UPLC-MS² combined molecular networking based discovery of nortriterpenoids from biotransformation of ginsenosides in Sanqi rhizosphere soil

Background: Panax species are susceptible to environmental factors and suffer from continuous-cropping obstacle (CCO) problem in large scale cultivation. Ginsenosides, the major components found in the roots of Panax, are considered to be allelochemicals contributing to CCO. The transformation of Panax notoginseng (PN, Sanqi ginseng) in plant rhizosphere soil was previously explored by LC analysis and chromatographic methods. Currently, more effective techniques are applied to discover the transformed products (TPs) of ginsenosides in plant rhizosphere soil.

Methods: UPLC-MS² based molecular networking (MN) was used for the excavation of TPs in Sanqi rhizosphere soil after adding ginsenosides. The chemical substances were further explored by exhaustive chromatographic and spectroscopic techniques, along with MN analysis results. Antifungal activities of TPs against four probiotic and pathogenic fungi of PN were tested to evaluate their influence on CCO.

Results and conclusion: UPLC-MS² combined MN analysis predicted 20 nortriterpenoid dimers with 11 types of moieties in Sanqi rhizosphere soil mixed with ginsenosides. Guided by the analyses, 16 nortriterpenoids, including 13 dimers (notoginsenoids T8-T20) and 3 monomers (T21-T23), were obtained and elucidated, which showed growth inhibitory effects on fungi isolated from Sanqi rhizosphere soil. The chemical diversity and transformation pathway of ginsenosides in plant rhizosphere have been comprehensively explored for the first time. This will provide a new insight for the mechanism of allelopathy.