Synthesis, Biological Evaluation, and Docking Studies of Antagonistic Hydroxylated Arecaidine Esters Targeting mAChRs.

The muscarinic acetylcholine receptor family is a highly sought-after target in drug and molecular imaging discovery efforts aimed at neurological disorders. Hampered by the structural similarity of the five subtypes' orthosteric binding pockets, these efforts largely failed to deliver subtype-selective ligands. Building on our recent successes with arecaidine-derived ligands targeting M1, herein we report the synthesis of a related series of 11 hydroxylated arecaidine esters. Their physicochemical property profiles, expressed in terms of their computationally calculated CNS MPO scores and HPLC-logD values, point towards blood-brain barrier permeability. By means of a competitive radioligand binding assay, the binding affinity values towards each of the individual human mAChR subtypes hM1-hM5 were determined. The most promising compound of this series 17b was shown to have a binding constant towards hM1 in the single-digit nanomolar region (5.5 nM). Similar to our previously reported arecaidine-derived esters, the entire series was shown to act as hM1R antagonists in a calcium flux assay. Overall, this study greatly expanded our understanding of this recurring scaffolds' structure-activity relationship and will guide the development towards highly selective mAChRs ligands.

Unexpected scaffold rearrangement product of pirenzepine found in commercial samples.

Pharmacovigilance aims at a better understanding of the molecular events triggered by medications to prevent adverse effects, which despite significant advances in our analytical repertoire plague the use of drugs until today. In this study, we find that clinically prescribed and commercially available pirenzepine may not be the correct compound. Pirenzepine can undergo an unexpected scaffold rearrangement from the pharmaceutical active ingredient (API) to a previously uncharacterized benzimidazole. The rearrangement occurs under highly acidic conditions, which were believed to favour the dihydrochloride formation of pirenzepine. The rearranged products of pirenzepine and the structurally related telenzepine have significantly decreased affinity for the muscarinic acetylcholine receptor, the pharmacological target of these compounds. Fortunately, in situ rearrangement after oral application is no safety issue, as we show that reaction kinetics in gastric acid prevent rearrangement. The research community should consider appropriate measures to perform reliable receiving inspections in the commercial supply of well described and frequently used chemicals, in particular if experiments yield unexpected results.

Discovery of melanin-concentrating hormone receptor 1 in brown adipose tissue.

Although extensive research on brown adipose tissue (BAT) has stimulated optimism in the battle against obesity and diabetes, BAT physiology and organ crosstalk are not fully understood. Besides BAT, melanin-concentrating hormone (MCH) and its receptor (MCHR1) play an important role in energy homeostasis. Because of the link between hypothalamic MCH neurons and sympathetic BAT activation via ß-adrenoceptors, we investigated the expression and physiological role of the MCHR1 in BAT. MCHR1 was detected in rodent and human BAT with RT-qPCR and western blot analyses. In vivo imaging in rats used the glucose analog [18 F]FDG and the MCHR1-tracer [11 C]SNAP-7941. We found that the ß3-adrenoceptor (ADRB3) agonist CL316,243 increased [11 C]SNAP-7941 uptake in BAT. Additionally, a pharmacological concentration of SNAP-7941-a low-affinity ADRB3 ligand-stimulated [18 F]FDG uptake, reflecting BAT activation. In cultured human adipocytes, CL316,243 induced MCHR1 expression, further supporting a direct interaction between MCHR1 and ADRB3. These findings characterized MCHR1 expression in rodent and human BAT for the first time, including in vitro and in vivo data demonstrating a link between MCHR1 and the ß3-adrenergic system. The presence of MCHR1 in BAT emphasizes the role of BAT in energy homeostasis and may help uncover treatment approaches for obesity.

Synthesis, Biological, and Computational Evaluation of Antagonistic, Chiral Hydrobenzoin Esters of Arecaidine Targeting mAChR M1.

Muscarinic acetylcholine receptors (mAChRs) are a pivotal constituent of the central and peripheral nervous system. Yet, therapeutic and diagnostic applications thereof are hampered by the lack of subtype selective ligands. Within this work, we synthesized and chemically characterized three different stereoisomers of hydrobenzoin esters of arecaidine by NMR, HR-MS, chiral chromatography, and HPLC-logP. All compounds are structurally eligible for carbon-11 labeling and show appropriate stability in Dulbecco's phosphate-buffered saline (DPBS) and F12 cell culture medium. A competitive radioligand binding assay on Chinese hamster ovary cell membranes comprising the human mAChR subtypes M1-M5 showed the highest orthosteric binding affinity for subtype M1 and a strong influence of stereochemistry on binding affinity, which corresponds to in silico molecular docking experiments. Ki values toward M1 were determined as 99 ± 19 nM, 800 ± 200 nM, and 380 ± 90 nM for the (R,R)-, (S,S)-, and racemic (R,S)-stereoisomer, respectively, highlighting the importance of stereochemical variations in mAChR ligand development. All three stereoisomers were shown to act as antagonists toward mAChR M1 using a Fluo-4 calcium efflux assay. With respect to future positron emission tomography (PET) tracer development, the (R,R)-isomer appears especially promising as a lead structure due to its highest subtype selectivity and lowest Ki value.

Enhanced arecoline derivatives as muscarinic acetylcholine receptor M1 ligands for potential application as PET radiotracers.

Supported by their involvement in many neurodegenerative disorders, muscarinic acetylcholine receptors (mAChRs) are an interesting target for PET imaging. Nevertheless, no radiotracer is established in clinical routine. Within this work we aim to develop novel PET tracers based on the structure of arecoline. Fifteen novel arecoline derivatives were synthesized, characterized and tested for their affinity to the mAChRs M1-M5 and the conceivable off-target acetylcholinesterase. Five arecoline derivatives and arecoline were labeled with carbon-11 in good yields. Arecaidine diphenylmethyl ester (3b), arecaidine bis(4-fluorophenyl)methyl ester (3c) and arecaidine (4-bromophenyl)(4-fluorophenyl)methyl ester (3e) showed a tremendous gain in mAChR affinity compared to arecoline and a pronounced subtype selectivity for M1. Metabolic stability and serum protein binding of [11C]3b and [11C]3c were in line with properties of established brain tracers. Nonspecific binding of [11C]3c was prevalent in kinetic and endpoint experiment on living cells as well as in autoradiography on native mouse brain sections, which motivates us to decrease the lipophilicity of this substance class prior to in vivo experiments.

In vitro Radiopharmaceutical Evidence for MCHR1 Binding Sites in Murine Brown Adipocytes.

[11C]SNAP-7941 and its radiofluorinated, fluoro-ethyl derivative [18F]FE@SNAP have been developed as the first positron emission tomography tracers for melanin-concentrating hormone receptor 1 (MCHR1) imaging. Accumulation of these MCHR1 PET-tracers in rat brown adipose tissue (BAT) in vivo provided first indication of MCHR1 expression in rodent BAT. To rule out off-target binding, affinity of both MCHR1 ligands toward adrenergic beta-3 receptors (ADRB3) was examined. Further, specific binding of [11C]SNAP-7941 to brown adipocytes and effects of MCHR1 ligands on brown adipocyte activation were investigated. SNAP-7941 and FE@SNAP evinced to be highly selective toward MCHR1. [11C]SNAP-7941 binding to brown adipocytes was shown to be mainly MCHR1-specific. This data strongly indicates MCHR1 expression in rodent BAT and moreover, a peripheral, anti-obesity effect of MCHR1 antagonists directly exerted in BAT is proposed. Moreover, MCHR1 expression in murine brown adipocytes was confirmed by protein and mRNA analysis. We conclude that MCHR1 PET imaging contributes to basic research in endocrinology by elucidating the involvement of the MCH system in peripheral tissues, such as BAT.

SNAPshots of the MCHR1: a Comparison Between the PET-Tracers [18F]FE@SNAP and [11C]SNAP-7941.

PURPOSE: The melanin-concentrating hormone receptor 1 (MCHR1) has become an important pharmacological target, since it may be involved in various diseases, such as diabetes, insulin resistance, and obesity. Hence, a suitable positron emission tomography radiotracer for the in vivo assessment of the MCHR1 pharmacology is imperative. The current paper contrasts the extensive in vitro, in vivo, and ex vivo assessments of the radiotracers [18F]FE@SNAP and [11C]SNAP-7941 and provides comprehensive information about their biological and physicochemical properties. Furthermore, it examines their suitability for first-in-man imaging studies. PROCEDURES: Kinetic real-time cell-binding studies with [18F]FE@SNAP and [11C]SNAP-7941 were conducted on adherent Chines hamster ovary (CHO-K1) cells stably expressing the human MCHR1 and MCHR2. Small animal imaging studies on mice and rats were performed under displacement and baseline conditions, as well as after pretreatment with the P-glycoprotein/breast cancer resistant protein inhibitor tariquidar. After the imaging studies, detailed analyses of the ex vivo biodistribution were performed. Ex vivo metabolism was determined in rat blood and brain and analyzed at various time points using a quantitative radio-HPLC assay. RESULTS: [11C]SNAP-7941 demonstrates high uptake on CHO-K1-hMCHR1 cells, whereas no uptake was detected for the CHO-K1-hMCHR2 cells. In contrast, [18F]FE@SNAP evinced binding to CHO-K1-hMCHR1 and CHO-K1-hMCHR2 cells. Imaging studies with [18F]FE@SNAP and [11C]SNAP-7941 showed an increased brain uptake after tariquidar pretreatment in mice, as well as in rats, and exhibited a significant difference between the time-activity curves of the baseline and blocking groups. Biodistribution of both tracers demonstrated a decreased uptake after displacement. [11C]SNAP-7941 revealed a high metabolic stability in rats, whereas [18F]FE@SNAP was rapidly metabolized. CONCLUSIONS: Both radiotracers demonstrate appropriate imaging properties for the MCHR1. However, the pronounced metabolic stability as well as superior selectivity and affinity of [11C]SNAP-7941 underlines the decisive superiority over [18F]FE@SNAP.

Pharmacy Practice and Education in Austria.

The PHARMINE (“Pharmacy Education in Europe”) project studied pharmacy practice and education in the European Union (EU) member states. The work was carried out using an electronic survey sent to chosen pharmacy representatives. The surveys of the individual member states are now being published as reference documents for students and staff interested in research on pharmacy education in the EU and in mobility. This paper presents the results of the PHARMINE survey on pharmacy practice and education in Austria. In the light of this, we examine the harmonisation of practice and education in Austria with EU norms.

In vivo evaluation of radiotracers targeting the melanin-concentrating hormone receptor 1: [11C]SNAP-7941 and [18F]FE@SNAP reveal specific uptake in the ventricular system.

The MCHR1 is involved in the regulation of energy homeostasis and changes of the expression are linked to a variety of associated diseases, such as diabetes and adiposity. The study aimed at the in vitro and in vivo evaluation of [11C]SNAP-7941 and [18F]FE@SNAP as potential PET-tracers for the MCHR1. Competitive binding studies with non-radioactive derivatives and small-animal PET/CT and MRI brain studies were performed under baseline conditions and tracer displacement with the unlabelled MCHR1 antagonist (±)-SNAP-7941. Binding studies evinced high binding affinity of the non-radioactive derivatives. Small-animal imaging of [11C]SNAP-7941 and [18F]FE@SNAP evinced high tracer uptake in MCHR1-rich regions of the ventricular system. Quantitative analysis depicted a significant tracer reduction after displacement with (±)-SNAP-7941. Due to the high binding affinity of the non-labelled derivatives and the high specific tracer uptake of [11C]SNAP-7941 and [18F]FE@SNAP, there is strong evidence that both radiotracers may serve as highly suitable agents for specific MCHR1 imaging.

New approaches for the reliable in vitro assessment of binding affinity based on high-resolution real-time data acquisition of radioligand-receptor binding kinetics.

BACKGROUND: Resolving the kinetic mechanisms of biomolecular interactions have become increasingly important in early-phase drug development. Since traditional in vitro methods belong to dose-dependent assessments, binding kinetics is usually overlooked. The present study aimed at the establishment of two novel experimental approaches for the assessment of binding affinity of both, radiolabelled and non-labelled compounds targeting the A3R, based on high-resolution real-time data acquisition of radioligand-receptor binding kinetics. A novel time-resolved competition assay was developed and applied to determine the Ki of eight different A3R antagonists, using CHO-K1 cells stably expressing the hA3R. In addition, a new kinetic real-time cell-binding approach was established to quantify the rate constants k on and k off, as well as the dedicated K d of the A3R agonist [125I]-AB-MECA. Furthermore, lipophilicity measurements were conducted to control influences due to physicochemical properties of the used compounds. RESULTS: Two novel real-time cell-binding approaches were successfully developed and established. Both experimental procedures were found to visualize the kinetic binding characteristics with high spatial and temporal resolution, resulting in reliable affinity values, which are in good agreement with values previously reported with traditional methods. Taking into account the lipophilicity of the A3R antagonists, no influences on the experimental performance and the resulting affinity were investigated. CONCLUSIONS: Both kinetic binding approaches comprise tracer administration and subsequent binding to living cells, expressing the dedicated target protein. Therefore, the experiments resemble better the true in vivo physiological conditions and provide important markers of cellular feedback and biological response.

[(18)F]FE@SNAP-a specific PET tracer for melanin-concentrating hormone receptor 1 imaging?

BACKGROUND: The melanin-concentrating hormone receptor 1 (MCHR1), which is highly expressed in the lateral hypothalamus, plays a key role in energy homeostasis, obesity and other endocrine diseases. Hence, there is a major interest in in vivo imaging of this receptor. A PET tracer would allow non-invasive in vivo visualization and quantification of the MCHR1. The aim of the study was the ex vivo evaluation of the MCHR1 ligand [(18)F]FE@SNAP as a potential PET tracer for the MCHR1. METHODS: [(18)F]FE@SNAP was injected directly into the jugular vein of awake naïve rats for ex vivo brain autoradiography, biodistribution and additional blood metabolite analysis. Blocking experiments were conducted using the unlabeled MCHR1 ligand SNAP-7941. RESULTS: A high uptake of [(18)F]FE@SNAP was observed in the lateral hypothalamus and the ventricular system. Both regions were significantly blocked by SNAP-7941. Biodistribution evinced the highest uptake in the kidneys, adrenals, lung and duodenum. Specific blocking with SNAP-7941 led to a significant tracer reduction in the heart and adrenals. In plasma samples, 47.73 ± 6.1 % of a hydrophilic radioactive metabolite was found 45 min after tracer injection. CONCLUSIONS: Since [(18)F]FE@SNAP uptake was significantly blocked in the lateral hypothalamus, there is strong evidence that [(18)F]FE@SNAP is a highly suitable agent for specific MCHR1 imaging in the central nervous system. Additionally, this finding is supported by the specific blocking in the ventricular system, where the MCHR1 is expressed in the ependymal cells. These findings suggest that [(18)F]FE@SNAP could serve as a useful imaging and therapy monitoring tool for MCHR1-related pathologies.

Synthesis and in silico evaluation of novel compounds for PET-based investigations of the norepinephrine transporter.

Since the norepinephrine transporter (NET) is involved in a variety of diseases, the investigation of underlying dysregulation-mechanisms of the norepinephrine (NE) system is of major interest. Based on the previously described highly potent and selective NET ligand 1-(3-(methylamino)-1-phenylpropyl)-3-phenyl-1,3-dihydro-2H-benzimidaz- ol-2-one (Me@APPI), this paper aims at the development of several fluorinated methylamine-based analogs of this compound. The newly synthesized compounds were computationally evaluated for their interactions with the monoamine transporters and represent reference compounds for PET-based investigation of the NET.

[18F]FE@SUPPY: a suitable PET tracer for the adenosine A3 receptor? An in vivo study in rodents.

PURPOSE: The adenosine A3 receptor (A3R) is involved in cardiovascular, neurological and tumour-related pathologies and serves as an exceptional pharmaceutical target in the clinical setting. A3R antagonists are considered antiinflammatory, antiallergic and anticancer agents, and to have potential for the treatment of asthma, COPD, glaucoma and stroke. Hence, an appropriate A3R PET tracer would be highly beneficial for the diagnosis and therapy monitoring of these diseases. Therefore, in this preclinical in vivo study we evaluated the potential as a PET tracer of the A3R antagonist [(18)F]FE@SUPPY. METHODS: Rats were injected with [(18)F]FE@SUPPY for baseline scans and blocking scans (A3R with MRS1523 or FE@SUPPY, P-gp with tariquidar; three animals each). Additionally, metabolism was studied in plasma and brain. In a preliminary experiment in a mouse xenograft model (mice injected with cells expressing the human A3R; three animals), the animals received [(18)F]FE@SUPPY and [(18)F]FDG. Dynamic PET imaging was performed (60 min in rats, 90 min in xenografted mice). In vitro stability of [(18)F]FE@SUPPY in human and rat plasma was also evaluated. RESULTS: [(18)F]FE@SUPPY showed high uptake in fat-rich regions and low uptake in the brain. Pretreatment with MRS1523 led to a decrease in [(18)F]FE@SUPPY uptake (p = 0.03), and pretreatment with the P-gp inhibitor tariquidar led to a 1.24-fold increase in [(18)F]FE@SUPPY uptake (p = 0.09) in rat brain. There was no significant difference in metabolites in plasma and brain in the treatment groups. However, plasma concentrations of [(18)F]FE@SUPPY were reduced to levels similar to those in rat brain after blocking. In contrast to [(18)F]FDG uptake (p = 0.12), the xenograft model showed significantly increased uptake of [(18)F]FE@SUPPY in the tissue masses from CHO cells expressing the human A3R (p = 0.03). [(18)F]FE@SUPPY was stable in human plasma. CONCLUSION: Selective and significant tracer uptake of [(18)F]FE@SUPPY was found in xenografted mice injected with cells expressing human A3R. This finding supports the strategy of evaluating [(18)F]FE@SUPPY in "humanized animal models". In conclusion, preclinical evaluation points to the suitability of [(18)F]FE@SUPPY as an A3R PET tracer in humans.

Development of potential selective and reversible pyrazoline based MAO-B inhibitors as MAO-B PET tracer precursors and reference substances for the early detection of Alzheimer's disease.

Since high MAO-B levels are present in early stages of AD, the MAO-B system can be designated as an appropriate and prospective tracer target of molecular imaging biomarkers for the detection of early AD. According to the preceding investigations of Mishra et al. the aim of this work was the development of a compound library of selective and reversible MAO-B inhibitors by performing bioisosteric modifications of the core structure of 3-(anthracen-9-yl)-5-phenyl-4,5-dihydro-1H-pyrazoles. In conclusion, 13 new pyrazoline based derivatives have been prepared, which will serve as precursor substances for future radiolabeling as well as reference compounds for the investigation of increased MAO-B levels in AD.

Comparative autoradiographic in vitro investigation of melanin concentrating hormone receptor 1 ligands in the central nervous system.

The MCHR1 is an interesting pharmacological and pharmaceutical target, due to its involvement in pathologies as diabetes, gut inflammation and adiposity. in vivo PET-studies of the MCHR1 in energy homeostasis and diabetes could be of great value for deeper understanding of endocrinological hormone status and consequential pharmacological interactions. Furthermore, PET-tracers would facilitate compound dose selection of MCHR1 antagonists for treatment. Therefore, we developed two potential PET-tracers, [(11)C]SNAP-7941 and [(18)F]FE@SNAP, for the in vivo visualization of this receptor. Aim of this study was a preclinical in vitro evaluation of both unlabeled ligands. Therefore, a comparative autoradiographic investigation on CNS (coronal rat brain and 4 different human brain regions) and peripheral tissues (rat tongue as target and rat testes as non-target region) was conducted. Competition experiments, using the two radioligands [(125)I]-MCH and [(125)I]-S36057, were performed with selective and specific MCHR1 ligands as PMC-3886, a MCHR1 agonist, SNAP-7941 and FE@SNAP, two MCHR1 antagonists. Additionally, immunohistochemical staining with a specific MCHR1 antibody was performed. Specific binding was found in all tissues known to express the MCHR1 as human and rat CNS and peripheral rat tongue tissue. No specific binding was found in the non-target region of rat testes. MCHR1 antibody staining complemented the outcome of the autoradiographic experiments. The compounds SNAP-7941 and FE@SNAP were generally comparable with PMC-3886. Hence, the in vitro autoradiographic study of the unlabeled compounds SNAP-7941 and FE@SNAP further qualifies the potential of the PET-tracers [(11)C]SNAP-7941 and [(18)F]FE@SNAP as useful MCHR1 PET-tracers.

A one-step microwave-assisted synthetic method for an O/S-chemoselective route to derivatives of the first adenosine A3 PET radiotracer.

The synthesis of reference standards and expected in vivo metabolites of the first adenosine A3 PET radiotracer [18F]FE@SUPPY ([18F]fluoroethyl 4,6-diethyl-5-[(ethyl-sulfanyl)carbonyl]-2-phenylpyridine-3-carboxylate) was achieved by using a straightforward microwave assisted alkylation method, which allowed O/S-chemoselective alkylation of the starting material 1 to give each target compound 2-8 in a single step.

Synthesis, radiosynthesis and first in vitro evaluation of novel PET-tracers for the dopamine transporter: [(11)C]IPCIT and [(18)F]FE@IPCIT.

INTRODUCTION: Present data indicate that merging beneficial structural elements from previously published DAT-ligands highest DAT affinity, selectivity and a suitable metabolic profile should be achieved. This combination led to the development of IPCIT and FE@IPCIT. METHODS: Precursor synthesis was done starting from cocaine in a six step reaction. O-[(11)C]-methylation was established using [(11)C]methyl iodide, optimized and subsequently automated. Small scale (18)F-fluroroethylation as well as optimization of reaction parameters and automation were performed. Affinity and selectivity of the candidate substances were tested in standard binding experiments on human membranes. Metabolic stability and blood-brain-barrier (BBB) penetration were determined. RESULTS: Precursor compound, IPCITacid, and reference compounds, IPCIT and FE@IPCIT, were obtained in 4.9%, 12.7% and 4.1% yield, respectively. Automated radiosynthesis of [(11)C]IPCIT yielded 1.9 ± 0.7 GBq (12.5 ± 4%, corrected for decay). Optimum parameters for (18)F-fluoroethylation were 110 °C for 15 min under TBAH catalysis, yielding 67 ± 16 % radiochemical incorporation. Affinity was determined as 1.7 ± 0.6 nM for IPCIT, 1.3 ± 0.2 nM for FE@IPCIT and 37 ± 13 nM for the precursor molecule, IPCIT-acid. Results from in vitro and in silico evaluations revealed high stability but also high lipophilicity. CONCLUSION: Present data indicate high affinity and stability of both IPCIT and FE@IPCIT. Radiolabelling, optimization of reaction parameters and automation succeeded. On the other hand, data concerning BBB-penetration are not promising.

Syntheses of precursors and reference compounds of the melanin-concentrating hormone receptor 1 (MCHR1) tracers [¹¹C]SNAP-7941 and [¹8F]FE@SNAP for positron emission tomography.

The MCH receptor has been revealed as a target of great interest in positron emission tomography imaging. The receptor's eponymous substrate melanin-concentrating hormone (MCH) is a cyclic peptide hormone, which is located predominantly in the hypothalamus with a major influence on energy and weight regulation as well as water balance and memory. Therefore, it is thought to play an important role in the pathophysiology of adiposity, which is nowadays a big issue worldwide. Based on the selective and high-affinity MCH receptor 1 antagonist SNAP-7941, a series of novel SNAP derivatives has been developed to provide different precursors and reference compounds for the radiosyntheses of the novel PET radiotracers [(11)C]SNAP-7941 and [(18)F]FE@SNAP. Positron emission tomography promotes a better understanding of physiologic parameters on a molecular level, thus giving a deeper insight into MCHR1 related processes as adiposity.

Preparation and First Preclinical Evaluation of [(18)F]FE@SNAP: A Potential PET Tracer for the Melanin-Concentrating Hormone Receptor-1 (MCHR1).

The melanin-concentrating hormone (MCH) system is a new target for the treatment of human disorders. Since the knowledge of the MCH system's involvement in a variety of pathologies (obesity, diabetes, and deregulation of metabolic feedback mechanism) is based on in vitro or preclinical studies, a suitable positron emission tomography (PET) tracer needs to be developed. We herein present the preparation and first preclinical evaluation of [(18)F]FE@SNAP - a new PET tracer for MCH receptor-1 (MCHR1). The synthesis was performed using a microfluidic device. Preclinical evaluation included binding affinity, plasma stability, plasma free fraction, stability against the cytochrome P-450 (CYP450) system using liver microsomes, stability against carboxyl-esterase, and methods to assess the penetration of the blood-brain barrier (BBB) such as logD analysis and immobilized artificial membrane (IAM) chromatography. Levels at 374 ± 202 MBq [(18)F]FE@SNAP were obtained after purification. The obtained K d value of [(18)F]FE@SNAP was 2.9 nM. [(18)F]FE@SNAP evinced high stability against carboxylesterase, CYP450 enzymes, and in human plasma. LogD (3.83) and IAM chromatography results (Pm=0.51) were in the same range as for known BBB-penetrating compounds. The synthesis of [(18)F]FE@SNAP was reliable and successful. Due to high binding affinity and stability, [(18)F]FE@SNAP is a promising tracer for MCHR1.

Synthesis and antiproliferative activity of new cytotoxic tri- and tetraazabenzo[3,2-a]fluorene-5,6-dione derivatives.

A new series of substituted tri-/tetraazabenzo[3,2-a]fluorene-5,6-diones and their corresponding oxime derivatives have been synthesized and spectroscopically characterized. The antiproliferative activities of all compounds were evaluated on at least three different cell lines.