Methodologies Limiting or Avoiding Contamination by Organotin Residues in Organic Synthesis.

The increasing application of positron emission tomography (PET) in nuclear medicine has stimulated the extensive development of a multitude of new radiotracers and novel radiolabeling procedures with the most prominent short-lived positron emitters carbon-11 and fluorine-18. Radiolabeling with these radionuclides represents a remarkable challenge. Special attention has to be paid to synthesis time and specific labeling techniques due to the short physical half life of the respective radionuclides 11C (t1/2 = 20.4 min) and 18F (t1/2 = 109.8 min). In the past, numerous transition metal-catalyzed reactions were employed in organic chemistry, even though only a handful of these coupling reactions were adopted in radiochemical practice. Thus, the implementation of modern synthesis methods like cross-coupling reactions offers the possibility to develop a wide variety of novel radiotracers. The introduction of catalysts based on transition metal complexes bears a high potential for rapid, efficient, highly selective and functional group-tolerating incorporation of carbon-11 and fluorine-18 into target molecules. This review deals with design, application and improvement of transition metal-mediated carbon-carbon as well as carbon-heteroatom cross-coupling reactions as a labeling feature with the focus on the preparation of radiolabeled compounds for molecular imaging.

/pdf/cross-coupling-reactions-as-valuable-tool-for-the-18b30qdgz3.pdf

Cross-coupling reactions as valuable tool for the preparation of PET radiotracers.

The discovery of endogenous peptide ligands for morphine binding sites occurred in parallel with the identification of three subclasses of opioid receptor (OR), traditionally designated as μ, δ, and κ, along with the more recently defined opioid-receptor-like (ORL1) receptor. Early efforts in opioid receptor radiochemistry focused on the structure of the prototype agonist ligand, morphine, although N-[methyl-11C]morphine, -codeine and -heroin did not show significant binding in vivo. [11C]Diprenorphine ([11C]DPN), an orvinol type, non-selective OR antagonist ligand, was among the first successful PET tracers for molecular brain imaging, but has been largely supplanted in research studies by the μ-preferring agonist [11C]carfentanil ([11C]Caf). These two tracers have the property of being displaceable by endogenous opioid peptides in living brain, thus potentially serving in a competition-binding model. Indeed, many clinical PET studies with [11C]DPN or [11C]Caf affirm the release of endogenous opioids in response to painful stimuli. Numerous other PET studies implicate μ-OR signaling in aspects of human personality and vulnerability to drug dependence, but there have been very few clinical PET studies of μORs in neurological disorders. Tracers based on naltrindole, a non-peptide antagonist of the δ-preferring endogenous opioid enkephalin, have been used in PET studies of δORs, and [11C]GR103545 is validated for studies of κORs. Structures such as [11C]NOP-1A show selective binding at ORL-1 receptors in living brain. However, there is scant documentation of δ-, κ-, or ORL1 receptors in healthy human brain or in neurological and psychiatric disorders; here, clinical PET research must catch up with recent progress in radiopharmaceutical chemistry.

https://www.mdpi.com/1420-3049/24/22/4190/pdf

A Survey of Molecular Imaging of Opioid Receptors.

1-Substituted-N-tosyl-1,2,3,4-tetrahydroisoquinoline analogs (4a–4l) were synthesized using the modified Pictet–Spengler reaction and evaluated for cytotoxicity. All tetrahydroisoquinolines displayed cytotoxicity against MOLT-3 cell lines, except for p-methoxy analog 4d. Interestingly, the o-hydroxy derivative 4k was shown to be the most potent cytotoxic against HuCCA-1, A-549 and MOLT-3 cell lines. The lowest IC50 value of 1.23 μM was observed for MOLT-3 cells. Trimethoxy analog 4f exerted the most potent activity against HepG2 with an IC50 of 22.70 μM, which is lower than the reference drug, etoposide. QSAR studies showed that total symmetry index (Gu), 3D-MoRSE (Mor31v and Mor32u) and 3D Petitjean index (PJI3) were the most important descriptors accounting for the observed cytotoxicities. The most potent cytotoxic compound (4k) against MOLT-3 had the highest Gu value, correspondingly the inactive p-methoxy analog (4d) had the lowest Gu value. On the other hand, the highest molecular mass compound (4f) was shown to be the most potent cytotoxic against HepG2 cells. The studies disclose that tetrahydroisoquinolines 4f and 4k are potentially interesting lead pharmacophores that should be further explored. The QSAR models provided insights into the physicochemical properties of the investigated compounds.

Synthesis, cytotoxicity and QSAR study of N-tosyl-1,2,3,4-tetrahydroisoquinoline derivatives

Vibrational spectroscopy and density functional theory study of 4-mercaptophenol

The palladium-catalyzed cross-coupling reactions between a (trimethylstannyl)arene and [ 11 C]methyl iodide (Stille reaction) or between an aryl halide and a [ 11 C]monomethyltin reagent issued from Lappert’s stannylene, were developed for the synthesis of polyfunctional [ 11 C]methyl quinolines and quinolinimides as potential tracers for positron emission tomography (PET).

Tetra-and Monoorganotin Reagents in Palladium-Mediated Cross-Coupling Reactions for the Labeling with Carbon-11 of PET Tracers

Synthesis and Biological Evaluation of N-Substituted Quinolinimides, as Potential Ligands for in Vivo Imaging Studies of δ-Opioid Receptors

Radiosynthesis and ex vivo evaluation of [11C]-SIB-1553A as a PET radiotracer for β4 selective subtype nicotinic acetylcholine receptor

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Tetra-and Monoorganotin Reagents in Palladium-Mediated Cross-Coupling Reactions for the Labeling with Carbon-11 of PET Tracers

Synthesis and Biological Evaluation of N-Substituted Quinolinimides, as Potential Ligands for in Vivo Imaging Studies of δ-Opioid Receptors

Radiosynthesis and ex vivo evaluation of [11C]-SIB-1553A as a PET radiotracer for β4 selective subtype nicotinic acetylcholine receptor