Microbial metabolism of pseudoprotodioscin

Microbial transformation of the furostanol saponin pseudoprotodioscin ( 1) using Aspergillus fumigatus resulted in the isolation of two new steroidal metabolites, 3- O-bis- alpha- L-rhamnopyranosyl-(1-->2 and 1-->4)- beta- D-glucopyranosyl]-22 R,25 R-spirost-5-ene-3 beta,20 alpha-diol ( 2) and 3- O-bis- alpha- L-rhamnopyranosyl-(1-->2 and 1-->4)- beta- D-glucopyranosyl]-25 R-furost-5-ene-3 beta,22 alpha,26-triol ( 3), in addition to the previously reported steroidal saponins: dioscin ( 4) and progenin II ( 5). The structure elucidation of these metabolites was based primarily on 1D and 2D NMR analyses. Metabolites 2 - 5 showed significant cytotoxicity against cancer cell lines A375, L929, and HeLa with IC (50) values ranging from 1.18 microM to 17.88 microM.