Development of fluorescent probes based on styryl dye and styryl BODIPY from focused libraries

Abstract

Fluorescent probes based on small molecules are versatile tools for optical imaging and analytical sensing owing to their high sensitivity levels, fast response times, and simplicity. In addition, the development of a new probe is as important as its usefulness. Although many researchers have developed numerous fluorescent molecular probes, systematic probe development approaches are still lacking. An early conventional strategy for probe development is the target-oriented approach. Probes have been designed based on available empirical knowledge of molecular recognition mechanisms for individual targets. However, this strategy has serious limitations when studying unknown targets. Meanwhile, diversity-oriented fluorescent probe libraries with broad chemical diversity can be an alternative means of discovering new probes for targets that may not be accessible with known sensing moieties. Nevertheless, this strategy has a very low success rate despite the great investments in labor and time. As an alternative to both strategies, we considered focused fluorescent probe libraries that were designed to aid in the development of fluorescent probes based on an understanding of the target or target family. Sensing moieties of our probes were focused on the target family. Herein, we demonstrate the effectiveness of a focused library consisting of sensing moieties and styryl-based fluorescent dyes to provide selective probes for the detection of various targets. First, we prepared a focused fluorescent probe library for metal cations that was developed by combining metal cation ligand moieties and picolinium/quinolinium moieties as combinatorial blocks, which were connected through a styryl group. Selective probes for Hg2+, Ag+, and Zn2+ can be found in this library. Secondly, we constructed a focused probe library for phosphorylated biomolecules using metal complexes obtained from the previous library having a high binding affinity levels for metal cations. From the metal complexes, a selective probe for dTTP was developed. Thirdly, several of our styryl dyes from the previous library showed enhanced fluorescence in cells, and we found fluorescent nucleic acid probes. The feasibility of these probes was confirmed by cellular nucleic acid digestion experiments. Fourth, we developed a ratiometric fluorescent hydrogen peroxide probe, 1A. This probe was used to quantify glucose in diluted urine with enzyme-assisted glucose oxidation. Furthermore, we demonstrated that probe 1A could detect the activities of various oxidases as well as the presence and quantity of specific biomolecules by means of enzyme-assisted metabolism. Lastly, we developed a fluorescent imaging probe based on styryl BODIPY, v-BDP, for a mitochondria-targeting cancer therapy study. This was developed to deliver anticancer drugs to the mitochondria through triggering with intracellular esterase.