Chlorinated chaetoviridin-type azaphilones discovered via metabolomics: structural diversity and suppression of STAT3 signaling in gastric cancer cells.

Azaphilones are structurally diverse polyketides with broad bioactivities, among which chaetoviridins are distinguished by their chlorinated frameworks and anticancer potential. To expand the chemical space of STAT3-relevant azaphilones, a metabolomics strategy integrated with OSMAC (one strain many compounds) fermentation was applied to a deep-sea Chaetomium globosum strain. Metabolomic analysis revealed pronounced metabolic divergence, with chlorinated metabolites as key discriminants. Molecular networking further localized these features into clusters associated with chaetoviridin-type scaffolds. Guided by this workflow, twelve new chaetoviridin-type azaphilones were isolated, including an unprecedented dichlorinated methyl-acetal, pyran- and isochromene-type derivatives, and a series of N-isoquinolinone congeners, along with five known analogues. Their structures feature a conserved azaphilone-derived 6/6/5 tricyclic core with diverse oxygenated and nitrogenated substituents. Structural assignments were accomplished using NMR, HRESIMS, X-ray diffraction, and TDDFT-ECD calculations. Several compounds exhibited cytotoxicity against gastric cancer cells, with compound 1 showing the most potent activity. Compound 1 engages STAT3 in cells, suppressing Tyr705 phosphorylation and thereby blocking nuclear translocation and STAT3-dependent transcription to suppress gastric cancer cell proliferation, migration, and induce apoptosis. This study highlights the utility of metabolomics for accessing azaphilone families and underscores deep-sea fungi as a rich source of structurally novel and biologically relevant natural products.