Advances in the synthesis and applications of macrocyclic polyamines

Macrocyclic polyamines constitute a significant class of macrocyclic compounds that play a pivotal role in the realm of supramolecular chemistry. They find extensive applications across diverse domains including industrial and agricultural production, clinical diagnostics, environmental protection and other multidisciplinary fields. Macrocyclic polyamines possess a distinctive cavity structure with varying sizes, depths, electron-richness degrees and flexibilities. This unique feature enables them to form specific supramolecular structures through complexation with diverse objects, thereby attracting considerable attention from chemists, biologists and materials scientists alike. However, there is currently a lack of comprehensive summaries on the synthesis methods for macrocyclic polyamines. In this review article, we provide an in-depth introduction to the synthesis of macrocyclic polyamines while analysing their respective advantages and disadvantages. Furthermore, we also present an overview of the recent 5-year advancements in using macrocyclic polyamines as non-viral gene vectors, fluorescent probes, diagnostic and therapeutic reagents as well as catalysts. Looking ahead to future research directions on the synthesis and application of macrocyclic polyamines across various fields will hopefully inspire new ideas for their synthesis and use.

Bioconjugated chelates based on (methylpyridinyl)tacn: synthesis, 64Cu labeling and in vitro evaluation for prostate cancer targeting

Three new bifunctional copper chelators based on the 1,4,7-triazacyclononane (tacn) platform have been synthesized and conjugated to peptide. The first one is constituted of the tacn with two methylpyridinyl and one methylthiazolyl carboxylic acid pendant arms, while, in the second and third ones, the macrocycle is functionalized by three methylpyridinyl groups, with an additional hexynoic acid chain on a carbon of one or two pyridine rings. These three bifunctional chelators have been conjugated to the antagonist JMV594 peptide for targeting the gastrin releasing peptide receptor (GRP-r), which is overexpressed in prostate cancer. The resulting monomeric bioconjugates have shown their efficiency to be radiolabeled with β+ emitter 64Cu, and the hydrophilicity and PC-3 cell internalisation properties of these radiolabeled conjugates have been studied. PC-3 cell binding affinity of mono- and dimeric metal-free and natCu metallated conjugates have been evaluated by IC50 measurements. The results demonstrate the potential of these methylpyridinyl tacn derivatives for radiopharmaceutical applications.

Complexation of C-Functionalized Cyclams with Copper(II) and Zinc(II): Similarities and Changes When Compared to Parent Cyclam Analogues

Herein, we report a comprehensive coordination study of the previously reported ligands cyclam, CB-cyclam, TMC, DMC, and CB-DMC and of their C-functional analogues, cyclam-E, CB-cyclam-E, TMC-E, DMC-E, and CB-DMC-E. This group of ligands includes cyclam, cross-bridged cyclams, their di- or tetramethylated derivatives, and the analogues bearing an additional hydroxyethyl group on one β-N position of the ring. The Cu(II) and Zn(II) complexes of these macrocycles have been highlighted previously for the biological interest, but the details of their structures in the solid state and in solution remained largely unexplored. In particular, we analyzed the impact that adding noncoordinating N-methyl and C-hydroxyethyl functionalities has in the structures of the complexes. All the Cu(II) and Zn(II) complexes were synthesized and investigated using single crystal X-ray diffraction and NMR, electronic absorption, and EPR spectroscopies, along with DFT studies. Dissociation kinetics experiments in acidic conditions and electrochemical studies were also performed. Special attention was paid to analyze the different configurations present in solution and in the solid state, as well as the impact of the C-appended hydroxyethyl group on the coordination behavior. Various ratios of the trans-I, trans-III, and cis-V configurations have been observed depending on the degree of N-methylation and the presence of the ethylene cross-bridge.

Molecular mechanisms underlying the renoprotective effects of 1,4,7-triazacyclononane: a βeta-lactamase inhibitor

Broad-spectrum β-lactam antibiotics such as penicillin are routinely used against both Gram-negative and Gram-positive bacteria. However, bacteria that produce β-lactamase have developed resistance against these antibiotics by cleaving the β-lactam ring and rendering the antibiotic inactive. To combat this effect, 1,4,7- Triazacyclononane (TACN), a cyclic organic compound derived from cyclononanes has been shown to preserve the activity of β-lactam antibiotics by inhibiting β-lactamase. However, its cytotoxic effects require elucidation. Given that the cytotoxic target for many therapeutics is the kidney, this study investigated the effects of TACN on human embryonic kidney cells (Hek293) cells. Hek293 cells were treated with TACN (0-500 µM) for 24 h and the cytotoxicity was assessed (MTT and LDH assay). Apoptosis was luminometrically detected by measuring phosphatidylserine externalisation and caspase activity and fluorescently detecting necrosis. DNA fragmentation was visualised using fluorescent microscopy. Expression of the apoptosis-related protein were determined by western blot. The results generated indicate that TACN does not initiate necrosis as LDH was decreased. Likewise, decreased apoptosis was supported by the decreased phosphatidylserine, caspases, Bax, cleaved PARP, IAP and NF-kB. However, increased DNA fragmentation was associated with increased p53. Therefore, effects of TACN at the nucleus, produced a p53 response to initiate DNA repair and did not culminate in cell death. The findings show that TACN is not cytotoxic to Hek293 cells via the apoptotic route. Since TACN did not induce cell death, its potential as a metallo-β-lactamase inhibitor (MBLI) may be exploited to counteract the effect of MBL-producing bacteria. Restoring β-lactam activity will curb the global menace of antibiotic resistance.

From Cyclic Peptoids to Peraza-macrocycles: A General Reductive Approach

Peraza-macrocycles form chelates of high thermodynamic and kinetic stability useful in diagnostic imaging (MRI, SPECT, PET), in coordination chemistry, and as catalysts. In this letter, we report an advantageous method to prepare these compounds via BH₃-induced reduction of cyclic peptoids. Using this procedure, 10 homo- and heterosubstituted aza-coronands, with different sizes and side chains, have been synthesized from the corresponding cyclic oligoamides. Solid structures of free, protonated, and Na⁺ coordinated polyaza-derivatives have been disclosed by single-crystal X-ray diffraction analysis.

Innovative Magnetic Nanoparticles for PET/MRI Bimodal Imaging

Superparamagnetic iron oxide nanoparticles were developed as positron emission tomography (PET) and magnetic resonance imaging (MRI) bimodal imaging agents. These nanoparticles (NPs), with a specific nanoflower morphology, were first synthesized and simultaneously functionalized with 3,4-dihydroxy-l-phenylalanine (LDOPA) under continuous hydrothermal conditions. The resulting NPs exhibited a low hydrodynamic size of 90 ± 2 nm. The functional groups of LDOPA (-NH₂ and -COOH) were successfully used for the grafting of molecules of interest in a second step. The nanostructures were modified by poly(ethylene glycol) (PEG) and a new macrocyclic chelator MANOTA for further ⁶⁴Cu radiolabeling for PET imaging. The functionalized NPs showed promising bimodal (PET and MRI) imaging capability with high r ₂ and r ₂* (T ₂ and T ₂* relaxivities) values and good stability. They were mainly uptaken from liver and kidneys. No cytotoxicity effect was observed. These NPs appear as a good candidate for bimodal tracers in PET/MRI.

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.

Synthesis of chiral nine and twelve-membered cyclic polyamines from natural building blocks

A rational strategy for the facile and efficient cyclization of amino acid-based linear precursors forming nine and twelve-membered cyclic peptidomimetics is reported.

MANOTA: a promising bifunctional chelating agent for copper-64 immunoPET

A comparison of four bifunctional chelating agents showed superior behaviour of a new NOTA derivative for ⁶⁴Cu labelling of antibody fragments.

Reinforced cyclam derivatives functionalized on the bridging unit

The introduction of one or two nitriles on the bridge of reinforced cyclams paves the way for the synthesis of new bifunctional chelating agents. X-ray structures of the chelators and of two copper complexes are reported.