Chlorination‐Driven BODIPY Fluorescent Probes for the Selective Monitoring of Myeloperoxidase Activity in Cells and Inflamed Mouse Models

ABSTRACT Myeloperoxidase (MPO) generates hypochlorous acid (HOCl), a major oxidant in inflammatory biology and an increasingly recognized pathogenic mediator and therapeutic target in oxidative and inflammatory diseases. However, selective detection of MPO activity remains challenging because most HOCl‐responsive fluorescent probes operate through nonspecific oxidative mechanisms, rendering them vulnerable to interference from competing reactive oxygen and nitrogen species. Here, we present an MPO‐reporting fluorescent platform based on a meso ‐carboxamide‐substituted 3,5‐dimethyl BODIPY scaffold that exploits the electrophilic chlorinating reactivity of MPO‐derived HOCl. The lead probe undergoes rapid chlorination at the 2,6‐positions, generating highly emissive products with ca. 40 nm bathochromic shifts and overcoming the minimal spectral responses and fluorescence quenching that have limited earlier chlorination‐based designs. The modular meso ‐carboxamide architecture further allows facile incorporation of targeting motifs without compromising probe performance. This platform enables quantitative MPO assays, cellular imaging of exogenous and endogenous MPO‐derived HOCl, discrimination between cancer and normal cells based on redox differences, and noninvasive visualization of MPO‐driven inflammation in a mouse model of atopic dermatitis. These results establish electrophilic chlorination as a viable design strategy for selective MPO‐responsive fluorescent probes and provide a versatile tool for investigating MPO‐associated inflammatory pathophysiology in biological and preclinical disease models.