Main group metal complexes of semicarbazones and thiosemicarbazones. A structural review

Zn(ii) complex with 2-quinolinecarboxaldehyde selenosemicarbazone: synthesis, structure, interaction studies with DNA/HSA, molecular docking and caspase-8 and -9 independent apoptose induction

A new Zn(ii)-based complex shows a concentration-dependent apoptotic response in highly resistant pancreatic adenocarcinoma cells with extensive activation of caspase-8 and -9.

Nickel(ii) and copper(ii) complexes constructed with N2S2 hybrid benzamidine–thiosemicarbazone ligand: synthesis, X-ray crystal structure, DFT, kinetico-catalytic and in vitro biological applications

We report nickel(ii) and copper(ii) complexes containing the benzamidine–thiosemicarbazone ligand together with DFT, enzyme kinetics and in vitro biological applications such as DNA/BSA affinities and anticancer properties.

Me3N-promoted synthesis of 2,3,4,4a-tetrahydroxanthen-1-one: preparation of thiosemicarbazone derivatives, their solid state self-assembly and antimicrobial properties

Thiosemicarbazones (5a–5j) have been synthesized from 2,3,4,4a-tetrahydroxanthen-1-one, obtained in high yield through Me₃N-promoted domino Baylis–Hillman/oxa-Michael reaction. Their solid-state self-assembly and antimicrobial properties are studied.

Synthesis, X-ray structure and in vitro cytotoxicity studies of Cu(i/ii) complexes of thiosemicarbazone: special emphasis on their interactions with DNA

The interactions of four Cu-TSC complexes with DNA & their cytotoxicity studies against the HeLa cell have been reported.

Robustness of a thioamide {⋯H–N–CS}2 synthon: synthesis and the effect of substituents on the formation of layered to cage-like supramolecular networks in coumarin–thiosemicarbazone hybrids

The study has been carried out to highlight the potential of thiosemicarbazones in crystal engineering.

Synthesis and structures of 5-nitro-salicylaldehyde thiosemicarb-azonates of copper(ii): molecular spectroscopy, ESI-mass studies, antimicrobial activity and cytotoxicity

Salicylaldehyde thiosemicarbazonates of copper(ii) have shown significant growth inhibitory activity againstS. aureus, MRSA,K. pneumonia,S. flexneri,P. aeruginosaandC. albicansand are bactericidal in nature with low cytotoxicity.

Activation of C–H bonds of thiosemicarbazones by transition metals: synthesis, structures and importance of cyclometallated compounds

Transition metals (Pd^II, Pt^II, Ru^II, Rh^IIIand Ir^III) have induced activation of C–H bonds of thiosemicarbazones and yielded mono-, di-, tri- and tetra-nuclear complexes.

Significant photocytotoxic effect of an iron(iii) complex of a Schiff base ligand derived from vitamin B6and thiosemicarbazide in visible light

An iron(iii)–Schiff base complex derived from vitamin B₆and thiosemicarbazide is significantly photocytotoxic to HeLa cancer cells in visible light (400 nm–700 nm) but non-toxic in the absence of light.

Robustness of thioamide dimer synthon, carbon bonding and thioamide–thioamide stacking in ferrocene-based thiosemicarbazones

The role of thioureas in crystal engineering as robust supramolecular synthons is now recognized, but their analogs, namely thiosemicarbazones/N-iminothioureas, have not received the attention they deserve.

Comprehensive insights into the structure and coordination behavior of thiosemicarbazone ligands: a computational assessment of the E–Z interconversion mechanism during coordination

The calculations transpired that the isomerization mechanism of thiosemicarbazones is influenced by the solvents, in which the inversion and tautomerization path is the likely mechanisms in aprotic and protic solvents, respectively.

Ruthenium(ii) complexes containing a phosphine-functionalized thiosemicarbazone ligand: synthesis, structures and catalytic C–N bond formation reactions via N-alkylation

We report the coordination flexibility of phosphino-thiosemicarbazone in ruthenium(ii) complexes, together with their catalytic properties with regards to N-alkylation.

Exploring the interaction of N/S compounds with a dicopper center: tyrosinase inhibition and model studies

Tyrosinase (Ty) is a copper-containing enzyme widely present in plants, bacteria, and humans, where it is involved in biosynthesis of melanin-type pigments. Development of Ty inhibitors is an important approach to control the production and the accumulation of pigments in living systems. In this paper, we focused our interest in phenylthiourea (PTU) and phenylmethylene thiosemicarbazone (PTSC) recognized as inhibitors of tyrosinase by combining enzymatic studies and coordination chemistry methods. Both are efficient inhibitors of mushroom tyrosinase and they can be considered mainly as competitive inhibitors. Computational studies verify that PTSC and PTU inhibitors interact with the metal center of the active site. The KIC value of 0.93 μM confirms that PTSC is a much more efficient inhibitor than PTU, for which a KIC value of 58 μM was determined. The estimation of the binding free energies inhibitors/Ty confirms the high inhibitor efficiency of PTSC. Binding studies of PTSC along with PTU to a dinuclear copper(II) complex ([Cu2(μ-BPMP)(μ-OH)](ClO4)2 (1); H-BPMP = 2,6-bis-[bis(2-pyridylmethyl)aminomethyl]-4-methylphenol) known to be a structural and functional model for the tyrosinase catecholase activity, have been performed. Interactions of the compounds with the dicopper model complex 1 were followed by spectrophotometry and electrospray ionization (ESI). The molecular structure of 1-PTSC and 1-PTU adducts were determined by single-crystal X-ray diffraction analysis showing for both an unusual bridging binding mode on the dicopper center. These results reflect their adaptable binding mode in relation to the geometry and chelate size of the dicopper center.

Effects of terminal dimethylation and metal coordination of proline-2-formylpyridine thiosemicarbazone hybrids on lipophilicity, antiproliferative activity, and hR2 RNR inhibition

The nickel(II), copper(II), and zinc(II) complexes of the proline-thiosemicarbazone hybrids 3-methyl-(S)-pyrrolidine-2-carboxylate-2-formylpyridine thiosemicarbazone (L-Pro-FTSC or (S)-H2L(1)) and 3-methyl-(R)-pyrrolidine-2-carboxylate-2-formylpyridine thiosemicarbazone (D-Pro-FTSC or (R)-H2L(1)), as well as 3-methyl-(S)-pyrrolidine-2-carboxylate-2-formylpyridine 4,4-dimethyl-thiosemicarbazone (dm-L-Pro-FTSC or (S)-H2L(2)), namely, [Ni(L-Pro-FTSC-2H)]2 (1), [Ni(D-Pro-FTSC-2H)]2 (2), [Ni(dm-L-Pro-FTSC-2H)]2 (3), [Cu(dm-L-Pro-FTSC-2H)] (6), [Zn(L-Pro-FTSC-2H)] (7), and [Zn(D-Pro-FTSC-2H)] (8), in addition to two previously reported, [Cu(L-Pro-FTSC-2H)] (4), [Cu(D-Pro-FTSC-2H)] (5), were synthesized and characterized by elemental analysis, one- and two-dimensional (1)H and (13)C NMR spectroscopy, circular dichroism, UV-vis, and electrospray ionization mass spectrometry. Compounds 1-3, 6, and 7 were also studied by single-crystal X-ray diffraction. Magnetic properties and solid-state high-field electron paramagnetic resonance spectra of 2 over the range of 50-420 GHz were investigated. The complex formation processes of L-Pro-FTSC with nickel(II) and zinc(II) were studied in aqueous solution due to the excellent water solubility of the complexes via pH potentiometry, UV-vis, and (1)H NMR spectroscopy. The results of the antiproliferative activity in vitro showed that dimethylation improves the cytotoxicity and hR2 RNR inhibition. Therefore, introduction of more lipophilic groups into thiosemicarbazone-proline backbone becomes an option for the synthesis of more efficient cytotoxic agents of this family of compounds.

Main group bismuth(III), gallium(III) and diorganotin(IV) complexes derived from bis(2-acetylpyrazine)thiocarbonohydrazone: synthesis, crystal structures and biological evaluation

Up to now, the metal complexes with thiocarbonohydrazones have been comparatively rare. Herein, three main group monometallic complexes formulated as [Bi(HL)(NO3)2(H2O)] (1), [Ga(HL)2]OAc·EtOH (2) and [(Ph)2Sn(HL)(OAc)]·DMF (3), where H2L = bis(2-acetylpyrazine)thiocarbonohydrazone, have been synthesized and characterized. The crystal structures of complexes 2 and 3 have been determined by single-crystal X-ray diffraction. Growth inhibition assays have indicated that both the free ligand and the title complexes are capable of inhibiting cell proliferation growth and could slightly distinguish the human hepatocellular carcinoma HepG2 cells from normal hepatocyte QSG7701 cells. Of particular note is the fact that the bismuth(III) complex 1 is the most active compound of this study and is 14-fold more cytotoxic than H2L with an IC50 value of 2.96 ± 0.25 μM. Its possible apoptotic mechanism has been evaluated in HepG2 cells. Complex 1 promotes a dose-dependent apoptosis in HepG2 cells and the apoptosis is associated with an increase in intracellular reactive oxygen species (ROS) production and reduction of mitochondrial membrane potential (MMP).

Vibrational spectroscopy (FT-IR and Laser-Raman) investigation, and computational (M06-2X and B3LYP) analysis on the structure of 4-(3-fluorophenyl)-1-(propan-2-ylidene)-thiosemicarbazone

In this study, the experimental and theoretical vibrational spectral analysis of 4-(3-fluorophenyl)-1-(propan-2-ylidene)-thiosemicarbazone have been carried out. The experimental FT-IR (4000-400 cm(-1)) and Laser-Raman spectra (4000-100 cm(-1)) have been recorded for the solid state samples. The theoretical vibrational frequencies and the optimized geometric parameters (bond lengths and angles) have been calculated for gas phase using density functional theory (DFT/B3LYP: Becke, 3-parameter, Lee-Yang-Parr) and M06-2X (the highly parametrized, empirical exchange correlation function) quantum chemical methods with 6-311++G(d,p) basis set. The diversity in molecular geometry of fluorophenyl substituted thiosemicarbazones has been discussed based on the X-ray crystal structure reports and theoretical calculation results from the literature. The assignments of the vibrational frequencies have been done on the basis of potential energy distribution (PED) analysis by using VEDA4 software. A good correlation was found between the computed and experimental geometric and vibrational data. In addition, the highest occupied (HOMO) and lowest unoccupied (LUMO) molecular orbital energy levels and other related molecular energy values of the compound have been determined using the same level of theoretical calculations.

Anti-cancer palladium complexes: a focus on PdX2L2, palladacycles and related complexes

Much success has been achieved with platinum-based chemotherapeutic agents, i.e. through interactions with DNA. The long-term application of Pt complexes is thwarted by issues, leading scientists to examine other metals such as palladium which could exhibit complementary modes of action (given emphasis wherever known). Over the last 10 years several research groups have focused on the application of an eclectic array of palladium complexes (of the type PdX2L2, palladacycles and related structures) as potential anti-cancer agents. This review therefore provides readers with an up to date account of the advances that have taken place over the past several decades.

Structure-Activity Relationship of Semicarbazone EGA Furnishes Photoaffinity Inhibitors of Anthrax Toxin Cellular Entry

EGA, 1, prevents the entry of multiple viruses and bacterial toxins into mammalian cells by inhibiting vesicular trafficking. The cellular target of 1 is unknown, and a structure-activity relationship study was conducted in order to develop a strategy for target identification. A compound with midnanomolar potency was identified (2), and three photoaffinity labels were synthesized (3-5). For this series, the expected photochemistry of the phenyl azide moiety is a more important factor than the IC50 of the photoprobe in obtaining a successful photolabeling event. While 3 was the most effective reversible inhibitor of the series, it provided no protection to cells against anthrax lethal toxin (LT) following UV irradiation. Conversely, 5, which possessed weak bioactivity in the standard assay, conferred robust irreversible protection vs LT to cells upon UV photolysis.

Synthesis, NMR structural characterization and molecular modeling of substituted thiosemicarbazones and semicarbazones using DFT calculations to prove the syn/anti isomer formation

Thiosemicarbazones possessing electron-donating and electron-withdrawing groups were prepared, and their spectral characteristics determined. In all cases, the spectra showed that one isomer was formed, allowing further functionalization to molecules of biological interest. We provide NMR data for some of the thiosemicarbazones and semicarbazones. We also provide evidence that for 2-pyridyl thiosemicarbazone, the syn isomer slowly converts into the anti isomer in dimethyl sulfoxide solvent with first-order kinetics. Molecular modeling and density functional theory calculations confirmed these observations.

Synthesis, characterization, electrochemical studies, and in vitro antibacterial activity of novel thiosemicarbazone and its Cu(II), Ni(II), and Co(II) complexes

Metal complexes were prepared by the reaction of thiosemicarbazone with CuCl₂, NiCl₂, CoCl₂, Cu(OAc)₂, Ni(OAc)₂, and Co(OAc)₂. The thiosemicarbazone coordinates to metal through the thionic sulfur and the azomethine nitrogen. The thiosemicarbazone was obtained by the thiosemicarbazide with 3-acetyl-2,5-dimethylthiophene. The identities of these compounds were elucidated by IR, ¹H, ¹³C-NMR, and GC-MS spectroscopic methods and elemental analyses. The antibacterial activity of these compounds was first tested in vitro by the disc diffusion assay against two Gram-positive and two Gram-negative bacteria, and then the minimum inhibitory concentration (MIC) was determined by using chloramphenicol as reference drug. The results showed that compound 1.1 is better inhibitor of both types of tested bacteria as compared to chloramphenicol.

Synthesis, spectral and electrochemical studies of binuclear Ru(III) complexes containing dithiosemicarbazone ligand

Synthesis of several new octahedral binuclear ruthenium(III) complexes of the general composition [(EPh3)2(X)Ru-L-Ru(X)(EPh3)2] containing benzene dithiosemicarbazone ligands (where E=P or As; X=Cl or Br; L=binucleating ligands) is presented. All the complexes have been fully characterized by elemental analysis, FT-IR, UV-vis and EPR spectroscopy together with magnetic susceptibility measurements. IR study shows that the dithiosemicarbazone ligands behave as dianionic tridentate ligands coordinating through the oxygen atom of the deprotonated phenolic group, nitrogen atom of the azomethine group and thiolate sulphur. In DMF solution, all the complexes exhibit intense d-d transition and ligand-to-metal charge transfer (LMCT) transition in the visible region. The magnetic moment values of the complexes are in the range 1.78-1.82 BM, which reveals the presence of one unpaired electron on each metal ion. The EPR spectra of the liquid samples at LNT show the presence of three different 'g' values (gx≠gy≠gz) indicate a rhombic distortion around the ruthenium ion. All the complexes exhibit two quasi-reversible one electron oxidation responses (Ru(III)-Ru(III)/Ru(III)-Ru(IV); Ru(III)-Ru(IV)/Ru(IV)-Ru(IV)) within the E1/2 range of 0.61-0.74 V and 0.93-0.98 V respectively, versus Ag/AgCl.

Efficient and versatile catalysis of N-alkylation of heterocyclic amines with alcohols and one-pot synthesis of 2-aryl substituted benzazoles with newly designed ruthenium(ii) complexes of PNS thiosemicarbazones

Efficient catalytic N-alkylation of amines using Ru(ii) catalysts with good yields and high selectivity.

Novel synthesis of palladium (II) complexes derived from 3-arylsydnone-4-carbaldehyde N(4)-phenylthiosemicarbazones and biological activity

Objectives

The aim of this research is to investigate whether the oxygen atom O(6) in the sydnone ring of 3-arylsydnone-4-carbaldehyde N(4)-phenylthiosemicarbazones (HArSYTSCs, 3a–d) is a good electron donor atom upon metal complexation. Furthermore, ligands 3a–d and the corresponding palladium complexes (Pd(ArSYTSC)Cl, 4a–d) would be expected to find their potent biological activities.

Methods

The desired palladium complexes 4a–d were first synthesized from thiosemicarbazones 3a–d. Then, the antiproliferative activity of ligands 3a–d and complexes 4a-d were tested against human hepatocellular carcinoma and human cervical epithelioid carcinoma (HeLa) cells by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl trazolium bromide (MTT) assay.

Key findings

According to X-ray analyses, ligands 3a–d are bonded to the Pd (II) center in an O, N, S-tridentate coordination mode through sydnone carbonyl oxygen O(6), azomethine nitrogen and the thiolate sulfur atom. The carbonyl oxygen of the sydnone ring is found to be a good electron donor site upon metal complexation. Moreover, MTT assay results reveal that the palladium complexes 4a–d have greater antiproliferative activity than 5-fluorouracil. In particular, the complexes exhibit obvious better activity than the corresponding ligands 3a–d against HeLa cell.

Conclusions

The results indicate that the synthesized novel palladium complexes have greater antiproliferative activity than both 5-fluorouracil and the corresponding ligands against HeLa cell. Accordingly, the study of sydnonyl complexes bearing anticancer activities may support the development of coordination chemistry.

Synthesis and structural characterization of fluorinated thiosemicarbazones

Six new fluorinated thiosemicarbazones R-C(R′)=N-NH-C(S)NH₂ (R = 2,4-C₆H₃F₂, R′ = H (1); R = 2,5-C₆H₃F₂, R′ = H (2); R = 2,6-C₆H₃F₂, R′ = H (3); R = 3,4-C₆H₃F₂, R′ = H (4); R = 3,5-C₆H₃F₂, R′ = H (5) and R = 4-C₆H₄F, R′ = C₆H₅, (6)) have been prepared. The molecular structures of compounds 1 to 6 have been determined.