Abstract

Four triterpenoid saponins (1-4) were isolated from the aerial parts of Trifolium argutum Sol. (sharptooth clover) and their structures were elucidated by comprehensive spectroscopic analysis, including 1D and 2D NMR techniques, mass spectrometry and chemical methods. Two of them are new compounds, characterized as 3-O-[alpha-L-rhamnopyranosyl-(1 -> 2)-beta-D-galactopyranosyl-(1 -> 2)-beta-D-glucuronopyranosyl]-3 beta, 24-dihydroxyolean-12-ene-22-oxo-29-oic acid (1) and 3-O-[beta-D-galactopyranosyl-(1 -> 2)-beta- D-glucuronopyranosyl]-3 beta, 24-dihydroxyolean-12-ene-22-oxo-29-oic acid (2). The occurrence of 3 beta, 24-dihydroxyolean-12-ene-22-oxo-29-oic acid (melilotigenin) in its natural form is reported for the first time as a triterpenoid aglycone within Trifolium species. The phytotoxicity of compounds was evaluated on four STS at concentration 1 mu M to 333 mu M. Compound 1 was the most active, showing more than 60% inhibition on the root growth of L. sativa at the higher dose, with IC50 (254.1 mu M) lower than that of Logran (R) (492.6 mu M), a commercial herbicide used as positive control. The structure-activity relationships indicated that both aglycones and glycosidic parts may influence the phytotoxicity of saponins. (C) 2015 Phytochemical Society of Europe. Published by Elsevier B.V. All rights reserved.