Development of a Fluorogenic Reactivity Palette for the Study of Nucleophilic Addition Reactions Based on meso-Formyl...

We describe herein a fluorescence-based assay to characterize and report on nucleophilic addition to carbonyl moieties and highlight the advantages a fluorescence-based assay and multiplex analysis can offer. The assay relies on the fluorogenic properties of meso-formyl boron-dipyrromethene (BODIPY) dyes that become emissive following nucleophilic addition. A reactivity palette is assembled based on the increasing electrophilic character of five meso-formyl BODIPY compounds tested. We show that increasing rates of emission enhancement correlate with the decreasing electrophilic character of BODIPY dyes in the presence of an acid catalyst and a nucleophile. These results are consistent with the rate-limiting step involving activation of the electrophile. Increasing product formation is shown to correlate with the increasing electrophilic character of the BODIPY dyes, as expected based on thermodynamics. In addition to providing rates of reaction, analysis of the fluorescence parameters for the reaction mixtures, including emission quantum yields and fluorescence lifetimes, enables us to determine the extent of reactant conversion at equilibrium (in our case the estimated yield of a transient species) and the presence of different products, without the need for isolation. We anticipate that our reactivity palette approach, combined with the in-depth fluorescence analysis discussed herein, will provide guidelines toward developing fluorogenic assays of reactivity offering multiplex information, beyond fluorescence intensity.