Synthesis of BODIPY-Amino Acids and the Potential Applications as Specific Dyes for the Cytoplasm of Langerhans β-Cells

In this work, we explored the synthesis of 4,4-difluoro-4-bora-3a,4a-diazas-indacene (BODIPYs) bound to five different amino acids (BODIPY-FAA) (glycine, alanine, leucine, phenylalanine, and tyrosine) (amino group is kept protected with fluorophore Fmoc) and evaluated these conjugates in terms of (i) their photophysical properties and (ii) their potential application as cell staining agents of suspension and adherent cells at healthy and stress conditions. In general, all synthesized BODIPY-FAA (3a-3e) were found to emit fluorescence in the blue and green regions of the spectrum (depending on the solvent conditions). However, BODIPY-FTyr(trt) (3e) showed the best molar extinction coefficient (ε = 28,198 M^-1 cm^-1) and quantum yield (Φ = 0.17). Biologically speaking, all synthesized conjugates demonstrated a selective affinity for the cytoplasm of Langerhans β-cells employed as a model, being the BODIPY-FLeu conjugate the one displaying the highest observed intensity. As such, our results reveal the BODIPY-FAA as a novel attractive tool for the specific staining of the cell cytoplasm, demonstrating not only a dual fluorescence emission but also a sensing capability to recognize different cell states.

Keywords:
BODIPY-amino acids dyes; bio-conjugation; cell staining