Synthesis, Characterization, and Binding to the Translocator Protein (18 kDa, TSPO) of a New Rhenium Complex as a Model of Radiopharmaceutical Agents

A new tridentate 2-phenyl-imidazopyridin-dipropylacetamide ligand (CB239-H) with high (nanomolar) affinity for the TSPO protein was synthesized and its coordination compound with rhenium tricarbonyl, fac-[Re(CO)3(CB239-N,N,O)] was investigated. The procedure established for the synthesis of the 187/185Re complex can be also used for the synthesis of 99mTc and 188/186Re analogues, which find application in SPECT diagnosis and in therapy. Because of the tridentate coordination of CB239-H and the kinetic inertness of the carbonyl ligands, the new complex was expected to exhibit low reactivity towards plasma proteins and hence greater resistance to deactivation. Being TSPO overexpressed in numerous types of cancers and in activated microglial cells occurring in inflammatory neurodegenerative diseases, TSPO ligands can be exploited as carriers for receptor-mediated drug targeting and hence can be used in diagnosis as well as in therapy. Very suprisingly, fac-[Re(CO)3(CB239-N,N,O)] resulted to be not very stable in diluted human serum but maintained a good affinity towards TSPO

The Synthesis, Structure and (FTIR-Spectro)Electrochemistry of W(CO)5 complexes of 4-oxo-4-(2,5-dimethyl-azaferrocen-1’-yl) butanoic and 5-oxo-5-(2,5-dimethylazaferrocen-1’-yl) pentanoic acids

With the aim of developing new IR-detectable metal–carbonyl tracers for the amino function, we have synthesized W(CO)5 complexes of 4-oxo-4-(2,5-dimethylazaferrocen-1′-yl)butanoic acid (2) and 5-oxo-5-(2,5-dimethylazaferrocen-1′-yl)pentanoic acid (3) by AlCl3-catalyzed Friedel–Crafts reaction of W(CO)5–2,5-dimethylazaferrocene (1) with succinic or glutaric anhydride. Complexes 2 and 3 are thermally stable and display sharp, intense absorption bands of tungsten-coordinated CO ligands at ca. 1923 cm–1. In the crystalline state, molecules of 2 and 3 are stabilized by a network of intra- and intermolecular hydrogen bonds, as shown by single-crystal X-ray structure analysis. Complex 2 was transformed into the corresponding N-succinimidyl ester 4. Its utility toward labeling of amino acids was tested in its reaction with glycine methyl ester. Corresponding glycine amide 5 was obtained in 82 % yield and is an air/thermally stable bioconjugate exhibiting intense sharp absorption bands of the W–CO reporting group at ca. 1923 cm–1. Cyclic voltammetry of 1, 2, 3, and acetyl derivative 6 shows the presence of two redox events in each case. The first redox couple is ascribed as an azaferrocene-centered oxidation–reduction, whereas the second, irreversible process at higher potential originates from a W(CO)5-centered oxidation. FTIR spectroelectrochemistry allowed us to monitor the spectroscopic changes accompanying the 1/1·+, 2/2·+, and 6/6·+ redox transformations. Significant W–CO absorption band shifts were recorded in the course of these experiments