Bis- and tris(pyridyl)amine-oxidovanadium complexes: characteristics and insulin-mimetic potential

Crystal structure of (μ-hydrogen di-sulfato)-μ-oxido-bis-[(4,4'-di-tert-butyl-2,2'-bi-pyridine)-oxidovanadium(IV/V)] aceto-nitrile monosolvate

The dinuclear oxidovanadium(IV/V) complex, [V2(HS2O8)O3(C18H24N2)2]·CH3CN or [V2O2(μ-O)(μ-H(SO4)2)(4,4'-tBubpy)2]·CH3CN (4,4'-tBubpy = 4,4'-di-tert-butyl-2,2'-bi-pyridine), has crystallographic C 2 symmetry and exhibits a distorted octa-hedral geometry around the vanadium center, where the two 4,4'-tBubpy ligands are nearly orthogonal to each other. The two vanadium ions are linked by an oxo anion and a unique protonated sulfate anion [H(SO4)2 3-]. In the crystal, inter-molecular C-H⋯π and π-π inter-actions between the 4,4'-tBubpy ligands are present, leading to a three-dimensional network.

Oxygen Activation by a Copper Complex with Sulfur-Only Coordination Relevant to the Formylglycine Generating Enzyme

Synthesizing hydrosulfido Cu thiolate complexes is quite challenging. In this report, two new and rare hydrosulfido Cu thiolate complexes, [Et₄N]₂[(mnt)Cu-SH] (2, mnt = maleonitrile dithiolene = S₂C₂(CN)₂) and [Et₄N]₃[(mnt)Cu-(μ-SH)-Cu(mnt)] (3), have been synthesized. Coordination sites and O₂ activation by complex 2 resemble the formylglycine generating enzyme (FGE), an enzyme recently crystallographically characterized with sulfur-only coordination around Cu (three thiolate ligands). The function of this enzyme (and complex 2) is surprising because vulnerable thiolates should not be well suited for O₂ activation rationally. Indeed, activation of oxygen by such an all-sulfur-coordinated Cu complex 2 is lacking in the literature. Aerial O₂ (ambient O₂ from the air) activation by complex 2 could proceed through a superoxide radical intermediate and a sulfur radical intermediate detected by resonance Raman (rR) spectroscopy and electron paramagnetic resonance (EPR) spectroscopy, respectively. The chemistry of 2 has been examined by its reactivity, crystal structure, and spectroscopic and cyclic voltammetric analyses. In addition, the results have been complemented with density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations.

Tris(2-Pyridylmethylamine)V(O)2 Complexes as Counter Ions of Diprotonated Decavanadate Anion: Potential Antineoplastic Activity

The synthesis and theoretical-experimental characterization of a novel diprotanated decavanadate is presented here due to our search for novel anticancer metallodrugs. Tris(2-pyridylmethyl)amine (TPMA), which is also known to have anticancer activity in osteosarcoma cell lines, was introduced as a possible cationic species that could act as a counterpart for the decavanadate anion. However, the isolated compound contains the previously reported vanadium (V) dioxido-tpma moieties, and the decavanadate anion appears to be diprotonated. The structural characterization of the compound was performed by infrared spectroscopy and single-crystal X-ray diffraction. In addition, DFT calculations were used to analyze the reactive sites involved in the donor-acceptor interactions from the molecular electrostatic potential maps. The level of theory mPW1PW91/6–31G(d)-LANL2DZ and ECP = LANL2DZ for the V atom was used. These insights about the compounds’ main interactions were supported by analyzing the noncovalent interactions utilizing the AIM and Hirshfeld surfaces approach. Molecular docking studies with small RNA fragments were used to assess the hypothesis that decavanadate’s anticancer activity could be attributed to its interaction with lncRNA molecules. Thus, a combination of three potentially beneficial components could be evaluated in various cancer cell lines.

Vanadium as potential therapeutic agent for COVID-19: A focus on its antiviral, antiinflamatory, and antihyperglycemic effects

An increasing evidence suggests that vanadium compounds are novel potential drugs in the treatment of diabetes, atherosclerosis, and cancer. Vanadium has also demonstrated activities against RNA viruses and is a promising candidate for treating acute respiratory diseases. The antidiabetic, antihypertensive, lipid-lowering, cardioprotective, antineoplastic, antiviral, and other potential effects of vanadium are summarized here. Given the beneficial antihyperglycemic and antiinflammatory effects as well as the potential mechanistic link between the COVID-19 and diabetes, vanadium compounds could be considered as a complement to the prescribed treatment of COVID-19. Thus, further clinical trials are warranted to confirm these favorable effects of vanadium treatment in COVID-19 patients, which appear not to be studied yet.

Vanadium in Biological Action: Chemical, Pharmacological Aspects, and Metabolic Implications in Diabetes Mellitus

Vanadium compounds have been primarily investigated as potential therapeutic agents for the treatment of various major health issues, including cancer, atherosclerosis, and diabetes. The translation of vanadium-based compounds into clinical trials and ultimately into disease treatments remains hampered by the absence of a basic pharmacological and metabolic comprehension of such compounds. In this review, we examine the development of vanadium-containing compounds in biological systems regarding the role of the physiological environment, dosage, intracellular interactions, metabolic transformations, modulation of signaling pathways, toxicology, and transport and tissue distribution as well as therapeutic implications. From our point of view, the toxicological and pharmacological aspects in animal models and humans are not understood completely, and thus, we introduced them in a physiological environment and dosage context. Different transport proteins in blood plasma and mechanistic transport determinants are discussed. Furthermore, an overview of different vanadium species and the role of physiological factors (i.e., pH, redox conditions, concentration, and so on) are considered. Mechanistic specifications about different signaling pathways are discussed, particularly the phosphatases and kinases that are modulated dynamically by vanadium compounds because until now, the focus only has been on protein tyrosine phosphatase 1B as a vanadium target. Particular emphasis is laid on the therapeutic ability of vanadium-based compounds and their role for the treatment of diabetes mellitus, specifically on that of vanadate- and polioxovanadate-containing compounds. We aim at shedding light on the prevailing gaps between primary scientific data and information from animal models and human studies.

Vanadium bromoperoxidase (VBrPO) mimics: synthesis, structure and a comparative account of the catalytic activity of newly synthesized oxidovanadium and oxido-peroxidovanadium complexes

The catalytic peroxidative bromination (VBrPO mimic) of organic substances by oxido and oxido-peroxidovanadium complexes suggests the superiority of the oxido-peroxido complex over the oxido one.

Why Antidiabetic Vanadium Complexes are Not in the Pipeline of "Big Pharma" Drug Research? A Critical Review

Public academic research sites, private institutions as well as small companies have made substantial contributions to the ongoing development of antidiabetic vanadium compounds. But why is this endeavor not echoed by the globally operating pharmaceutical companies, also known as "Big Pharma"? Intriguingly, today's clinical practice is in great need to improve or replace insulin treatment against Diabetes Mellitus (DM). Insulin is the mainstay therapeutically and economically. So, why do those companies develop potential antidiabetic drug candidates without vanadium (vanadium- free)? We gathered information about physicochemical and pharmacological properties of known vanadium-containing antidiabetic compounds from the specialized literature, and converted the data into explanations (arguments, the "pros and cons") about the underpinnings of antidiabetic vanadium. Some discoveries were embedded in chronological order while seminal reviews of the last decade about the Medicinal chemistry of vanadium and its history were also listed for further understanding. In particular, the concepts of so-called "noncomplexed or free" vanadium species (i.e. inorganic oxido-coordinated species) and "biogenic speciation" of antidiabetic vanadium complexes were found critical and subsequently documented in more details to answer the question.

Novel water soluble neutral vanadium(IV)-antibiotic complex: Antioxidant, immunomodulatory and molecular docking studies

A novel water soluble five coordinate oxovanadium(IV) complex, [VO(C16H15N4O8S)HSO4] incorporating cefuroxime, a cephalosporin group of antibiotic have been prepared from an interaction of vanadyl sulfate and cefuroxime in aqueous solution. The compound was characterized by Fourier transform infrared spectroscopy (FTIR), CHN microanalyses, ultraviolet-visible spectroscopy (UV-Vis), fast atom bombardment (FAB) mass spectrometry and thermogravimetric analysis (TGA). Density Functional Theory (DFT) computation using Gaussian 09 program at B3LYP level revealed a distorted square pyramidal energy optimized geometry for the vanadyl(IV) complex. The molecular docking studies show that the interaction between the vanadium complex and protein receptor, clathrin is dominated by hydrophobic forces. The experimental (1)H nuclear magnetic resonance (NMR) features of the analogous Zn(II) complex matched well with the theoretically computed values further affirming the distorted square pyramidal geometry for the vanadyl(IV) complex. Cyclic voltammetry revealed a metal centered single-electron oxidation-reduction response for VO(IV)/VO(V) couple. The antioxidant activity of the vanadium(IV)-complex vis-à-vis the antibiotic has been assessed by 1,1-diphenyl-2-picrylhydrazyl (DPPH) method. The vanadium complex showed comparatively better radical scavenging ability compared to the antibiotic cefuroxime. The antimicrobial activity of the compound has been assayed for five different microbial strains using minimum inhibitory concentration (MIC) method. Immunomodulatory studies carried out using phagocytosis index, myeloperoxidase release and cytokine assay indicated the vanadium(IV)-complex to be immunosuppressant. The cytotoxicity of the compound was evaluated by MTT (3-(4, 5-dimethyl thiazol-2-yl)-2, 5-diphenyl tetrazolium bromide) reduction assay.

Synthesis and characterization of V(IV)O complexes of picolinate and pyrazine derivatives. Behavior in the solid state and aqueous solution and biotransformation in the presence of blood plasma proteins

Oxidovanadium(IV) complexes with 5-cyanopyridine-2-carboxylic acid (HpicCN), 3,5-difluoropyridine-2-carboxylic acid (HpicFF), 3-hydroxypyridine-2-carboxylic acid (H2hypic), and pyrazine-2-carboxylic acid (Hprz) have been synthesized and characterized in the solid state and aqueous solution through elemental analysis, IR and EPR spectroscopy, potentiometric titrations, and DFT simulations. The crystal structures of the complexes (OC-6-23)-[VO(picCN)2(H2O)]·2H2O (1·2H2O), (OC-6-24)-[VO(picCN)2(H2O)]·4H2O (2·4H2O), (OC-6-24)-Na[VO(Hhypic)3]·H2O (4), and two enantiomers of (OC-6-24)-[VO(prz)2(H2O)] (Λ-5 and Δ-5) have been determined also by X-ray crystallography. 1 presents the first crystallographic evidence for the formation of a OC-6-23 isomer for bis(picolinato) V(IV)O complexes, whereas 2, 4, and 5 possess the more common OC-6-24 arrangement. The strength order of the ligands is H2hypic ≫ HpicCN > Hprz > HpicFF, and this results in a different behavior at pH 7.40. In organic and aqueous solution the three isomers OC-6-23, OC-6-24, and OC-6-42 are formed, and this is confirmed by DFT simulations. In all the systems with apo-transferrin (VO)2(apo-hTf) is the main species in solution, with the hydrolytic V(IV)O species becoming more important with lowering the strength of the ligand. In the systems with albumin, (VO)(x)HSA (x = 5, 6) coexists with VOL2(HSA) and VOL(HSA)(H2O) when L = picCN, prz, with [VO(Hhypic)(hypic)](-), [VO(hypic)2](2-), and [(VO)4(μ-hypic)4(H2O)4] when H2hypic is studied, and with the hydrolytic V(IV)O species when HpicFF is examined. Finally, the consequence of the hydrolysis on the binding of V(IV)O(2+) to the blood proteins, the possible uptake of V species by the cells, and the possible relationship with the insulin-enhancing activity are discussed.

The potentiality of vanadium in medicinal applications

In the early treatment of diabetes with vanadium, inorganic vanadium compounds have been the focus of attention; organic vanadium compounds are nowadays increasingly attracting attention. A key compound is bis(maltolato)oxidovanadium, which became introduced into clinical tests Phase IIa. Organic ligands help modulate the bioavailability, transport and targeting mechanism of a vanadium compound. Commonly, however, the active onsite species is vanadyl (VO(2+)) or vanadate (H(2)VO(4) (-)), generated by biospeciation. The mode of operation can be ascribed to interaction of vanadate with phosphatases and kinases, and to modulation of the level of reactive oxygen species interfering with phosphatases and/or DNA. This operating mode has also been inferred for most cancerostatic vanadium compounds, although some, for example vanadocenes, may directly intercalate with DNA. Novel medicinal potentiality of vanadium compounds is geared towards endemic diseases in tropical countries, in particular leishmaniasis, Chagas' disease and amoebiasis, and viral infections such as Dengue fever, SARS and HIV.

SSAO substrates exhibiting insulin-like effects in adipocytes as a promising treatment option for metabolic disorders

BACKGROUND

Benzylamine exerts insulin-like effects in adipocytes (e.g., glucose uptake and antilipolysis) and improves glucose handling in rodents.

RESULTS

In murine adipocytes, benzylamine mimics another insulin action: it enhances apelin expression in a manner that is blocked by the semicarbazide-sensitive amine oxidase/vascular adhesion protein-1 (SSAO/VAP-1) inhibitor semicarbazide. It is shown that in human adipocytes, benzylamine activates glucose transport, but its effects are not additive to maximal insulin stimulation. Benzylamine effects are hydrogen peroxide dependent. They can be reproduced by novel substrates, but not by benzaldehyde.

CONCLUSION

Owing to the parallelism between the in vitro insulin mimicry and the in vivo improvement of glucose handling elicited by benzylamine in rodents, the SSAO/VAP-1 substrates, with stronger effects on human adipocytes than benzylamine, show promising applications for the treatment of insulin resistance.

o-Iminobenzosemiquinonate and o-imino-p-methylbenzosemiquinonate anion radicals coupled VO2+ stabilization

The diamagnetic VO(2+)-iminobenzosemiquinonate anion radical (L(R)(IS)(•-), R = H, Me) complexes, (L(-))(VO(2+))(L(R)(IS)(•-)): (L(1)(-))(VO(2+))(L(H)(IS)(•-))•3/2MeOH (1•3/2MeOH), (L(2)(-))(VO(2+))(L(H)(IS)(•-)) (2), and (L(2)(-))(VO(2+))(L(Me)(IS)(•-))•1/2 L(Me)(AP) (3•1/2 L(Me)(AP)), incorporating tridentate monoanionic NNO-donor ligands {L = L(1)(-) or L(2)(-), L(1)H = (2-[(phenylpyridin-2-yl-methylene)amino]phenol; L(2)H = 1-(2-pyridylazo)-2-naphthol; L(H)(IS)(•-) = o-iminobenzosemiquinonate anion radical; L(Me)(IS)(•-) = o-imino-p-methylbenzosemiquinonate anion radical; and L(Me)(AP) = o-amino-p-methylphenol} have been isolated and characterized by elemental analyses, IR, mass, NMR, and UV-vis spectra, including the single-crystal X-ray structure determinations of 1•3/2MeOH and 3•1/2 L(Me)(AP). Complexes 1•3/2MeOH, 2, and 3•1/2 L(Me)(AP) absorb strongly in the visible region because of intraligand (IL) and ligand-to-metal charge transfers (LMCT). 1•3/2MeOH is luminescent (λ(ext), 333 nm; λ(em), 522, 553 nm) in frozen dichloromethane-toluene glass at 77 K due to π(diimine→)π(diimine)* transition. The V-O(phenolato) (cis to the V═O) lengths, 1.940(2) and 1.984(2) Å, respectively, in 1•3/2MeOH and 3•1/2 L(Me)(AP) are consistent with the VO(2+) description. The V-O(iminosemiquinonate) (trans to the V═O) lengths, 2.1324(19) in 1•3/2MeOH and 2.083(2) Å in 3•1/2 L(Me)(AP), are expectedly ∼0.20 Å longer due to the trans influence of the V═O bond. Because of the stronger affinity of the paramagnetic VO(2+) ion to the L(H)(IS)(•-) or L(Me)(IS)(•-), the V-N(iminosemiquinonate) lengths, 1.908(2) and 1.921(2) Å, respectively, in 1•3/2MeOH and 3•1/2 L(Me)(AP), are unexpectedly shorter. Density functional theory (DFT) calculations using B3LYP, B3PW91, and PBE1PBE functionals on 1 and 2 have established that the closed shell singlet (CSS) solutions (VO(3+)-amidophenolato (L(R)(AP)(2-)) coordination) of these complexes are unstable with respect to triplet perturbations. But BS (1,1) M(s) = 0 (VO(2+)-iminobenzosemiquinonate anion radical (L(R)(IS)(•-)) coordination) solutions of these species are stable and reproduce the experimental bond parameters well. Spin density distributions of one electron oxidized cations are consistent with the [(L(-))(VO(2+))(L(R)(IQ))](+) descriptions [VO(2+)-o-iminobenzoquinone (L(R)(IQ)) coordination], and one electron reduced anions are consistent with the [(L(•2-))(VO(3+))(L(R)(AP)(2-))](-) descriptions [VO(3+)-amidophenolato (L(R)(AP)(2-)) coordination], incorporating the diimine anion radical (L(1)(•2-)) or azo anion radical (L(2)(3-)). Although, cations and anions are not isolable, but electro-and spectro-electrochemical experiments have shown that 3(+) and 3(-) ions are more stable than 1(+), 2(+) and 1(-), 2(-) ions. In all cases, the reductions occur with simultaneous two electron transfer, may be due to formation of coupled diimine/azo anion radical-VO(2+) species as in [(L(•2-))(VO(2+))(L(R)(AP)(2-))](2-).