Bromine-Substituted Tricyanofuran-Based Fluorogenic Probes for the Sensitive Detection of Glycosidases under Acidic pH.

Glycosidases participate in modulating a number of biological processes, and their overexpression is a hallmark of several human diseases. Considering the localization of glycosidases predominantly in the lysosomes, it is imperative to develop molecular probes that are resistant to interference from acidic pH. Herein, tricyanofuran-based long-wavelength fluorogenic probes are synthesized, and it is demonstrated that the introduction of bromine to the ortho-position of the phenol alcohol of the probe substantially enhances its fluorescence over an acidic pH range of 3.0-10.0. These probes, when modified with glycosyl substrates, have proved applicable for the sensitive fluorogenic detection of glycosidases under acidic pH, and fluorescence-based imaging of endogenous β-galactosidase and β-glucosidase activities in live cells. The imaging results are validated by quantitative real-time polymerase chain reaction and immunoblotting.