A Diazaborine Activity-Based Sensing Fluorescent Probe Reports Endogenously Produced Mitochondrial Peroxynitrite in Live Macrophages.

We present the synthesis, properties, and imaging applications of a new class of diazaborine-based probes (Peroxynitrite Probe-1, PNP-1) 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.

ortho-Boronic Acid Carbonyl Compounds and Their Applications in Chemical Biology.

Iminoboronates and diazaborines are related classes of compounds that feature an imine ortho to an arylboronic acid (iminoboronate) or a hydrazone that cyclizes with an ortho arylboronic acid (diazaborine). Rather than acting as independent chemical motifs, the arylboronic acid impacts the rate of imine/hydrazone formation, hydrolysis, and exchange with competing nucleophiles. Increasing evidence has shown that the imine/hydrazone functionality also impacts arylboronic acid reactivity toward diols and reactive oxygen and nitrogen species (ROS/RNS).

Diazaborines oxidize slowly with HO but rapidly with peroxynitrite in aqueous buffer.

Reactive oxygen species (ROS) such as hydrogen peroxide (HO) and peroxynitrite (ONOO) oxidize arylboronic acids to their corresponding phenols. When used in molecular imaging probes and in ROS-responsive molecules, however, simple arylboronic acids struggle to discriminate between HO and ONOO because of their fast rate of reaction with both ROS. Here, we show that diazaborines (DABs) react slowly with HO but rapidly with peroxynitrite in an aqueous buffer.