Chemical capture of diazo metabolites reveals biosynthetic hydrazone oxidation

Chemically reactive microbial natural products have enabled therapeutic development^1,2 via their well-established bioactivities including anticancer,³ antibiotic,^4,5 and antioxidant⁶ activities. However, discovery of reactive metabolites is particularly challenging because they may not tolerate traditional bioactivity-guided isolation workflows.⁷ Diazo-containing natural products are a subset of highly reactive microbial metabolites that display potent bioactivity^8-11 and enable powerful (bio)synthetic transformations;^12,13 however, instability of the diazo group to light,^14,15 heat,^16,17 mild acid,¹⁸ and mechanical shock¹⁹ has precluded their efficient discovery and application. Here, we develop a reactivity-based screening approach to capture diazo-containing metabolites and facilitate their discovery by mass spectrometry. This workflow revealed two novel diazo-containing natural products, 4-diazo-3-oxo-butanoic acid and diazoacetone, from the human lung pathogen Nocardia ninae. Biosynthetic investigations revealed a distinct enzymatic logic for diazo formation involving hydrazone oxidation catalyzed by the metalloenzyme Dob3, and biochemical characterization of Dob3 suggests promising future applications in biocatalysis. Overall, our work highlights the power of reactivity-guided strategies for identifying reactive metabolites and facilitating the discovery of unique enzymatic transformations.