Isolation and characterization of ginsenoside-Rg2, 20R-prosapogenin, 20S-prosapogenin and delta 20-prosapogenin. Chemical studies on saponins of Panax ginseng C. A. Meyer, Third report.

In the course of a chemical study on pure ginsenosides, a ginsenoside-Rg2 was isolated as colorless needles, from the lateral root of Panax ginseng C. A. Meyer. For the characterization of Rg2, a chikusetsusaponin-I (ginsenoide-Rg2) was isolated as colorless needles from rhizome of Panax japonicus C. A. Meyer. The optical rotation value of both saponins were opposite to the published data. On the large scale isolation of ginsenosides, trace amount of ginsenoside-Rg2 was isolated as crystals. Three compounds, A, B and C, were isolated from the reaction mixture on hydrolysis of ginsenoside-Rb1, Rb2 and Rc with 50% aqacetic acid. A was 20R-prosapogenin and it was identical with Rg3. On the other hand, B was found to be 20S-prosapogenin. And C was estimated to be prosagenin dehydrated at C20-OH and named as delta 20-prosapogenin. It was found that an equilibration is present among A, B and C at the earlier stage on acid hydrolysis.