Pyrrolizidine alkaloids from Echium rauwolfii and Echium horridum (Boraginaceae)

Echimidine was isolated from Echium rauwolfii and Echium horridum and identified by MS, H-1- and C-13 NMR as a major alkaloid. In addition, structures of 12 minor alkaloids were inferred from GLC and GLC-MS analyses: 7-angeloylretronecine, 7-tigloylretronecine, lycopsamine, 7-acetyllycopsamine, uplandicine, 7-angeloyllycopsamine, 7-tigloyllycopsamine, tigloyl isomer of echimidine, 7-angeloyl-9-(2-methylbutyryl)retronecine, 7-tigloyl-9-(2-methylbutyryl)retronecine, 7-angeloyl-9-(2,3-dihydroxybutyryl)retro and 7-tigloyl-9-(2,3-dihydroxybutyryl)retronecine. Both species had similar alkaloid profiles. Alkaloid extracts exhibited antibacterial effects with a MIC of 1.7 mg/ml in E. coli. Microscopic examination of E. coli treated with different subtoxic alkaloid concentrations (13-52 mu g/ml) revealed extensive filamentation.