| Summary: | Diosgenin (DSG), a steroidal sapogenin derived from the tuberous roots of yam, possesses multiple biological properties. DSG has been widely used as a starting material for the industrial production of steroid drugs. Despite its significant pharmacological activities, moderate potency and low solubility hinder the medicinal application of DSG. Biotransformation is an efficient method to produce valuable derivatives of natural products. In this work, we performed the biotransformation of DSG using five <i>Rhodococcus</i> strains. Compounds <b>1</b>–<b>4</b> were isolated and identified from <i>Rhodococcus erythropolis</i>. Compounds <b>1</b> and <b>2</b> showed potent cytotoxicity against the A549, MCF-7, and HepG2 cell lines. Compounds <b>3</b> and <b>4</b> are novel entities, and each possesses a terminal carboxyl group attached to the spiroacetal ring. Remarkably, <b>4</b> exhibited significant cell protective effects for kidney, liver, and vascular endothelial cells, suggesting the therapeutic potential of this compound in chronic renal diseases, atherosclerosis, and hypertension. We further optimized the fermentation conditions aiming to increase the titer of compound <b>4</b>. Finally, the yield of compound <b>4</b> was improved by 2.9-fold and reached 32.4 mg/L in the optimized conditions. Our study lays the foundation for further developing compound <b>4</b> as a cell protective agent.
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