Click Chelators for Platinum-Based Anticancer Drugs

Developments in the Application of 1,2,3-Triazoles in Cancer Treatment

BACKGROUND

The impact of cancer on modern society cannot be emphasized enough in terms of both economic and human costs. Cancer treatments are known, unfortunately, for their side effects - frequently numerous and severe. Drug resistance is another issue medical professionals have to tackle when dealing with neoplastic illnesses. Cancer rates are rising worldwide due to various factors - low-quality nutrition, air and water pollution, tobacco use, etc. For those and many other reasons, drug discovery in the field of oncology is a top priority in modern medical science.

OBJECTIVE

To present the reader with the latest in cancer drug discovery with regard to 1,2,3-triazole- containing molecules in a clear, concise way so as to make the present review a useful tool for researchers.

METHODS

Available information present on the role of 1,2,3-triazoles in cancer treatment was collected. Data was collected from scientific literature, as well as from patents.

RESULTS

A vast number of triazole-containing molecules with antiproliferative properties have been proposed, synthesized and tested for anticancer activity both in vitro and in vivo. The substances vary greatly when considering molecular structure, proposed mechanisms of action and affected cancer cell types.

CONCLUSION

Triazole-containing molecules with anticancer activity are being widely synthesized and extensively tested. They vary significantly in terms of both structure and mechanism of action. The methods for their preparation and administration are well established and with proven reproducibility. These facts suggest that triazoles may play an important role in the discovery of novel antiproliferative medications with improved effectiveness and safety profile.

A new 1,2,3-triazole and its rhodamine B derivatives as a fluorescence probe for mercury ions

A newly synthesized compound, 5-methyl-1-phenyl-1H-1,2,3-triazole-4- carboxylic acid (MPC) was analyzed for its quantum chemical parameters and theoretical spectrum by computational chemistry. The calculated spectrum was in accord with the experimental measurements in a great degree. Then MPC was successfully designed and synthesized to a novel rhodamine B derivative RMPC. The RMPC exhibited about a 4000-fold increase in fluorescence intensity in the presence of Hg²⁺ ions over most other competitive metal ions. The triazole appended colorless chemodosimeter RMPC turns to pink upon the complex formation only with Hg²⁺ ions as a 1: 2 M ratio and enables naked-eye detection. The coordination mechanism of turning on/off fluorescence for Hg²⁺ ions were well proposed by explaining Hg²⁺ inducing the ring-opened rhodamine B moiety. The fluorescence imaging experiments of Hg²⁺ in HeLa cell demonstrated that the probe was labeled and it could be used in biological systems.

Visible-light-induced addition of carboxymethanide to styrene from monochloroacetic acid

Where monochloroacetic acid is widely used as a starting material for the synthesis of relevant groups of compounds, many of these synthetic procedures are based on nucleophilic substitution of the carbon chlorine bond. Oxidative or reductive activation of monochloroacetic acid results in radical intermediates, leading to reactivity different from the traditional reactivity of this compound. Here, we investigated the possibility of applying monochloroacetic acid as a substrate for photoredox catalysis with styrene to directly produce γ-phenyl-γ-butyrolactone. Instead of using nucleophilic substitution, we cleaved the carbon chlorine bond by single-electron reduction, creating a radical species. We observed that the reaction works best in nonpolar solvents. The reaction does not go to full conversion, but selectively forms γ-phenyl-γ-butyrolactone and 4-chloro-4-phenylbutanoic acid. Over time the catalyst precipitates from solution (perhaps in a decomposed form in case of fac-[Ir(ppy)₃]), which was proven by mass spectrometry and EPR spectroscopy for one of the catalysts (N,N-5,10-di(2-naphthalene)-5,10-dihydrophenazine) used in this work. The generation of HCl resulting from lactone formation could be an additional problem for organometallic photoredox catalysts used in this reaction. In an attempt to trap one of the radical intermediates with TEMPO, we observed a compound indicating the generation of a chloromethyl radical.

The specific binding of a new 1,2,3-triazole to three blood proteins and it's appended rhodamine complex for selective detection of Hg2

A synthesized compound, ethyl 2,5-diphenyl-2H-1,2,3-triazole-4- carboxylate (EDTC) was investigated on its physiochemical parameters and structural properties by using the quantum-chemical method. The results on the theoretical spectrum of EDTC were line with experimental fluorescence and absorption spectrum in large degree. Then EDTC was successfully synthesized to a novel rhodamine-based fluorescent probe (REDTC), which showed a distinct fluorescence enhancement upon the presence of Hg²⁺ in dimethyl formamide-water (DMF-H₂O) buffer solution (pH 7.4). Meanwhile, the triazole appended colorless compound turns to pink upon complex formation with Hg²⁺ ions as 1:2 molar ratios and enables naked-eye detection. The chromogenic mechanism was determined by using spectroscopic measurements and TD DFT calculation. The fluorescence imaging experiments of Hg²⁺ in HeLa cell revealed that the probe REDTC could be labeled and it could be used in biological systems. Also, the intermediate EDTC was developed as a sensitive fluorescent probe for specific studies on the interactions to three kinds of blood proteins including human serum albumin (HSA), human immunoglobulin (HIg) and bovine hemoglobin (BHb) by using a series of spectroscopic methods and molecular docking under the simulative physiological conditions. The interactions between EDTC and these proteins led to the distinct fluorescence enhancement. The thermodynamic measured results further suggested that hydrophobic forces play a dominating role in stabilizing the complexes, which are in correspondence with the results from molecular docking. The UV-visible, synchronous, and three-dimensional (3D) fluorescence measurements demonstrated that EDTC influences the conformational of proteins and the microenvironment surrounding HSA, HIg, or BHb in aqueous solution.

Synthesis, characterization and catalytic activity of novel ruthenium complexes bearing NNN click based ligands

Novel air stable ruthenium(ii) complexes bearing tridentate ligands bis((1-benzyl-1H-1,2,3-triazol-4-yl)methyl)amine (L1), 1-(1-benzyl-1H-1,2,3-triazol-4-yl)-N-(pyridin-2-ylmethyl)methanamine (L2) or 2-(4-phenyl-1H-1,2,3-triazol-1-yl)-N-(pyridin-2-ylmethyl)ethan-1-amine (L3) were synthesised. The nitrogen based ligands were easily prepared by virtue of click chemistry using cheap and commercially available reagents. The ruthenium complexes were obtained by heating the Ru(PPh3)3Cl2 precursor and the tridentate NNN ligand in toluene under reflux for 2 hours, achieving yields of 82-87%. These complexes were fully characterized by means of NMR, FT-IR and high resolution ESI spectroscopy. The crystal structure of one of the complexes was determined. These complexes showed excellent activity and selectivity in the hydrogenation of ketones and aldehydes. DFT calculations show that complex 3 may react through an outer-sphere catalytic cycle rather than via an inner-sphere mechanism.

A visible-light photoactivatable di-nuclear PtIV triazolato azido complex

A novel PtIV triazolato azido complex [3]-[N1,N3] has been synthesised via a strain-promoted double-click reaction (SPDC) between a PtIV azido complex (1) and the Sondheimer diyne (2). Photoactivation of [3]-[N1,N3] with visible light (452 nm) in the presence of 5'-guanosine monophosphate (5'-GMP) produced both PtIV and PtII 5'-GMP species; EPR spectroscopy confirmed the production of both azidyl and hydroxyl radicals. Spin-trapping of photogenerated radicals - particularly hydroxyl radicals - was significantly reduced in the presence of 5'-GMP.

Luminescent iridium(iii) complexes of N-heterocyclic carbene ligands prepared using the ‘click reaction’

Luminescent and electrochemiluminescent N-heterocyclic carbene-combined 1,2,3-triazole and 1,2,3-triazolylidene Ir(iii) complexes have been prepared and their potential as luminescent probes in cell imaging has been evaluated.

The structural properties of 5-methyl-2-phenyl-2H-1,2,3-triazole-4- carboxylic acid and chromogenic mechanism on its rhodamine B derivatives to Hg2+ ions

5-Methyl-2-phenyl-2H-1,2,3-triazole-4-carboxylic acid (MPTC), a newly synthesized compound, was explored to study the structural properties and theoretical spectra by using GaussView5.0 program package and the time dependent density functional theory (TD DFT). The calculated quantum chemical values suggested that it is easy for MPTC to lose electron with weak electron accepting ability. And the results of experimental measurements on fluorescence and absorption spectra were consistent with that of the calculated spectra in great degree. In addition, MPTC was successfully used and synthesized a novel rhodamine B derivative RMPTC containing 1,2,3-triazole unit. It is found that there is special chromogenic response of RMPTC to Hg²⁺ ions in N, N-dimethylformamide (DMF)-H₂O (v/v=1/1, Tris-HCl, pH7.4) with the triazole appended colorless chemosensor turned to pink and enabled naked-eye detection. The fluorescence signal for RMPTC-Hg²⁺ system was not affected by other coexisting metal ions. The 1:2 stoichiometric structure of RMPTC and Hg²⁺ is confirmed using a Job's plot estimation and TD DFT calculations. The corresponding "off-on" fluorescence mechanism of RMPTC binding to Hg²⁺ which were ascribed to Hg²⁺ inducing the ring-opened rhodamine B moiety were proposed. This study was an advancement for the application of 1,2,3-triazole compound in photophysical chemistry field and provides guidance for exploring simple and high-selectivity Hg²⁺ probes in aqueous solutions under physiological conditions.

Computational investigations of click-derived 1,2,3-triazoles as keystone ligands for complexation with transition metals: a review

In recent years, metal complexes of organo 1,2,3-triazole click-derived ligands have attracted significant attention as catalysts in many chemical transformations and also as biological and pharmaceutical active agents. Regarding the important applications of these metal-organo 1,2,3-triazole-based complexes, in this review, we focused on the recently reported investigations of the structural, electronic, and spectroscopic aspects of the complexation process in transition metal complexes of 1,2,3-triazole-based click ligands. In line with this, the coordination properties of these triazole-based click ligands with transition metals were studied via several quantum chemistry calculations. Moreover, considering the complexation process, we have presented comparative discussions between the computational results and the available experimental data.

1,2,3-Triazolium-Based Peptoid Oligomers

The cis-directing effect of the 1,2,3-triazolium-type side chain was studied on dimeric peptoid models with various patterns: αα, αβ, βα and ββ. Low influences of the sequence and of the solvent were observed, the cis conformation of the amide carrying the triazolium ranging from 83 to 94% in proportion. The synthesis of peptoid homooligomers with four or eight pendant 1,2,3-triazolium side chains is described. α-, β- and α,β-peptoids carrying propargyl groups were subjected to CuAAC reaction using alkyl azides, and the resulting triazoles were quaternized providing well-defined multitriazolium platforms. The influence of the counteranion (PF₆^-, BF₄^- or I^-) on the conformation was also studied.

CuSO4/KI As Catalyst for the Synthesis of 1,4-Disubstituted-1,2,3-Triazolo-Nucleosides

A simple and inexpensive procedure has been developed for the selective formation of 1,4-disubstituted-1,2,3-triazolo-nucleosides starting from organic azides and terminal alkynes, mediated by in situ generated copper(I) catalyst from readily available CuSO4 and KI.

Novel triazole-based ligands and their zinc(ii) and nickel(ii) complexes with a nitrogen donor environment as potential structural models for mononuclear active sites

A tridentate N,N,N-1,2,3-triazole-based ligand successfully coordinated to nickel ions through the less Lewis basic N2 atom of the triazole ring.

Complexes of (η6-benzene)ruthenium(ii) with 1,4-bis(phenylthio/seleno-methyl)-1,2,3-triazoles: synthesis, structure and applications in catalytic activation of oxidation and transfer hydrogenation

1,4-Bis(phenylthio/seleno methyl)-1,2,3-triazoles (L1–L4) synthesized by a ‘Click’ reaction form complexes [(η⁶-C₆H₆)RuClL]PF₆ (L = L1–L4) suitable as catalyst for oxidation/transfer hydrogenation.

Rhenium and technetium bi- and tricarbonyl complexes in a new strategy for biomolecule incorporation using click chemistry

A versatile strategy to prepare fac-[M(I)(CO)3](+) and cis-[M(I)(CO)2](+) (M = Re, (99m)Tc) complexes was developed using Huisgen click chemistry and monodentate phosphine ligands to readily incorporate biomolecules and tailor the chemical properties.

Synthesis and cytotoxicity studies of novel triazolo-benzoxazepine as new anticancer agents

Cancer continues to be one of the biggest threats to the human civilization because there is no cure of it. Small heterocyclic molecule with low molecular weight and novel structural feature is therapeutically highly demanding. These molecules have the capability to disrupt signaling pathways leading to anticancer activities. Therefore, the search for new anticancer agents continues to draw attention to the research community. In this study, a small triazolo-benzoxazepine scaffolds was synthesized using a one-pot four-step synthetic methodology involving click reaction. Small libraries of 12 compounds were successfully synthesized and screened them against different cancer cell lines. Low micromolar anticancer activity was recorded using MTT assay, and further confirmation of cell death was obtained by phase contrast, fluorescent, and confocal images.

[Fe₂L₃]⁴⁺ cylinders derived from bis(bidentate) 2-pyridyl-1,2,3-triazole "click" ligands: synthesis, structures and exploration of biological activity

A series of metallosupramolecular [Fe₂L₃](BF₄)₄ “click” cylinders have been synthesized in excellent yields (90%–95%) from [Fe(H₂O)₆](BF₄)₂ and bis(bidentate) pyridyl-1,2,3-triazole ligands. All complexes were characterized by elemental analysis, IR, UV-vis, ¹H-, ¹³C- and DOSY-NMR spectroscopies and, in four cases, the structures confirmed by X-ray crystallography. Molecular modeling indicated that some of these “click” complexes were of similar size and shape to related biologically active pyridylimine-based iron(II) helicates and suggested that the “click” complexes may bind both duplex and triplex DNA. Cell-based agarose diffusion assays showed that the metallosupramolecular [Fe₂L₃](BF₄)₄ “click” cylinders display no antifungal activity against S. cerevisiae. This observed lack of antifungal activity appears to be due to the poor stability of the “click” complexes in DMSO and biological media.

H(2)azapa: a versatile acyclic multifunctional chelator for (67)Ga, (64)Cu, (111)In, and (177)Lu

Preliminary experiments with the novel acyclic triazole-containing bifunctional chelator H2azapa and the radiometals (64)Cu, (67)Ga, (111)In, and (177)Lu have established its significant versatile potential as an alternative to 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) for metal-based radiopharmaceuticals. Unlike DOTA, H2azapa radiolabels quantitatively with (64)Cu, (67)Ga, (111)In, and (177)Lu in 10 min at room temperature. In vitro competition experiments with human blood serum show that (64)Cu remained predominantly chelate-bound, with only 2% transchelated to serum proteins after 20 h. Biodistribution experiments with [(64)Cu(azapa)] in mice reveal uptake in various organs, particularly in the liver, lungs, heart, intestines, and kidneys. When compared to [(64)Cu(DOTA)](2-), the lipophilic neutral [(64)Cu(azapa)] was cleared through the gastrointestinal tract and accumulated in the liver, which is common for lipophilic compounds or free (64)Cu. The chelator H2azapa is a model complex for a click-based bifunctional chelating agent, and the lipophilic benzyl "place-holders" will be replaced by hydrophilic peptides to modulate the pharmacokinetics and direct activity away from the liver and gut. The solid-state molecular structure of [In(azapa)(H2O)][ClO4] reveals a very rare eight-coordinate distorted square antiprismatic geometry with one triazole arm bound, and the structure of [(64)Cu(azapa)] shows a distorted octahedral geometry. The present study demonstrates significant potential for bioconjugates of H2azapa as alternatives to DOTA in copper-based radiopharmaceuticals, with the highly modular and "clickable" molecular scaffold of H2azapa easily modified into a variety of bioconjugates. H2azapa is a versatile addition to the "pa" family, joining the previously published H2dedpa ((67/68)Ga and (64)Cu), H4octapa ((111)In, (177)Lu, and (90)Y), and H5decapa ((225)Ac) to cover a wide range of important nuclides.