Convergent and Functional-Group-Tolerant Synthesis of B-Organo BODIPYs

Acid-Resistant BODIPY Amino Acids for Peptide-Based Fluorescence Imaging of GPR54 Receptors in Pancreatic Islets

The G protein-coupled kisspeptin receptor (GPR54 or KISS1R) is an important mediator in reproduction, metabolism and cancer biology; however, there are limited fluorescent probes or antibodies for direct imaging of these receptors in cells and intact tissues, which can help to interrogate their multiple biological roles. Herein, we describe the rational design and characterization of a new acid-resistant BODIPY-based amino acid (Trp-BODIPY PLUS), and its implementation for solid-phase synthesis of fluorescent bioactive peptides. Trp-BODIPY PLUS retains the binding capabilities of both short linear and cyclic peptides and displays notable turn-on fluorescence emission upon target binding for wash-free imaging. Finally, we employed Trp-BODIPY PLUS to prepare some of the first fluorogenic kisspeptin-based probes and visualized the expression and localization of GPR54 receptors in human cells and in whole mouse pancreatic islets by fluorescence imaging.

Acid-Resistant BODIPY Amino Acids for Peptide-Based Fluorescence Imaging of GPR54 Receptors in Pancreatic Islets

The G protein-coupled kisspeptin receptor (GPR54 or KISS1R) is an important mediator in reproduction, metabolism and cancer biology; however, there are limited fluorescent probes or antibodies for direct imaging of these receptors in cells and intact tissues, which can help to interrogate their multiple biological roles. Herein, we describe the rational design and characterization of a new acid-resistant BODIPY-based amino acid (Trp-BODIPY PLUS), and its implementation for solid-phase synthesis of fluorescent bioactive peptides. Trp-BODIPY PLUS retains the binding capabilities of both short linear and cyclic peptides and displays notable turn-on fluorescence emission upon target binding for wash-free imaging. Finally, we employed Trp-BODIPY PLUS to prepare some of the first fluorogenic kisspeptin-based probes and visualized the expression and localization of GPR54 receptors in human cells and in whole mouse pancreatic islets by fluorescence imaging.

Aryl-Boron-Substituted BODIPYs: Direct Access via Aluminum-Chloride-Mediated Arylation from Arylstannanes and Tuning the Optoelectronic Properties

An efficient procedure is presented for functionalization of BODIPYs at boron with arylstannanes as weak nucleophiles in the presence of aluminum chloride, providing new aryl-boron-substituted BODIPY and aza-BODIPY derivatives of singular importance. Most of these aryl-boron-substituted BODIPYs showed bright emission in the aqueous solution with significant aggregation-induced emission enhancement and high solid-state emission as a result of the restricted rotation of the meso-phenyl group and boron-substituted aryl groups as well as the formation of J-type aggregates.

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.

The Synthesis of Picolinamide-Supported Tetracoordinated Organoboron Complexes with Aggregation-Induced Emission Property

The picolinamide-supported tetracoordinated organoboron complexes containing diaryl boronyl segments have been synthesized for the first time. Aryl trifluoroborates were utilized as the BAr₂ sources to introduce different aryl motifs with diverse functional groups. The optical experiments discovered these five-membered boron-containing complexes were aggregation-induced emission (AIE) active, thus affording a new class of AIE molecules.

Synthesis, Reactivity, and Properties of a Class of π-Extended BODIPY Derivatives

A new family of π-extended BODIPY derivatives were obtained through the condensation of aldehyde and pyrrole in aqueous solution in the presence of HCl. The new rigid π-framework extends beyond the dipyrromethene unit, which is significantly different from classical BODIPYs in the electronic configuration. Both π-extended BODIPYs displayed intense absorption and moderate emission with maxima around 565 and 620 nm, respectively, and showed interesting reactivity toward various nucleophiles. Moreover, these π-extended BODIPYs were developed as fluorescent probes for rapid and selective detection of GSH and were successfully applied for live-cell imaging.

Convenient Preparation and Structure Determination of Air- and Moisture-Tolerant Difluoromethylborates

Convenient and reliable synthetic methods for difluoromethylborates have been established. The intermediary generated difluoromethylsilicate species from TMSCF₂ H (TMS=trimethylsilyl) and potassium tert-butoxide were allowed to react with pinBPh (Me₄ C₂ O₂ BPh) in the presence of 18-crown-6 to give the corresponding borate compound [pinB(Ph)CF₂ H]^- K⁺ (18-crown-6) as an air- and moisture-tolerant solid. The unambiguously determined crystal structure of [pinB(Ph)CF₂ H]^- K⁺ (18-crown-6) revealed that the difluoromethylborate unit partially coordinated on the potassium ion. Reaction of [pinB(Ph)CF₂ H]^- K⁺ (18-crown-6) with potassium difluoride (KHF₂ ) in acetic acid enabled substitution of the pinacol unit and phenyl group with fluorides, and gave (difluoromethyl)trifluoroborate [F₃ BCF₂ H]^- K⁺ (18-crown-6) in a good yield. The crystal structure of air- and moisture-tolerant [F₃ BCF₂ H]^- K⁺ (18-crown-6), which would be a promising reagent for synthesis of various difluoromethylboron species, showed a polyrotaxane-like polymeric structure based on the K⋅⋅⋅F interactions between the K⁺ (18-crown-6), CF₂ H, and BF₃ units.

Photophysical properties and application in live cell imaging of B,B-fluoro-perfluoroalkyl BODIPYs

The photophysical properties of newly identified B,B-fluoro-perfluoroalkyl BODIPYs (2 and 3), which possess a fluoro group and a trifluoromethyl or pentafluoroethyl group at the boron center, were investigated. B,B-Fluoro-perfluoroalkyl BODIPYs 2 and 3 exhibited better photophysical/chemical properties than B,B-difluoro-BODIPY 1, as follows: (1) higher photostability both in methanol solvent and in a live cell environment, (2) higher stability against acid degradation, and (3) improved fluorescence signal-to-noise ratios in a cell system. These favorable properties of B,B-fluoro-perfluoroalkyl BODIPYs are likely due to the highly electron-withdrawing nature of the perfluoroalkyl groups on the boron atom, which reduces the reactivity to 1O2 and strengthens the complexation of the dipyrromethene ligands to the boron atom. Thus, B,B-fluoro perfluoroalkyl BODIPYs may be useful functional molecules for various applications.