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International audience; A phenanthrene unit has been functionalized by several methylthiophene units in order to bring it a photochromic behavior. These compounds were characterized by NMR, absorption and emission spectroscopies, theoretical calculations as well as cyclic voltammetry. The association of a phenanthrene group with a photochromic center could open the door to a new generation of organic field-effect transistors.

International audience; Tyrosinase enzymes (Tys) are involved in the key steps of melanin (protective pigments) biosynthesis and molecules targeting the binuclear copper active site on tyrosinases represent a relevant strategy to regulate enzyme activities. In this work, we studied the possible synergic effect generated by combination of known inhibitors. For this, derivatives containing kojic acid (KA) and 2-Hydroxypyridine-N-oxide (HOPNO) combined with a thiosemicarbazone (TSC) moiety were synthetized. Their inhibition activities were evaluated on purified tyrosinases from different sources (mushroom, bacterial and human) as well as on melanin production by lysates from human melanoma MNT-1 cell line. Results showed significant enhancement of the inhibitory effects compared to the parent compounds, in particular for HOPNO-TSC. In order to elucidate the interaction mode with the dicopper(II) active site, we investigated the binding studies towards a tyrosinase bio-inspired model of the dicopper(II) center. The structure of the isolated adduct between one ditopic inhibitor (KA-TSC) and the model complex reveals that the binding to a dicopper center can occur with both chelating sites. Computational studies on model complexes and docking studies on enzymes led to the identification of KA and HOPNO moieties as interacting groups with the dicopper active site.

Disulfide/thiolate interconversion controlled by Cu is proposed to be involved in relevant biological processes. In analogy to Cu, it can be envisaged that Fe also participates in the control of similar biological processes. We describe here Fe complexes that undergo FeIII -thiolate/FeII -disulfide (inter)conversion mediated by halide (de)coordination, and by the nature of the solvent. The dinuclear FeII -disulfide complex [FeII2 (LSSL)]2+ ((LS)2- =2,2'-(2,2'-bipyridine-6,6'-diyl)bis(1,1-diphenylethanethiolate), (LSSL)2- =the corresponding disulfide ligand) shows solvent-dependent properties. Whereas in a non-coordinating solvent (CH2 Cl2 ) the dinuclear FeII -disulfide complex is the only stable form, in the presence of coordinating solvents like MeCN or DMF it is partly or fully converted into mononuclear FeIII -thiolate species having a bound solvent molecule ([FeIII (LS)(Solv)]+ , Solv=DMF, MeCN). Addition of Cl- to a CH2 Cl2 solution containing the FeII -disulfide dinuclear complex leads to the fast and quantitative formation of a mononuclear FeIII -thiolate species with a bound Cl- , that is, ([FeIII (LS)Cl]). The reverse reaction can be achieved by addition of Li[[B(C6 F5 )4 ]. In relation to the metal-sulfur electronic distribution, the comparison between the redox properties of the Fe, Mn and Co complexes involved in these MIII -thiolate/MII -disulfide interconversion processes allow one to rationalize their respective efficiency.

Three copper(II) complexes of the (R,R)-N,N'-bis(3,5-di-tert-butyl-2-aminobenzylidene)-1,2-diaminocyclohexane ligand, namely [Cu(

Where is the radical? The π-system of the diiminobenzene bridge adds a putative oxidation site to prophenoxyl copper(II) salophen complexes. It is shown that the bridge is effectively redox active and that the radical site (phenoxyl vs. diiminobenzene bridge) in the above cations is tuned by selective methoxy substitution (see figure).

Two di-tert-butylphenols incorporating an N-methylbenzimidazole moiety in the ortho or para position have been synthesised (MeOH and pMeOH, respectively). Their X-ray structures evidence a hydrogen bond between the phenolic proton and the iminic nitrogen atom, whose nature is intra- and intermolecular, respectively. The present studies demonstrate that MeOH is readily oxidised by an intramolecular PET mechanism to form the hydrogen-bonded phenoxyl-N-methylbenzimidazolium system (MeOH) .+ , whereas oxidation of pMeOH occurs by intermolecular PET, affording the neutral phenoxyl benzimidazole (pMeO). system. The deprotonations of MeOH and pMeOH yield the corresponding phenolate species (MeO)- and (pMeO)-, respectively, whilst that of the previously reported HOH (analogous to MeOH but lacking the N-methyl group) produces an unprecedented hydrogen-bonded phenol benzimidazolate species, as evidenced by its X-ray structure. The latter is believed to be in equilibrium in solution with its tautomeric phenolate form, as suggested by NMR, electrochemistry and DFT studies. The one-electron oxidations of the anions occur by a simple ET process affording phenoxyl radical species, whose electronic structure has been studied by HF-EPR spectroscopy and DFT calculations. In particular, analysis of the g1 tensor shows the order 2.0079>2.0072>2.0069>2.0067 for (MeO)., (HO)., (MeOH).+ and (HOH).+, respectively. (MeO). exhibits the largest g1 tensor (2.0079), consistent with the absence of intramolecular hydrogen bond. The g1 tensor of (HO). is intermediate between those of (MeOH).+ and (MeO). (g1=2.0072), indicating that the phenoxyl oxygen is hydrogen-bonded with a neutral benzimidazole partner.

Four tripodal ligands with an N 3 O coordination sphere were synthesized: (2-hydroxy-3-tert-butyl-5-nitro-benzyl)bis(2-pyridylmethyl)amine (LNO 2 H), (2-hydroxy-3-tert-butyl-5-fluorobenzyl)bis(2-pyridylmethyl)amine (LFH), (2-hydroxy-3,5-di-tert-butylbenzyl)bis(2-pyridylmethyl)amine (LtBuH) and (2-hydroxy-3-tert-butyl-5-methoxy-benzyl)bis(2-pyridylmethyl)amine (LOMeH). Their square-pyramidal cop-per(II) complexes, in which the phenol subunit occupies an axial position, were prepared and characterized by X-ray crystallography and UV/Vis and EPR spectroscopy. The phenolate moieties of the copper(II) complexes of LtBuH and LOMeH were electrochemically oxidized to phenoxyl radicals. These complexes are EPR-active (S=1), highly stable (k d e c a y =0.008 min - 1 for [Cu I I (LOMe . )(CH 3 CN)] 2 + ) and stoichiometrically oxidise benzyl alcohol. Two additional tripodal ligands providing an N 2 O 2 coordination sphere were also studied: (2-pyridylmethyl)(2-hydroxy-3-tert-butyl-5-methoxybenzyl)-(2-hydroxy-3-tert-butyl-5-nitrobenzyl)-amine (L'OMeNO 2 H 2 ) and (2-pyridyl-methyl)bis(2-hydroxy-3-tert-butyl-5-methoxy)benzylamine (L'OMe 2 H 2 ). Their copper(II) complexes were isolated as dimers ([Cu I I 2(L'OMe 2 ) 2 ], [Cu I I 2(L'OMeNO 2 ) 2 ]) that are converted to monomers on addition of pyridine. The complexes were investigated by X-ray crystallography and UV/Vis and EPR spectroscopy. Their one-electron electrochemical oxidation leads to cop-per(II)-phenoxyl systems that are less stable than those of the N 3 O complexes. The N 2 O 2 complexes are more reactive than the N 3 O analogues: they aerobically oxidize benzyl alcohol to benzaldehyde at a higher rate, as well as ethanol to acetaldehyde (40-80 turnovers).

Several N-aryl-substituted thioamides with an axis of chirality along the N-C(aryl) bond were prepared in good to excellent yields. NMR spectra revealed preferences for the E rotamer (along the N-C(=S) bond). X-ray crystallographic analysis showed that the planes of the aryl and thioamide groups were almost perpendicular (79 degrees). For the first time, these atropisomeric thioamides were used for an asymmetric Claisen rearrangement. LDA deprotonation led selectively to the enethiolates of Z stereochemistry, and subsequent reaction with a variety of allyl halides furnished S-allyl keteneaminothioacetals. These intermediates were not detected as they rearranged readily to gamma-unsaturated thioamides in good to high yields and diastereoselectivities up to 88:12. Chemical correlation allowed the assignment of the (aR*,2R*) configuration to the major diastereoisomer. A model was proposed to explain the stereochemical course of the thio-Claisen rearrangement.