A Diazaborine-Based Fluorescent Probe Tracks Endogenously Produced Peroxynitrite in Live Cells

We present the synthesis, properties, and imaging applications of Peroxynitrite Probe-1 (PNP-1), a novel organoboron-based probe for selective peroxynitrite (ONOO-) imaging in live cells. PNP-1 features a diazaborine-based reaction motif that provides excellent discrimination between H2O2 and ONOO-, solving a persistent challenge of organoboron-based fluorescent probes for oxidative metabolite imaging. We demonstrate the utility of PNP-1 to detect endogenously produced ONOO- in live RAW 264.7 macrophages, with probe selectivity confirmed by inhibition of NADPH oxidases and nitric oxide synthase, the requisite enzy-matic machinery for ONOO- production. Beyond the direct application of PNP-1, our results reveal that diazaborines are a modular reaction motif for selective ONOO- reactivity, positioning them for incorporation into other ONOO--specific chemical biology tools.