Biotransformation Of Rb₁, Rb₂ And Rc By Alternaria Porri (Ellis) Cifferri

Panax ginseng C. A. Meyer, a plant of Araliaceae, is a famous medicine, one of whose primary active components are ginsenosides. The minor ginsenosides, whose yield in ginseng plants is relatively low, possess unique pharmacological activity compared with the major ones. Recently, it has been found that the biotransformation of ginsenosides was the most excellent measure to obtain the minor ginsenosides. This study consists of two parts: one is screening fungi to find those possessing the ability to convert the major ginsenosides into the minor ginsenosides, and the other is research of transformation of ginsenosides Rb1, Rb2 and Rc by Alternaria porri (Ellis) Cifferri, respectively.This study tried to find fungi which can transform major protopanaxadiol ginsenosides to minor ginsenosides with high selectivity and efficiency. Among 27 test fungal strains, only one has no effect on the ginsenoside substrates used in this paper. The results that other 26 fungal strains transformed protopanaxadiol ginsenosides were as follows: 2 fungal strains could hydrolyze four sugar residues on ginsenosides Rb1, Rb2 and Rc thoroughly; 8 fungal strains were able to transform protopanaxadiol ginsenosides to C-K as final product; 12 fungal strains had the ability to convert the mixture of ginsenosides Rb1, Rb2 and Rc to ginsenoside F2 finally; 4 fungal strains catalyzed the reaction of Rb1 to Rd; 3 fungal strains contributed to the biotransformations whose TLC maps showed Rg3 as a product faintly. There were seven products in the transformation process of ginsenosides Rb1, Rb2 and Rc by Alternaria alternata, illuminating that this fungal strain has high efficiency and low selectivity.Furthermore, the biotransformation of ginsenosides Rb1, Rb2 and Rc by Alternaria porri (Ellis) Cifferri and its exocellular glycosidases were deeply studied. We obtained one of the products in the transformation by A. porri, and determined that it was identical to ginsenoside F2 by 13C-NMR characterization. The paths through which this fungus transformed Rb1, Rb2 and Rc were Rb1→Rd→F2→C-K, Rb2→C-O→C-Y, and Rc→Mb→Mc, respectively. It was found that A. porri has no ability to hydrolyze arabinose residue. The crude enzyme was obtained and separated into 3 fractions by DEAE-cellulose, each of which had the ability to transform gensenosides. Fractions I and II converted protopanaxadiol ginsenosides to compound-K as final product and the biotransformation of the same substrates by Fraction III terminated at Rd. Fractions I possessed higher efficiency of biotransformation than spores.