Cytotoxic Cholestane and Pregnane Glycosides from Tribulus macropterus

The methanol extract of the whole parts of Tribulus macropterus Boiss. (family Zygophyllaceae) showed cytotoxic activity against a human tumour cell line (hepatocyte generation 2, HepG2) (IC50 = 2.9 μg/ml). The n-butanolic fraction obtained from successive fractionation of the methanolic extract exhibited activity against HepG2 (IC50 = 2.6 μg/ml). Therefore, this fraction was subjected to separation using different chromatographic techniques. Five compounds, 1-5, were isolated and identified as: (22S,25S)-16β,22,26-trihydroxy-cholest-4- en-3-one-16-O-β-D-glucopyranosyl-(1→3)-β-D-xylopyranoside (1), (22S,25S)-16β,22,26-trihydroxy- cholest-4-en-3-one-16-O-β-D-glucopyranosyl-(1→3)-β-d-glucopyranoside (2), sucrose (3), d-pinitol (4) and 3β-hydroxy-5α-pregn-16(17)en-20-one-3-O-β-D-xylopyranosyl-(1→2)- [β-d-xylopyranosyl-(1→3)]-β-D-glucopyranosyl-(1→4)-[α-L-rhamnopyranosyl-(1→2)]-β-D-galactopyranoside (5) on the basis of spectroscopic and chemical data. The three steroidal compounds 1, 2 and 5 were also tested against the same cell line HepG2 and their IC50 values were 2.4, 2.2 and 1.1 μg/ml, respectively.