Development of Sulfite-Specific Fluorescent Probes Based on Isolongifolanone and Their Applications in Biological Imaging.

Isolongifolanone, a natural product, offers several advantages over traditional small organic molecules, including excellent biocompatibility, high reactivity, low cytotoxicity, affordability, and environmental friendliness. While numerous compounds derived from isolongifolanone have been developed, most research has focused primarily on its antitumor properties, with limited exploration of its potential applications as a fluorescent probe. In this study, we designed and synthesized a series of novel natural small-molecule fluorescent probes based on isolongifolanone, utilizing pyrazole compounds as the fluorophore, vanillin or p-hydroxybenzaldehyde as the linker, and levulinate as the sulfite-specific recognition group. The probes react with sulfite through a nucleophilic addition reaction, resulting in a strong fluorescence signal, demonstrating high sensitivity and good selectivity for sulfite detection. Quantitative detection of sulfite can thus be achieved by monitoring the fluorescence intensity. The chemical structure and reaction mechanism of the fluorescent probes were characterized using NMR, LC-MS, and HRMS. Additionally, the isolongifolanone-based fluorescent probes were successfully applied for the detection of sulfites in tumor cells, significantly broadening the application scope and value of isolongifolanone.