A Family of (N-Salicylidene-α-amino acidato)vanadate Esters Incorporating Chelated Propane-1,3-diol and Glycerol: Synthesis, Structure, and Reaction

Ligand controlled synthesis of mixed-ligand oxovanadium(V) and oxovanadium(IV) complexes

Reaction of VIVO(acac)2 (where Hacac = acetylacetone) with 2-hydroxybenzylalcohol (H2L) produces [VVO(L)(acac) (H2O)], 1 but the above reaction mixture produces [VVO(L)(hq)(CH3OH)], 2 and [VIVO(HL)(pa)(CH3OH)], 3 in presence of 8-hydroxyquinoline(Hhq) and picolinic acid(Hpa), respectively.

Synthesis and characterization of oxidovanadium complexes as enzyme inhibitors targeting dipeptidyl peptidase IV

Two oxidovanadium(IV) complexes carrying Schiff base ligands obtained from the condensation of 4,5-dichlorobenzene-1,2-diamine and salicylaldehyde derivatives were synthesised and characterised, including their X-ray crystallographic structures. They were evaluated as dipeptidyl peptidase IV (DPP-IV) inhibitors for the treatment of type 2 diabetes. These compounds were moderate inhibitors of DPP-IV, with IC₅₀ values of ca. 40μM. In vivo tests showed that complexes 1 and 2 could lower significantly the level of glucose in the blood of alloxan-diabetic mice at doses of 22.5mgV·kg^-1 and 29.6mgV·kg^-1, respectively. Moreover, molecular modeling studies suggested that the oxidovanadium complexes 1 and 2 could fit well into the active-site cleft of the kinase domain of DPP-IV. To the best of our knowledge, this is the first report of vanadium complexes capable of inhibiting DPP-IV.

Thirty years through vanadium chemistry

The relevance of vanadium in biological systems is known for many years and vanadium-based catalysts have important industrial applications, however, till the beginning of the 80s research on vanadium chemistry and biochemistry did not receive much attention from the scientific community. The understanding of the broad bioinorganic implications resulting from the similarities between phosphate and vanadate(V) and the discovery of vanadium dependent enzymes gave rise to an enormous increase in interest in the chemistry and biological relevance of vanadium. Thereupon the last 30years corresponded to a period of enormous research effort in these fields, as well as in medicinal applications of vanadium and in the development of catalysts for use in fine-chemical synthesis, some of these inspired by enzymatic active sites. Since the 80s my group in collaboration with others made contributions, described throughout this text, namely in the understanding of the speciation of vanadium compounds in aqueous solution and in biological fluids, and to the transport of vanadium compounds in blood plasma and their uptake by cells. Several new types of vanadium compounds were also synthesized and characterized, with applications either as prospective therapeutic drugs or as homogeneous or heterogenized catalysts for the production of fine chemicals. The developments made are described also considering the international context of the evolution of the knowledge in the chemistry and bioinorganic chemistry of vanadium compounds during the last 30years. This article was compiled based on the Vanadis Award presentation at the 9th International Vanadium Symposium.

Inhibition protein tyrosine phosphatases by an oxovanadium glutamate complex, Na2[VO(Glu)2(CH3OH)](Glu = glutamate)

The insulin-sensitizing effect of vanadium complexes has been linked to their ability to inhibit protein tyrosine phosphatases (PTPs). Considering that vanadium complexes may exchange in vivo with amino acids, forming in situ vanadium-amino acid complexes, we have synthesized and characterized an oxovanadium glutamate complex, Na(2)[V(IV)O(Glu)(2)(CH(3)OH)]H(2)O (1·H(2)O). The complex showed potent inhibition against four human PTPs (PTP1B, TCPTP, HePTP, and SHP-1) with IC(50) in the 0.21-0.37 μM ranges. Fluorescence titration studies suggest that the complex binds to PTP1B with the formation of a 2:1 complex. Enzyme kinetics analysis using Lineweaver-Burk plots indicates a typical competitive inhibition mode.

Synthesis, Reactivity, and X-ray Crystal Structure of Some Mixed-Ligand Oxovanadium(V) Complexes: First Report of Binuclear Oxovanadium(V) Complexes Containing 4,4‘-Bipyridine Type Bridge

Reaction of the tridentate ONO Schiff-base ligand 2-hydroxybenzoylhydrazone of 2-hydroxybenzoylhydrazine (H2L) with VO(acac)2 in ethanol medium produces the oxoethoxovanadium(V) complex [VO(OEt)L] (A), which reacts with pyridine to form [VO(OEt)L.(py)] (1). Complex 1 is structurally characterized. It has a distorted octahedral O4N2 coordination environment around the V(V) acceptor center. Both complexes A and 1 in ethanol medium react with neutral monodentate Lewis bases 2-picoline, 3-picoline, 4- picoline, 4-amino pyridine, imidazole, and 4-methyl imidazole, all of which are stronger bases than pyridine, to produce dioxovanadium(V) complexes of general formula BH[VO2L]. Most of these dioxo complexes are structurally characterized, and the complex anion [VO2L]- is found to possess a distorted square pyramidal structure. When a solution/suspension of a BH[VO2L] complex in an alcohol (ROH) is treated with HCl in the same alcohol, it is converted into the corresponding monooxoalkoxo complex [VO(OR)L], where R comes from the alcohol used as the reaction medium. Both complexes A and 1 produce the 4,4'-bipyridine-bridged binuclear complex [VO(OEt)L]2(mu-4,4'-bipy) (2), which, to the best of our knowledge, represents the first report of a structurally characterized 4,4'-bipyridine-bridged oxovanadium(V) binuclear complex. Two similar binuclear oxovanadium(V) complexes 3 and 4 are also synthesized and characterized. All these binuclear complexes (2-4), on treatment with base B, produce the corresponding mononuclear dioxovanadium(V) complexes (5-10).

Interactions of oxovanadium(IV) and the quinolone family member--ciprofloxacin

The interactions of quinolone ciprofloxacin (cfH) and oxovanadium(IV) were studied by various methods. Green crystals of a complex [V(IV)O(cf)(2)(H(2)O)] were isolated and the molecular connectivities established, although the crystal structure was not perfectly refined due to the instability of the crystals. Based on a plausible interpretation of the data sets, two cf anions bidentately coordinate to a vanadyl cation through carboxylate and carbonyl oxygen atoms; in addition, there is a water molecule in the coordination sphere. Solution techniques (cyclic voltammetry, electronic and electron paramagnetic resonance spectroscopy, potentiometric measurements) confirmed the presence of various species in the solution, the composition of which strongly depends on the conditions in the system. The antibacterial activity of the complex against various microorganisms was tested and it was established that its activity is similar to that of free ciprofloxacin.

Insights into substrate binding and catalytic mechanism of human tyrosyl-DNA phosphodiesterase (Tdp1) from vanadate and tungstate-inhibited structures

Tyrosyl-DNA phosphodiesterase (Tdp1) is a DNA repair enzyme that catalyzes the hydrolysis of a phosphodiester bond between a tyrosine residue and a DNA 3'-phosphate. The only known example of such a linkage in eukaryotic cells occurs normally as a transient link between a type IB topoisomerase and DNA. Thus human Tdp1 is thought to be responsible for repairing lesions that occur when topoisomerase I becomes stalled on the DNA in the cell. Tdp1 has also been shown to remove glycolate from single-stranded DNA containing a 3'-phosphoglycolate, suggesting a role for Tdp1 in repair of free-radical mediated DNA double-strand breaks. We report the three-dimensional structures of human Tdp1 bound to the phosphate transition state analogs vanadate and tungstate. Each structure shows the inhibitor covalently bound to His263, confirming that this residue is the nucleophile in the first step of the catalytic reaction. Vanadate in the Tdp1-vanadate structure has a trigonal bipyramidal geometry that mimics the transition state for hydrolysis of a phosphodiester bond, while Tdp1-tungstate displays unusual octahedral coordination. The presence of low-occupancy tungstate molecules along the narrow groove of the substrate binding cleft is suggestive evidence that this groove binds ssDNA. In both cases, glycerol from the cryoprotectant solution became liganded to the vanadate or tungstate inhibitor molecules in a bidentate 1,2-diol fashion. These structural models allow predictions to be made regarding the specific binding mode of the substrate and the mechanism of catalysis.

A family of vanadate esters of monoionized and diionized aromatic 1,2-diols: synthesis, structure, and redox activity

The concerned diols (general abbreviation, H(2)L) are catechol (H(2)L(1)) and its 3,5-Bu(t)(2) derivative (H(2)L(2)). Esters of the type VO(xsal)(HL), 2, are obtained by reacting H(2)L with VO(xsal)(H(2)O) or VO(xsal)(OMe)(HOMe), where xsal(2-) is the diionized salicylaldimine of glycine (x = g), L-alanine (x = a), or L-valine (x = v). The reaction of VO(acac)(2) with H(2)L and the salicylaldimine (Hpsal) of 2-picolylamine has furnished VO(psal)(L), 3. In the structures of VO(gsal)(HL(1)), 2a, and VO(vsal)(HL(2)), 2f, the HL(-) ligand is O,O-chelated, the phenolic oxygen lying trans to the oxo oxygen atom. The xsal(2-) coligand has a folded structure and the conformation of 2f is exclusively endo. In both 2a and 2f the phenolic oxygen atom is strongly hydrogen bonded (O...O, 2.60 A) to a carboxylic oxygen atom of a neighboring molecule. In VO(psal)(L(2)).H(2)O, 3b, the diionized diol is O,O-chelated to the metal and the water molecule is hydrogen bonded to a phenoxidic oxygen atom (O.O, 2.84 A). The C-O and C-C distances in the V(diol) fragment reveal that 2 is a pure catecholate and 3 is a catecholate-semiquinonate hybrid. In solution each ester gives rise to a single (51)V NMR signal (no diastereoisomers), which generally shifts downfield with a decrease in the ester LMCT band energy. The V(V)/V(IV) and catecholate-semiquinonate reduction potentials lie near -0.75 and 0.35, and 1.10 and 0.70 V vs SCE for 2 and 3, respectively. Molecular oxygen reacts smoothly with 2 quantitatively furnishing the corresponding o-quinone, and in the presence of H(2)L the reaction becomes catalytic. In contrast, type 3 esters are inert to oxygen. The initial binding of O(2) to 2 is proposed to occur via hydrogen bonding with chelated HL(-).

Carbohydrate Binding to VO(3+). Sugar Vanadate Esters Incorporating L-Amino Acid Schiff Bases as Coligands

The glycosides methyl-2,6-dimethoxy-beta-D-galactopyranoside (beta-D-H(2)Me(3)GP), methyl-4,6-dimethoxy-alpha-D-mannopyranoside (alpha-D-H(2)Me(3)MP), and methyl-5-methoxy-beta-D-ribofuranoside (beta-D-H(2)Me(2)RF) have been synthesized, and their reaction with VO(L-Asal)(OMe)(OHMe) in dichloromethane has afforded esters of the type VO(beta-D-HMe(3)GP)(L-Asal), VO(alpha-D-HMe(3)MP)(L-Asal), and VO(beta-D-HMe(2)RF)(L-Asal) as dark-colored solids (red in solution). Here, L-Asal(2)(-) is the deprotonated salicylaldimine of L-alanine (A = a), L-valine (A = v), and L-phenylalanine (A = p). The X-ray structures of VO(beta-D-HMe(3)GP)(L-vsal).H(2)O and VO(alpha-D-HMe(3)MP)(L-psal).H(2)O have revealed five-membered (O,O)-chelation by monoionized carbohydrates, the undissociated hydroxyl group lying trans to the oxo oxygen atom. In the carbohydrate frame, the alkoxidic oxygen atom is axial in the former ester and equatorial in the latter. The V-O(alkoxidic) and V-O(alcoholic) distances are, respectively, approximately 1.80 and approximately 2.30 Å. The ONO coordinating tridentate salicylaldimine ligand is folded (by approximately 35 degrees ) along a C-N bond. The chiral configuration of the metal site corresponds exclusively to the endo disposition of the V=O and the amino acid C-R (R = Me, CHMe(2), CH(2)Ph) bonds. In VO(beta-D-HMe(3)GP)(L-vsal).H(2)O two ester molecules constitute the asymmetric unit and these along with the two water molecules form a macrocyclic supramolecule (diameter, approximately 6.1 Å) held by hydrogen bonds involving alcohol and an OMe function as well as water (O.O distance, 2.59-2.86 Å). On the other hand, in VO(alpha-D-HMe(3)MP)(L-psal).H(2)O the water molecule bridges two symmetry-related ester molecules via alkoxide.water and alcohol.water hydrogen bonds forming an infinite chain structure (O.O lengths, 2.65 and 2.85 Å). The molecular structures observed in the solid state are preserved in solution ((1)H and (51)V NMR). No isomerization is detectable either at the metal site or at the anomeric carbon atom, and the V-O(alkoxidic) and V-O(alcoholic) sites and the metal-carbohydrate binding remain in tact. The VO(beta-D-HMe(2)RF)(L-Asal) species did not afford single crystals but NMR results are consistent with (O,O)-chelation by the ribose fragment, the alkoxidic carbon being C3. Crystal data are as follows. VO(beta-D-HMe(3)GP)(L-vsal).H(2)O: chemical formula, C(21)H(32)NO(11)V; crystal system, orthorhombic; space group, P2(1)2(1)2(1); a = 13.146(7) Å, b = 15.142(5) Å, c = 25.631(9) Å; Z = 8. VO(alpha-D-HMe(3)MP)(L-psal).H(2)O: chemical formula, C(25)H(32)NO(11)V; crystal system, monoclinic; space group, P2(1); a = 13.645(4) Å, b = 7.022(2) Å, c = 15.500(4) Å; beta = 113.98(2) degrees; Z = 2.