# Safirinium Fluorescent “Click” Molecular Probes: Synthesis, CuAAC Reactions, and Microscopic Imaging

## TL;DR

This paper introduces new Safirinium-based fluorescent probes for click chemistry, showing they are stable, non-toxic, and suitable for microscopic imaging.

## Contribution

The synthesis and characterization of Safirinium-based azide and alkyne probes for CuAAC labeling is presented.

## Key findings

- Safirinium-based probes are chemically stable and suitable for fluorescent microscopy.
- Most probes show no toxic effects on CHO-K1 and NIH-3T3 cells.
- The probes successfully undergo CuAAC reactions with model compounds.

## Abstract

Fluorescent labeling utilizing Cu(I)-catalyzed azide–alkyne cycloaddition reactions (CuAAC) is among the leading applications of the “click” chemistry strategy. Fluorescent probes for this approach can be constructed by linking an azide or alkyne group to a fluorophore, such as the recently developed Safirinium derivatives. These compounds are water-soluble, highly fluorescent heterocycles based on 1,2,4-triazolium, with significant potential for various labeling applications, although they have not yet been converted to azide or alkyne probes. Herein, we report the synthesis of Safirinium-based azide and alkyne functionalized molecular probes for “click” chemistry labeling. We also describe their CuAAC reactions with model compounds, including a lipid mimetic long-chain azide, an azido sugar derivative, and azidothymidine, as well as two model alkynes. We demonstrate that the Safirinium-based probes and their derivatives are chemically stable, suitable for fluorescent microscopy observations, and safe to use. Most of these probes show no toxic effects on CHO-K1 and NIH-3T3 cells.