New Triterpenic Saponins from the Aerial Parts of Medicago arabica (L.) 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, 2 beta,3 beta-dihydroxyolean-12-en-28-oic acid, hederagenin, bayogenin and soyasapogenol B. Five saponins, identified as 3-O-[-alpha-L-arabinopyranosyl(1 -> 2)-beta-D-glucuronopyranosyl]-30-O-beta-D-glucopyranosyl 2 beta,3 beta,30-trihydroxyolean-12-en-28-oic acid (1), 3-O-[alpha-L-arabinopyranosyl(1 -> 2)-beta- -D-glucuronopyranosyl]-30-O-[beta-D-glucopyranosyl]3 beta,30-dihydroxyolean-12-en-28-oic acid (2), 3-O-[beta-D-glucuronopyranosyl]-30-O-[alpha-L-arabinopyranosyl(1 -> 2)-beta-D-glucopyranosyl]2 beta,3 beta,30-trihydroxyolean-12-en-28-oic acid (3), 3-O-[beta-D-glucuronopyranosyl]-30-O[alpha-L-arabinopyranosyl(1 -> 2)-beta-D-glucopyranosyl] 3 beta,30-dihydroxyolean-12-en-28-oic acid (4) and 3-O-[beta-D-glucuronopyranosyl]-30-O-[beta-D-glucopyranosyl] 2 beta,3 beta,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.