New triterpenic saponins from the aerial parts of medicago arabica huds

The reinvestigation of saponin composition from Medicago arabica from Italy allowed the detection of nineteen (1−19) saponins. All of them were purified by reverse-phase chromatography and their structures elucidated by spectroscopic and spectrometric (1D and 2D NMR; ESI-MS/MS) and chemical methods. Fourteen were known saponins, previously found in other plants including other Medicago species. They have been identified as glycosides of oleanolic acid, 2β,3β-dihydroxyolean-12-en-28-oic acid, hederagenin, bayogenin and soyasapogenol B. Five saponins, identified as 3-O-[-α-l-arabinopyranosyl(1→2)-β-d-glucuronopyranosyl]-30-O-β-D-glucopyranosyl 2β,3β,30-trihydroxyolean-12-en-28-oic acid (1), 3-O-[α-l-arabinopyranosyl(1→2)-β-D-glucuronopyranosyl]-30-O-[β-D-glucopyranosyl] 3β,30-dihydroxyolean-12-en-28-oic acid (2), 3-O-[β-D-glucuronopyranosyl]-30-O-[α-l-arabinopyranosyl(1→2)-β-D-glucopyranosyl] 2β,3β,30-trihydroxyolean-12-en-28-oic acid (3), 3-O-[β-D-glucuronopyranosyl]-30-O-[α-l-arabinopyranosyl(1→2)-β-D-glucopyranosyl] 3β,30-dihydroxyolean-12-en-28-oic acid (4) and 3-O-[β-D-glucuronopyranosyl]-30-O-[β-D-glucopyranosyl] 2β,3β,30-trihydroxyolean-12-en-28-oic acid (5), are reported here as new natural compounds. These new saponins, possessing a hydroxy group at the 30-methyl position of the triterpenic skeleton, have never been previously found in the genus Medicago. Keywords: Medicago arabica L. Huds; saponins; chemical structure; triterpene glycosides; queretaroic acid; ESI-MS/MS; NMR