BODIPY fluorescent dyes for selective staining of intracellular organelles

Abstract

By use of a simple synthetic methodology for peptide coupling by HATU reagent, two BODIPY amides 4 and 5 were synthesized, that were at the meso-position substituted with a morphline moiety targeting lysosomes, or sulfonamide group targeting endoplasmic reticulum (ER), respectively. Furthermore, by use of Cu-catalyzed click chemistry, dye 6 was synthesized from a BODIPY alkyne, that was at the meso-position substituted with a triphenylphosponium salt via a triazol linker, for targeting mitochondria. Photophysical and spectral properties of BODIPY dyes 4–6 were characterized in nonpolar, polar aprotic and protic solvent. All compounds in all solvents have high values of fluorescence quantum yields (Φ_F = 0.5–0.8), and single-exponential decay of fluorescence with singlet excited state lifetimes τ = 2.5–3.8 ns. The substituents in the meso-position that direct the dyes towards different intracellular organelles do not affect the photophysical properties. The dyes showed excellent photostability upon irradiation in aqueous solution with 488 nm laser. Moreover, the stability of amides 4 and 5 was tested with lipases CAL-B and PPL, whereupon they showed hydrolytic stability. The applicability of dyes 4–6 in fluorescent staining of organelles in HeLa cell line was tested in colocalization microscopy studies with commercial dyes Lysotracker RED, ER tracer and Mitotracker Red. They showed excellent localization in lysosomes, ER and mitochondria with the values of Pearson's coefficients 0.90, 0.94, and 0.93, respectively. Furthermore, ability of dyes 4–6 to stain live HeLa cells was demonstrated. Consequently, BODIPY derivatives 4–6 have potential to be used in biology as selective organelle targeting dyes. Moreover, our simple synthetic protocol for the preparation of dyes in principle allows for the synthesis of plethora of different BODIPY derivatives with selective localization in different organelles.