments has been used to profile the triterpene glycosides occurring in the butanol extract of the whole plant. On the basis of the results of the online screening by HPLC-ESIMSn, 22 oleanane-type triterpene glycosides, including ten compounds never reported before, were isolated, and their structures were established by the extensive use of 1D and 2D-NMR experiments along with ESIMS and HRMS analysis. Noteworthy, cycloartane-type triterpene glycosides, the main constituents of Astragalus spp., were not found. This peculiar feature characterizes a very limited group of Astragalus spp. The antiproliferative activity of the isolated compounds 1-12, 15, 17-19 was evaluated against a small panel of cancer cell lines. Only compound 11 showed an IC50 of 22 mu M against human leukemia cell line (U937). The other tested compounds, in a range of concentrations between 1 and 50 mu M, did not cause any significant reduction of the cell number. (C) 2012 Elsevier Ltd. All rights reserved.