Hypervalent organotellurium compounds as inhibitors of P. falciparum calcium-dependent cysteine proteases

Electricity-driven, oxidative C-H selenylative and tellurylative annulation of N-(2-alkynyl)anilines: sustainable synthesis of 3-selanyl/tellanylquinolines

A metal- and oxidant-free, radical C-H selenylative and tellurylative annulation of N-(2-alkynyl)anilines with diorganyl dichalcogenides is developed under electrochemical conditions for the sustainable synthesis of valuable 3-selanyl/tellanylquinolines up to 92% yield at room temperature. The developed protocol required only electricity as the green reagent and offers high atom economy, broad substrate scope, and efficient scalability.

Tellurium-induced cyclization of olefinic compounds

In this article, we discuss about the importance of Tellurium (Te) in organic synthesis. Tellurium-induced cyclization of alkenyl compounds, as well as alkynyl compounds, are considered for the study. The developments in this area are incorporated in great detail. The mechanism of the reactions does not follow any straightforward process. This study opens up the possibility of stereocontrolled synthesis of complex natural products.

Synthesis, Mechanism Elucidation and Biological Insights of Tellurium(IV)-Containing Heterocycles

Inspired by the synthetic and biological potential of organotellurium substances, a series of five- and six-membered ring organotelluranes containing a Te-O bond were synthesized and characterized. Theoretical calculations elucidated the mechanism for the oxidation-cyclization processes involved in the formation of the heterocycles, consistent with chlorine transfer to hydroxy telluride, followed by a cyclization step with simultaneous formation of the new Te-O bond and deprotonation of the OH group. Moreover, theoretical calculations also indicated anti-diastereoisomers to be major products for two chirality center-containing compounds. Antileishmanial assays against Leishmania amazonensis promastigotes disclosed 1,2λ⁴ -oxatellurane LQ50 (IC₅₀ =4.1±1.0; SI=12), 1,2λ⁴ -oxatellurolane LQ04 (IC₅₀ =7.0±1.3; SI=7) and 1,2λ⁴ -benzoxatellurole LQ56 (IC₅₀ =5.7±0.3; SI=6) as more powerful and more selective compounds than the reference, being up to four times more active. A stability study supported by ¹²⁵ Te NMR analyses showed that these heterocycles do not suffer structural modifications in aqueous-organic media or at temperatures up to 65 °C.

Bis(2-nitrophenyl) selenide, bis(2-aminophenyl) selenide and bis(2-aminophenyl) telluride: structural and theoretical analysis

Three organoselenium and organotellurium compounds containing ortho substitutents, namely, bis(2-nitrophenyl) selenide, C₁₂H₈N₂O₄Se, 2, bis(2-aminophenyl) selenide, C₁₂H₁₂N₂Se, 3, and bis(2-aminophenyl) telluride, C₁₂H₁₂N₂Te, 7, have been investigated by both structural and theoretical methods. In the structures of all three compounds, there are intramolecular contacts between both Se and Te with the ortho substituents. In the case of 2, this is achieved by rotation of the nitro group from the arene plane. For 3, both amino groups exhibit pyramidal geometry and are involved in intramolecular N-H...Se interactions, with one also participating in intermolecular N-H...N hydrogen bonding. While 3 and 7 are structurally similar, there are some significant differences. In addition to both intramolecular N-H...Te interactions and intermolecular N-H...N hydrogen bonding, 7 also exhibits intramolecular N-H...N hydrogen bonding. In the packing of these molecules, for 2, there are weak intermolecular C-H...O contacts and these, along with the O...N interactions mentioned above, link the molecules into a three-dimensional array. For 3, in addition to the N-H...N and N-H...Se interactions, there are also weak intermolecular C-H...Se interactions, which also link the molecules into a three-dimensional array. On the other hand, 7 shows intermolecular N-H...N interactions linking the molecules into R₂²(16) centrosymmetric dimers. In the theoretical studies, for compound 2, AIM (atoms in molecules) analysis revealed critical points in the Se...O interactions with values of 0.017 and 0.026 a.u. These values are suggestive of weak interactions present between Se and O atoms. For 3 and 7, the molecular structures displayed intramolecular, as well as intermolecular, hydrogen-bond interactions of the N-H...N type. The strength of this hydrogen-bond interaction was calculated by AIM analysis. Here, the intermolecular (N-H...N) hydrogen bond is stronger than the intramolecular hydrogen bond. This was confirmed by the electron densities for 3 and 7 [ρ_(r) = 0.015 and 0.011, respectively].

preADMET analysis and clinical aspects of dogs treated with the Organotellurium compound RF07: A possible control for canine visceral leishmaniasis?

Tellurium compounds have been described as potential leishmanicides, bearing promising leishmanicidal and antimalarial effects. Therefore, the present study investigated the pharmacological potential of the organotellurane compound RF07 through preADMET parameters, such as absorption, distribution, metabolism and excretion. After studying the pharmacokinetic properties of RF07, studies were carried out on dogs naturally infected with visceral leishmaniasis after the administration of RF07, in order to assess pathophysiological parameters. Thus, dogs were divided into 4 groups with administration of daily intraperitoneal injections for 3 weeks (containing RF07 or placebo). During the trial, hematological parameters, renal and hepatic toxicity were evaluated. Serum urea, creatinine, alkaline phosphatase, transaminases (GOT and GPT), as well as hemogram results, were evaluated before the first administration and during the second and third weeks after the start of the treatment. In dogs with VL, RF07 improved liver damage, regulated GPT levels and significantly decreased leukocyte count, promoting its regularization. These phenomena occurred at the end of the third week of treatment. The administration of RF07 promoted a significant decrease in the average levels of GOT and GPT after the third week of treatment and did not significantly alter the hematological parameters. The application of RF07 in the treatment of visceral leishmaniasis suggests that it is an alternative to the disease, since the reversal of clinical signs in dogs with VL requires the use of 0.6 mg/kg.

Development of a methodology for reversible chemical modification of silicon surfaces with application in nanomechanical biosensors

Hypervalent tellurium compounds have a particular reactivity towards thiol compounds which are related to their biological properties. In this work, this property was assembled to tellurium-functionalized surfaces. These compounds were used as linkers in the immobilization process of thiolated biomolecules (such as DNA) on microcantilever surfaces. The telluride derivatives acted as reversible binding agents due to their redox properties, providing the regeneration of microcantilever surfaces and allowing their reuse for further biomolecules immobilizations, recycling the functional surface. Initially, we started from the synthesis of 4-((3-((4-methoxyphenyl) tellanyl) phenyl) amino)-4-oxobutanoic acid, a new compound, which was immobilized on a silicon surface. In nanomechanical systems, the detection involved a hybridization study of thiolated DNA sequences. Fluorescence microscopy technique was used to confirm the immobilization and removal of the telluride-DNA system and provided revealing results about the potentiality of applying redox properties to chalcogen derivatives at surfaces.

Antitumor effect of chiral organotelluranes elicited in a murine melanoma model

Protease roles in cancer progression have been demonstrated and their inhibitors display antitumor effects. Cathepsins are lysosomal cysteine proteases that have increased expression in tumor cells, and tellurium compounds were described as potent cysteine protease inhibitors and also assayed in several animal models. In this work, the two enantiomeric forms of 1-[Butyl(dichloro)-λ⁴-tellanyl]-2-[1S-methoxyethyl]benzene (organotelluranes RF-13R and RF-13S) were evaluated as inhibitors of cathepsins B and L, showing significant enantiodiscrimination. We observed their cytotoxic effects on a murine melanoma model, effectively inhibiting tumor progression in vivo. The enantiomers were able to inhibit melanoma cell viability, migration and invasion in vitro. Besides, RF-13S and RF-13R were able to inhibit endothelial cell angiogenesis using a tube formation assay in vitro, in a stereodependent manner. These organotelluranes affected cell morphology, showing disassembling of the actin cytoskeleton. These results suggest organotelluranes as potential antitumor agents, acting directly on tumor cell proliferation, migration and invasion, and on endothelial cells, disrupting angiogenesis, showing low toxicity and high efficiency. Taken together our results suggest that this class of compounds should be further studied to reveal their potential as antitumoral agents.

Investigation of Chemical Stability of Dihalogenated Organotelluranes in Organic-Aqueous Media: The Protagonism of Water

The biological activity of tellurium compounds is closely related to the tellurium oxidation state or some of their structural features. Hypervalent dihalogenated organotelluranes 1-[butyl(dichloro)-λ⁴-tellanyl]-2-(methoxymethyl)benzene (1a) and 1-[butyl(dibromide)-λ⁴-tellanyl]-2-(methoxymethyl)benzene (1b) have been described as inhibitors of proteases (cysteine and threonine) and tyrosine phosphatases. However, poor attention has been given to their physicochemical properties. Here, a detailed investigation of the stability in water of these organotelluranes is reported using ¹²⁵Te NMR analysis. Dihalogenated organotelluranes 1a and 1b were both stable in DMSO- d₆ (from 25 to 75 °C), demonstrating their thermal stability. However, the addition of a phosphate buffer solution (pH 2-8) to 1a or 1b resulted in an immediate conversion to a new Te species, assumed to be the corresponding telluroxide. Similar behavior was observed in pure water, demonstrating the low chemical stability of these dihalogenated species in the presence of water. These results allow concluding that previous biological activity reported for dihalogenated organotelluranes 1a and 1b could be attributed to the corresponding derivatives from the reaction with water. In the same way as for AS-101, we demonstrated that organotelluranes 1a and 1b are not stable in aqueous solution. It suggests a proactive role of these organotelluranes in previously reported biological activity.

Crystallographic and docking (Cathepsins B, K, L and S) studies on bioactive halotelluroxetanes

The molecular structures of the halotelluroxetanes p-MeOC6H4Te(X)[C(=C(H)X′)C(CH2)nO], X=X′=Cl and n=6 (1) and X=Cl, X′=Br and n=5 (4), show similar binuclear aggregates sustained by {· · ·Te–O}2 cores comprising covalent Te–O and secondary Te· · ·O interactions. The resulting C2ClO2(lone-pair) sets define pseudo-octahedral geometries. In each structure, C–X· · ·π(arene) interactions lead to supramolecular layers. Literature studies have shown these and related compounds (i.e. 2: X=X′=Cl and n=5; 3: X=X′=Br and n=5) to inhibit Cathepsins B, K, L and S to varying extents. Molecular docking calculations have been conducted on ligands (i.e. cations derived by removal of the tellurium-bound X atoms) 1′–3′ (note 3′=4′) enabling correlations between affinity for sub-sites and inhibition. The common feature of all docked complexes was the formation of a Te–S covalent bond with cysteine residues, the relative stability of the ligands with an E-configuration and the formation of a C–O· · ·π interaction with the phenyl ring; for 1′ the Te–S covalent bond was weak, a result correlating with its low inhibition profile. At the next level differences are apparent, especially with respect to the interactions formed by the organic-ligand-bound halides. While these atoms do not form specific interactions in Cathepsins B and K, in Cathepsin L, these halides are involved in C–O· · ·X halogen bonds.

Stability Study of Hypervalent Tellurium Compounds in Aqueous Solutions

Hypervalent tellurium compounds (telluranes) are promising therapeutical agents with negligible toxicities for some diseases in animal models. The C-Te bond of organotellurium compounds is commonly considered unstable, disfavoring their applicability in biological studies. In this study, the stability of a set of telluranes composed of an inorganic derivative and noncharged and charged organic derivatives was monitored in aqueous media with ¹H, ¹³C, and ¹²⁵Te NMR spectroscopy and high-resolution mass spectrometry. Organic telluranes were found to be remarkably resistant and stable to hydrolysis, whereas the inorganic tellurane AS101 is totally converted to the hydrolysis product, trichlorooxytellurate, [TeOCl ₃ ]^-, which was also observed in the hydrolysis of TeCl ₄ . The noteworthy stability of organotelluranes in aqueous media makes them prone to further structure-activity relationship studies and to be considered for broad biological investigations.

Antiparasitic activity of 1,3-dioxolanes containing tellurium in Trichomonas vaginalis

The increased prevalence of metronidazole-resistant infections has resulted in a search for alternative drugs for the treatment of trichomoniasis. In the present study, we report the preparation and in vitro activity of three 1,3-dioxolanes that contain tellurium (PTeDOX 01, PTeDOX 02, and PTeDOX 03) against Trichomonas vaginalis. Six concentrations of these compounds were analyzed for in vitro activity against ATCC 30236 isolate of T. vaginalis. PTeDOX 01 reported a cytotoxic effect against 100% of T. vaginalis trophozoites at a final concentration of 90μM with an IC₅₀ of 60μM. The kinetic growth curve of trophozoites indicated that PTeDOX 01 reduced the growth by 22% at a concentration of 90μM after an exposure of 12h, and induced complete parasite death at 24h. It induced cytotoxicity of 44% at 90μM concentration but and had no effect in lower concentrations in a culture of CHO-K1 cells. These results confirmed that PTeDOX 01 is an important drug for the treatment of T. vaginalis, and should be evaluated in other infectious agents as well.

Calpain research for drug discovery: challenges and potential

Calpains are a family of proteases that were scientifically recognized earlier than proteasomes and caspases, but remain enigmatic. However, they are known to participate in a multitude of physiological and pathological processes, performing 'limited proteolysis' whereby they do not destroy but rather modulate the functions of their substrates. Calpains are therefore referred to as 'modulator proteases'. Multidisciplinary research on calpains has begun to elucidate their involvement in pathophysiological mechanisms. Therapeutic strategies targeting malfunctions of calpains have been developed, driven primarily by improvements in the specificity and bioavailability of calpain inhibitors. Here, we review the calpain superfamily and calpain-related disorders, and discuss emerging calpain-targeted therapeutic strategies.