New triterpenic saponins from the aerial parts of Medicago arabica (L.) huds.

ABSTRACT

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, 2beta,3beta-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 2beta,3beta,30-trihydroxyolean-12-en-28-oic acid (1), 3-O-[alpha-L-arabinopyranosyl(1-->2)-beta-D-glucuronopyranosyl]-30-O-[beta-D-glucopyranosyl] 3beta,30-dihydroxyolean-12-en-28-oic acid (2), 3-O-[beta-D-glucuronopyranosyl]-30-O-[alpha-L-arabinopyranosyl(1-->2)-beta-d-glucopyranosyl] 2beta,3beta,30-trihydroxyolean-12-en-28-oic acid (3), 3-O-[beta-D-glucuronopyranosyl]-30-O-[alpha-L-arabinopyranosyl(1-->2)-beta-D-glucopyranosyl] 3beta,30-dihydroxyolean-12-en-28-oic acid (4) and 3-O-[beta-D-glucuronopyranosyl]-30-O-[beta-D-glucopyranosyl] 2beta,3beta,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.