Lucerne saponins: IV.—Relationship between their chemical constitution, and haemolytic and antifungal activities

By precipitation with animal or plant sterols (cholesterol or β‐sitosterol), saponins extracts from lucerne tops (SEt) or roots (SEr) were separated into two main groups of saponins. The aglycone moiety of the group precipitated by sterol is composed of medicagenic acid and an unidentified lucerne sapogenin, whereas the non‐precipitable saponins contain a variety of soyasapogenols as their aglycones. No qualitative difference could be observed in the composition of the sugar moiety of the two groups of saponins. It was found that only the sterol‐precipitable saponins are able to lyse red blood cells and arrest the growth of the fungus Sclerotium rolfsii Sacc. Though the origin of the sterol has no influence on the composition and biological properties of the saponins precipitated by them, the antifungal activity of lucerne saponins could be counteracted only by the addition of cholesterol, but not of β‐sitosterol to the culture medium. Lucerne saponins precipitated by sterol were separated by thin‐layer chromatography into three fractions. Antifungal and haemolytic activities are concentrated mainly in the fractions having high Rf values. The absence of these fractions from SEt accounts for the lower degree of biological activity exhibited by SEt as compared with that of SEr. The antifungal activity of the various sapogenins is found to be concentrated mainly in medicagenic acid and to a lesser extent in the unidentified sapogenin. Blocking the functional groups of medicagenic acid greatly diminished its antifungal activity.