Kinetics improvement of protease-mediated formation of pyronin dyes

A fluorescent probe for protease sensing and based on the ``covalent-assembly'' principle is reported. The basic rational for this unusual class of chemodosimeters proposed by the Anslyn and Yang groups entails the synthesis of non-fluorophore caged precursors full-stable and reactive towards the targeted analyte. Unlike the first generation of protease-sensitive ``covalent-assembly'' type probes recently published by ourselves (Org. Biomol. Chem. 2017, 15, 2575-2584), the availability of dicyanomethylidenyl and enzyme-labile phenylacetamide moieties within the core structure of mixed bis-aryl ether 2 enables its rapid conversion into a fluorescent pyronin dye at physiological pH and upon activation with penicillin G acylase (PGA). This is real progress towards the practical implementation of this ingenious activation mechanism to the detection of enzymes in their native environment (in cellulo or in vivo). (C) 2018 Elsevier Ltd. All rights reserved.