Isolation, structure determination, synthesis, and antifungal activity of a new native alfalfa-root saponin

An alfalfa-root saponin (compound F) was isolated and its chemical structure determined as 3β-[O-α-d-glucopyranosyl-(1→4)-β-d-glucopyranosyl]-2β-hydroxy-Δ¹²-oleanene-23,28-dioic acid (3β-medicagenic acid β-maltoside). It was synthesized via a modified Koenigs-Knorr reaction employing light-sensitive esters as protective groups for the aglycon. The saponin has antimycotic activity against some plant pathogenic fungi similar to that of its aglycon and a previously isolated homologous saponin, the percent inhibition being 90, 57, 67, 89, 62, and 68 for Sclerotium rolfsii, Fusarium oxysporum f. sp. lycopersici, Rhizoctonia solani, Trichoderma viride, Aspergillus niger, and Pythium aphanidermatum, respectively, at a concentration of 40 μg/mL.