Synthesis of Ionizable Calix[4]arenes for Chelation of Selected Divalent Cations

Two sets of functionalised calix[4]arenes, either with a 1,3-crown ether bridge or with an open-chain oligo ether moiety in 1,3-position were prepared and further equipped with additional deprotonisable sulfonamide groups to establish chelating systems for selected cations Sr2+, Ba2+, and Pb2+ ions. To improve the complexation behaviour towards these cations, calix[4]arenes with oligo ether groups and modified crowns of different sizes were synthesized. Association constants were determined by UV/Vis titration in acetonitrile using the respective perchlorate salts and logK values between 3.2 and 8.0 were obtained. These findings were supported by the calculation of the binding energies exemplarily for selected complexes with Ba2+. Keywords: calixarenes; barium; chelatio

Synthesis and Molecular Structure of 2-(Diphenylphosphano)phenyl Benzoate Borane Adduct

The crystal and molecular structure of 2-(diphenylphosphano)phenyl benzoate borane adduct are reported. The title compound crystallizes from a petroleum ether/ethyl acetate mixture in the triclinic space group P  with two molecules in the unit cell. The unit cell parameters are: a = 8.67(1) Å, b = 9.202(1) Å, c = 14.224(2) Å; α = 72.600(7)°, β = 73.577(7)°, γ = 84.349(7)° and V = 1039.5(2) Å3. Bond lengths and angles are typical for this phosphane borane adduct

Methods to Increase the Metabolic Stability of 18F-Radiotracers

The majority of pharmaceuticals and other organic compounds incorporating radiotracers that are considered foreign to the body undergo metabolic changes in vivo. Metabolic degradation of these drugs is commonly caused by a system of enzymes of low substrate specificity requirement, which is present mainly in the liver, but drug metabolism may also take place in the kidneys or other organs. Thus, radiotracers and all other pharmaceuticals are faced with enormous challenges to maintain their stability in vivo highlighting the importance of their structure. Often in practice, such biologically active molecules exhibit these properties in vitro, but fail during in vivo studies due to obtaining an increased metabolism within minutes. Many pharmacologically and biologically interesting compounds never see application due to their lack of stability. One of the most important issues of radiotracers development based on fluorine-18 is the stability in vitro and in vivo. Sometimes, the metabolism of 18F-radiotracers goes along with the cleavage of the C-F bond and with the rejection of [18F]fluoride mostly combined with high background and accumulation in the skeleton. This review deals with the impact of radiodefluorination and with approaches to stabilize the C-F bond to avoid the cleavage between fluorine and carbon

Synthesis and Molecular Structure of tert-Butyl 4-(2-tert-butoxy-2-oxoethyl)piperazine-1-carboxylate

The crystal and molecular structure of tert-butyl 4-(2-tert-butoxy-2-oxoethyl)-piperazine-1-carboxylate is reported. The title compound crystallizes from a petroleum ether/ethyl acetate mixture in the monoclinic space group P 21/c with four molecules in the unit cell. The unit cell parameters are: a = 8.4007(2) Å, b = 16.4716(4) Å, c = 12.4876(3) Å; β = 90.948(1)° and V = 1727.71(7) Å3. Bond lengths and angles of this piperazine-carboxylate are typical

The Radiochemical and Radiopharmaceutical Applications of Radium

This review focuses on the chemistry and application of radium isotopes to environmental monitoring, analytical, and medicinal uses. In recent years, radium has been used primarily as a tracer to study the migration of radioactive substances in environmental systems. Tracing the naturally occurring radium isotopes in mineral and water sources allows for the determination of source location, residence time, and concentrations. An understanding of the concentration of radionuclides in our food and water sources is essential to everyone’s health as alpha particle decay is highly damaging in vivo. Due to this high radiobiological effectiveness, there is increased interest in using alpha-emitting radionuclides to prepare new, therapeutic radiopharmaceutical drugs. Selected studies from the recent literature are provided as examples of these modern applications of radium isotopes

Recent Trends in Bioorthogonal Click-Radiolabeling Reactions Using Fluorine-18

The increasing application of positron emission tomography (PET) in nuclear medicine has stimulated the extensive development of a multitude of novel and versatile bioorthogonal conjugation techniques especially for the radiolabeling of biologically active high molecular weight compounds like peptides, proteins or antibodies. Taking into consideration that the introduction of fluorine-18 (t1/2 = 109.8 min) proceeds under harsh conditions, radiolabeling of these biologically active molecules represents an outstanding challenge and is of enormous interest. Special attention has to be paid to the method of 18F-introduction. It should proceed in a regioselective manner under mild physiological conditions, in an acceptable time span, with high yields and high specific activities. For these reasons and due to the high number of functional groups found in these compounds, a specific labeling procedure has to be developed for every bioactive macromolecule. Bioorthogonal strategies including the Cu-assisted Huisgen cycloaddition and its copper-free click variant, both Staudinger Ligations or the tetrazine-click reaction have been successfully applied and represent valuable alternatives for the selective introduction of fluorine-18 to overcome the afore mentioned obstacles. This comprehensive review deals with the progress and illustrates the latest developments in the field of bioorthogonal labeling with the focus on the preparation of radiofluorinated building blocks and tracers for molecular imaging

Crystal structure of 2-(diphenylphosphanyl)phenyl 4-(hydroxymethyl)benzoate

The title compound, C26H21O3P, was obtained as by-product due to the hydrolysis of the desired tosylated compound. The dihedral angles between the three aromatic rings attached to the P atom lie in the range 78.1 (1)–87.6 (1)°. The hydroxymethyl group is disordered between two conformations in a 0.719 (9):0.281 (9) ratio. The hydroxy H atom is not involved in intermolecular interactions, while the hydroxy O atom serves as a donor for weak C—H...O hydrogen bonds, which link the molecules into chains propagating in [0-11]

X-ray Structures of Succinimidyl Halobenzoates

The crystal and molecular structures of five succinimidyl halobenzoates are reported. Corresponding derivatives with the respective halo-radionuclide (18F, 76Br, 123I/124I/125I/131I) were prepared and used for the radiolabeling of biologically active (macro-)molecules (peptides, proteins, antibodies) under mild labeling conditions. All compounds were crystalized from petroleum ether/ethyl acetate mixtures