Design, synthesis, and evaluation of coumarin-based molecular probes for imaging of myelination

Shining a Light on Venom-Peptide Receptors: Venom Peptides as Targeted Agents for In Vivo Molecular Imaging

Molecular imaging has revolutionised the field of biomedical research by providing a non-invasive means to visualise and understand biochemical processes within living organisms. Optical fluorescent imaging in particular allows researchers to gain valuable insights into the dynamic behaviour of a target of interest in real time. Ion channels play a fundamental role in cellular signalling, and they are implicated in diverse pathological conditions, making them an attractive target in the field of molecular imaging. Many venom peptides exhibit exquisite selectivity and potency towards ion channels, rendering them ideal agents for molecular imaging applications. In this review, we illustrate the use of fluorescently-labelled venom peptides for disease diagnostics and intraoperative imaging of brain tumours and peripheral nerves. Finally, we address challenges for the development and clinical translation of venom peptides as nerve-targeted imaging agents.

Synthesis, DFT studies on a series of tunable quinoline derivatives

The synthesis, Density Functional Theory (DFT) calculations, and photo physical characteristics of a range of quinoline derivatives have been described in the present work. Initially, the innovative derivatives are synthesized through the cyclization of 2-amino-5-nitrobenzophenone with either acetyl acetone or ethyl acetoacetate, followed by reducing the nitro group to an amine. Subsequently, these compounds undergo an acid-amine cross-coupling reaction. The investigation shows the DFT and photo physical properties of these substances. It is noteworthy that compound 6z exhibits the most remarkable Stokes shift among the fluorophores investigated. Furthermore, the research also provides insights into the electrophilicity index, Electronegativity, chemical potential, chemical hardness and softness properties. These properties are determined by utilizing Density Functional Theory (DFT) calculations and evaluating electron potential efficiency and using computational methods Time-Dependent Density Functional Theory (TD-DFT) to predict absorption spectra in molecules at the B3LYP/6-31G'(d,p) level/basis.

Exploring the impact of novel thiazole-pyrazole fused benzo-coumarin derivatives on human serum albumin: Synthesis, photophysical properties, anti-cholinergic activity, and interaction studies

Derivatives of thiazole-pyrazole fused benzo-coumarin compounds were successfully synthesized and characterized, followed by a comprehensive spectroscopic investigation on various photophysical properties in different media. The multipronged approach using steady state and time resolved fluorescence spectroscopy pointed out the impact of substitution in the estimated spectroscopic and other physicochemical properties of the systems. Further, the evaluation of anti-acetylcholinesterase (anti-AChE) activity yielded significant insight into the therapeutic potential of the synthesized coumarinyl compounds for the treatment of Alzheimer's disease (AD). The findings revealed a non-competitive mode of inhibition mechanism, with an estimated IC50 value of 67.72 ± 2.00 nM observed for one of the investigated systems as AChE inhibitor. Notably, this value is even lower than that of an FDA-approved AD drug Donepezil (DON), indicating the enhanced potency of the coumarin derivatives in inhibiting AChE. Interestingly, significant diminution in inhibition was observed in presence of human serum albumin (HSA) as evidenced by the relative increase in IC50 value by 8 ∼ 39 % in different cases, which emphasized the role of albumin proteins to control therapeutic efficacies of potential medications. In-depth spectroscopic and in-silico analysis quantified the nature of interactions of the investigated systems with HSA and AChE. Overall, the outcomes of this study provide significant understanding into the biophysical characteristics of novel thiazole-pyrazole fused benzo-coumarin systems, which could aid in the development of new cholinergic agents for the treatment of AD and materials based on coumarin motifs.

Fluorescence imaging of peripheral nerve function and structure

Peripheral nerve injuries are common and can cause catastrophic consequences. Although peripheral nerves have notable regenerative capacity, full functional recovery is often challenging due to a number of factors, including age, the type of injury, and delayed healing, resulting in chronic disorders that cause lifelong miseries and significant financial burdens. Fluorescence imaging, among the various techniques, may be the key to overcome these restrictions and improve the prognosis because of its feasibility and dynamic real-time imaging. Intraoperative dynamic fluorescence imaging allows the visualization of the morphological structure of the nerve so that surgeons can reduce the incidence of medically induced injury. Axoplasmic transport-based neuroimaging allows the visualization of the internal transport function of the nerve, facilitating early, objective, and accurate assessment of the degree of regenerative repair, allowing early intervention in patients with poor recovery, thereby improving prognosis. This review briefly discusses peripheral nerve fluorescent dyes that have been reported or could potentially be employed, with a focus on their role in visualizing the nerve's function and anatomy.

Photoredox Catalysis-Enabled C-H Difluoromethylation of Heteroarenes with Pentacoordinate Phosphorane as the Reagent

Difluoromethylated heterocyclic compounds have found broad applications in numerous bioactive molecules. Herein, we report photoredox catalysis-induced direct C-H difluoromethylation of heterocycles by using bis(difluoromethyl) pentacoordinate phosphorane (PPh3(CF2H)2, 1) as the reagent. A variety of heterocycles, such as quinoxalin-2(1H)-one, thiophene, indole, and coumarin, are readily tailored with a difluoromethyl group. The method is featured as transition-metal-free by using an organic compound Erythrosin B as the catalyst and O2 as the oxidant.

Synthesis and bioactivity evaluation of a myelin-specific contrast agent for magnetic resonance imaging of myelination in central nervous system

Demyelination exists in many neurological diseases of nervous system, such as stroke. Currently, magnetic resonance imaging (MRI) has been the main tool for diagnosing and monitoring the myelin related diseases. However, the conventional MRI unable to distinguish demyelinating lesions from other inflammatory lesions. To address this problem, we have designed and prepared a myelin specific magnetic resonance contrast agent, Gd-DTDAS, which was based myelin specific moiety MeDAS^g and Gd-DTPA^h. In this work, we verified the specificity and sensitivity of Gd-DTDAS to myelin. Moreover, we investigated the specific binding ability of Gd-DTDAS to myelin sheath in the MCAO miceⁱ models. The in vivo imaging results showed that Gd-DTDAS can bind to the undamaged myelin sheath in the BBB disruption areas, and in turn reduce the relaxation time. The fluorescence images also showed significant fluorescence in the brain right infarct area of the MCAO model mice with administration of Gd-DTDAS. The above results confirmed that Gd-DTDAS could be preferentially distributed in areas with high myelination and can detect focally induced demyelination.

Alkyl esters of 7-hydroxycoumarin-3-carboxylic acid as potent tissue-specific uncouplers of oxidative phosphorylation: Involvement of ATP/ADP translocase in mitochondrial uncoupling

An impressive body of evidence has been accumulated now on sound beneficial effects of mitochondrial uncouplers in struggling with the most dangerous pathologies such as cancer, infective diseases, neurodegeneration and obesity. To increase their efficacy while gaining further insight in the mechanism of the uncoupling action has been remaining a challenge. Encouraged by our previous promising results on lipophilic derivatives of 7-hydroxycoumarin-4-acetic acid (UB-4 esters), here, we use a 7-hydroxycoumarin-3-carboxylic acid scaffold to synthesize a new series of 7-hydroxycoumarin (umbelliferone, UB)-derived uncouplers of oxidative phosphorylation - alkyl esters of umbelliferone-3-carboxylic acid (UB-3 esters) with varying carbon chain length. Compared to the UB-4 derivatives, UB-3 esters proved to be stronger uncouplers: the most effective of them caused a pronounced increase in the respiration rate of isolated rat heart mitochondria (RHM) at submicromolar concentrations. Both of these series of UB derivatives exhibited a striking difference between their uncoupling patterns in mitochondria isolated from liver and heart or kidney, namely: a pronounced but transient decrease in membrane potential, followed by its recovery, was observed after the addition of these compounds to isolated rat liver mitochondria (RLM), while the depolarization of RHM and rat kidney mitochondria (RKM) was rather stable under the same conditions. Interestingly, partial reversal of this depolarization in RHM and RKM was caused by carboxyatractyloside, an inhibitor of ATP/ADP translocase, thereby pointing to the involvement of this mitochondrial membrane protein in the uncoupling activity of both UB-3 and UB-4 esters. The fast membrane potential recovery in RLM uncoupled by the addition of the UB esters was apparently associated with hydrolysis of these compounds, catalyzed by mitochondrial aldehyde dehydrogenase (ALDH2), being in high abundance in liver compared to other tissues. Protonophoric properties of the UB derivatives in isolated mitochondria were confirmed by measurements of RHM swelling in the presence of potassium acetate. In model bilayer lipid membranes (BLM), proton-carrying activity of UB-3 esters was demonstrated by measuring fluorescence response of the pH-dependent dye pyranine in liposomes. Electrophysiological experiments on identified neurons from Lymnaea stagnalis demonstrated low neurotoxicity of UB-3 esters. Resazurin-based cell viability assay showed low toxicity of UB-3 esters to HEK293 cells and primary human fibroblasts. Thus, the present results enable us to consider UB-3 esters as effective tissue-specific protonophoric mitochondrial uncouplers.

Bulky selenium ligand stabilized trans-palladium dichloride complexes as catalyst for silver-free decarboxylative coupling of coumarin-3-carboxylic acids

This report describes synthesis of three new trans -palladium dichloride complexes of bulky selenium ligands. These complexes possess a Cl-Pd-Cl rotor spoke attached to a Se-Pd-Se axle. The new ligands and palladium complexes ( C1 - C3 ) were characterized with the help of NMR, HRMS, UV-Vis., IR, and elemental analysis. The single crystal structure of metal complex C2 confirmed a square planer geometry of complex with trans -orientation. The X-ray structure revealed intramolecular secondary interactions (SeCH---Cl) between chlorine of PdCl 2 and CH 2 proton of selenium ligand. Variable temperature NMR data shows coalescence of diastereotopic protons, which indicates pyramidal inversion of selenium atom at elevated temperature. The relaxed potential energy scan of C2 suggests a rotational barrier of ~12.5 kcal/mol for rotation of chlorine atom through Cl-Pd-Cl rotor. The complex C3 possess dual intramolecular secondary interactions (OCH 2 ---Cl and SeCH 2 ---Cl) with stator ligand. Molecular rotor C2 was found to be most efficient catalyst for the decarboxylative Heck-coupling under mild reaction conditions. The protocol is applicable to a broad range of substrates with large functional group tolerance and low catalyst loading (2.5 mol %). The mechanism of decarboxylative Heck-coupling reaction was investigated through experimental and computational studies. Importantly the reaction works under silver-free conditions which reduces the cost of overall protocol. Further, the catalyst also worked for decarboxylative arylation and decarboxylative Suzuki-Miyaura coupling reactions with good yields of the coupled products.

3-Phenylcoumarins as a Privileged Scaffold in Medicinal Chemistry: The Landmarks of the Past Decade

3-Phenylcoumarins are a family of heterocyclic molecules that are widely used in both organic and medicinal chemistry. In this overview, research on this scaffold, since 2010, is included and discussed, focusing on aspects related to its natural origin, synthetic procedures and pharmacological applications. This review paper is based on the most relevant literature related to the role of 3-phenylcoumarins in the design of new drug candidates. The references presented in this review have been collected from multiple electronic databases, including SciFinder, Pubmed and Mendeley.

Positron emission tomography in multiple sclerosis - straight to the target

Following the impressive progress in the treatment of relapsing-remitting multiple sclerosis (MS), the major challenge ahead is the development of treatments to prevent or delay the irreversible accumulation of clinical disability in progressive forms of the disease. The substrate of clinical progression is neuro-axonal degeneration, and a deep understanding of the mechanisms that underlie this process is a precondition for the development of therapies for progressive MS. PET imaging involves the use of radiolabelled compounds that bind to specific cellular and metabolic targets, thereby enabling direct in vivo measurement of several pathological processes. This approach can provide key insights into the clinical relevance of these processes and their chronological sequence during the disease course. In this Review, we focus on the contribution that PET is making to our understanding of extraneuronal and intraneuronal mechanisms that are involved in the pathogenesis of irreversible neuro-axonal damage in MS. We consider the major challenges with the use of PET in MS and the steps necessary to realize clinical benefits of the technique. In addition, we discuss the potential of emerging PET tracers and future applications of existing compounds to facilitate the identification of effective neuroprotective treatments for patients with MS.

Coumarins as Tool Compounds to Aid the Discovery of Selective Function Modulators of Steroid Hormone Binding Proteins

Steroid hormones play an essential role in a wide variety of actions in the body, such as in metabolism, inflammation, initiating and maintaining sexual differentiation and reproduction, immune functions, and stress response. Androgen, aromatase, and sulfatase pathway enzymes and nuclear receptors are responsible for steroid biosynthesis and sensing steroid hormones. Changes in steroid homeostasis are associated with many endocrine diseases. Thus, the discovery and development of novel drug candidates require a detailed understanding of the small molecule structure–activity relationship with enzymes and receptors participating in steroid hormone synthesis, signaling, and metabolism. Here, we show that simple coumarin derivatives can be employed to build cost-efficiently a set of molecules that derive essential features that enable easy discovery of selective and high-affinity molecules to target proteins. In addition, these compounds are also potent tool molecules to study the metabolism of any small molecule.

Synthesis and biological evaluation of radioiodinated 3-phenylcoumarin derivatives targeting myelin in multiple sclerosis

Myelin is a lipid multilayer involved in the rate of nerve transmission, and its loss is a pathological feature of multiple sclerosis in brains. Since in vivo imaging of myelin may be useful for drug development, early diagnosis, and monitoring the disease stage, we designed, synthesized, and evaluated eight novel radioiodinated 3-phenylcoumarin derivatives as imaging probes targeting myelin. In the biodistribution study using normal mice, all compounds displayed sufficient brain uptake, ranging from 2.5 to 5.0% ID/g, at 2 min postinjection. On ex vivo autoradiography, [¹²⁵I]18 and [¹²⁵I]21, which have a dimethylamino group, showed high binding affinity for myelin in the normal mouse brain. In addition, the radioactivity accumulation of [¹²⁵I]21 in the white matter of the spinal cord in the experimental autoimmune encephalomyelitis mice was lower than that in naive mice. These results suggest that [¹²³I]21 shows potential as a single photon emission computed tomography probe targeting myelin.

Nerve Segmentation with Deep Learning from Label-Free Endoscopic Images Obtained Using Coherent Anti-Stokes Raman Scattering

Semantic segmentation with deep learning to extract nerves from label-free endoscopic images obtained using coherent anti-Stokes Raman scattering (CARS) for nerve-sparing surgery is described. We developed a CARS rigid endoscope in order to identify the exact location of peripheral nerves in surgery. Myelinated nerves are visualized with a CARS lipid signal in a label-free manner. Because the lipid distribution includes other tissues as well as nerves, nerve segmentation is required to achieve nerve-sparing surgery. We propose using U-Net with a VGG16 encoder as a deep learning model and pre-training with fluorescence images, which visualize the lipid distribution similar to CARS images, before fine-tuning with a small dataset of CARS endoscopy images. For nerve segmentation, we used 24 CARS and 1,818 fluorescence nerve images of three rabbit prostates. We achieved label-free nerve segmentation with a mean accuracy of 0.962 and an F1 value of 0.860. Pre-training on fluorescence images significantly improved the performance of nerve segmentation in terms of the mean accuracy and F1 value (p<0.05). Nerve segmentation of label-free endoscopic images will allow for safer endoscopic surgery, while reducing dysfunction and improving prognosis after surgery.

Fluorescence Imaging of Nerves During Surgery

OBJECTIVE

This review details the agents for fluorescence-guided nerve imaging in both preclinical and clinical use to identify factors important in selecting nerve-specific fluorescent agents for surgical procedures.

BACKGROUND

Iatrogenic nerve injury remains a significant cause of morbidity in patients undergoing surgical procedures. Current real-time identification of nerves during surgery involves neurophysiologic nerve stimulation, which has practical limitations. Intraoperative fluorescence-guided imaging provides a complimentary means of differentiating tissue types and pathology. Recent advances in fluorescence-guided nerve imaging have shown promise, but the ideal agent remains elusive.

METHODS

In February 2018, PubMed was searched for articles investigating peripheral nerve fluorescence. Key terms used in this search include: "intraoperative, nerve, fluorescence, peripheral nerve, visualization, near infrared, and myelin." Limits were set to exclude articles exclusively dealing with central nervous system targets or written in languages other than English. References were cross-checked for articles not otherwise identified.

RESULTS

Of the nonspecific agents, tracers that rely on axonal transport showed the greatest tissue specificity; however, neurovascular dyes already enjoy wide clinical use. Fluorophores specific to nerve moieties result in excellent nerve to background ratios. Although noteworthy findings on tissue specificity, toxicity, and route of administration specific to each fluorescent agent were reported, significant data objectively quantifying nerve-specific fluorescence and toxicity are lacking.

CONCLUSIONS

Fluorescence-based nerve enhancement has advanced rapidly over the past 10 years with potential for continued utilization and progression in translational research. An ideal agent would be easily administered perioperatively, would not cross the blood-brain barrier, and would fluoresce in the near-infrared spectrum. Agents administered systemically that target nerve-specific moieties have shown the greatest promise. Based on the heterogeneity of published studies and methods for reporting outcomes, it appears that the development of an optimal nerve imaging agent remains challenging.

Metal-free regioselective C-H chalcogenylation of coumarins/(hetero)arenes at ambient temperature

A novel, practical and metal-free approach for the regioselective selenation of coumarins employing (bis(trifluoroacetoxy)iodo)benzene (PIFA) at room temperature is presented. The developed method is suitable for a wide substrate scope and affords 3-selenyl coumarins in good to excellent yields with high selectivity. A radical mechanism is proposed for this new transformation. Furthermore, the application of sulfenylation with coumarines and selenation with other (hetero)arenes in this transformation is successful.

Spectral Properties of Highly Emissive Derivative of Coumarin with N,N-Diethylamino, Nitrile and Tiophenecarbonyl Moieties in Water-Methanol Mixture

The new derivative of coumarin (E)-3-[7-(diethyloamino)-2-oxo-chromen-3yl]-2-(tiophene-2-carbonyl)prop-2-enenitrile (NOSQ) was easy synthesized with commercial substrates as a result of the search of new Michael type addition sensors based on coumarins. Spectral properties of highly emissive NOSQ were investigated by steady state analysis (absorption and fluorescence measurements) and time-resolved analysis (fluorescence lifetime measurements). The effect of water-methanol mixture on the photophysical properties of the NOSQ molecule was analyzed. With increasing of volumetric fraction of water the intensity of absorbance and fluorescence was strongly reduced. The NOSQ quantum yield in methanol was quite high and the first portions of water caused a significant increase in this value. Water, which is usually a quencher, in this case caused the increase in the quantum yield. The fluorescence lifetimes had second-order decay and the values of fluorescence lifetime increased with increasing alcohol content. Density functional theory (DFT) calculations and experimental data remained in agreement and showed that the interaction between the NOSQ molecule and the solvent affects the appearance of the new conformer.

Recent Advances in Live Imaging of Cells of the Oligodendrocyte Lineage

Myelination is an important process that takes place also in the periphery during development and in the adulthood. Myelin serves as an electric isolator for axons, leading to a fast conduction of the action potential, and provides trophic support for the axon, both aspects highly important for the proper function of the nervous system. In the central nervous system, myelination starts shortly after birth and cells from the oligodendrocyte lineage tightly regulate this process during the whole life span. Initially, it was thought that under physiological conditions myelin generation only occurs in early postnatal development and that myelination stops at early adult ages. Historically, the process of myelination has mainly been studied in fixed tissue, and predominantly analyzed by electron microscopy, bringing valuable insights in the structure and distribution of myelin in the central nervous system. Nevertheless, the outdated notion of the static nature of myelin during adulthood was challenged in the past decades by the development of new techniques bringing in a new picture of a lively structure that is in constant remodeling under physiological and disease conditions. As fixed tissue can only provide information at a specific timepoint, the necessity of new techniques to study this process in vivo has become clear. In this chapter, we will review some of the latest techniques developed in order to study myelin and the oligodendrocyte lineage, as these cells are important for the formation and restructuration of the myelin. We will also introduce a protocol to prepare a cranial window to study NG2-glia (also known as oligodendrocyte progenitor cells) of the cerebral cortex in vivo, by 2-photon laser scanning microscopy. However, this technique can also be performed to study other cell populations or structures such as myelin, which will be discussed in this chapter as well. Despite being simple, this protocol has shown to be powerful to study the oligodendrocyte lineage and potentially is applicable to study myelin in vivo, which could turn into a key technique in the understanding of myelination and other functions that the oligodendrocyte lineage might have under physiological and disease conditions.

Heterogeneously Catalyzed Pechmann Condensation Employing the Tailored Zn0.925Ti0.075O NPs: Synthesis of Coumarin

A novel heterogeneous catalytic method was developed for the synthesis of coumarin and its derivatives using the Ti(IV)-doped ZnO matrix forming catalyst Zn_0.925Ti_0.075O having a high surface area and good Lewis acidity. The catalyst shows high activity toward a broad spectrum of the substituted phenols with β-ketoesters such as ethyl acetoacetate, ethyl butyryl acetate, ethyl benzoyl acetate, and so forth in good yields over short reaction times during the synthesis of coumarins. The methodology was further extended for the synthesis of ayapin molecules. The catalyst also shows recycle activity up to seven cycles with very good stability.

Novel 18F-Labeled Radioligands for Positron Emission Tomography Imaging of Myelination in the Central Nervous System

Myelin is the protective sheath that surrounds nerves in vertebrates to protect axons, which thereby facilitates impulse conduction. Damage to myelin is associated with many neurodegenerative diseases such as multiple sclerosis and also includes spinal cord injury (SCI). The small size of the spinal cord poses formidable challenges to in vivo monitoring of myelination, which we investigated via conducting a structure-activity relationship study to determine the optimum positron-emitting agent to use for imaging myelin using positron emission tomography (PET). From these studies, [¹⁸F]PENDAS was identified as the lead agent to use in conjunction with PET imaging to delineate the integrity of spinal cord myelin. A subsequent in vivo PET imaging study of [¹⁸F]PENDAS in rats with SCI showed promising pharmacokinetic results that justify further development of imaging markers for diagnosing myelin-related diseases. Additionally, [¹⁸F]PENDAS could be valuable in determining the efficacy of therapies that are currently under development.

Visible-light-driven copper-catalyzed aerobic oxidative cascade cyclization of N-tosylhydrazones and terminal alkynes: regioselective synthesis of 3-arylcoumarins

An intuitive visible-light-driven copper-catalyzed process can accomplish regioselective functionalized 3-arylcoumarins via oxidative annulation of simple N-tosylhydrazones with terminal alkynes under O₂ (1 atm.) at room temperature.

Exploring the heterogeneity of MS lesions using positron emission tomography: a reappraisal of their contribution to disability

The biological mechanisms driving disability worsening in multiple sclerosis (MS) are only partly understood. Monitoring changes in lesion load on MRI has a limited predictive value on the progression of clinical disability, and there is an essential need for novel imaging markers specific for the main candidate mechanisms underlying neurodegeneration which include failing myelin repair, innate immune cell activation and gray matter neuronal damage. Positron Emission Tomography (PET) is an imaging technology based on the injection of radiotracers directed against specific molecular targets, which has recently allowed the selective quantification in-vivo of the key biological mechanisms relevant to MS pathophysiology. Pilot PET studies performed in patients with all forms of MS allowed to revisit the contribution of MS lesions to disability worsening and showed that the evolution of lesions toward chronic activation, together with their remyelination profile were relevant predictors of disability worsening. PET offers the opportunity to bridge a critical gap between neuropathology and in-vivo imaging. This technique provides an original approach to disentangle some of the most relevant pathological components driving MS progression, to follow-up their temporal evolution, to investigate their clinical relevance and to evaluate novel therapeutics aimed to prevent disease progression.

Nerve-targeted probes for fluorescence-guided intraoperative imaging

A fundamental goal of many surgeries is nerve preservation, as inadvertent injury can lead to patient morbidity including numbness, pain, localized paralysis and incontinence. Nerve identification during surgery relies on multiple parameters including anatomy, texture, color and relationship to surrounding structures using white light illumination. We propose that fluorescent labeling of nerves can enhance the contrast between nerves and adjacent tissue during surgery which may lead to improved outcomes.

Methods: Nerve binding peptide sequences including HNP401 were identified by phage display using selective binding to dissected nerve tissue. Peptide dye conjugates including FAM-HNP401 and structural variants were synthesized and screened for nerve binding after topical application on fresh rodent and human tissue and in-vivo after systemic IV administration into both mice and rats. Nerve to muscle contrast was quantified by measuring fluorescent intensity after topical or systemic administration of peptide dye conjugate.

Results: Peptide dye conjugate FAM-HNP401 showed selective binding to human sural nerve with 10.9x fluorescence signal intensity (1374.44 ± 425.96) compared to a previously identified peptide FAM-NP41 (126.17 ± 61.03). FAM-HNP401 showed nerve-to-muscle contrast of 3.03 ± 0.57. FAM-HNP401 binds and highlight multiple human peripheral nerves including lower leg sural, upper arm medial antebrachial as well as autonomic nerves isolated from human prostate.

Conclusion: Phage display has identified a novel peptide that selectively binds to ex-vivo human nerves and in-vivo using rodent models. FAM-HNP401 or an optimized variant could be translated for use in a clinical setting for intraoperative identification of human nerves to improve visualization and potentially decrease the incidence of intra-surgical nerve injury.

Development of a PET radioligand for potassium channels to image CNS demyelination

Central nervous system (CNS) demyelination represents the pathological hallmark of multiple sclerosis (MS) and contributes to other neurological conditions. Quantitative and specific imaging of demyelination would thus provide critical clinical insight. Here, we investigated the possibility of targeting axonal potassium channels to image demyelination by positron emission tomography (PET). These channels, which normally reside beneath the myelin sheath, become exposed upon demyelination and are the target of the MS drug, 4-aminopyridine (4-AP). We demonstrate using autoradiography that 4-AP has higher binding in non-myelinated and demyelinated versus well-myelinated CNS regions, and describe a fluorine-containing derivative, 3-F-4-AP, that has similar pharmacological properties and can be labeled with ¹⁸F for PET imaging. Additionally, we demonstrate that [¹⁸F]3-F-4-AP can be used to detect demyelination in rodents by PET. Further evaluation in Rhesus macaques shows higher binding in non-myelinated versus myelinated areas and excellent properties for brain imaging. Together, these data indicate that [¹⁸F]3-F-4-AP may be a valuable PET tracer for detecting CNS demyelination noninvasively.

Dye Tool Box for a Fluorescence Enhancement Immunoassay

Immunochemical analytical methods are very successful in clinical diagnostics and are nowadays also emerging in the control of food as well as monitoring of environmental issues. Among the different immunoassays, luminescence based formats are characterized by their outstanding sensitivity making this format especially attractive for future applications. The need for multiparameter detection capabilities calls for a tool box of dye labels in order to transduce the biochemical reaction into an optically detectable signal. Here, in a multiparameter approach each analyte may be detected by a different dye with a unique emission color (covering the blue to red spectral range) or a unique luminescence decay kinetics. In the case of a competitive immunoassay format for each of the different dye labels an individual antibody would be needed. In the present paper a slightly modified approach is presented using a 7-aminocoumarin unit as the basic antigen against which highly specific antibodies were generated. Leaving the epitope region in the dyes unchanged but introducing a side group in positon 3 of the coumarin system allowed us to tune the optical properties of the coumarin dyes without the necessity of new antibody generation. Upon modification of the parent coumarin unit the full spectral range from blue to deep red was accessed. In the manuscript the photophysical characterization of the coumarin derivatives and their corresponding immunocomplexes with two highly specific antibodies is presented. The coumarin dyes and their immunocomplexes were characterized by steady-state and time-resolved absorption as well as emission spectroscopy. Moreover, fluorescence depolarization measurements were carried out to complement the data stressing the different binding modes of the two antibodies. The binding modes were evaluated using the photophysics of 7-aminocoumarins and how it was affected in the respective immunocomplexes, namely, the formation of the intramolecular charge transfer (ICT) as well as the twisted intramolecular charge transfer (TICT). In contrast to other antibody-dye pairs reported a distinct fluorescence enhancement upon formation of the antibody-dye complex up to a factor of 50 was found. Because of the easy emission color tuning by tailoring the coumarin substitution for the antigen binding in nonrelevant position 3 of the parent molecule, a dye tool box is on hand which can be used in the construction of competitive multiparameter fluorescence enhancement immunoassays (FenIA).

Imaging Central Nervous System Demyelination and Remyelination by Positron-Emission Tomography

Positron Emission Tomography (PET), an imaging technique based on the injection of radiotracers directed against specific biological targets within brain tissues, within brain tissues, is a specific and sensitive technique which offers the unique opportunity to quantify myelin dynamics in the central nervous system. Several stilbene and benzothiazole derivatives have been repurposed to image myelin by PET. In demyelinating and dysmyelinating models, selected radiotracers were shown to reliably quantify demyelination and remyelination, allowing a translational approach in humans. A pilot study in subjects with active relapsing MS using PET and the most available benzothiazole derivative, [¹¹C]PIB, supported the hypothesis that this technique is able to quantify myelin content in multiple sclerosis (MS) lesions and to capture dynamic demyelination and remyelination over time. This study highlighted for the first time in vivo the prognostic value of individual profiles of remyelination on the disease course. In future, the clinical application of myelin PET will be pushed forward thanks to the availability of novel fluorinated tracers for myelin, together with the setting up of non invasive quantification procedures and the use of powerful PET-MR systems. This will enable to address in vivo critical unanswered questions about the pathogenesis of remyelination, and to measure the efficacy of emerging promyelinating drugs in early-phase therapeutic trials.

Regioselective C-3 arylation of coumarins with arylhydrazines via radical oxidation by potassium permanganate

An efficient protocol for oxidative C-3 arylation of coumarins with arylhydrazine has been developed using potassium permanganate as an oxidant. The arylated coumarins with different electronic properties were obtained in moderate to good yields. The developed protocol for direct C-3 arylation of coumarins could be extended to quinolinones.

Design, Synthesis, and Evaluation of Fluorinated Radioligands for Myelin Imaging

Myelination is one of the fundamental processes in vertebrates. A major challenge is to quantitatively image myelin distribution in the central nervous system. For this reason, we designed and synthesized a series of fluorinated radioligands that can be radiolabeled as radiotracers for positron emission tomography (PET) imaging of myelin. These newly developed radioligands readily penetrate the blood-brain barrier and selectively bind to myelin membranes in the white matter region. Structure-activity relationship studies of such ligands suggested that optimal permeability could be achieved with calculated lipophilicty in the range of 3-4. After radiolabeling with fluorine-18, the brain uptake and retention of each radioligand were determined by microPET/CT imaging studies. These pharmacokinetic studies led us to identify a lead compound ([(18)F]FMeDAS, 32) with promising in vivo binding properties, which was subsequently validated by ex vivo autoradiography.

Regioselective α-arylation of coumarins and 2-pyridones with phenylhydrazines under transition-metal-free conditions

A transition-metal-free regioselective α-arylation of coumarins and 2-pyridones has been accomplished by the reaction of phenylhydrazines with coumarins or 2-pyridones.

KMnO4/AcOH-mediated C3-selective direct arylation of coumarins with arylboronic acids

An efficient protocol for KMnO₄/AcOH-mediated C3-direct radical arylation of coumarins with arylboronic acids to afford 3-arylcoumarin derivatives is described.

An efficient approach toward formation of polycyclic coumarin derivatives via carbocation-initiated [4+2] cycloaddition and atom-economical photo-irradiated cyclization

Polycyclic coumarin derivatives were easily prepared by carbocation initiated [4+2] cycloaddition of propargyl silyl ethers with ynamides and fluorescent analysis-oriented photo-irradiated cyclization.

Radical C–H functionalization to construct heterocyclic compounds

Radical C–H functionalization is a promising and dramatic approach to synthesize heterocyclic compounds with high efficiency and environmental sustainability.

Quantification of [(11)C]PIB PET for imaging myelin in the human brain: a test-retest reproducibility study in high-resolution research tomography

An accurate in vivo measure of myelin content is essential to deepen our insight into the mechanisms underlying demyelinating and dysmyelinating neurological disorders, and to evaluate the effects of emerging remyelinating treatments. Recently [(11)C]PIB, a positron emission tomography (PET) tracer originally conceived as a beta-amyloid marker, has been shown to be sensitive to myelin changes in preclinical models and humans. In this work, we propose a reference-region methodology for the voxelwise quantification of brain white-matter (WM) binding for [(11)C]PIB. This methodology consists of a supervised procedure for the automatic extraction of a reference region and the application of the Logan graphical method to generate distribution volume ratio (DVR) maps. This approach was assessed on a test-retest group of 10 healthy volunteers using a high-resolution PET tomograph. The [(11)C]PIB PET tracer binding was shown to be up to 23% higher in WM compared with gray matter, depending on the image reconstruction. The DVR estimates were characterized by high reliability (outliers <1%) and reproducibility (intraclass correlation coefficient (ICC) >0.95). [(11)C]PIB parametric maps were also found to be significantly correlated (R(2)>0.50) to mRNA expressions of the most represented proteins in the myelin sheath. On the contrary, no correlation was found between [(11)C]PIB imaging and nonmyelin-associated proteins.