In this communication, we report the synthesis and characterization of a library of small molecule antagonists of the human gonadotropin releasing hormone receptor based upon the 2-(4-tert-butylphenyl)-4-piperazinyl-benzimidazole scaffold via Cu-catalysed azide alkyne cycloaddition.

Herein, we report a straightforward sequential acylation-Finkelstein approach to achieve iodination of amine containing bioactives. The utility was demonstrated by successful radiolabelling with 123 I in high radiochemical yield. Moreover, microwave-assisted Finkelstein reaction can be employed to enhance conversion and reaction rates to obtain the desired iodides. The method is of interest for radioiodination of amine-containing bioactives. The mechanistic details of the iodination process were studied by kinetics and density functional theory calculations, which revealed the mechanistic complexity of the reaction involving amide group anchimeric assistance. We disclose a number of fundamental aspects of amide group anchimeric assistance in substitution reactions.

The increased expression of gonadotropin releasing hormone receptor (GnRH-R) in brain has been strongly linked to Alzheimer disease. Therefore, the development of radiolabeled imaging agents for GnRH-R is relevant for early diagnosis of Alzheimer disease. We have recently disclosed the discovery of two promising compounds displaying nanomolar-range affinity for the GnRH-R. In the present study, a preclinical evaluation of the compound properties was performed to evaluate their potential as single photon emission computed tomography (SPECT) radiotracers for imaging the GnRH-receptor. The compounds were assessed in vitro by performing serum stability analysis by human and rat serum, metabolic profiling by human liver microsomes, and exploratory rat brain autoradiography. The investigated compounds displayed satisfactory stability against human, rat serum, and liver microsomal metabolism, which favors their potential as SPECT-imaging agents. Additionally, we identified and quantified the formation rate of the metabolites by fragmentation of up to LIST OF ABBREVIATIONS: GNRH, gonadotropin releasing hormone; GNRH-R, gonadotropin releasing hormone receptor; HPG, hypothalamic pituitary gland; HPLC-MS/MS, high performance liquid chromatography mass spectrometry; IHC, immunohistochemistry; LC-MS, liquid chromatography mass spectrometry; LHRH, luteinizing hormone releasing hormone; NADP, nicotinamide adenine dinucleotide phosphate; NADPH, dihydronicotinamide adenine dinucleotide phosphate; SPECT, single photon emission computed tomography. 72J Label Compd Radiopharm. 2020;63:72-84. wileyonlinelibrary.com/journal/jlcr five mass spectrometric stages. The GnRH-R rat brain specificity of these compounds was tested in competition with a known ligand for the receptor and the in vitro autoradiography confirmed that compounds 3 and 4 binds to rat GnRH-R in different rat brain regions. K E Y W O R D Sautoradiography, gonadotropin, in vitro, metabolic profiling, SPECT

We report the synthesis, radiosynthesis and biological characterisation of two gonadotropin‐releasing hormone receptor (GnRH−R) antagonists with nanomolar binding affinity. A small library of GnRH−R antagonists was synthesised in 20–67 % overall yield with the aim of identifying a high‐affinity antagonist capable of crossing the blood–brain barrier. Binding affinity to rat GnRH−R was determined by autoradiography in competitive‐binding studies against [125I]buserelin, and inhibition constants were calculated by using the Cheng–Prusoff equation. The radioligands were obtained in 46–79 % radiochemical yield and >95 % purity and with a molar activity of 19–38 MBq/nmol by direct nucleophilic radiofluorination. Positron emission tomography imaging in rat under baseline conditions in comparison to pretreatment with a receptor‐saturating dose of GnRH antagonist revealed saturable uptake (0.1 %ID/mL) into the brain.

ObjectivesIn vivo evaluations of a gonadotropin releasing hormone-receptor single photon emission computed tomography radiotracer for non-invasive detection of gonadotropin releasing homone-receptors in brain.ResultsWe have used a simple, robust and high-yielding procedure to radiolabel an alpha-halogenated bioactive compound with high radiochemical yield. Literature findings showed similar alpha-halogenated compounds suitable for in vivo evaluations. The compound was found to possess nano molar affinity for the gonadotropin releasing hormone-receptor in a competition dependent inhibition study. Furthermore, liquid chromatography-mass spectrometry analysis in saline, human and rat serum resulted in 46%, 52% and 44% stability after incubation for 1 h respectively. In addition, rat brain single photon emission computed tomography and biodistribution studies gave further insight into the nature of the compound as a radiotracer.Electronic supplementary materialThe online version of this article (10.1186/s13104-018-3924-2) contains supplementary material, which is available to authorized users.

No abstract

The copper-mediated azide-alkyne cycloaddition has been studied to achieve late-stage introduction of iodine onto novel triazole-benzimidazole Gonadotropin Releasing Hormone (GnRH)-receptor antagonists. Moreover, the reaction conditions can affect a direct regioselective C–H iodination of the benzimidazole, leading to a range of novel iodo-analogues. The methodologies are powerful strategies for late-stage 123I-labelling of complex bioactives. Our investigations have generated two highly promising 123I-labelled radiotracer candidates that retain high affinities for the GnRH-receptor.

Background The need for a stability evaluation of [18F]FDG is evident. The main purpose of this study was to make recommendations for determining the shelf life based on the available stability literature and our own two-centre stability studies. Results We performed a non-systematic literature study to find the most relevant stability data for [18F]FDG. The amount of radioactivity, radio-stabilizers, choice of synthesis, dilution, pH, temperature, storage and the choice of stability tests and acceptance criteria were the most important factors to evaluate for the implementation of good manufacturing practice. Moreover, we discuss some limitations of the study, especially the choice of synthesis, photostability, the environment, temperature and storage. Based on these data, we designed our own two-centre stability studies. All the defined acceptance criteria were met. Conclusions We have made recommendations for future stability evaluations based on our findings. The most important findings were that the amount of the radio-stabilizer ethanol should be > 0.1 % ethanol for activities up to 4 GBq/mL and > 0.2 % ethanol for activities up to 22.7 GBq/mL to keep [18F]FDG stable.