Triterpenoid saponins from the aerial parts of Trifolium argutum Sol. and their phytotoxic evaluation

Abstract

Four triterpenoid saponins (1–4) were isolated from the aerial parts of Trifolium argutum Sol. (sharp-tooth 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-[α-l-rhamnopyranosyl-(1→2)-β-d-galactopyranosyl-(1→2)-β-d-glucuronopyranosyl]-3β,24-dihydroxyolean-12-ene-22-oxo-29-oic acid (1) and 3-O-[β-d-galactopyranosyl-(1→2)-β-d-glucuronopyranosyl]-3β,24-dihydroxyolean-12-ene-22-oxo-29-oic acid (2). The occurrence of 3β,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 1μM to 333μM. Compound 1 was the most active, showing more than 60% inhibition on the root growth of L. sativa at the higher dose, with IC50 (254.1μM) lower than that of Logran® (492.6μM), a commercial herbicide used as positive control. The structure–activity relationships indicated that both aglycones and glycosidic parts may influence the phytotoxicity of saponins.