Conversion of Ginsenoside Rb1 into Six Types of Highly Bioactive Ginsenoside Rg3 and Its Derivatives by FeCl3 Catalysis

摘要

Ginsenoside Rb1 is an important saponin of ginseng(s); however, Rb1, with 3- O - and 20- O -sugar moieties, has low bioavailability. Here, we report the derivatization of ginsenoside Rb1 to completely generate six types of highly bioactive minor ginsenoside Rg3 and its derivatives by FeCl₃ catalysis, the reaction conditions are similar to enzymatic reaction conditions. In FeCl₃ catalysis, the only 20- O -sugar-moiety of ginsenoside Rb1 was decomposed into the minor ginsenosides Rk1 and Rg5 with newly produced C-20 ethylene bands; but also hydrolyzed into 20( S )-Rg3 and 20( R )-Rg3; subsequently the C-24(25) ethylene bands of 20( S )-Rg3 and 20( R )-Rg3 were hydrated to 20( S )-25-OH-Rg3 and 20( R )-25-OH-Rg3. After separation of reaction mixture from 34?g ginsenoside-Rb1 by silica-gel-column, the 3.3?g sample I of TLC top-band consisting of Rg5 and Rk1, 8.7?g sample II of TLC middle-band consisting of 20( S )-Rg3 and 20( R )-Rg3, 3.5?g sample III of TLC bottom-band consisting of unknown product-I and -II including 20( S )-25-OH-Rg3, were obtained. The sample III consisting of unknown product-I and -II was purified by crystallization, and identified to 20( S )-25-OH-Rg3 and 20( R )-25-OH-Rg3 by HPLC-Evaporative Light Scattering Detector (ELSD) and NMR. Therefore, six types of minor-ginsenosides Rk1, Rg5, 20( S )-Rg3, 20( R )-Rg3, 20( S )-25-OH-Rg3 and 20( R )-25-OH-Rg3 were successfully prepared from ginsenoside Rb1 by FeCl₃ catalysis. FeCl₃ has low toxicity and is inexpensive, and the reaction conditions are similar to enzymatic reaction conditions; thus, this method is applicable to the development of ginseng-based drugs.