A strategy for efficient discovery of new natural compounds by integrating orthogonal column chromatography and liquid chromatography/mass spectrometry analysis: Its application in Panax ginseng, Panax quinquefolium and Panax notoginseng to characterize 437 potential new ginsenosides

To discover new natural compounds from herbal medicines tends to be more and more difficult. In this paper, a strategy integrating orthogonal column chromatography and liquid chromatography/mass spectrometry (LC/MS) analysis was proposed, and was applied for rapid discovery of new ginsenosides from Panax ginseng (PG), Panax quinquefolium (PQ), and Panax notoginseng (PN). The ginsenosides extracts were fractionated by MCI gel × silica gel orthogonal column chromatography. The fractions were then separated on a C18 HPLC column, eluted with a three-component mobile phase (CH3CN/CH3OH/3 mM CH3COONH4H2O), and detected by electrospray ionization tandem mass spectrometry. The structures of unknown ginsenosides were elucidated by analyzing negative and positive ion mass spectra, which provided complementary information on the sapogenins and oligosaccharide chains, respectively. A total of 623 comprising 437 potential new ginsenosides were characterized from the ethanol extracts of PG, PQ and PN. New acylations, diversified saccharide chains and C-17 side chains constituted novelty of the newly identified ginsenosides. An interpretation guideline was proposed for structural characterization of unknown ginsenosides by LC/MS. To confirm reliability of this strategy, two targeted unknown trace ginsenosides were obtained in pure form by LC/MS-guided isolation. Based on extensive NMR spectroscopic analysis and other techniques, they were identified as 3-O-[6-O-(E)-butenoyl-β-d-glucopyranosyl(1,2)-β-d-glucopyranosyl]-20(S)-protopanaxadiol-20-O-β-d-glucopyranosyl(1,6)-β-d-glucopyranoside (named ginsenoside IV) and 3-O-β-d-glucopyranosyl(1,2)-β-d-glucopyranosyl-3β,12β,20(S),24(R)-tetra hydroxy-dammar-25-ene-20-O-β-d-glucopyranosyl(1,6)-β-d-glucopyranoside (ginsenoside V), respectively. The fully established structures were consistent with the MS-oriented structural elucidation. This study expanded our understanding on ginsenosides of Panax species, and the proposed strategy was proved efficient and reliable in the discovery of new minor compounds from herbal extracts.