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 Rb₁, Rb₂, 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 published¹H-and ¹³C-nuclear magnetic resonance (NMR) spectra were inaccurate. This study employed two-dimensional NMR experiments, including ¹H-¹H correlation spectroscopy, heteronuclear single quantum correlation, and heteronuclear multiple bond connectivity, to determine exact peak assignments.