An enhanced strategy for discovery and annotation of easily in‐sourced dissociation diterpene lactones from plant natural products: taking Andrographis paniculate (Burm. f.) as an example

Rationale

Diterpene lactones in Andrographis paniculata (AP) are known as “natural antibiotics” for their excellent antibacterial activity. During MS analysis, the hydroxyl groups in the AP diterpene lactone skeleton are prone to neutral loss of H₂O, producing high in-source fragment peaks and affecting the characterization of these components.

Methods

Mass tags were applied during the MS data acquisition step, and special adduct ions form were used to guide the data processing and characterization steps. Besides, the total number of characterized AP diterpene lactones was significantly increased when combining the number of neutrally lost H₂O from AP diterpene lactones, incorporating information of the diagnostic ions, and adopting molecular networks generated with the Global Natural Products Social Molecular Networking (GNPS) database.

Results

Ninety-nine diterpene lactones were characterized from AP, including six monohydroxyl groups, 20 dihydroxyl groups, 27 trihydroxy groups, and 46 Diterpene lactones with more than three hydroxyl groups. In addition, according to the characteristic fragments in the product ions (C₃H₄, Δm/z = 40.03 Da), it could be assumed that there were 90 diterpene lactones with the C19-OH structure among the identified diterpene lactones. The current study provides a new approach for collecting, processing, and characterizing MS analysis of natural diterpene lactones prone to in-source fragmentation.

Conclusions

The MS characterization of AP diterpene lactones was significantly improved, and many potential new compounds were found in AP. It provides new ideas for the purification and identification of AP diterpene lactones.