Enzymatic preparation of 20(S, R)-protopanaxadiol by transformation of 20(S, R)-Rg3 from black ginseng

20(S)-protopanaxadiol (PPD(S)) and 20(R)-protopanaxadiol (PPD(R)), the main metabolites of ginsenosides Rg3(S) and Rg3(R) in black ginseng, are potential candidates for anti-cancer therapy due to their pharmacological activities such as anti-tumor properties. In the present study, we report the preparation of PPD(S, R) by a combination of steaming and biotransformation treatments from ginseng. Aspergillus niger was isolated from soil and showed a strong ability to transform Rg3(S, R) into PPD(S, R) with 100% conversion. Furthermore, the enzymatic reactions were analyzed by reversed-phase HPLC, showing the biotransformation pathways: Rg3(S)-->Rh2(S)-->PPD(S) and Rg3(R)-->Rh2(R)-->PPD(R), respectively. In addition, 12 ginsenosides including 3 pairs of epimers, namely Rg3(S), Rg3(R), Rh2(S), Rh2(R), PPD(S) and PPD(R), were simultaneously determined by reversed-phase HPLC. Our study may be highly applicable for the preparation of PPD(S) and PPD(R) for medicinal purposes and also for commercial use.