Integrating MassQL and Molecular Networking to Identify Bioactive Compounds in Idesia polycarpa Maxim

Idesia polycarpa Maxim (Salicaceae) is a well-studied plant producing various hydroxycyclohexenone (HCH) ester derivatives, which constitute most of its secondary metabolites. However, these major metabolites have been reported as unrelated to the alpha-melanocyte stimulating hormone (α-MSH) induced microphthalmia-associated transcription factor (MITF) expression observed in B16F10 melanoma cells, suggesting they may not be responsible for the antimelanogenic effect previously seen with the crude extract. To resolve this discrepancy and identify the bioactive metabolites in the crude extracts, the chemical diversity of I. polycarpa was reanalyzed using Mass Spec Query Language (MassQL)-enhanced molecular networking analysis, which indicated the presence of molecular families of phenolic glycosides without HCH esters. Following the MassQL-guided strategy to uncover the compounds responsible for the bioactivity, a targeted isolation study yielded five previously undescribed compounds and three known compounds, consistent with the MassQL annotations. Notably, one of the isolated non-HCH ester compounds, compound 1, demonstrated significant inhibition of α-MSH-induced melanogenesis via tyrosinase inhibition and MITF downregulation. This finding provides a potential explanation for the previously observed antimelanogenic activity of the crude extract, addressing the inconsistency associated with the major metabolites.