Polyfluorinated bis-styrylbenzenes as amyloid-β plaque binding ligands

A closer look at amyloid ligands, and what they tell us about protein aggregates

The accumulation of amyloid fibrils is characteristic of neurodegenerative diseases such as Alzheimer's disease (AD) and Parkinson's disease. Detecting these fibrils with fluorescent or radiolabelled ligands is one strategy for diagnosing and better understanding these diseases. A vast number of amyloid-binding ligands have been reported in the literature as a result. To obtain a better understanding of how amyloid ligands bind, we have compiled a database of 3457 experimental dissociation constants for 2076 unique amyloid-binding ligands. These ligands target Aβ, tau, or αSyn fibrils, as well as relevant biological samples including AD brain homogenates. From this database significant variation in the reported dissociation constants of ligands was found, possibly due to differences in the morphology of the fibrils being studied. Ligands were also found to bind to Aβ(1-40) and Aβ(1-42) fibrils with similar affinities, whereas a greater difference was found for binding to Aβ and tau or αSyn fibrils. Next, the binding of ligands to fibrils was shown to be largely limited by the hydrophobic effect. Some Aβ ligands do not fit into this hydrophobicity-limited model, suggesting that polar interactions can play an important role when binding to this target. Finally several binding site models were outlined for amyloid fibrils that describe what ligands target what binding sites. These models provide a foundation for interpreting and designing site-specific binding assays.

Regioselective Aromatic Perfluoro-tert-butylation Using Perfluoro-tert-butyl Phenyl Sulfone and Arynes

The selective introduction of perfluoro-tert-butyl group (PFtB, the bulkier analogue of CF₃ group) into arenes has long been sought after but remains a formidable task. We herein report the first general synthetic protocol to realize aromatic perfluoro-tert-butylation. The key to the success is the identification of PFtB phenyl sulfone as a new source of PFtB anion, which reacts with arynes in a highly regioselective manner to afford perfluoro-tert-butylated arenes in high yields. The application of the method is demonstrated by the preparation of sensitive ¹⁹F-labeled NMR probes with an extraordinary resolving ability.

Transient directing group controlled regiodivergent C(sp3)–H and C(sp2)–H polyfluoroalkoxylation of aromatic aldehydes

A novel method for achieving regiodivergent C(sp3)–H and C(sp2)–H polyfluoroalkoxylation in the o-methyl benzaldehyde framework by altering the transient directing group is disclosed.

Perfluoro-tert-butanol: a cornerstone for high performance fluorine-19 magnetic resonance imaging

As a versatile quantification and tracking technology, 19F magnetic resonance imaging (19F MRI) provides quantitative "hot-spot" images without ionizing radiation, tissue depth limit, and background interference. However, the lack of suitable imaging agents severely hampers its clinical application. First, because the 19F signals are solely originated from imaging agents, the relatively low sensitivity of MRI technology requires high local 19F concentrations to generate images, which are often beyond the reach of many 19F MRI agents. Second, the peculiar physicochemical properties of many fluorinated compounds usually lead to low 19F signal intensity, tedious formulation, severe organ retention, etc. Therefore, the development of 19F MRI agents with high sensitivity and with suitable physicochemical and biological properties is of great importance. To this end, perfluoro-tert-butanol (PFTB), containing nine equivalent 19F and a modifiable hydroxyl group, has outperformed most perfluorocarbons as a valuable building block for high performance 19F MRI agents. Herein, we summarize the development and application of PFTB-based 19F MRI agents and analyze the strategies to improve their sensitivity and physicochemical and biological properties. In the context of PFC-based 19F MRI agents, we also discuss the challenges and prospects of PFTB-based 19F MRI agents.

A versatile platform for adding functional properties to amyloid fibrils

Herein we report the design, synthesis, and testing of prototype members of a family of amyloid-binding molecular tools that can manipulate the fibrils by giving them various new functional properties. Potential applications include manipulating disease-relevant fibrils, developing novel functional nanomaterials, and studying the molecular details of fibril structures.

Synthesis of Perfluoro-tert-butyl Tyrosine, for Application in 19F NMR, via a Diazonium-Coupling Reaction

A practical synthesis of the novel highly fluorinated amino acid Fmoc-perfluoro-tert-butyl tyrosine was developed. The sequence proceeds in two steps from commercially available Fmoc-4-NH₂-phenylalanine via diazotization followed by diazonium coupling reaction with perfluoro-tert-butanol. In peptides, perfluoro-tert-butyl tyrosine was detected in 30 s by NMR spectroscopy at 500 nM peptide concentration due to nine chemically equivalent fluorines that are a sharp singlet by ¹⁹F NMR. Perfluoro-tert-butyl ether has an estimated σ_p Hammett substituent constant of +0.30.

A Novel Liposomal Nanoparticle for the Imaging of Amyloid Plaque by Magnetic Resonance Imaging

Amyloid binding molecules with greater hydrophilicity than existing ligands were synthesized. The lead candidate ET6-21 bound amyloid fibrils, and amyloid deposits in dog brain and human brain tissue ex vivo. The ligand was used to prepare novel amyloid-targeted liposomal nanoparticles. The preparation was tested in the Tg2576 and TetO/APP mouse models of amyloid deposition. Gd chelates and Indocyanine green were included in the particles for visualization by MRI and near-infrared microscopy. Upon intravenous injection, the particles successfully traversed the blood-brain barrier in these mice, and bound to the plaques. Magnetic resonance imaging (T1-MRI) conducted 4 days after injection demonstrated elevated signal in the brains of mice with amyloid plaques present. No signal was observed in amyloid-negative mice, or in amyloid-positive mice injected with an untargeted version of the same agent. The MRI results were confirmed by immunohistochemical and fluorescent microscopic examination of mouse brain sections, showing colocalization of the fluorescent tags and amyloid deposits.

Gadolinium-complexed Aβ-binding contrast agents for MRI diagnosis of Alzheimer's Disease

MRI contrast agents, containing peptide sequences that bind β-amyloid and gadolinium ions ligated to DOTA have been synthesized for evaluation in early diagnosis of Alzheimer's Disease in transgenic mice models. A number of brain penetration modifications were incorporated and sufficient amounts of contrast agent in the brain were achieved only by addition of a cationic cell penetration sequence along with the use of microparticle assisted ultrasound activation. In the T1 mode of a MRI scan, the peptide (R2) illuminated areas of brain rich in amyloid plaques.