Structural and biological studies of mononuclear palladium(II) complexes containing N-substituted thiosemicarbazones

Synthesis of 5-hydroxyisatin thiosemicarbazones, spectroscopic investigation, protein-ligand docking, and in vitro anticancer activity

A series of novel modifications were performed at the N(4) position of 5-hydroxyisatin thiosemicarbazone (TSC). The structure-activity approach is applied to design and synthesize derivatives by condensing thiosemicarbazides with 5-hydroxy isatin. The TSCs were characterized by various spectroscopic techniques viz. FTIR, 1H NMR, 13C NMR, UV-Vis, HRMS data, CHN elemental analysis, and single crystal X-ray diffraction. Biological evaluation of the synthesized compounds revealed the anticancer potency of the TSC analogues against breast cancer (MD-AMD-231, MCF-7), lung cancer (A549, NCI-H460), prostate cancer (PC3), and skin cancer (A431). The molecules, L2, L3, and L6 showed activity in the micromolar range (IC50; 0.19-2.19 μM). L6 exhibited the highest potency against skin cancer A431 cell line, with an IC50 of 0.19 μM compared to 1.8 μM with triapine and showed low toxicity against PNT-2 cells with an SI index of >100 μM. The mechanistic study revealed that L6 inhibited cancer cell proliferation, colony formation, and 3-dimensional spheroid formation by targeting the Ras/MAPK axis. It induced DNA damage and impaired DNA damage repair machinery, which led to the accumulation of DSB. Also, it lowered the ERK1/2 expression, which affected the caspase 3 activity and showed higher binding affinity compared to the FDA-approved drug Lenalidomide in molecular docking studies. Our findings demonstrated the possible future anticancer drug potency of L6 in the skin cancer A431 cells.

Anticancer, antimicrobial and photocatalytic activities of a new pyrazole containing thiosemicarbazone ligand and its Co(III) and Ni(II) complexes: Synthesis, spectroscopic characterization and X-ray crystallography

A new pyrazole based thiosemicarbazone ligand, 5-methyl-3-formylpyrazole-N(4)-isopropylthiosemicarbazone, (HMPzNHPri) (compound I), and its cobalt(III) and nickel(II) complexes, [Co(MPzNHPri)2]Cl (compound II) and [Ni(HMPzNHPri)2]Br2 (compound III), respectively, have been synthesized and characterized through various physico-chemical and spectroscopic studies. Both the reported Co(III) and Ni(II) complexes are cationic in nature and behave as 1:1 and 1:2 electrolytes in MeOH, respectively. Electronic spectral features of the complexes have classified them as distorted octahedral ones. IR spectral data (4000-450 cm-1) have suggested a monoprotic tridentate (NNS) function of compound I coordinating to the Co(III) ion via the pyrazolyl (tertiary) ring nitrogen, azomethine nitrogen and thiolato sulphur atom; while for compound III, compound I has been found to act as neutral NNS tridentate one, coordinating to Ni(II) via the pyrazolyl iminic nitrogen, azomethine nitrogen and thioketo sulphur. Structural features of all the compounds are confirmed by the single crystal X-ray data. All the compounds reported here have been found to exhibit significant photocatalytic activity towards degradation of Methylene Blue (MB) under UV radiation. Anticancer activity of all the three compounds against cancer cell lines (HeLa and A549) and a normal cell line (HEK293) have been investigated. Compound II has been found to be more efficient against the human cervical cancer cell (HeLa) and the lung cancer cell (A549) than compounds I and III. The ligand and both the complexes display potential activities against both gram-positive (Bacillus subtilis MTCC 7193) and gram-negative bacteria (E. coli MTCC 1610).

Research Progress on the Biological Activities of Metal Complexes Bearing Polycyclic Aromatic Hydrazones

Due to the abundant and promising biological activities of aromatic hydrazones, it is of great significance to study the biological activities of their metal complexes for the research and development of metal-based drugs. In this review, we focus on the metal complexes of polycyclic aromatic hydrazones, which still do not receive much attention, and summarize the studies related to their biological activities. Although the large number of metal complexes in phenylhydrazone prevent them all from being summarized, the significant value of polycyclic aromatic hydrocarbons themselves (such as naphthalene and anthracene) as pharmacophores are also considered. Therefore, the bioactivities of the metal complexes of naphthylhydrazone and anthrahydrazone are focused on, and the recent research progress on the metal complexes of anthrahydrazone by the authors is also included. In terms of biological activities, these complexes mainly show antibacterial and anticancer activities, along with less bioactivities. The present review demonstrates that the structural design and bioactivities of these complexes are fundamental, which also indicates a certain structure-activity relationship (SAR) in some substructural areas. However, a systematic and comprehensive conclusion of the SAR is still not available, which suggests that more attention should be paid to the bioactivities of the metal complexes of polycyclic aromatic hydrazones since their potential in structural design and biological activity remains to be explored. We hope that this review will attract more researchers to devote their interest and energy into this promising area.

New Pd(II) complexes of the bisthiocarbohydrazones derived from isatin and disubstituted salicylaldehydes: Synthesis, characterization, crystal structures and inhibitory properties against some metabolic enzymes

Pd(II) complexes (Pd1, Pd2, and Pd3) were synthesized for the first time using asymmetric isatin bisthiocarbohydrazone ligands and PdCl₂(PPh₃)₂. All complexes were characterized by a range of spectroscopic and analytical techniques. The molecular structures of Pd1 and Pd3 have been determined by single-crystal X-ray diffraction analysis. The complexes are diamagnetic and exhibit square planar geometry. The asymmetric isatin bisthiocarbohydrazone ligands coordinate to Pd(II) ion in a tridentate manner, through the phenolic oxygen, imine nitrogen and thiol sulfur, forming five- and six-membered chelate rings within their structures. The fourth coordination site in these complexes is occupied by PPh₃ (triphenylphosphine). The free ligands and their Pd(II) complexes were evaluated for their carbonic anhydrase I, II (hCAs) and acetylcholinesterase (AChE) inhibitor activities. They showed a highly potent inhibition effect on AChE and hCAs. K_i values are in the range of 9 ± 0.6 - 30 ± 5.4 nM for AChE, 7 ± 0.5 - 16 ± 2.2 nM for hCA I and 3 ± 0.3-24 ± 1.9 nM for hCA II isoenzyme. The results clearly demonstrated that the ligands and their Pd(II) complexes effectively inhibited the used enzymes.

Stabilization of a potential anticancer thiosemicarbazone derivative in Sudlow site I of human serum albumin: In vitro spectroscopy coupled with molecular dynamics simulation

Human Serum Albumin (HSA) is the most important protein in human blood plasma and can acts as a major transporting agent for various drug molecules with flexible binding interaction. To elucidate the interaction of a newly designed potential anticancer thiosemicarbazone based luminophore (E)-1-(4-(diethylamino)-2-hydroxybenzylidene)-4,4-dimethyl-thiosemicarbazide (DAHTS) with HSA under physiological condition, in vitro optical spectroscopic experiments viz UV-Vis absorption, steady state fluorescence, fluroscence anisotropy, time resolved fluorscence (TRF) and cicular dichroism (CD) spectroscopy have been scrutinised. The experimental findings have been corroborated with in silico molecular docking analysis and Molecular Dynamics (MD) simulation. The spectroscopic results demonstrated that the conventionally anion-favouring Sudlow site I of HSA copiously adapt neutral DAHTS molecule with moderate binding affinity. The mean fluorescence lifetime of the sole tryptophan (Trp-214) present in the macromolecule experiences an appreciable diminution with an increase in concentration of the synthesized molecule. DAHTS localize itself close to Trp-214 within subdomain IIA (Sudlow site I) and surrounded by multiple hydrophobic amino acid residues (Val-235, Val-231, Ala-229, Phe-228, Val-325, Phe-326, Leu-327, Met-329, Phe-330, Leu-331, Tyr-332, Leu-346, Leu-347, Val-482, Leu-349, Ala-350, Ala-210, Trp-214, Ala- 213 and Val-216) in HSA. The distinct fluorescence lifetime, diverse pathways and changing rate of population indicates that the rotamerisation of Trp-214 residue is controlled by the guest molecule. Sudlow site I of HSA behaves flexibly and induces an allosteric modulation in the macromolecule resulting a minor deformation in the protein secondary structure as observed in CD (observed 11% change of α-helix content) as well as in MD simulation. The integrated multi-spectroscopic research described herein provides several important information about the binding interaction of a thiosemicarbazone Schiff base with HSA, which can be very significant for thiosemicarbazone based drug designing for academia as well as industry.

Synthesis and spectral characterizations of water soluble Cu(ii) complexes containing N-heterocyclic chelates: cell-proliferation, antioxidant and nucleic acid/serum albumin interactions

Water soluble N-heterocyclic copper(ii) complexes were synthesized, characterized and studied their DNA/protein binding interactions, antioxidation and antiproliferative potentials. The complex 4 found to be better than other complexes.

Example of two novel thiocyanato bridged copper (II) complexes derived from substituted thiosemicarbazone ligand: structural elucidation, DNA/albumin binding, biological profile analysis, and molecular docking study

Two novel copper (II) substituted thiosemicarbazone Schiff base complexes [Cu(L₁)(µ-SCN)]_n(NO₃)₂ (1) and [Cu₂(µ-SCN)(SCN)(L₂)₂](NO₃) (2) have been synthesized by condensing substituted thiosemicarbazides like 4-methyl-3-thiosemicarbazide or 4-ethyl-3-thiosemicarbazide with 2-acetylpyridine. Both the metal complexes 1 and 2 are characterized using different spectroscopic techniques like IR, UV-Vis, ESR spectroscopy followed by elemental analysis, cyclic voltammetric measurement and single crystal X-ray structure analysis. X-ray crystal structure analysis reveal that complex 1 is polymeric while complex 2 is dimeric in nature. The coordination geometry around Cu(II) are square pyramidal in which thiosemicarbazone Schiff base ligand coordinate to the central Cu(II) atom in tridentate fashion. The prominent interaction patterns of 1 and 2 with CT-DNA were examined by employing electronic absorption and emission spectral titrations, cyclic voltammetry and viscosity measurements. All the results show that CT-DNA binds with both copper (II) complexes 1 and 2. Furthermore, protein binding ability in vitro of complexes 1 and 2 with both BSA and HSA were carried out using multispectroscopic techniques and a static quenching pattern was observed in both cases. Molecular docking study was employed to ascertain the exact mechanism of action of 1 and 2 with DNA and protein molecules (BSA and HSA). In vitro cytotoxicity activity of complexes 1 and 2 toward AGS and A549 was evaluated using MTT assay which demonstrates that both complexes 1 and 2 have superior prospectus to act as anticancer agents. Communicated by Ramaswamy H. Sarma.

Morphological and in vitro evaluation of programmed cell death in MCF-7 cells by new organoruthenium(ii) complexes

Cyclopentadienyl ruthenium(ii) thiosemicarbazone complexes with the formula [Ru(η⁵-C₅H₅)(Ac-tsc)PPh₃]·Cl (1), [Ru(η⁵-C₅H₅)(Ac-mtsc)PPh₃]·Cl (2), [Ru(η⁵-C₅H₅)(Ac-etsc)PPh₃]·Cl (3) and [Ru(η⁵-C₅H₅)(Ac-ptsc)PPh₃] (4) were synthesized and characterized by various spectroscopic techniques (¹H NMR,¹³C NMR, IR and UV-vis).

Substitutional impact on biological activity of new water soluble Ni(II) complexes: Preparation, spectral characterization, X-ray crystallography, DNA/protein binding, antibacterial activity and in vitro cytotoxicity

A series of new water soluble nickel(II) complexes containing triphenylphosphine and 4-methoxysalicylaldehyde-4(N)-substituted thiosemicarbazones were synthesized and characterized. Crystallographic investigations confirmed the structure of the complexes (1-4) having the general structure [Ni(4-Msal-Rtsc)(PPh₃)] (Where R=H (1); CH₃ (2); C₂H₅ (3); C₆H₅ (4)) which showed that thiosemicarbazone ligands coordinated to nickel(II) ion as ONS tridentate bibasic donor. DNA/BSA protein binding ability of the ligands and their new complexes were studied by taking calf-thymus DNA (CT-DNA) and Bovine serum albumin (BSA) through absorption and emission titrations. Ethidium bromide (EB) displacement study showed the intercalative binding trend of the complexes to DNA. From the albumin binding studies, the mechanism of quenching was found as static and the alterations in the secondary structure of BSA by the compounds were confirmed with synchronous spectral studies. The binding affinity of the complexes to CT-DNA and BSA has the order of [Ni(4-Msal-etsc)(PPh₃)] (3) >[Ni(4-Msal-mtsc)(PPh₃)] (2) >[Ni(4-Msal-tsc)(PPh₃)] (1) >[Ni(4-Msal-ptsc)(PPh₃)] (4). In vitro cytotoxicity of the complexes was tested on human lung cancer cells (A549), human cervical cancer cells (HeLa), human liver carcinoma cells (Hep G2). All the complexes exhibited significant activity against three cancer cells. Among them, complex 4 exhibited almost 2.5 fold activity than cisplatin in A549 and HepG2 cell lines. In HeLa cell line, the complexes exhibited significant activity which is less than cisplatin. While comparing the activity of the complexes in A549 and HepG2 cell lines it falls in the order 4>1>2>3>cisplatin. The results obtained from DNA, protein binding and cytotoxicity studies, it is concluded that the cytotoxicity of the complexes as determined by MTT assay were not unduly influenced by the complexes having different binding efficiency with DNA and protein. The complexes exhibited good spectrum of antibacterial activity against four pathogenic bacteria such as E. faecalis (gram +ve), S. aureus (gram +ve), E. coli (gram -ve) and P. aeruginosa (gram -ve).

Crystal structure of (E)-2-hydroxy-4′-methoxyazastilbene

The title compound has an E conformation with respect to the azomethine C=N bond and the aromatic rings are inclined to one another by 3.29 (4)°. In the crystal, mol­ecules are linked via C—H⋯O hydrogen bonds, forming zigzag chains along [10-1].

The title aza­stilbene derivative, C₁₄H₁₃NO₂ {systematic name: (E)-2-[(4-meth­oxy­benzyl­idene)amino]­phenol}, is a product of the condensation reaction between 4-meth­oxy­benzaldehyde and 2-amino­phenol. The mol­ecule adopts an E conformation with respect to the azomethine C=N bond and is almost planar, the dihedral angle between the two substituted benzene rings being 3.29 (4)°. The meth­oxy group is coplanar with the benzene ring to which it is attached, the C_meth­yl—O—C—C torsion angle being −1.14 (12)°. There is an intra­molecular O—H⋯N hydrogen bond generating an S(5) ring motif. In the crystal, mol­ecules are linked via C—H⋯O hydrogen bonds, forming zigzag chains along [10-1]. The chains are linked via C—H⋯π inter­actions, forming a three-dimensional structure.

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.

Indole-7-carbaldehyde thiosemicarbazone as a flexidentate ligand toward ZnII, CdII, PdII and PtII ions: cytotoxic and apoptosis-inducing properties of the PtII complex

A new thiosemicarbazone (LH2) derived from indole-7-carbaldehyde was synthesized and reacted with Zn(II), Cd(II), Pd(II) and Pt(II) salts. The reactions with zinc and cadmium salts in 2 : 1 (ligand-metal) molar ratio afforded complexes of the type MX2(LH2)2, (X = Cl, Br or OAc), in which the thiosemicarbazone acts as a neutral S-monodentate ligand. In the presence of potassium hydroxide, the reaction of LH2 with ZnBr2 resulted in deprotonation of the thiosemicarbazone at the hydrazine and indole nitrogens to form Zn(L)(CH3OH). The reaction of LH2 with K2PdCl4 in the presence of triethylamine, afforded Pd(L)(LH2) which contains two thiosemicarbazone ligands: one being dianionic N,N,S-tridentate while the other one is neutral S-monodentate. When PdCl2(PPh3)2 was used as the Pd(II) ion source, Pd(L)(PPh3) was obtained. In a similar manner, the analogous platinum complex, Pt(L)(PPh3), was synthesized. The thiosemicarbazone in the latter two complexes behaves in a dianionic N,N,S-tridentate fashion. The platinum complex was found to have significant cytotoxicity toward four cancer cells lines, namely MDA-MB-231, MCF-7, HT-29, and HCT-116 but not toward the normal liver WRL-68 cell line. The apoptosis-inducing properties of the Pt complex was explored through fluorescence microscopy visualization, DNA fragmentation analysis and propidium iodide flow cytometry.