Synthesis, characterization, reactivity and computational studies of new rhenium(I) complexes with thiosemicarbazone ligands derived from 4-(methylthio)benzaldehyde

Coordination Chemistry of Potentially S,N,Npy-Tridentate Thiosemicarbazones with the {Re(CO)3}+ Fragment and Formation of Hemiaminal Derivatives

Nine potentially S,N,N_py-tridentate thiosemicarbazones (HL) derived from pyridine-2-carbaldehyde or 1-(2-pyridyl)ethanone have been prepared and fully characterized. The X-ray crystal structures of six of them and two hydrochlorides were determined and analyzed. The reaction of the [ReX(CH₃CN)₂(CO)₃]/[ReX(CO)₅] (X = Cl and Br) precursors with these ligands yielded different kinds of compounds: the adducts [ReX(HL)(CO)₃], in which the ligands were S,N-bidentate; the trinuclear species [Re₃Cl₂(L²³)(HL²³)(CO)₉]; and the thiosemicarbazonate compounds [Re(L)(CO)₃], where the ligand is S,N,N_py-tridentate. Besides, the reaction in methanol or ethanol of the thiosemicarbazones derived from aldehydes yielded S,N,N_py-tridentate hemiaminal cationic [Re(HL^OR)(CO)₃]X and neutral [Re(L^OMe)(CO)₃] complexes after the coordinated ligand underwent addition of the alcohol group to the imine bond. The reactivity of the complex [ReX(HL)(CO)₃] in MeOH and NEt₃ led to the formation of dinuclear [Re₂(L)₂(CO)₆], where the thiosemicarbazonate is again S,N-bidentate. The influence that the substituents on the thiosemicarbazone ligands have on the stability of the complexes and the effect of the reaction medium on the resulting compounds have been analyzed.

Synthesis of Novel Dinuclear N-Substituted 4-(Dimethylamino)benzaldehyde Thiosemicarbazonates of Rhenium(I): Formation of Four- and/or Five-Membered Chelate Rings, Conformational Analysis, and Reactivity

The reaction of fac-[ReX(CH₃CN)₂(CO)₃] (X = Cl, Br) with N-phenyl-[4-(dimethylamino)benzaldehyde] thiosemicarbazone (HL^A) or N-4-methoxybenzyl-[4-(dimethylamino)benzaldehyde] thiosemicarbazone (HL^B) under controlled synthetic conditions gave 4 mononuclear [ReX(HL)(CO)₃] (X = Cl, Br) and 16 dinuclear [Re₂L₂(CO)₆] compounds. These complexes were obtained as single crystals, and their structures were established by X-ray diffraction. The structural study of these dimers showed the formation of several solvates, the presence of linkage isomerism, and the stabilization of four- and/or five-membered chelate rings. The different ligand coordination modes (a new μ-κ²-S,N2:κ-N3 coordination mode for a thiosemicarbazone ligand was observed), the conformation of the thiosemicarbazone chain in each case, the formal symmetry of the dimers, and the role of the synthetic procedure in the stability of the different chelate rings were analyzed and are discussed. Theoretical calculations in the gas phase were performed for the dimers with the HL^A ligand in order to identify the thermodynamically most stable species. The behavior and structural stability of dimers in dimethyl sulfoxide and acetone solutions was investigated by ¹H NMR spectroscopy. The strength of the Re^I-L bond in solution was evidenced by the formation of [Re₂(L^NO₂)₂(CO)₆] and [Re(L^A)(py)(CO)₃] upon reaction of the corresponding dimer with concentrated nitric acid and pyridine, respectively.

Thiosemicarbazonate complexes with affinity for amyloid-β fibers: synthesis, characterization and biological studies

Aim: Obtain radioimages of amyloid-β fibers using 99mTc-complexes. Methodology: Tridentate thiosemicarbazone and thiocarbonohydrazone ligands containing fragments (stilbene, azobenzene, benzothiazole or benzoxazole) with affinity for amyloid-ß fibers and its Re(I) complexes have been prepared. The molecular structures of several ligands and complexes were determined by x-ray diffraction. Binding affinity studies toward Aß1-42 fibers were performed for the ligands and Re(I) complexes. The ability of formation of some 99mTc(I) complexes, their biodistribution and in vivo stability have been established. Results & conclusion: Complexes of stilbene and benzothiazole thiosemicarbazonates show similar affinity for amyloid-β fibers to the free ligand. These 99mTc complexes present a reasonable in vivo stability and a low capability to cross the blood–brain barrier although not sufficient to brain amyloid imaging.

Structural study of mono-, di- and tetranuclear complexes of the {Re(CO)3}+ fragment with thiosemicarbazone/thiosemicarbazonate ligands containing benzothiazole or benzoxazole groups

Thiosemicarbazone form mononuclear and dinuclear complexes as bidentate ligands with {Re(CO)₃}⁺ and a tetranuclear complex with unusual bideprotonated thiosemicarbazonate.

A novel series of thiosemicarbazone drugs: from synthesis to structure

A new series of thiosemicarbazones (TSCs) and their 1,3,4-thiadiazolines (TDZs) containing acetamide group have been synthesized from thiosemicarbazide compounds by the reaction of TSCs with cyclic ketones as well as aromatic aldehydes. The structures of newly synthesized 1,3,4-thiadiazole derivatives obtained by heterocyclization of the TSCs with acetic anhydride were experimentally characterized by spectral methods using IR, (1)H NMR, (13)C NMR and mass spectroscopic methods. Furthermore, the structural, thermodynamic, and electronic properties of the studied compounds were also studied theoretically by performing Density Functional Theory (DFT) to access reliable results to the experimental values. The molecular geometry, the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO) and Mulliken atomic charges of the studied compounds have been calculated at the B3LYP method and standard 6-31+G(d,p) basis set starting from optimized geometry. The theoretical (13)C chemical shift results were also calculated using the gauge independent atomic orbital (GIAO) approach and their respective linear correlations were obtained.

Synthesis, characterization and binding affinities of rhenium(I) thiosemicarbazone complexes for the estrogen receptor (α/β)

The binding affinities towards estrogen receptors (ERs) α and β of a set of thiosemicarbazone ligands (HL(n)) and their rhenium(I) carbonyl complexes [ReX(HL(n))(CO)3] (X=Cl, Br) were determined by a competitive standard radiometric assay with [(3)H]-estradiol. The ability of the coordinated thiosemicarbazone ligands to undergo deprotonation and the lability of the ReX bond were used as a synthetic strategy to obtain [Re(hpy)(L(n))(CO)3] (hpy=3- or 4-hydroxypyridine). The inclusion of the additional hpy ligand endows the new thiosemicarbazonate complexes with an improved affinity towards the estrogen receptors and, consequently, the values of the inhibition constant (Ki) could be determined for some of them. In general, the values of Ki for both ER subtypes suggest an appreciable selectivity towards ERα.