Formation of an unusual pyridoxal derivative: Characterization of Cu(II), Ni(II) and Zn(II) complexes and evaluation of binding to DNA and to human serum albumin

ON donor tethered copper (II) and vanadium (V) complexes as efficacious anti-TB and anti-fungal agents with spectroscopic approached HSA interactions

Antimicrobial drug resistance poses a significant threat worldwide, hence triggering an urgent situation for developing feasible drugs. 3D-transition metal coordination complexes being multifaceted, offer tremendous potency as drug candidates. However, there are fewer reports on non-toxic and safe transition metal complexes; therefore, we hereby attempted to develop novel copper and vanadium-based therapeutic agents. We have synthesised six metal complexes viz., [V^VO₂(Quibal-INH)] (1), [Cu^II(Quibal-INH)₂] (2), [V^VO(Quibal-INH) (cat)] (3), [Cu^II(Quibal-INH) (cat)] (4), [V^VO(Quibal-INH) (bha)] (5) and [Cu^II(Quibal-INH) (bha)] (6). Quibal-INH (L) is an ON bidentate donor ligand synthesized from Schiff base reaction between 4-(2-(7-chloroquinolin-3-yl)vinyl)benzaldehyde (Quibal) and Isoniazid (INH). The synthesized compounds were characterized using analytical techniques involving ATR-IR, UV-Vis, EPR, ¹H NMR, ¹³C NMR, and ⁵¹V NMR. Ligand (L) and compound 3 exhibited moderate growth inhibitory activity towards Candida albicans and Cryptococcus neoformans fungal species. Compound 6 has been identified as active against the above fungal species with no toxicity and hemolysis activity on the healthy cells. Compound 5 exhibited significant activity against the Mycobacterium tuberculosis H ₃₇ R _v strain. Further, compounds 4, 5 and 6 exhibited excellent free radical scavenging activity. All the developed compounds were found to exhibit stability over a wide range of pH conditions. The complexes were additionally studied for their interaction with human serum albumin (HSA) with the UV-vis spectroscopic technique.

Copper(II) and oxidovanadium(IV) complexes of chromone Schiff bases as potential anticancer agents

We report the synthesis, characterization and biological screening of new chromone Schiff bases derived from the condensation of three 6-substituted-3-formyl-chromones with pyridoxal (HL^1-3) and its Cu(II) complexes [Cu(L^1-3)Cl], 1-3. For the 6-methyl derivative, HL², the V^IVO-complex [VO(L²)Cl] (5), as well as ternary Cu and V^IVO complexes with 1,10-phenanthroline (phen), [Cu(L²)(phen)Cl] (4) and [VO(L²)(phen)Cl] (6), were also prepared and evaluated. Their stability in aqueous medium and radical scavenging activity toward DPPH are screened, with [Cu(L²)(phen)Cl] (4) showing hydrolytic stability and [VO(L²)(phen)Cl] (6) high radical scavenging activity. Spectroscopic studies establish bovine serum albumin (BSA), a model for HSA, as a potential reversible carrier of [Cu(L²)(phen)Cl] in blood with K_BC ≈ 10⁵ M^-1. The cytotoxic activity of a group of compounds is evaluated against a panel of human cancer cell lines of different origin (ovary, cervix, brain and breast) and compared to normal cells. Our results indicate that Cu complexes are more cytotoxic than the ligands but not selective towards cancer cells. The most potent complexes (4 and 6) are further evaluated for their apoptotic potential, induction of reactive oxygen species (ROS) and genotoxicity. Both complexes efficiently triggered cell death through apoptosis as evaluated by DNA morphology and TUNEL assay, increased ROS formation as determined by DCFDA (2',7'-dichlorodihydrofluorescein diacetate) analysis, and induced genotoxic damage as visualized via COMET assay in all cancer cells under study. Therefore, 4 and 6 may be potential precursor anticancer molecules, yet they need to be targeted toward cancer cells.

Recent reports on Pyridoxal derived Schiff base complexes

Pyridoxal and Pyridoxal 5-phosphate are two among the six aqua soluble vitamers of vitamin B6. They can form Schiff bases readily due to the presence of aldehyde group. Schiff bases can offer diverse coordination possibilities for many transition metals as has been found in a large volume of research till now. The coordination complexes thus formed gives insight into the active core structure and enzymatic activities of vit B6 containing enzymes. Apart from that, these complexes have been found useful as catalysts for synthesis of fine chemicals, as sensors and for their diverse biological activities.

Helical water-soluble NiII complexes with pyridoxal ligand derivatives: Structural evaluation and interaction with biomacromolecules

This article deals with the synthesis of Schiff-based bis-azomethine-based ligands derived from pyridoxal and aliphatic dihydrazides and the synthesis of nickel(II) complexes C1-C4. The synthesized complexes had their structures elucidated by monocrystal X-ray diffraction and were characterized by vibrational and absorption spectroscopy. The synthesized ligands have characteristics that allow the formation of self-assembly processes, thus, the flexibility or rigidity of the coordination of organic molecules added to the orbitals of the Ni^II cation leads to the formation of helical complexes with double helix and a dinucler nickel(II) complex. Moreover, compounds was their interactions with CT-DNA and HSA absorption and emission analysis and molecular docking calculations.

Biscoumarin-pyrimidine conjugates as potent anticancer agents and binding mechanism of hit candidate with human serum albumin

In our continuing efforts to develop therapeutically active coumarin-based compounds, a series of new C4-C4' biscoumarin-pyrimidine conjugates (1a-l) was synthesized via S_N 2 reaction of substituted 4-bromomethyl coumarin with thymine. All compounds were characterized using spectroscopic techniques, that is, attenuated total reflection infrared (ATR-IR), CHN elemental analysis, and ¹ H and ¹³ C NMR (nuclear magnetic resonance). In addition, the structure of compound 1d (1,3-bis[(7-chloro-2-oxo-2H-chromen-4-yl)methyl]-5-methylpyrimidine-2,4(1H,3H)-dione) was established through X-ray crystallography. Compounds 1a-l were screened for in vitro anticancer activity against C6 rat glioma cells. Among the screened compounds, 1,3-bis[(6-chloro-2-oxo-2H-chromen-4-yl)methyl]-5-methylpyrimidine-2,4(1H,3H)-dione (1c) was identified as the best antiproliferative candidate, exhibiting an IC₅₀ value of 4.85 μM. All the compounds (1a-l) were found to be nontoxic toward healthy human embryonic kidney cells (HEK293), indicating their selective nature. In addition, the most active compound (1c) displayed strong binding interactions with the drug carrier protein, human serum albumin, and exhibited good solution stability at biological pH conditions. Fluorescence, UV-visible spectrophotometry and molecular modeling methodologies were employed for studying the interaction mechanism of compound 1c with protein.

Potent drug candidature of an ONS donor tethered copper (II) complex: Anticancer activity, cytotoxicity and spectroscopically approached BSA binding studies

In our continued efforts to develop metal based therapeutic agents, we have synthesized a novel copper(II) complex, [{Cu(hpdbal-sbdt)}₂] (2) tethered with a biocompatible ONS^2- donor backbone [H₂hpdbal-sbdt] (1) [H₂hpdbal-sbdt is a tridentate ligand derived from S-benzyldithiocarbazate (Hsbdt) and 2-hydroxy-5-(phenyldiazenyl)benzaldehyde (Hhpdbal)]. The metal complex (2) was characterized using attenuated total reflection-infrared (ATR-IR) spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, thermogravimetry and differential scanning calorimetric (TG-DSC) analysis, field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS) and elemental (CHNS) analysis. The antineoplastic ability of copper complex was evaluated in vitro against human cervical cancer (HeLa) cells. MTT assay results showed that the copper complex exhibited significant growth inhibition of HeLa cells with an IC₅₀ value of 4.46 μM and this value was compared with reported standards. Cytotoxicity of the copper complex towards human embryonic kidney cells (HEK-293) was also evaluated. The potentially active copper complex was studied for its solution state stability at a pH range of 3-9. Following this, the interactive behaviour of the bioactive copper complex with a drug transporter protein (BSA) was deciphered through multi-spectrosopic investigations like steady-state fluorescence, three-dimensional fluorescence, deconvoluted-IR and UV-Visible techniques.

In vitro apoptosis-induction, antiproliferative and BSA binding studies of a oxidovanadium(V) complex

In our ongoing efforts to develop novel trace metal complexes with therapeutically interesting properties, a neutral mono nuclear oxidomethoxidovanadium(V) complex, [V^VO(OCH₃)(hpdbal-sbdt)] (1) and a μ-O bridged dinuclear oxidovanadium(V) complex, [{V^VO(hpdbal-sbdt)}₂μ-O] (2) [H₂hpdbal-sbdt (I) is a tridentate and dibasic ONS^2- donor ligand obtained through the Schiff base reaction of 2-hydroxy-5-(phenyldiazenyl)benzaldehyde (Hhpdbal) and S-benzyldithiocarbazate (Hsbdt)] have been synthesized and characterized by various analytical techniques such as TGA, EDS, ATR-IR, UV-Vis, CV, ¹H NMR, ¹³C NMR and ⁵¹V NMR. Single-crystal X-ray diffraction analysis of 1 confirms the coordination of phenolate oxygen, imine nitrogen and thioenolate sulfur of the ligand to the vanadium center with a distorted tetragonal-pyramidal geometry. The compound 2 triggered apoptotic and reproductive death of the cancer cells in vitro with 76% and 62% growth inhibition of human breast adenocarcinoma (MCF-7) and human lung carcinoma cells (A549) respectively. The compound 2 was found to be sufficiently stable over a wide window of physiological pH. The complex 2 was studied further for its interaction with a drug carrier protein BSA with the aid of spectroscopic techniques viz. fluorescence, temperature controlled UV-vis and deconvoluted IR techniques.

Photophysical properties and biological evaluation of a Zinc(II)-5-methyl-1H-pyrazole Schiff base complex

A new ZnL₂ complex containing two molecules of a tridentate Schiff base derived from 5-methyl-1H-pyrazole (HL) is synthesized and characterized. The photophysical properties of HL and ZnL₂ are disclosed and supported by CAMB3LYP DFT/TDDFT calculations. It is shown that there is keto-tautomer stabilization upon excitation with an energetically accessible triplet state in HL, not present in ZnL₂, this explaining the differences found in the emissions of the compounds. The intrinsic fluorescence of ZnL₂ is used as probe for a detailed study of its binding to human serum albumin. The protein-complex association is thermodynamically favourable and it is shown by fluorescence quenching and time-resolved analysis that the fluorescence quenching involves a mixed mechanism with prevalence of static quenching, which corroborates adduct formation at site I, close to the Trp214 residue. The ability of ZnL₂ to bind DNA was also evaluated, as well as its cytotoxic activity against MCF7 (breast), PC3 (prostate) cancer cells and hamster V79 fibroblasts. ZnL₂ is a moderate DNA intercalator (K_app = 3.9 × 10⁴ M^-1) and depicts a quite low IC₅₀ value at 48 h against MCF7 cells (IC₅₀ = 530 nM), but much higher for PC3 and V79 cells. The relevance of a more careful speciation evaluation of ZnL₂ and other potential metal-based drugs in incubation media used in in vitro tests is highlighted.

A Co(ii) complex of a vitamer of vitamin B6acts as a sensor for Hg2+and pH in aqueous media

A new Co(ii) complex was prepared by template reaction, acting as a dual fluorescent sensor for Hg²⁺ions and pH in aqueous solution.

Thirty years through vanadium chemistry

The relevance of vanadium in biological systems is known for many years and vanadium-based catalysts have important industrial applications, however, till the beginning of the 80s research on vanadium chemistry and biochemistry did not receive much attention from the scientific community. The understanding of the broad bioinorganic implications resulting from the similarities between phosphate and vanadate(V) and the discovery of vanadium dependent enzymes gave rise to an enormous increase in interest in the chemistry and biological relevance of vanadium. Thereupon the last 30years corresponded to a period of enormous research effort in these fields, as well as in medicinal applications of vanadium and in the development of catalysts for use in fine-chemical synthesis, some of these inspired by enzymatic active sites. Since the 80s my group in collaboration with others made contributions, described throughout this text, namely in the understanding of the speciation of vanadium compounds in aqueous solution and in biological fluids, and to the transport of vanadium compounds in blood plasma and their uptake by cells. Several new types of vanadium compounds were also synthesized and characterized, with applications either as prospective therapeutic drugs or as homogeneous or heterogenized catalysts for the production of fine chemicals. The developments made are described also considering the international context of the evolution of the knowledge in the chemistry and bioinorganic chemistry of vanadium compounds during the last 30years. This article was compiled based on the Vanadis Award presentation at the 9th International Vanadium Symposium.