Efficient synthesis of fluorescent-PET probes based on [¹⁸F]BODIPY dye

Advances in peptide-based drug delivery systems

Drug delivery systems (DDSs) are designed to deliver drugs to their specific targets to minimize their toxic effects and improve their susceptibility to clearance during targeted transport. Peptides have high affinity, low immunogenicity, simple amino acid composition, and adjustable molecular size; therefore, most peptides can be coupled to drugs via linkers to form peptide-drug conjugates (PDCs) and act as active pro-drugs. PDCs are widely thought to be promising DDSs, given their ability to improve drug bio-compatibility and physiological stability. Peptide-based DDSs are often used to deliver therapeutic substances such as anti-cancer drugs and nucleic acid-based drugs, which not only slow the degradation rate of drugs in vivo but also ensure the drug concentration at the targeted site and prolong the half-life of drugs in vivo. This article provides an profile of the advancements and future development in functional peptide-based DDSs both domestically and internationally in recent years, in the expectation of achieving targeted drug delivery incorporating functional peptides and taking full advantage of synergistic effects.

In Vivo Near-Infrared Fluorescence Imaging Selective for Soluble Amyloid β Aggregates Using y-Shaped BODIPY Derivative

Soluble amyloid β (Aβ) aggregates, suggested to be the most toxic forms of Aβ, draw attention as therapeutic targets and biomarkers of Alzheimer's disease (AD). As soluble Aβ aggregates are transient and diverse, imaging their diverse forms in vivo is expected to have a marked impact on research and diagnosis of AD. Herein, we report a near-infrared fluorescent (NIRF) probe, BAOP-16, targeting diverse soluble Aβ aggregates. BAOP-16, whose molecular shape resembles "y", showed a marked selective increase in fluorescence intensity upon binding to soluble Aβ aggregates in the near-infrared region and a high binding affinity for them. Additionally, BAOP-16 could detect Aβ oligomers in the brains of Aβ-inoculated model mice. In an in vivo fluorescence imaging study of BAOP-16, brains of AD model mice displayed significantly higher fluorescence signals than those of wild-type mice. These results indicate that BAOP-16 could be useful for the in vivo NIRF imaging of diverse soluble Aβ aggregates.

Picomolar-sensitive β-amyloid fibril fluorophores by tailoring the hydrophobicity of biannulated π-elongated dioxaborine-dyes

The pathological origin of Alzheimer's disease (AD) is still shrouded in mystery, despite intensive worldwide research efforts. The selective visualization of β-amyloid (Aβ), the most abundant proteinaceous deposit in AD, is pivotal to reveal AD pathology. To date, several small-molecule fluorophores for Aβ species have been developed, with increasing binding affinities. In the current work, two organic small-molecule dioxaborine-derived fluorophores were rationally designed through tailoring the hydrophobicity with the aim to enhance the binding affinity for Aβ1-42 fibrils -while concurrently preventing poor aqueous solubility-via biannulate donor motifs in D-π-A dyes. An unprecedented sub-nanomolar affinity was found (K d = 0.62 ± 0.33 nM) and applied to super-sensitive and red-emissive fluorescent staining of amyloid plaques in cortical brain tissue ex vivo. These fluorophores expand the dioxaborine-curcumin-based family of Aβ-sensitive fluorophores with a promising new imaging agent.

PET/Fluorescence Imaging: An Overview of the Chemical Strategies to Build Dual Imaging Tools

Molecular imaging is a biomedical research discipline that has quickly emerged to afford the observation, characterization, monitoring, and quantification of biomarkers and biological processes in living organism. It covers a large array of imaging techniques, each of which provides anatomical, functional, or metabolic information. Multimodality, as the combination of two or more of these techniques, has proven to be one of the best options to boost their individual properties, hence offering unprecedented tools for human health. In this review, we will focus on the combination of positron emission tomography and fluorescence imaging from the specific perspective of the chemical synthesis of dual imaging agents. Based on a detailed analysis of the literature, this review aims at giving a comprehensive overview of the chemical strategies implemented to build adequate imaging tools considering radiohalogens and radiometals as positron emitters, fluorescent dyes mostly emitting in the NIR window and all types of targeting vectors.

A Structure-Activity Relationship Study of Bimodal BODIPY-Labeled PSMA-Targeting Bioconjugates

The aim of this study was to identify a high-affinity BODIPY peptidomimetic that targets the prostate-specific membrane antigen (PSMA) as a potential bimodal imaging probe for prostate cancer. For the structure-activity study, several BODIPY (difluoroboron dipyrromethene) derivatives with varying spacers between the BODIPY dye and the PSMA Glu-CO-Lys binding motif were prepared. Corresponding affinities were determined by competitive binding assays in PSMA-positive LNCaP cells. One compound was identified with comparable affinity (IC50 =21.5±0.1 nM) to Glu-CO-Lys-Ahx-HBED-CC (PSMA-11) (IC50 =18.4±0.2 nM). Radiolabeling was achieved by Lewis-acid-mediated 19 F/18 F exchange in moderate molar activities (∼0.7 MBq nmol-1 ) and high radiochemical purities (>99 %) with mean radiochemical yields of 20-30 %. Cell internalization of the 18 F-labeled high-affinity conjugate was demonstrated in LNCaP cells showing gradual increasing PSMA-mediated internalization over time. By fluorescence microscopy, localization of the high-affinity BODIPY-PSMA conjugate was found in the cell membrane at early time points and also in subcellular compartments at later time points. In summary, a high-affinity BODIPY-PSMA conjugate has been identified as a suitable candidate for the development of PSMA-specific dual-imaging agents.

A Highly Selective Turn-On Fluorescent Probe for the Detection of Zinc

A novel turn-on fluorescence probe L has been designed that exhibits high selectivity and sensitivity with a detection limit of 9.53 × 10⁻⁸ mol/L for the quantification of Zn²⁺. ¹H-NMR spectroscopy and single crystal X-ray diffraction analysis revealed the unsymmetrical nature of the structure of the Schiff base probe L. An emission titration experiment in the presence of different molar fractions of Zn²⁺ was used to perform a Job’s plot analysis. The results showed that the stoichiometric ratio of the complex formed by L and Zn²⁺ was 1:1. Moreover, the molecular structure of the mononuclear Cu complex reveals one ligand L coordinates with one Cu atom in the asymmetric unit. On adding CuCl₂ to the ZnCl₂/L system, a Cu-Zn complex was formed and a strong quenching behavior was observed, which inferred that the Cu²⁺ displaced Zn²⁺ to coordinate with the imine nitrogen atoms and hydroxyl oxygen atoms of probe L.

Late-Stage 18F/19F Isotopic Exchange for the Synthesis of 18F-Labeled Sulfamoyl Fluorides

Synthesis of sulfamoyl [¹⁸F]fluorides has been a challenging topic owing to the inefficient nucleophilic radiofluorination of sulfamoyl derivatives. Herein, we report an ¹⁸F/¹⁹F isotopic exchange approach to synthesize various sulfamoyl [¹⁸F]fluorides, otherwise inaccessible via direct synthesis from amines, with high radiochemical yields up to 97% (30 examples). This late-stage labeling protocol offers an efficient route to yield functionalized molecules by diversifying the chemical library possessing sulfamoyl functionalities through nucleophilic ¹⁸F incorporation within nitrogen-containing sulfur(VI) frameworks.

18F-labelled BODIPY dye as a dual imaging agent: Radiofluorination and applications in PET and optical imaging

Dual Positron emission tomography (PET)/optical imaging techniques have captured scientific interest for clinical applications due to their potential as an effective tool for visualizing in vivo information such as disease processes. 4,4'-Difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) dye has been considered an ideal platform strategy to achieve dual PET/optical imaging due to its photochemical nature and chemical structure. Various radiofluorination methods to prepare [18F]BODIPY dye have been developed and established, ranging from nucleophilic substitution reactions to isotope exchange reactions. In addition, 18F-labelled BODIPY dyes for biologically important targets have been used for in vivo and ex vivo studies. These studies proved the practicality of [18F]BODIPY dyes as a hybrid PET/optical imaging probe. In this review, recent advances in the synthesis and biological evaluation of 18F-labelled BODIPY dyes are described.

Fluorine-18-Labeled Fluorescent Dyes for Dual-Mode Molecular Imaging

Recent progress realized in the development of optical imaging (OPI) probes and devices has made this technique more and more affordable for imaging studies and fluorescence-guided surgery procedures. However, this imaging modality still suffers from a low depth of penetration, thus limiting its use to shallow tissues or endoscopy-based procedures. In contrast, positron emission tomography (PET) presents a high depth of penetration and the resulting signal is less attenuated, allowing for imaging in-depth tissues. Thus, association of these imaging techniques has the potential to push back the limits of each single modality. Recently, several research groups have been involved in the development of radiolabeled fluorophores with the aim of affording dual-mode PET/OPI probes used in preclinical imaging studies of diverse pathological conditions such as cancer, Alzheimer's disease, or cardiovascular diseases. Among all the available PET-active radionuclides, 18F stands out as the most widely used for clinical imaging thanks to its advantageous characteristics (t1/2 = 109.77 min; 97% β+ emitter). This review focuses on the recent efforts in the synthesis and radiofluorination of fluorescent scaffolds such as 4,4-difluoro-4-bora-diazaindacenes (BODIPYs), cyanines, and xanthene derivatives and their use in preclinical imaging studies using both PET and OPI technologies.

BODIPYS and aza-BODIPY derivatives as promising fluorophores for in vivo molecular imaging and theranostic applications

Since their discovery in 1968, the BODIPYs dyes (4,4-difluoro-4-bora-3a, 4a diaza-s-indacene) have found an exponentially increasing number of applications in a large variety of scientific fields. In particular, studies reporting bioapplications of BODIPYs have increased dramatically. However, most of the time, only in vitro investigations have been reported. The in vivo potential of BODIPYs and aza-BODIPYs is more recent, but considering the number of in vivo studies with BODIPY and aza-BODIPY which have been reported in the last five years, we can now affirm that this family of fluorophores can be considered important as cyanine dyes for future in vivo and even clinical applications. This review aims to present representative examples of recent in vivo applications of BODIPYs or aza-BODIPYs, and to highlight the potential of these dyes for optical molecular imaging.

Rhenium and technetium-complexed silicon rhodamines as near-infrared imaging probes for bimodal SPECT- and optical imaging

The first technetium-99m tricarbonyl core labelled fluorescent Si-rhodamine and its rhenium analogue for bimodal SPECT- and near-infrared fluorescence imaging is presented.

Rhenium(i) complexation–dissociation strategy for synthesising fluorine-18 labelled pyridine bidentate radiotracers

A novel fluorine-18 radiolabelling method employing rhenium(i) mediation is described herein. In less than 1 minute, fluorine-18 labelled complexes and ligands were synthesised in greater than 80% and 60% radiochemical yields (RCY), respectively.

Design and synthesis of a novel BODIPY-labeled PSMA inhibitor

Prostate-specific membrane antigen (PSMA) is a zinc-bound metalloprotease which is highly expressed in metastatic prostate cancer. It has been considered an excellent target protein for prostate cancer imaging and targeted therapy because it is a membrane protein and its active site is located in the extracellular region. We successfully synthesized and evaluated a novel PSMA ligand conjugated with BODIPY_650/665. Compound 1 showed strong PSMA-inhibitory activity and selective uptake into PSMA-expressing tumors. Compound 1 has the potential to be utilized as a near infrared (NIR) optical imaging probe targeting PSMA-expressing cancers.

Radiolabeled BODIPYs: An overview

Fluorescence and SPECT/PET imaging are powerful tools currently in use by the scientific community and receiving a great attention for the development of dual-modality imaging agents. BODIPYs are among the most promising candidates to be used for such functions due their excellent absorbance and fluorescence properties as well as their ease of radiolabeling without compromising their biological properties. In this manuscript we present an overview of BODIPY radiolabeling methods and their relevance to the development of multimodality agents.

18F-Labeled BODIPY Dye: A Potential Prosthetic Group for Brain Hybrid PET/Optical Imaging Agents

There are few hybrid positron emission tomography (PET)/fluorescence imaging agents available for brain imaging. For this purpose, BODIPY dye is very attractive because one of its fluorine atoms can be readily exchanged with ¹⁸F, and it can be modified to produce red-shifted fluorescence. In this study, therefore, we synthesized and investigated a ¹⁸F-labeled red-shifted BODIPY dye as a prosthetic group for brain hybrid PET/optical imaging agents and determined the optimal dose of this radioligand for hybrid imaging. The red-shifted BODIPY dye (1) was synthesized, and one of its fluorine atoms was exchanged with ¹⁸F using SnCl₄ in high yield. Partition coefficients of ¹⁸F-labeled BODIPY dye ([¹⁸F]1) and 1 were measured using its radioactivity and fluorescence, respectively, which were shown to be suitable for brain penetration. Optimal dose for hybrid imaging was determined by analysis of PET/CT and optical images of Balb/C nude mice injected with [¹⁸F]1 and 1, respectively. Hybrid PET/optical images of mice injected with optimal dose of [¹⁸F]1 showed strong radioactivity and fluorescence signal in the brain at 2 min after injection, with rapid clearance by 30 min. Tissue distribution data confirmed the in vivo and ex vivo PET/optical imaging data, indicating desirable brain pharmacokinetics of the radioligand. Taken together, the results of this study suggest that [¹⁸F]1 can be widely used as a prosthetic group for brain hybrid PET/optical imaging agents.

[18F]BODIPY-triglyceride-containing chylomicron-like particles as an imaging agent for brown adipose tissue in vivo

Brown adipose tissue (BAT) is present in human adults and the current gold standard to visualize and quantify BAT is [¹⁸F]FDG PET-CT. However, this method fails to detect BAT under insulin-resistant conditions associated with ageing and weight gain, such as type 2 diabetes. The aim of this study was to develop a novel triglyceride-based tracer for BAT. For this purpose we designed a dual-modal fluorescent/PET fatty acid tracer based on commercially available BODIPY-FL-C₁₆, which can be esterified to its correspondent triglyceride, radiolabeled and incorporated into pre-synthesized chylomicron-like particles. BODIPY-FL-C₁₆ was coupled to 1,2-diolein with a subsequent radiolabeling step resulting in [¹⁸F]BODIPY-C₁₆-triglyceride that was incorporated into chylomicron-like particles. Various quality control steps using fluorescent and radioactive methods were conducted before BAT visualization was tested in mice. Triglyceride synthesis, radiolabeling and subsequent incorporation into chylomicron-like particles was carried out in decent yields. This radiotracer appeared able to visualize BAT in vivo, and the uptake of the radiotracer was stimulated by cold exposure. The here reported method can be used to incorporate radiolabeled triglycerides into pre-synthesized chylomicron-like particles. Our approach is feasible to visualize and quantify the uptake of triglyceride-derived fatty acids by BAT.

Chemistry for Positron Emission Tomography: Recent Advances in 11 C-, 18 F-, 13 N-, and 15 O-Labeling Reactions

Positron emission tomography (PET) is a molecular imaging technology that provides quantitative information about function and metabolism in biological processes in vivo for disease diagnosis and therapy assessment. The broad application and rapid advances of PET has led to an increased demand for new radiochemical methods to synthesize highly specific molecules bearing positron-emitting radionuclides. This Review provides an overview of commonly used labeling reactions through examples of clinically relevant PET tracers and highlights the most recent developments and breakthroughs over the past decade, with a focus on 11 C, 18 F, 13 N, and 15 O.

Solvent-Sensitive Emitting Urea-Bridged bis-BODIPYs: Ready Access by a One-Pot Tandem Staudinger/Aza-Wittig Ureation

Herein we describe the synthesis, and computationally aided photophysical characterization of a new set of urea-bridged bis-BODIPY derivatives. These new dyads are efficiently obtained by a one-pot tandem Staudinger/aza-Wittig ureation protocol, from easily accessible meso-phenyl ortho-azidomethyl BODIPYs. These symmetric bis-BODIPYs outstand by a high absorption probability and excellent fluorescence and laser emission in less polar media. Nevertheless, this emission ability decreases in more polar media, which is ascribed to a light-induced charge-transfer from the urea spacer to the dipyrrin core, a process that can be modulated by appropriate changes in the substitution pattern of the BODIPY core. Furthermore, this ureation protocol can also be employed for the direct conjugation of our BODIPY-azides to amine-containing compounds, thus providing access to fluorescent non-symmetric ureas.

Synthesis, radiosynthesis and in vitro evaluation of 18F-Bodipy-C16/triglyceride as a dual modal imaging agent for brown adipose tissue

Background

Brown adipose tissue research is in the focus in the field of endocrinology. We designed a dual-modal fluorescent/PET fatty acid based tracer on commercially available Bodipy-C₁₆, which can be synthesized to its corresponding triglyceride and which combines the benefits of fluorescent and PET imaging.

Methods

Bodipy-C₁₆ was coupled to 1,3-diolein resulting in Bodipy-triglyceride. Bodipy-C₁₆ and Bodipy-triglyceride compounds were radiolabeled with ¹⁸F using an ¹⁸F/¹⁹F exchange reaction to yield a dual-modal imaging molecule. Uptake of radiolabeled and non-labeled Bodipy-C₁₆ and Bodipy-triglyceride was analyzed by fluorescence imaging and radioactive uptake in cultured adipocytes derived from human brown adipose tissue and white adipose tissue.

Results

Bodipy-C₁₆ and Bodipy-triglyceride were successfully radiolabeled and Bodipy-C₁₆ showed high shelf life and blood plasma stability (99% from 0–4 h). The uptake of Bodipy-C₁₆ increased over time in cultured adipocytes, which was further enhanced after beta-adrenergic stimulation with norepinephrine. The uptake of Bodipy-C₁₆ was inhibited by oleic acid and CD36 inhibitor sulfosuccinimidyl-oleate. The poor solubility of Bodipy-triglyceride did not allow stability or in vitro experiments.

Conclusion

The new developed dual modal fatty acid based tracers Bodipy-C₁₆ and Bodipy-triglyceride showed promising results to stimulate further in vivo evaluation and will help to understand brown adipose tissues role in whole body energy expenditure.

Radioiodination of BODIPY and its application to a nuclear and optical dual functional labeling agent for proteins and peptides

In molecular imaging research, the development of multimodal imaging probes has recently attracted much attention. In the present study, we prepared radioiodinated BODIPY and applied it as a nuclear and optical dual functional labeling agent for proteins and peptides. We designed and synthesized [¹²⁵I]BODIPY with a N-hydroxysuccinimide (NHS) ester, and evaluated its utility as a nuclear and fluorescent dual labeling agent for proteins and peptides. In the radioiodination reaction of BODIPY-NHS with [¹²⁵I]NaI, [¹²⁵I]BODIPY-NHS was obtained at a 48% radiochemical yield. When we carried out the conjugation reaction of [¹²⁵I]BODIPY-NHS with bovine serum albumin (BSA) and RGD (Arg-Gly-Asp) peptide as a model protein and peptide, respectively, [¹²⁵I]BODIPY-BSA and [¹²⁵I]BODIPY-RGD peptide were successfully prepared at 98 and 82% radiochemical yields, respectively. Furthermore, we prepared [¹²³I]BODIPY-trastuzumab by this conjugation reaction and successfully applied it to single photon emission computed tomography (SPECT) imaging studies using tumor-bearing mice, suggesting that radioiodinated BODIPY-NHS serves as a dual functional labeling agent for proteins and peptides. Since iodine has various radioisotopes that can be used for SPECT and positron emission tomography (PET) imaging, biological research, and radiotherapy, the radioiodinated BODIPY may be extensively applicable from basic to clinical research.

Heat-induced-radiolabeling and click chemistry: A powerful combination for generating multifunctional nanomaterials

A key advantage of nanomaterials for biomedical applications is their ability to feature multiple small reporter groups (multimodality), or combinations of reporter groups and therapeutic agents (multifunctionality), while being targeted to cell surface receptors. Here a facile combination of techniques for the syntheses of multimodal, targeted nanoparticles (NPs) is presented, whereby heat-induced-radiolabeling (HIR) labels NPs with radiometals and so-called click chemistry is used to attach bioactive groups to the NP surface. Click-reactive alkyne or azide groups were first attached to the nonradioactive clinical Feraheme (FH) NPs. Resulting "Alkyne-FH" and "Azide-FH" intermediates, like the parent NP, tolerated 89Zr labeling by the HIR method previously described. Subsequently, biomolecules were quickly conjugated to the radioactive NPs by either copper-catalyzed or copper-free click reactions with high efficiency. Synthesis of the Alkyne-FH or Azide-FH intermediates, followed by HIR and then by click reactions for biomolecule attachment, provides a simple and potentially general path for the synthesis of multimodal, multifunctional, and targeted NPs for biomedical applications.

Synthesis and evaluation of a [18F]BODIPY-labeled caspase-inhibitor

BODIPYs (boron dipyrromethenes) are fluorescent dyes which show high stability and quantum yields. They feature the possibility of selective ¹⁸F-fluorination at the boron-core. Attached to a bioactive molecule and labeled with [¹⁸F]fluorine, the resulting compounds are promising tracers for multimodal imaging in vivo and can be used for PET and fluorescence imaging. A BODIPY containing a phenyl and a hydroxy substituent on boron was synthesized and characterized. Fluorinated and hydroxy substituted dyes were coupled to an isatin-based caspase inhibitor via cycloaddition and the resulting compounds were evaluated in vitro in caspase inhibition assays. The metabolic stability and the formed metabolites were investigated by incubation with mouse liver microsomes and LC-MS analysis. Subsequently the fluorophores were labeled with [¹⁸F]fluorine and an in vivo biodistribution study using dynamic PET was performed.

Preparation of [18F]-NHC-BF3 conjugates and their applications in PET imaging

[¹⁸F]-NHC-BF₃ functionalized bioactive molecules can be successfully synthesized by ¹⁸F–¹⁹F isotopic exchange in one labelling step affording highly stable PET probes which can visualize targeted tumours in mice.

Dual-Modality Optical/PET Imaging of PARP1 in Glioblastoma

PURPOSE

The current study presents [(18)F]PARPi-FL as a bimodal fluorescent/positron emission tomography (PET) agent for PARP1 imaging.

PROCEDURES

[(18)F]PARPi-FL was obtained by (19)F/(18)F isotopic exchange and PET experiments, biodistribution studies, surface fluorescence imaging, and autoradiography carried out in a U87 MG glioblastoma mouse model.

RESULTS

[(18)F]PARPi-FL showed high tumor uptake in vivo and ex vivo in small xenografts (< 2 mm) with both PET and optical imaging technologies. Uptake of [(18)F]PARPi-FL in blocked U87 MG tumors was reduced by 84 % (0.12 ± 0.02 %injected dose/gram (%ID/g)), showing high specificity of the binding. PET imaging showed accumulation in the tumor (1 h p.i.), which was confirmed by ex vivo phosphor autoradiography.

CONCLUSIONS

The fluorescent component of [(18)F]PARPi-FL enables cellular resolution optical imaging, while the radiolabeled component of [(18)F]PARPi-FL allows whole-body deep-tissue imaging of malignant growth.

Fluorine-18 patents (2009-2015). Part 2: new radiochemistry

Fluorine-18 ((18)F) is one of the most common positron-emitting radionuclides used in the synthesis of positron emission tomography radiotracers due to its ready availability, convenient half-life and outstanding imaging properties. In Part 1 of this review, we presented the first analysis of patents issued for novel radiotracers labeled with fluorine-18. In Part 2, we follow-up with a focus on patents issued for new radiochemistry methodology using fluorine-18 issued between January 2009 and December 2015.

Synthesis and Evaluation of [(18) F]-Ammonium BODIPY Dyes as Potential Positron Emission Tomography Agents for Myocardial Perfusion Imaging

Recently, we demonstrated the potential of a [(18) F]-trimethylammonium BODIPY dye for cardiac imaging. This is the first example of the use of the [(18) F]-ammonium BODIPY dye for positron emission tomography (PET) myocardial perfusion imaging (MPI). In this report, we extend our study to other ammonium BODIPY dyes with different nitrogen substituents. These novel ammonium BODIPY dyes were successfully prepared and radiolabeled by the SnCl4 -assisted (18) F-(19) F isotopic exchange method. The microPET results and the biodistribution data reveal that nitrogen substituent changes have a significant effect on the in vivo and pharmacological properties of the tracers. Of the novel [(18) F]-ammonium BODIPY dyes prepared in this work, the [(18) F]-dimethylethylammonium BODIPY is superior in terms of myocardium uptake and PET imaging contrast. These results support our hypothesis that the ammonium BODIPY dyes have a great potential for use as PET/optical dual-modality MPI probes.

Synthesis and spectroscopic properties of β,β'-dibenzo-3,5,8-triaryl-BODIPYs

A series of β,β'-bicyclo-3,5-diaryl-BODIPYs were synthesized from the corresponding β,β'-bicyclo-3,5-diiodo-BODIPYs (1a,b) via Pd(0)-mediated Suzuki cross-coupling reactions in 82-92% yields. Subsequent aromatization with DDQ afforded the corresponding β,β'-dibenzo-aryl-BODIPYs, which showed red-shifted absorptions and emissions in the near-IR range. The dibenzo-appended BODIPYs showed characteristic 1H-, 13C-, 11B- and 19F-NMR shifts, and nearly planar conformations by X-ray crystallography.

Synthesis and in vivo stability studies of [18F]-zwitterionic phosphonium aryltrifluoroborate/indomethacin conjugates

Conjugation of ortho-phosphonium phenyltrifluoroborates with indomethacin affords conjugates which have been radiolabeled by ¹⁸F–¹⁹F isotopic exchange in aqueous solutions and imaged by positron emission tomography in mice.

Development of PEGylated peptide probes conjugated with (18)F-labeled BODIPY for PET/optical imaging of MT1-MMP activity

Since the processing activity of the matrix metalloproteinase MT1-MMP regulates various cellular functions such as motility, invasion, growth, differentiation and apoptosis, precise in vivo evaluation of MT1-MMP activity in cancers can provide beneficial information for both basic and clinical studies. For this purpose, we designed a cleavable Positron Emission Tomography (PET)/optical imaging probe consisting of BODIPY650/665 and polyethylene glycol (PEG) conjugated to opposite ends of MT1-MMP substrate peptides. We used in vitro and in vivo fluorescence experiments to select suitable substrate peptide sequences and PEG sizes for the MT1-MMP probes and obtained an optimized structure referred to here as MBP-2k. Radiofluorinated MBP-2k ([(18)F]MBP-2k) was then successfully synthesized via an (18)F-(19)F isotopic exchange reaction in BODIPY650/665. After intravenous injection into mice with xenografted tumors, [(18)F]MBP-2k showed significantly higher accumulation in HT1080 tumors with high MT1-MMP activity than in A549 tumors that have low MT1-MMP activity. Moreover, PET images showed better contrast in HT1080 tumors. These results show that [(18)F]MBP-2k can be used as a hybrid PET/optical imaging agent and is a promising probe for non-invasive monitoring of MT1-MMP activity in cancers. This probe may also efficiently combine targeted tumor imaging with image-guided surgery that could be beneficial for patients in the future.

[(18)F]-Group 13 fluoride derivatives as radiotracers for positron emission tomography

The field of (18)F chemistry is rapidly expanding because of the use of this radionuclide in radiotracers for positron emission tomography (PET). Until recently, most [(18)F]-radiotracers were generated by the direct attachment of (18)F to a carbon in the organic backbone of the radiotracer. The past decade has witnessed the emergence of a new strategy based on the formation of an (18)F-group 13 element bond. This approach, which is rooted in the field of fluoride anion complexation/coordination chemistry, has led to the development of a remarkable family of boron, aluminium and gallium [(18)F]-fluoride anion complexing agents which can be conjugated with peptides and small molecules to generate disease specific PET radiotracers. This review is dedicated to the chemistry of these group 13 [(18)F]-fluorides anion complexing agents and their use in PET. Some of the key fluoride-binding motifs covered in this review include the trifluoroborate unit bound to neutral or cationic electron deficient backbones, the BF2 unit of BODIPY dyes, and AlF or GaF3 units coordinated to multidentate Lewis basic ligands. In addition to describing how these moieties can be converted into their [(18)F]-analogs, this review also dicusses their incorporation into bioconjugates for application in PET.

Thermal property of an aggregation-induced emission fluorophore that forms metal–ligand complexes with Zn(ClO4)2 of salicylaldehyde azine-functionalized polybenzoxazine

A salicylaldehyde azine-functionalized benzoxazine monomer formed zinc ion complexes not only improved the thermal properties but also facilitated ring-opening polymerization.

Fluorescent sensing of fluoride in cellular system

Fluoride ions have the important roles in a lot of physiological activities related with biological and medical system, such as water fluoridation, caries treatment, and bone disease treatment. Great efforts have been made to develop new methods and strategies for F(-) detection in the past decades. Traditional methods for the detection of F(-) including ion chromatography, ion-selective electrodes, and spectroscopic techniques have the limitations in the biomedicine research. The fluorescent probes for F(-) are very promising that overcome some drawbacks of traditional fluoride detection methods. These probes exhibit high selectivity, high sensitivity as well as quick response to the detection of fluoride anions. The review commences with a brief description of photophysical mechanisms for fluorescent probes for fluoride, including photo induced electron transfer (PET), intramolecular charge transfer (ICT), fluorescence resonance energy transfer (FRET), and excited-state intramolecular proton transfer (ESIPT). Followed by a discussion about common dyes for fluorescent fluoride probes, such as anthracene, naphalimide, pyrene, BODIPY, fluorescein, rhodamine, resorufin, coumarin, cyanine, and near-infrared (NIR) dyes. We divide the fluorescent probes for fluoride in cellular application systems into nine groups, for example, type of hydrogen bonds, type of cleavage of Si-O bonds, type of Si-O bond cleavage and cylization reactions, etc. We also review the recent reported carriers in the delivery of fluorescent fluoride probes. Seventy-four typical fluorescent fluoride probes are listed and compared in detail, including quantum yield, reaction medium, excitation and emission wavelengths, linear detection range, selectivity for F(-), mechanism, and analytical applications. Finally, we discuss the future challenges of the application of fluorescent fluoride probes in cellular system and in vivo. We wish that more and more excellent fluorescent fluoride probes will be developed and applied in the biomedicine field in the future.