Triterpenoid Glycosides from Leaves of Medicago arborea L.

Eighteen triterpene saponins (1−18) from Medicago arborea leaves have been isolated and their structures elucidated by spectroscopic, spectrometric (1D and 2D NMR, FAB-MS, ESI-MS/MS), and chemical methods. They have been identified as glycosides of medicagenic, zanhic, and 2β-hydroxyoleanolic acids, soyasapogenol B, bayogenin, and 2β,3β-dihydroxyolean-12-en-23-al-28-oic acid. Twelve of them, identified as 3-O-β-D-glucopyranosyl-28-O-[α-l-arabinopyranosyl(1→3)-α-l-rhamnopyranosyl(1→2)-α-l-arabinopyranoside] zanhic acid (3), 3-O-β-D-glucopyranosyl-28-O-{β-d-xylopyranosyl(1→4)-[α-l-arabinopyranosyl-(1→3)]-α-l-rhamnopyranosyl(1→2)-α-l-arabinopyranoside} zanhic acid (4), 3-O-[α-l-rhamnopyranosyl(1→2)-α-l-arabinopyranosyl(1→2)-β-d-glucopyranosyl]-2β-hydroxyoleanolic acid (5), 3-O-β-D-glucuronopyranosyl-28-O-[α-l-rhamnopyranosyl(1→2)-α-l-arabinopyranoside]medicagenic acid (6), 3-O-β-D-glucuronopyranosyl-28-O-[β-d-xylopyranosyl(1→4)-α-l-rhamnopyranosyl(1→2)-α-l-arabinopyranoside]bayogenin (9), 3-O-β-D-glucuronopyranosyl-28-O-[β-D-xylopyranosyl(1→4)-α-l-rhamnopyranosyl(1→2)-α-l-arabinopyranoside]-2β,3β-dihydroxyolean-12-en-23-al-28-oic acid (10), 3-O-β-D-glucuronopyranosyl-28-O-{β-D-xylopyranosyl(1→4)-[β-D-apiofuranosyl(1→3)]-α-l-rhamnopyranosyl(1→2)-α-l-arabinopyranoside}zanhic acid (12), 3-O-β-D-glucuronopyranosyl-28-O-{β-d-xylopyranosyl(1→4)-[α-l-arabinopyranoside(1→3)]-α-l-rhamnopyrano-syl(1→2)-α-l-arabinopyranoside}zanhic acid (13), 3-O-β-D-glucuronopyranosyl-28-O-[β-D-xylopyrano-syl(1→4)-α-l-rhamnopyranosyl(1→2)-α-l-arabinopyranoside]zanhic acid (14), 3-O-[α-l-arabinopyranosyl-(1→2)-β-D-glucopyranosyl(1→2)-β-D-glucopyranosyl]-28-O-{β-D-xylopyranosyl(1→4)-[β-D-apiofurano-syl(1→3)]-α-l-rhamnopyranosyl(1→2)-α-l-arabinopyranoside}zanhic acid (16), 3-O-[β-D-glucopyrano-syl(1→2)-β-D-glucopyranosyl]-28-O-{β-d-xylopyranosyl(1→4)-[α-l-arabinopyranosyl(1→3)]-α-l-rhamno-pyranosyl (1→2)-α-l-arabinopyranoside}zanhic acid (17), and 3-O-β-D-glucuronopyranosyl-28-O-{β-D-xylopyranosyl(1→4)-[β-D-apiofuranosyl(1→3)]-α-l-rhamnopyranosyl(1→2)-α-l-arabinopyrano-side}medicagenic acid (18), are reported as new natural compounds. The presence of the aldehydic group on the sapogenin moiety of saponin 10 is discussed in the framework of a possible elucidation of the biosynthesis of these metabolites. Keywords: Medicago arborea L.; saponins; chemical structure; triterpene glycosides; FAB-MS; ESI-MS/MS; NMR