Multigram Four-Step Synthesis of 1,4,7-Triazacyclononanes with 2Ra/RbN-Functionalization Pattern by Starting from Diethylenetriamine

, a Chelator for 68Ga Positron Emission Tomography: Hydroxide Coordination Increases Biological Stability of [68Ga][Ga(Bn2DT3A)(OH)]. Inorg Chem 2022;61:17059-17067. [PMID: 36251390 DOI: 10.1021/acs.inorgchem.2c01992] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

The chelator Bn₂DT3A was used to produce a novel ⁶⁸Ga complex for positron emission tomography (PET). Unusually, this system is stabilized by a coordinated hydroxide in aqueous solutions above pH 5, which confers sufficient stability for it to be used for PET. Bn₂DT3A complexes Ga³⁺ in a hexadentate manner, forming a mer-mer complex with log K([Ga(Bn₂DT3A)]) = 18.25. Above pH 5, the hydroxide ion coordinates the Ga³⁺ ion following dissociation of a coordinated amine. Bn₂DT3A radiolabeling displayed a pH-dependent speciation, with [⁶⁸Ga][Ga(Bn₂DT3A)(OH)]^- being formed above pH 5 and efficiently radiolabeled at pH 7.4. Surprisingly, [⁶⁸Ga][Ga(Bn₂DT3A)(OH)]^- was found to show an increased stability in vitro (for over 2 h in fetal bovine serum) compared to [⁶⁸Ga][Ga(Bn₂DT3A)]. The biodistribution of [⁶⁸Ga][Ga(Bn₂DT3A)(OH)]^- in healthy rats showed rapid clearance and excretion via the kidneys, with no uptake seen in the lungs or bones.

New Triazacycloalkane Derivatives as Cytotoxic Agents for CLL Treatment: From Proof of Concept to the Targeting Biomolecule

The 1,4,7-tris-(2-pyridinylmethyl)-1,4,7-triazacyclononane ligand (no3py) and its bifunctional analogue no3pyCOOK were synthesized to investigate their action toward zinc(II) depletion related to the apoptosis phenomenon in chronic lymphocytic leukemia (CLL) cells. no3py was used as the "free" ligand, while its "graftable" derivative was conjugated on a newly synthesized bifunctional sialoglycan, 6'-SL-NH₂, selected to specifically bind CD22 biomarker expressed on the B-CLL cell surface. Both compounds were produced with good yields thanks to a Sonogashira coupling reaction and an orthoester function, respectively, for the chelator and the targeting moiety. The newly reported bioconjugate 6'-SL-no3py was then obtained through a peptidic coupling reaction. Biological in vitro studies of no3py and 6'-SL-no3py consisting of real-time detection of cell health (cytotoxicity and proliferation) and caspases 3/7 activation (crucial enzymes whose activation triggers cell death signaling pathways) have been investigated. First, Ramos, Daudi, and Raji B-cell lines, which present different sensitivity to zinc(II) content variation, were incubated with no3py and 6'-SL-no3py. Then, a videomicroscope allowed the real-time monitoring of the morphological changes leading to cell death from the detection of the cytotoxicity, the antiproliferative effect, and the caspasic activity. In terms of mechanism, the Zn²⁺ chelator cytotoxic effect of no3py has been evidenced by a culture medium ion supplementation study and by the decrease of intracellular fluorescence of Zn-specific fluorophore zinquin in the presence of no3py and 6'-SL-no3py chelators. Finally, flow cytometry analysis with classical Annexin V staining was conducted to detect no3py- and 6'-SL-no3py-induced apoptotic cell death in B-CLL cells. Time-course analysis, using the Incucyte Live-Cell Analysis System, demonstrated that no3py induced cell death in a time- and dose-dependent manner with variability across cell lines. 6'-SL-no3py exhibited the same dose-dependent trend as no3py, showing the efficiency of the targeting moiety. In both cases, the chelators depicted proliferation curves that were inversely correlated with kinetic death. Morphological changes specific to apoptosis and caspase 3/7 activation were observed for the three cell lines treated with no3py and 6'-SL-no3py, highlighting their role as apoptotic agents. A higher concentration of 6'-SL-no3py is needed to reach 50% of the B-CLL mortality, confirming a targeting of the chelator to the cell membrane. Overall, our results proved that the biological properties of the triazamacrocyclic chelator still remain even after addition of the targeting moiety. The free chelator as well as the bioconjugate constitute promising cytotoxic agents for CLL therapy through apoptosis induction.

Chromoselective access to Z- or E- allylated amines and heterocycles by a photocatalytic allylation reaction

The most useful strategies for the alkylation of allylic systems are related to the Tsuji–Trost reaction or the use of different Lewis acids. Herein we report a photocatalytic approach for the allylation reaction of a variety of nucleophiles, such as heteroarenes, amines and alcohols. This method is compatible with a large variety of pyrroles and indoles, containing different substituents such as electron-withdrawing and electron-donating groups, unprotected nitrogen atoms and bromo derivatives. Moreover, this methodology enables the chromoselective synthesis of Z- or E-allylated compounds. While the use of UV-light irradiation has allowed the synthesis of the previously inaccessible Z-allylated products, E-isomers are prepared simply by changing both the light source to the visible region, and the catalytic system. Based on mechanistic and photochemical proofs, laser flash photolysis studies and DFT calculations, a rational mechanism is presented.

Tsuji–Trost allylation is a traditional method for selective C-C bond formation that involves the use of palladium-based catalysts. Here, the authors report a metal-free, photocatalytic allylation of several heterocycles, amines and alcohols, which can be easily tuned towards the Z- or E- allylated product.

Methylthiazolyl Tacn Ligands for Copper Complexation and Their Bifunctional Chelating Agent Derivatives for Bioconjugation and Copper-64 Radiolabeling: An Example with Bombesin

We present here the synthesis of two new bifunctionalized azachelators, no2th-EtBzNCS and Hno2th1tha, as bioconjugable analogues of two previously described di- and trimethylthiazolyl 1,4,7-triazacyclononane (tacn) ligands, no2th and no3th, for potential uses in copper-64 (⁶⁴Cu) positron emission tomography imaging. The first one bears an isothiocyanate group on the remaining free nitrogen atom of the tacn framework, while the second one presents an additional carboxylic function on one of the three heterocyclic pendants. Their syntheses required regiospecific N-functionalization of the macrocycles. In order to investigate their suitability for in vivo applications, a complete study of their copper(II) chelation was performed. The acid-base properties of the ligands and their thermodynamic stability constants with copper(II) and zinc(II) cations were determined using potentiometric techniques. Structural studies were conducted in both solution and the solid state, consolidated by theoretical calculations. The kinetic inertness in an acidic medium of both copper(II) complexes was determined by spectrophotometry, while cyclic voltammetry experiments were performed to evaluate the stability at the copper(I) redox state. UV-vis, NMR (of the zinc complexes), electron paramagnetic resonance spectroscopy, and density functional theory studies showed excellent agreement between the solution structures of the complexes and their crystallographic data. These investigations unambiguously prove that these bifunctional derivatives display similar coordination properties as their no2th and no3th counterparts, opening the door to targeted bioapplications. The no2th-EtBzNCS and Hno2th1tha ligands were then conjugated to a bombesin antagonist peptide for targeting the gastrin-releasing peptide receptor (GRPr). To highlight the potential of the two chelators for radiopharmaceutical development, the ⁶⁴Cu-radiolabeling properties, in vitro stability, and binding affinity to GRPr of the corresponding bioconjugates were determined. Altogether, the results of this work warrant the further development of ⁶⁴Cu-based radiopharmaceuticals comprising our novel bifunctional chelators.