Syntheses and Investigations of Conformationally Restricted, Linker-Free α-Amino Acid-BODIPYs via Boron Functionalization

BODIPY-Based Molecules for Biomedical Applications

BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) derivatives have attracted attention as probes in applications like imaging and sensing due to their unique properties like (1) strong absorption and emission in the visible and near-infrared regions of the electromagnetic spectrum, (2) strong fluorescence and (3) supreme photostability. They have also been employed in areas like photodynamic therapy. Over the last decade, BODIPY-based molecules have even emerged as candidates for cancer treatments. Cancer remains a significant health issue world-wide, necessitating a continuing search for novel therapeutic options. BODIPY is a flexible fluorophore with distinct photophysical characteristics and is a fascinating drug development platform. This review provides a comprehensive overview of the most recent breakthroughs in BODIPY-based small molecules for cancer or disease detection and therapy, including their functional potential.

Red-to-Near-Infrared Emitting PyrrolylBODIPY Dyes: Synthesis, Photophysical Properties and Bioimaging Application

Near-infrared (NIR) fluorophores with characteristics such as deep tissue penetration, minimal damage to the biological samples, and low background interference, are highly sought-after materials for in vivo and deep-tissue fluorescence imaging. Herein, series of 3-pyrrolylBODIPY derivatives and 3,5-dipyrrolylBODIPY derivatives have been prepared by a facile regioselective nucleophilic aromatic substitution reaction (S_N Ar) on 3,5-halogenated BODIPY derivatives (3,5-dibromo or 2,3,5,6-tetrachloroBODIPYs) with pyrroles. The installation of a pyrrolic unit onto the 3-position of the BODIPY chromophore leads to a dramatic red shift of both the absorption (up to 160 nm) and the emission (up to 260 nm) in these resultant 3-pyrrolylBODIPYs with respect to that of the BODIPY chromophore. Their further 5-positional functionalization provides a facile way to fine tune their photophysical properties, and these resulting dipyrrolylBODIPYs and functionalized pyrrolylBODIPYs show strong absorption in the deep red-to-NIR regions (595-684 nm) and intense NIR fluorescence emission (650-715 nm) in dichloromethane. To demonstrate the applicability of these functionalized pyrrolylBODIPYs as NIR fluorescent probes for cell imaging, pyrrolylBODIPY 6 a containing mitochondrion-targeting butyltriphenylphosphonium cationic species was also prepared. It selectively localized in mitochondria of HeLa cells, with low cytotoxicity and intense deep red fluorescence emission.

Investigations on the Synthesis, Reactivity, and Properties of Perfluoro-α-Benzo-Fused BOPHY Fluorophores

The synthesis and reactivity of 3,8-dibromo-dodecafluoro-benzo-fused BOPHY 2 are reported, via S_N Ar with O-, N- S- and C-nucleophiles, and in Pd(0)-catalyzed cross-coupling reactions (Suzuki and Stille). The resulting perfluoro-BOPHY derivatives were investigated for their reactivity in the presence of various nucleophiles. BOPHY 3 displays reversible color change and fluorescence quenching in the presence of bases (Et₃ N, DBU), whereas BOPHY 7 reacts preferentially at the α-pyrrolic positions, and BOPHY 8 undergoes regioselective fluorine substitution in the presence of thiols. The structural and electronic features of the fluorinated BOPHYs were studied by TD-DFT computations. In addition, their spectroscopic and cellular properties were investigated; BOPHY 10 shows the most red-shifted absorption/emission (λ_max 659/699 nm) and 7 the highest fluorescence (Φ_f =0.95), while all compounds studied showed low cytotoxicity toward human HEp2 cells and were efficiently internalized.

Substitution at boron in BODIPYs

Recent synthetic achievements have led to 4,4-disubstituted-4-bora-3a,4a-diaza-s-indacenes (BODIPYs) with varying substituents at the meso, pyrrolic and/or boron sites, with each influencing photophysical properties and utility. This Feature article gives an overview of chemistry at the boron atom in BODIPYs, highlighting our contributions that evolved from synthetic curiosities and now offer this dipyrrolic skeleton potential across a wider range of applications. We first summarise preparative routes to BODIPYs through complexation of boron with the dipyrrinato ligand. The role of boron in protecting dipyrrins is then discussed, followed by strategies by which to achieve facile substitution at the boron atom.

Silver-mediated, direct phosphorylation of BODIPY dyes at the 3- or 3,5-positions with H-phosphonates

A direct and regioselective C-H/P-H cross-coupling of dialkyl phosphites, and diphenylphosphine oxide to easily available BODIPYs through an Ag-mediated radical addition, resulted in a series of new α-phosphorylated BODIPY fluorophores under mild conditions. Hydrolysis of the phosphonate gave the corresponding BODIPY phosphoric acid, which is soluble and fluorescent in water with a high quantum yield of 0.83.