Native Chemical Ligation‐Based Fluorescent Probes for Cysteine and Aminopeptidase N Using meso‐thioester‐BODIPY.

meso‐Carboxyl‐BODIPY responds to small electronic changes resulting from acyl substitution reactions with a marked change in fluorescence. Herein, the minute changes that accompany the thioester to amide conversion encountered in native chemical ligation (NCL) are exploited in the construction of fluorescent "turn‐on" probes. Two fluorogenic probes, 1 a and 4, derived from a meso‐thioester‐BODIPY scaffold, were designed for the selective detection of cysteine (1 a) and aminopeptidase N (4), respectively. The aromatic (1 a) and aliphatic (4) thioesters of meso‐carboxyl‐BODIPY are nonfluorescent. However, specific analyte‐induced conversion to the meso‐amide derivative caused significant spectral changes and a dramatic fluorescence enhancement. Probe 1 a exhibited a large fluorescence "turn‐on" response with high selectivity toward cysteine via a tandem NCL reaction. Probe 4 was successfully applied to the monitoring and imaging of endogenous aminopeptidase N in live cancer cells. [ABSTRACT FROM AUTHOR]