Physicochemical Characterization and NMR Assignments of Ginsenosides Rb1, Rb2, Rc, and Rd Isolated from Panax ginseng

The fresh ginseng roots were extracted with aqueous methanol, and the obtained extracts were partitioned using ethyl acetate, n-butanol, and water, successively. The repeated silica gel and octadecyl silica gel column chromatogaraphy for n-butanol fraction afforded four diol ginseng saponins, ginsenosides Rb-1, Rb-2, Rc, and Rd. The physicochemical, spectroscopic, and chromatographic characteristics of these ginsenosides were measured and compared with those reported in the literature. Some of the peak assignments in previously published H-1- and C-13-nuclear magnetic resonance (NMR) spectra were inaccurate. This study employed two-dimensional NMR experiments, including H-1-H-1 correlation spectroscopy, heteronuclear single quantum correlation, and heteronuclear multiple bond connectivity, to determine exact peak assignments.