Highly selective biotransformation of ginsenoside Rb1 to Rd by the phytopathogenic fungus Cladosporium fulvum (syn. Fulvia fulva)

Fourteen phytopathogenic fungi were tested for their ability to transform the major ginsenosides to the active minor ginsenoside Rd. The transformation products were identified by TLC and HPLC, and their structures were assigned by NMR analysis. Cladosporium fulvum, a tomato pathogen, was found to transform major ginsenoside Rb-1 to Rd as the sole product. The following optimum conditions for transforming Rd by C. fulvum were determined: the time of substrate addition, 24 h; substrate concentration, 0.25 mg ml(-1); temperature, 37A degrees C; pH 5.0; and biotransformation period, 8 days. At these optimum conditions, the maximum yield was 86% (molar ratio). Further, a preparative scale transformation with C. fulvum was performed at a dose of 100 mg of Rb-1 by a yield of 80%. This fungus has potential to be applied on the preparation for Rd in pharmaceutical industry.