Synthesis, Characterisation and Antiviral Activity of Platinum(II) Complexes with 1,10-Phenanthrolines and the Antiviral Agents Acyclovir and Penciclovir

Self-Assembled Molecular Complexes of 1,10-Phenanthroline and 2-Aminobenzimidazoles: Synthesis, Structure Investigations, and Cytotoxic Properties

Three new molecular complexes (phen)3(2-amino-Bz)2(H+)(BF4-)·3H2O 5, (phen)3(2-amino-5(6)-methyl-Bz)2(H+)(BF4-)·H2O 6, and (phen)(1-methyl-2-amino-Bz)(H+)(BF4-) 7, were prepared by self-assembly of 1,10-phenanthroline (phen) and various substituted 2-aminobenzimidazoles. Confirmation of their structures was established through spectroscopic methods and elemental analysis. The X-ray diffraction analysis revealed that the crystal structure of 7 is stabilized by the formation of hydrogen bonds and short contacts. In addition, the molecular geometry and electron structure of molecules 5 and 6 were theoretically evaluated using density functional theory (DFT) methods. According to the DFT B3LYP/6-311+G* calculations, the protonated benzimidazole (Bz) units act as NH hydrogen bond donors, binding two phenanthrolines and a BF4- ion. Non-protonated Bz unit form hydrogen bonds with the N-atoms of a third molecule phen. The molecular assembly is held together by π-π stacking between benzimidazole and phenanthroline rings, allowing for N-atoms to associate with water molecules. The complexes were tested in vitro for their tumor cell growth inhibitory effects on prostate (PC3), breast (MDA-MB-231 and MCF-7), and cervical (HeLa) cancer cell lines using MTT-dye reduction assay. The in vitro cytotoxicity analysis and spectrophotometric investigation in the presence of ct-DNA, showed that self-assembled molecules 5-7 are promising DNA-binding anticancer agents warranting further in-depth exploration.

Platinum-Nucleos(t)ide Compounds as Possible Antimetabolites for Antitumor/Antiviral Therapy: Properties and Perspectives

Nucleoside analogues (NAs) are a family of compounds which include a variety of purine and pyrimidine derivatives, widely used as anticancer and antiviral agents. For their ability to compete with physiological nucleosides, NAs act as antimetabolites exerting their activity by interfering with the synthesis of nucleic acids. Much progress in the comprehension of their molecular mechanisms has been made, including providing new strategies for potentiating anticancer/antiviral activity. Among these strategies, new platinum-NAs showing a good potential to improve the therapeutic indices of NAs have been synthesized and studied. This short review aims to describe the properties and future perspectives of platinum-NAs, proposing these complexes as a new class of antimetabolites.

Synthesis of N-Tetradecyl-1,10-phenathrolinium-Based New Salts for Biological Applications

New organic salts were synthesized by quaternizing 1,10-phenanthroline using 1-bromotetradecane. The first step yielded an organic salt of formula [C₂₆H₃₇N₂]Br. Anion exchange reaction using Li[(CF₃SO₂)₂N] resulted in a more stable salt of formula [C₂₆H₃₇N₂][(CF₃SO₂)₂N]. The organic salts were investigated by spectrometry (¹H, ¹³C, ¹⁹F NMR, X-ray photoelectron spectroscopy (XPS), UV-Vis, and matrix-assisted laser desorption/ionization mass spectroscopy (MALDI MS), CHNSBr elemental analysis, and thermal analysis (TGA and DSC). The thermal characterization showed the melting and decomposition points of [C₂₆H₃₇N₂][(CF₃SO₂)₂N] to be 48°C and 290°C, respectively, which indicates it is an ionic liquid with large liquidus range. The biological activities of the salts were investigated against two Gram-positive (Staphylococcus aureus and Streptococcus pyogenes) and two Gram-negative (Escherichia coli and Klebsiella pneumoniae) bacteria, and they are found to be active against all of them. They were compared with [Cu(1,10-phenanthroline)₂Cl]Cl. They are found more active against the Gram-negative bacteria. The salts demonstrated minimum inhibitory concentration as low as 50 µg/L. These results suggest the synthesized salts can be considered as a better alternative to certain transition metal complex drugs. This minimizes the concern of introducing metal ions into the organism.

Monofunctional platinum(II) complexes with potent tumor cell growth inhibitory activity: the effect of a hydrogen-bond donor/acceptor N-heterocyclic ligand

In this paper we investigate the possibility of further increase the role of the N-donor aromatic base in antitumor Hollis-type compounds by conferring the possibility to act as a hydrogen-bond donor/acceptor. Therefore, we synthesized the Pt(II) complex cis-[PtCl(NH3 )2 (naph)]NO3 (1) containing the 1,8-naphthyridine (naph) ligand. The naphthyridine ligand is generally monodentate, and the second nitrogen atom can act as H-bond donor/acceptor depending upon its protonation state. The possibility of forming such an H-bond could be crucial in the interaction of the drug with DNA or proteins. Apart from the synthesis of the compound, in this study we evaluated its in vitro antitumor activity in a wide panel of tumor cell lines, also including cells selected for their sensitivity/resistance to oxaliplatin, which was compared with that of previously reported complex 2 ([PtI(2,9-dimethyl-1,10-phenanthroline)(1-methyl-cytosine)]I) and oxaliplatin and cisplatin as reference compounds. The cytotoxicity data were correlated with the cellular uptake and the DNA platination levels. Finally, the reactivity of 1 towards guanosine 5'-monophosphate (5'-GMP) and glutathione was investigated to provide insights into its mechanism of action.

A model radiopharmaceutical agent targeted to translocator protein 18 kDa (TSPO)

A stable Re complex containing an imidazopyridine ligand with a high affinity for TSPO has been synthesized as a model for new (99m)Tc or (188/186)Re-based radiopharmaceuticals to be used in SPECT diagnosis or in therapy, respectively. The new complex fac-[ReBr(CO)3(TZ6)], structurally characterized, showed high affinity (nanomolar concentration) for the target protein.

Platinum(II) and palladium(II) complexes of pyridine-2-carbaldehyde thiosemicarbazone as alternative antiherpes simplex virus agents

The cytotoxicity and the antivirus activity of Pd(II) and Pt(II) complexes with pyridine-2-carbaldehyde thiosemicarbazone (HFoTsc) against HSV replication were evaluated on four HSV strains—two wt strains Victoria (HSV-1) and BJA (HSV-2) and two ACV^R mutants with different tk gene mutations R-100 (TK^A, HSV-1) and PU (TK^N, HSV-2). The experiments were performed on continuous MDBK cells and four HSV 1 and HSV 2 strains were used, two sensitive to acyclovir and two resistant mutants. The five complexes of HFoTsc, [Pt(FoTsc)Cl], [Pt(FoTsc)(H₂FoTsc)]Cl₂, [Pt(FoTsc)₂], [Pd(FoTsc)(H₂FoTsc)]Cl₂, and [Pd(FoTsc)₂], were found to be effective inhibitors of HSV replication. The most promising, active, and selective anti-HSV agent was found to be complex [Pt(FoTsc)(H₂FoTsc)]Cl₂. This complex could be useful in the treatment of HSV infections, since it is resistant to ACV mutants. PCR study of immediate early 300 bp ReIV Us1 region reveals that the complex [Pt(FoTsc)(H₂FoTsc)]Cl₂ specifically suppressed wt HSV-1 genome 2 hours after the infection, not inducing apoptosis/necrosis on the 8 hours after virus infection. The target was found to be most probably the viral, instead of the host cell DNA.

Synthesis and preliminary DNA-binding studies of diimineplatinum(ii) complexes containing 3- or 4-pyridineboronic acid

A series of platinum(II) complexes of the type [Pt(NN)(pyB)2](NO3)2 (NN = bipy, phen; pyB = 3- or 4-pyridineboronic acid) were successfully prepared and fully characterised by 1D- and 2D-multinuclear NMR spectroscopy and ESI-MS. Using VT 1H NMR spectroscopy, rotational isomers for [Pt(NN)(3-pyB)2](NO3)2 were identified and the free energies of activation for rotation of 3-pyB about the Pt-N bond were determined to be DeltaG++310) = 69.2 +/- 0.1 kJ mol(-1) and DeltaG++(305) = 66.0 +/- 0.1 kJ mol(-1) for [Pt(bipy)(3-pyB)2](NO3)2 and [Pt(phen)(3-pyB)2](NO3)2, respectively. The 3- and 4-pyB ligands readily deboronate in boiling H2O to afford [Pt(NN)(py)2](NO3)2; the structure of [Pt(phen)(py)2](2+) (as its PF6- salt) was confirmed by X-ray crystallography. Preliminary thermal denaturation studies revealed only minimal interactions between [Pt(NN)(pyB)2](NO3)2 and calf-thymus DNA and is attributed to hydroxylation of the boronic acid groups at pH 7.4 to afford the corresponding zwitterionic boronate species. This was confirmed by means of variable pH 1H and 11B{1H} NMR spectroscopy.

Ternary complexes metal [Co(II), Ni(II), Cu(II) and Zn(II)]--ortho-iodohippurate (I-hip)--acyclovir. X-ray characterization of isostructural [(Co, Ni or Zn)(I-hip)(2)(ACV)(H(2)O)(3)] with stacking as a recognition factor

Four ternary metal--ortho-iodohippurate (I-hip)--acyclovir (ACV) complexes, [M(I-hip)(2)(ACV)(H(2)O)(3)] where M is Co(II) (1), Ni(II) (2), Cu (3) and Zn(II) have been obtained by reaction between the corresponding binary complexes M(II)(I-hip)(2)xnH(2)O and ACV. Three ternary complexes (M=Co, Ni and Zn) and the corresponding Zn(II)--ortho-iodohippurate binary derivative have been structurally characterized by X-ray diffraction: The studies show these three ternary complexes are isostructural and present, in solid state, an interesting stacking between the nucleobase and the aryl ring of the hippurate moiety, which probably promotes the formation of ternary complexes. Moreover, the two different ligands interact between them by means of ancillary hydrogen bonds with water molecules coordinated to the metal ion. It must be mentioned that these two recognition factors, hydrogen bonds plus stacking, could explain the reason for the isostructurality of these ternary derivatives with so different three metal ions, with diverses trends in coordination numbers and geometries. In solid state, there are two enantiomeric molecules that are related by an inversion center as the crystal-building unit (as a translational motif) for the ternary complexes.

A calorimetric study of 3d metal ions-acyclovir interactions. The 2-hydroxyethoxymethyl group of acyclovir mimics the role of ribose in deoxy-guanosine and guanosine promoting the coordination through N(7)

The equilibrium constants and enthalpic values of metal acyclovir complexes have been determined by calorimetry for Co(II) (log K=0.96+/-0.05, DeltaH (kJ/mol)=-19.7+/-1.3), Ni(II) (log K=1.39+/-0.03, DeltaH (kJ/mol)=-21.5+/-1.0), Cu(II) (log K=1.83+/-0.03, DeltaH (kJ/mol)=-23.2+/-0.8) and Zn(II) (log K=0.71+/-0.06, DeltaH (kJ/mol)=-18.6+/-1.5). The equilibrium constants are similar to those of the divalent ions with guanosine and 2,9-dimethylpurine. By comparison with previous thermodynamic data, it can be shown that the 2-hydroxyethoxymethyl group promotes coordination through N(7) versus N(1) of the guanine ring for 3d metal ions. These results reveal that the 2-hydroxyethoxymethyl group placed on the purine ring of guanine in acyclovir causes a greater effect than that of the 9-methyl in purines and similar to or greater than that of the ribose moiety in guanosine. The 2-hydroxyethyoxymethyl group of acyclovir mimics the role of ribose in deoxy-guanosine and guanosine promoting a similar coordination chemistry (with very close log K and DeltaH values) for acyclovir, deoxy-guanosine and guanosine with divalent metals.