Two new antifungal saponins from the Tibetan herbal medicine Clematis tangutica

Bioassay-guided fractionation of the ethanol extract of the aerial parts of Clematis tangutica led to the isolation of two new antifungal triterpene saponins. Their structures were determined to be 3- O-alpha- L-arabinopyranosyl hederagenin 28- O-alpha- L-rhamnopyranosyl ester ( 1) and 3- O-beta- D-glucopyranosyl-(1--> 4)-alpha- L-arabinopyranosyl hederagenin 28- O-alpha- L-rhamnopyranosyl ester ( 2) on the basis of spectral data and chemical evidence. Inhibitory activities of the two saponins against seven fungal strains were evaluated. Compounds 1 and 2 showed evident antifungal activity (MIA approximately 2.5 micrograms/disc) against Saccharomyces cerevisiae, similar to the positive control amphotericin B and ordinary activities (MIA approximately 10 micrograms/disc) against Penicillium avellaneum UC-4376, Candida glabrata, Trichosporon beigelii and Pyricularia oryzae. Compound 2 is a better antifungal agent than compound 1 against most of the fungal strains that were tested.