A molecular networking-assisted automatic database screening strategy for comprehensive annotation of small molecules in complex matrices

Liquid chromatography-tandem with high-resolution mass spectrometry (LC-HRMS) has proven challenging for annotating multiple small molecules within complex matrices due to the complexities of chemical structure and raw LC-HRMS data, as well as limitations in previous literatures and reference spectra related to those molecules. In this study, we developed a molecular networking assisted automatic database screening (MN/auto-DBS) strategy to examine the combined effect of MS1 exact mass screening and MS2 similarity analysis. We compiled all previously reported compounds from the relevant literatures. With the development of a Python software, the in-house database (DB) was created by automatically calculating the m/z and data from experimental MS1 hits were rapid screened with DB. We then performed a feature-based molecular network analysis on the auto-MS2 data for supplementary identification of unreported compounds, including clustered FBMN and annotated GNPS compounds. Finally, the results from both strategies were merged and manually curated for correct structural assignment. To demonstrate the applicability of MN/auto-DBS, we selected the Huangqi-Danshen herb pair (HD), commonly used in prescriptions or patent medicines to treat diabetic nephropathy and cerebrovascular disease. A total of 223 compounds were annotated, including 65 molecules not previously reported in HD, such as aromatic polyketides, coumarins, and diarylheptanoids. Using MN/auto-DBS, we can profile and mine a wide range of complex matrices for potentially new compounds.

Automated summary

In this study, a molecular networking assisted automatic database screening (MN/auto-DBS) strategy was developed to annotate multiple small molecules within complex matrices. The strategy combines MS1 exact mass screening and MS2 similarity analysis to identify compounds. Results from both strategies were merged and manually curated for correct structural assignment.