Secondary Metabolites from Pterocaulon alopecuroides and their Antiproliferative Activities

Objective: To isolate secondary metabolites from the aerial parts of Pterocaulon alopecuroides, elucidate their structures and evaluate their antiproliferative activities on selected human cancer cell lines. Materials and Methods: The ethanolic extract of P. alopecuroides afforded five compounds, which were characterized using spectroscopic techniques and by comparison with data from the literature. Antiproliferative activities of all isolates were evaluated. Results: The compounds 7-(2,3-dihydroxy-3-methylbutoxy)-6-methoxycoumarin (1), 5,6-methylenedioxy- 7-(2,3-dihydroxy-3-methylbutoxy) coumarin (2), Dihydrokaempferol (3), 5,7,4´-trihydroxy- 6-(α,α-dimethylallyl)dihydroflavonol (4) and 5,4´-dihydroxy-7-(γ,γ-dimethylallyloxy)dihydroflavonol (5) were isolated. The antiproliferative activity of all compounds was evaluated in a panel of six human solid tumor cell lines showing GI₅₀ values for the most active compounds in the low micromolar range. Conclusion: Compound 2 is reported for first time from P. alopecuroides. Isolated coumarins show no antiproliferative activity, whilst among flavonoids compound 5 showed the best antiproliferative activity.