Selective imaging of hydrogen peroxide over peroxynitrite by a boronate-based fluorescent probe engineered via a doubly activated electrophilicity-increasing strategy

Boronate-based fluorescent probes are widely used for the imaging of hydrogen peroxide (H2O2). However, their selectivity might be subjected to the interference of other reactive oxygen species, especially peroxynitrite (ONOO-), due to the reaction of boronates with ONOO- being several orders of magnitude faster than with H2O2. This work highlights a doubly activated electrophilicity-increasing strategy to develop a boronate-based fluorescent probe THMP for selective imaging of H2O2 over ONOO-, where a boronate-modified pyridiniumylacrylonitrile is grafted on the 2-(2′-hydroxy-3′-methoxyphenyl) benzothiazole scaffold. Specifically, the boronate oxidation of THMP by H2O2 leads to the release of the free fluorophore THMP-N, triggering a ratiometric fluorescence response from red to green. The presence of a doubly activated electrophilic site on the carbon-carbon double bond of THMP, by both the strong electron-withdrawing cyano group and the pyridinium moiety, allows selective oxidative cleavage of the double bond by ONOO- to an aldehyde HMBT-CHO, thereby excluding the interference of ONOO- in monitoring H2O2. With the aid of the probe, we successfully visualized increased levels of H2O2 during ferroptosis of HepG2 cells, and burst of H2O2 in brains of live mice during cerebral ischemia reperfusion injury.