Macrocyclic Pyrrolizidine Alkaloids and Silphiperfolanol Angelate Esters from Solanecio mannii

Abstract

Three new compounds, the silphiperfolanol angelate ester umutagarananol (1), the macrocyclic pyrrolizidine alkaloids umutagarinine A and B (2–3), and five known secondary metabolites (4–8) were isolated from the CH2Cl2−MeOH (1 : 1) extract of the roots and the stem bark of Solanecio mannii (Hook. f.) (Asteraceae). The isolated compounds were characterized by NMR and IR spectroscopic, and mass spectrometric analyses, whereas the relative stereochemistry of 4 was established by NAMFIS‐based combined computational and solution NMR analysis. Synthetic modification of 5 provided two new compounds, 2‐angeloyloxy‐4,8‐epoxypresilphiperfolane (9) and 2‐angeloyloxy‐4,8‐epoxypresilphi‐perfolane (10). The crude extracts and the isolated constituents showed weak antibacterial activities (EC50 0.7–13.3 mM) against the Gram‐negative Escherichia coli and the Gram‐positive Bacillus subtilis. Compounds 2, 3 and 4 exhibited strong cytotoxicity against MCF‐7 human breast cancer cells, with EC50 values of 35.6, 21.7 and 12.5 μM, respectively.