Microbial transformation of Pseudoprotodioscin by Chaetomium olivaceum

• Eight derivatives were isolated from the fermented broth and five of them were new compounds.
• Stereo selective epoxidation, methoxylation and oxidation at various positions of pseudoprotodioscin were observed, and these reactions were hard to be achieved through chemical modification.
• A time course study was carried out, and the reaction time significantly influenced metabolites.
• The possible biotransformation pathway of pseudoprotodioscin was proposed.
• Two derivatives showed protective effects against H2O2-induced myocardial cell injury.

Pseudoprotodioscin (1) is a steroidal saponin from plants with diverse biological activities. In order to obtain new and useful derivatives for further study, Chaetomium olivaceum was used to transform pseudoprotodioscin. Five new (4, 5, 6, 8, and 9) and three known (2, 3 and 7) steroidal saponins were obtained in this study. These reactions were hard to be achieved through chemical modification. The structures of these metabolites were elucidated on the basis of spectroscopic data. The possible biotransformation pathway of 1 by Chaetomium olivaceum was also proposed. Protective effects against H2O2-induced H9c2 cardiomyocyte injury of compounds 1–9 were evaluated. Compounds 1, 4 and 6 showed some cell-protection activity.

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