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The first cobalt-catalysed cycloisomerisation of alkynoic acids is reported, thanks to the design of a well-defined diradical cobalt(iii) catalyst, in the absence of any additives. The high efficiency, regioselectivity and chemoselectivity are comparable to those of noble metal-based systems. The unique reactivity might be attributed to second coordination sphere effects. [ABSTRACT FROM AUTHOR]

The synthesis of two new iron chelators built on the tris-L-serine trilactone scaffold of enterobactin and bearing a 8-hydroxyquinoline (oxinobactin) or 8-hydroxyquinoline-5-sulfonate (sulfoxinobactin) unit has been described. The X-ray structure of the ferric oxinobactin has been determined, exhibiting a slightly distorted octahedral environment for Fe(Ⅲ) and a Δ configuration. The Fe(Ⅲ) chelating properties have been examined by Potentiometrie and spectrophotometric titrations in methanol--water 80/20% w/w solvent for oxinobactin and in water for sulfoxinobactin. They reveal the extraordinarily completing ability (pFeⅢ values) of oxinobactin over the p[H] range 2--9, the pFe value at p[H] 7.4 being 32.8. This was supported by spectrophotometric competition showing that oxinobactin removes Fe (Ⅲ) from ferric enterobactin at p[H] 7.4. In contrast, the Fe (III) affinity of sulfoxinobactin was largely lower as compared to oxinobactin but similar to that of the ligand O-TRENSOX having a TREN backbone. These results are discussed in relation to the predisposition by the trilactone scaffold of the chelating units. Some comparisons are also made with other quinoline-based ligands and hydroxypyridinonate ligand (hopobactin). [ABSTRACT FROM AUTHOR]

Abstract: The story of the highly selective iron(III) chelating agent O-TRENSOX is presented. The promising (and somewhat unexpected in regard to partition coefficients) properties of this molecule induced the development of several tools for iron metabolism studies. The tuning of the properties of O-TRENSOX by chemical modifications of the parent molecules is also developed. Finally, fascinating perspectives are opened by amphiphilic derivatives which mimic marine siderophores from phytoplankton. The self-assembling properties of amphiphilic abiotic chelators and their iron derivatives, as well as the first results concerning iron nutrition of Erwinia chrysanthemi and some mutants, have been studied. [Copyright &y& Elsevier]

Reports on the synthesis of water-soluble thionitrites RSNO from the nitrosation of cysteamine and mercaptoethanol derivatives. Influence of substitutions at the alpha and beta carbon atoms on the stability of the sulphur-nitric oxide bond; Rate at which nitric oxide was released; Effect of beta substituents.

Abstract: Oxinobactin, a siderophore analogue to enterobactin but possessing 8-hydroxyquinoline instead of catechol complexing subunits, has been synthesized starting from l-serine and 8-hydroxyquinoline. Comparative iron binding studies showed that oxinobactin is as effective as enterobactin for the complexation of FeIII at physiological pH but with improved complexing ability at acidic pH. [Copyright &y& Elsevier]

Background: Despite the development of positron emission tomography (PET), single photon emission computed tomography (SPECT) still accounts for around 80% of all examinations performed in nuclear medicine departments. The search for new radiotracers or chelating agents for Technetium-99m is therefore still ongoing. O-TRENSOX and O-TRENOX two synthetic siderophores would be good candidates for this purpose as they are hexadentate ligands based on the very versatile and efficient 8-hydroxyquinoline chelating subunit. First, the radiolabeling of O-TRENOX and O-TRENSOX with 99mTc was investigated. Different parameters such as the quantity of chelating agent, type of reducing agent, pH and temperature of the reaction mixture were adjusted in order to find the best radiolabeling conditions. Then an assessment of the partition coefficient by measuring the distribution of each radiosynthesized complex between octanol and phosphate-buffered saline was realized. The complex's charge was evaluated on three different celluloses (neutral, negatively charged P81 and positively charged DE81), and finally in vivo studies with biodistribution and SPECT imaging of [99mTc]Tc-O-TRENOX and [99mTc]Tc-O-TRENSOX were performed. Results: The radiolabeling studies showed a rapid and efficient complexation of 99mTc with both chelating agents. Using tin pyrophosphate as the reducing agent and a minimum of 100 nmol of ligand, we obtained the [99mTc]Tc-O-TRENOX complex with a radiochemical purity of more than 98% and the [99mTc]Tc-O-TRENSOX complex with one above 97% at room temperature within 5 min. [99mTc]Tc-O-TRENOX complex was lipophilic and neutral, leading to a hepatobiliary elimination in mice. On the contrary, the [99mTc]Tc-O-TRENSOX complex was found to be hydrophilic and negatively charged. This was confirmed by a predominantly renal elimination in mice. Conclusions: These encouraging results allow us to consider the O-TRENOX/99mTc and O-TRENSOX/99mTc complexes as serious candidates for SPECT imaging chelators. This study should be continued by conjugating these tris-oxine ligands to peptides or antibodies and comparing them with the other bifunctional agents used with Tc. [ABSTRACT FROM AUTHOR]

In the title compound, [Sm(NO3)3(C24H28N4O2)], the Sm atom has tenfold coordination, built up from two imino N atoms, two deprotonated phenolic O atoms and three bidentate nitrate groups. The Sm ion is incorporated in an out-of-plane position relative to the macrocyclic ligand, which adopts a folded conformation. [ABSTRACT FROM AUTHOR]

In human, Tyrosinase enzyme (TyH) is involved in the key steps of protective pigments biosynthesis (in skin, eyes and hair). The use of molecules targeting its binuclear copper active site represents a relevant strategy to regulate TyH activities. In this work, we targeted 2-Hydroxypyridine- N -oxide analogs (HOPNO, an established chelating group for the tyrosinase dicopper active site) with the aim to combine effects induced by combination with a reference inhibitor (kojic acid) or natural substrate (tyrosine). The HOPNO–MeOH (3) and the racemic amino acid HOPNO-AA compounds (11) were tested on purified tyrosinases from different sources (fungal, bacterial and human) for comparison purposes. Both compounds have more potent inhibitory activities than the parent HOPNO moiety and display strictly competitive inhibition constant, in particular with human tyrosinase. Furthermore, 11 appears to be the most active on the B16–F1 mammal melanoma cells. The investigations were completed by stereospecificity analysis. Racemic mixture of the fully protected amino acid 10 was separated by chiral HPLC into the corresponding enantiomers. Assignment of the absolute configuration of the deprotected compounds was completed, based on X-ray crystallography. The inhibition activities on melanin production were tested on lysates and whole human melanoma MNT-1 cells. Results showed significant enhancement of the inhibitory effects for the (S) enantiomer compared to the (R) enantiomer. Computational studies led to an explanation of this difference of activity based for both enantiomers on the respective position of the amino acid group versus the HOPNO plane. [Display omitted] • Hydroxypyridine- N -oxide analogs prepared including a non-canonic amino acid. • Inhibition on tyrosinase enzymes from mushroom, bacterial and human sources tested. • Inhibition stereoselectivity demonstrated (enzymes and cell-based assays). [ABSTRACT FROM AUTHOR]

The nickel(ii) complexes of three unsymmetrical thiosemicarbazone-based ligands featuring a sterically hindered salicylidene (1), aminophenol (2) or thiophenol (3) moiety were synthesized and structurally characterized. The metal ion lies in an almost square planar geometry in all the complexes. The cyclic voltammetry (CV) curve of 1 shows an irreversible oxidation wave at ESTACKABOVEa/ABOVEBELOWp/BELOW/STACK = 0.49 V, which is assigned to the phenoxyl/phenolate redox couple. The CV curves of 2 and 3 display a reversible one-electron oxidation wave (E1/2 = 0.26 and 0.22 V vs. Fc+/Fc, respectively) and an one-electron reduction wave (E1/2 = −1.55 and −1.46 V, respectively). The cations 2+ and 3+ as well as the anions 2− and 3− were generated. The EPR spectra of the cations in THF show a rhombic signal at g1 = 2.034, g2 = 2.010 and g3 = 1.992 (2+) and g1 = 2.069, g2 = 2.018, g3 = 1.986 (3+) that is consistent with a main radical character of the complexes. The difference in anisotropy is assigned to the different nature of the radical, iminosemiquinonate vs. iminothiosemiquinonate. The anions display an isotropic EPR signal at giso = 2.003 (2+) and 2.006 (3+), which is indicative of a main α-diimine radical character of the compounds. Both the anions and cations exhibit charge transfer transitions of low to moderate intensity in their visible spectrum. Quantum chemical calculations (B3LYP) reproduce both the g-values and Vis-NIR spectra of the complexes. The radical anions readily react with dioxygen to give the radical cations. 2+ catalyzes the aerobic oxidation of benzyl alcohol into benzaldehyde. [ABSTRACT FROM AUTHOR]

Two copper(II) complexes were synthesized from tridentate ligands involving a (Nquinoline,Nazo,Ophenol) donor set. The copper(II) ion is tetracoordinate with a chloride ion occupying the fourth position of the coordination sphere. Both X-ray diffraction and electron paramagnetic resonance (EPR) spectroscopy reveal that the copper(II) ion geometry is square planar in 1. In contrast, significant tetrahedral distortions are observed in 2, as a result of the steric clash between the hydrogen atoms of the methyl substituent of the quinoline group and the chloride ion. Cyclic voltammetry curves of 1 and 2 in CH2Cl2 display a reversible oxidation wave at E1/2 = 0.59 V and 0.56 V versus ferrocenium/ferrocene, respectively, which was assigned to the phenoxyl/phenolate redox couple. Compounds 1+ and 2+ were generated and characterized by UV/Vis and EPR spectroscopy. Their reactivity with benzyl alcohol was investigated by kinetic measurements. [ABSTRACT FROM AUTHOR]

Abstract: In the perspective of expanding the use of annexin A5 (anx A5) as radioactive tracer of cell death in vivo, we recently described its radiolabeling with 99mTc-tricarbonyl [99mTc(H2O)3(CO)3]+ via the mercaptobutyrimidyl group (anx A5-SH). The aim of the present article was to compare this new method with the HYNIC strategy (anx A5-HYNIC), recognized at present as the reference for the radiolabeling of proteins with 99mTc. Similar radiolabeling yields and better chemical stability were obtained with the [anx A5-SH-99mTc-tricarbonyl] complex. Since the [anx A5-HYNIC-99mTc(tricine)2] conjugate shows isomeric forms which can affect the biological properties whereas [anx A5-SH-99mTc-tricarbonyl] is less or not prone to such drawback, the latter seems superior to the former. Furthermore, (anx A5-SH) is readily obtained via commercial sources of Traut''s reagent whereas (anx A5-HYNIC) is not. The results provide encouraging evidence in the development of anx A5-labeled reagent for apoptose imaging. [Copyright &y& Elsevier]