Synthesis, Structure and Biological Activity of Indole-Imidazole Complexes with ZnCl2: Can Coordination Enhance the Functionality of Bioactive Ligands?

The ability of the indole-imidazole hybrid ligands to coordinate with the Zn(II) ion and the resulting structures of this new class of coordination compounds were analyzed in order to determine their structural properties and biological functionalities. For this purpose, six novel Zn(II) complexes, [Zn(InIm)₂Cl₂] (1), [Zn(InMeIm)₂Cl₂] (2), [Zn(IniPrIm)₂Cl₂] (3), [Zn(InEtMeIm)₂Cl₂] (4), [Zn(InPhIm)₂Cl₂] (5) and [Zn₂(InBzIm)₂Cl₂] (6) (where InIm is 3-((1H-imidazol-1-yl)methyl)-1H-indole), were synthesized by the reactions of ZnCl₂ and the corresponding ligand in a 1:2 molar ratio in methanol solvent at an ambient temperature. The structural and spectral characterization of these complexes was performed using NMR, FT-IR and ESI-MS spectrometry and elemental analysis, and the crystal structures of 1-5 were determined using single-crystal X-ray diffraction. Complexes 1-5 form polar supramolecular aggregates by utilizing, for this purpose, the N-H(indole)∙∙∙Cl(chloride) intermolecular hydrogen bonds. The assemblies thus formed differ depending on the distinctive molecular shape, which can be either compact or extended. All complexes were screened for their hemolytic, cytoprotective, antifungal, and antibacterial activities. The results show that the cytoprotective activity of the indole/imidazole ligand significantly increases upon its complexation with ZnCl₂ up to a value comparable with the standard antioxidant Trolox, while the response of its substituted analogues is diverse and less pronounced.

Indole Derivatives Bearing Imidazole, Benzothiazole-2-Thione or Benzoxazole-2-Thione Moieties-Synthesis, Structure and Evaluation of Their Cytoprotective, Antioxidant, Antibacterial and Fungicidal Activities

In the search for new bioactive compounds, a methodology based on combining two molecules with biological properties into a new hybrid molecule was used to design and synthesize of a series of ten indole derivatives bearing imidazole, benzothiazole-2-thione, or benzoxazole-2-thione moieties at the C-3 position. The compounds were spectroscopically characterized and tested for their antioxidant, antibacterial, and fungicidal activities. The crystal structures were determined for five of them. Comparison of the closely related structures containing either benzothiazole-2-thione or benzoxazole-2-thione clearly shows that the replacement of -S- and -O- ring atoms modify molecular conformation in the crystal, changes intermolecular interactions, and has a severe impact on biological activity. The results indicate that indole-imidazole derivatives with alkyl substituent exhibit an excellent cytoprotective effect against AAPH-induced oxidative hemolysis and act as effective ferrous ion chelating agents. The indole-imidazole compound with chlorine atoms inhibited the growth of fungal strains: Coriolus versicolor (Cv), Poria placenta (Pp), Coniophora puteana (Cp), and Gloeophyllum trabeum (Gt). The indole-imidazole derivatives showed the highest antibacterial activity, for which the largest growth-inhibition zones were noted in M. luteus and P. fluorescens cultures. The obtained results may be helpful in the development of selective indole derivatives as effective antioxidants and/or antimicrobial agents.

Synthesis, antioxidant and cytoprotective activity evaluation of C-3 substituted indole derivatives

A series of fifteen indole derivatives substituted at the C-3 position were synthesized and characterized. The antioxidant activity of all derivatives was investigated by three in vitro antioxidant assays, and the derivative with pyrrolidinedithiocarbamate moiety was the most active as a radical scavenger and Fe³⁺-Fe²⁺ reducer. It can be stated that possible hydrogen and electron transfer mechanism is suggested for the quenching of the free radical. Moreover, the indolyl radical stabilization and the presence of unsubstituted indole nitrogen atom are mandatory for the observed antioxidant activity, which strongly depends on the type of the substituent directly connected to the methylene group at the C-3 position. Human red blood cells (RBC) have been used as a cell model to study derivatives interaction with the cell membrane. Haemolytic activity and RBC shape transformation were observed for certain derivatives in a concentration-dependent manner. However, most of the derivatives at sublytic concentration showed high cytoprotective activity against oxidative haemolysis induced by 2,2′-azobis(2-methylpropionamidine) dihydrochloride (AAPH). The cytoprotective properties of derivatives can be explained mostly due to their interactions with the RBC membrane components. Taking together, theoretical estimations and experimental data confirm the beneficial interactions between the selected C-3 substituted indole derivatives and the RBC membrane under oxidative stress conditions. These results encourage us to further structural optimization of C-3 substituted indole derivatives as potent antioxidant compounds.

Mononuclear gold(iii) complexes with diazanaphthalenes: the influence of the position of nitrogen atoms in the aromatic rings on the complex crystalline properties

The [AuCl₃(benzodiazine)] complexes form centrosymmetric crystals, while the [AuCl₃(naphthyridine)] complexes assemble into non-centrosymmetric aggregates, making them potential alternatives for advanced nonlinear optical materials due to their polarity.

Mononuclear gold(iii) complexes with l-histidine-containing dipeptides: tuning the structural and biological properties by variation of the N-terminal amino acid and counter anion

Gold(iii) complexes with different l-histidine-containing dipeptides, [Au(Gly-l-His-N_A,N_P,N3)Cl]Cl·3H₂O (1a), [Au(Gly-l-His-N_A,N_P,N3)Cl]NO₃·1.25H₂O (1b), [Au(l-Ala-l-His-N_A,N_P,N3)Cl][AuCl₄]·H₂O (2a), [Au(l-Ala-l-His-N_A,N_P,N3)Cl]NO₃·2.5H₂O (2b), [Au(l-Val-l-His-N_A,N_P,N3)Cl]Cl·2H₂O (3), [Au(l-Leu-l-His-N_A,N_P,N3)Cl]Cl (4a) and [Au(l-Leu-l-His-N_A,N_P,N3)Cl][AuCl₄]·H₂O (4b), have been synthesized and structurally characterized by spectroscopic (¹H NMR, IR and UV-vis) and single-crystal X-ray diffraction techniques. The antimicrobial efficiency of these gold(iii) complexes, along with K[AuCl₄] and the corresponding dipeptides, was evaluated against the broad panel of Gram-positive and Gram-negative bacteria and fungi, displaying their moderate inhibiting activity. Moreover, the cytotoxic properties of the investigated complexes were assessed against the normal human lung fibroblast cell line (MRC5) and two human cancer, cervix (HeLa) and lung (A549) cell lines. None of the complexes exerted significant cytotoxic activity; nevertheless complexes that did show selectivity in terms of cancer vs. normal cell lines (2a/b and 4a/b) have been evaluated using zebrafish (Danio rerio) embryos for toxicity and antiangiogenic potential. Although the gold(iii) complexes achieved an antiangiogenic effect comparable to the known angiogenic inhibitors auranofin and sunitinib malate at 30-fold higher concentrations, they had no cardiovascular side effects, which commonly accompany auranofin and sunitinib malate treatment. Finally, binding of the gold(iii) complexes to the active sites of both human and bacterial (Escherichia coli) thioredoxin reductases (TrxRs) was demonstrated by conducting a molecular docking study, suggesting that the mechanism of biological action of these complexes can be associated with their interaction with the TrxR active site.

One-step Access to Resorcinsalens-Solvent-Dependent Synthesis, Tautomerism, Self-sorting and Supramolecular Architectures of Chiral Polyimine Analogues of Resorcinarene

Substituted 2,4- and 4,6-dihydroxyisophthalaldehydes were condensed with optically pure and racemic trans-1,2-diaminocyclohexane to form resorcinarene-like polyimine macrocycles (resorcinsalens), the structure and stoichiometry of which were controlled by the choice of the reaction medium. Particularly, the cyclocondensation reactions were driven by the solubility, tautomerization, or by social self-sorting. The resorcinsalens crystallized as inclusion compounds, in which the guest molecules were situated either in channels or in voids. In the highly hydrated crystals of one of the [2+2] macrocycles and chloroform-solvated crystals of a [4+4] product the channels were interconnected, as in zeolites, enabling possible migration of loosely bound solvent molecules in three dimensions. The association mode depended on the structural modification of the host molecule and the type of included solvent molecule(s).

Consistent supramolecular assembly arising from a mixture of components – self-sorting and solid solutions of chiral oxygenated trianglimines

The formation of trianglimines and their aggregates is stereoselective, and uniformly chiral macrocycles differing in chemical composition crystallize as solid solutions.

Benzhydryl Ethers of Tartaric Acid Derivatives: Stereochemical Response of a Dynamically Chiral Propeller

The benzhydryl (diphenylmethyl) group is a molecular propeller that can act as a chirality reporter if it is introduced nearby a stereogenic center by making an ether bond. The hydrophobic character of the benzhydryl group allows transformation of insoluble natural tartaric acid derivatives into soluble entities in a nonpolar environment. Electronic circular dichroism spectra, recorded within the short-wavelength region of the phenyl ¹ B transitions (190-200 nm) shows strong bisignate Cotton effects. The signs and magnitudes of these Cotton effects are a function of absolute configuration and conformation of the molecule and do not primarily arise from exciton coupling of chiral benzhydryl chromophores. In crystals, the main-chain conformation is stabilized by intramolecular hydrogen bonds and CH-CO dipolar interactions. The number of the donor NH groups has a pronounced effect on the preferred conformations and inclusion properties of benzhydryl-(R,R)-tartaric acid diamides. Evidence is shown for the solvent dependency of the conformations of NH amides of tartaric acid diphenylmethyl ethers.

Synthesis, structural characterization and biological evaluation of dinuclear gold(iii) complexes with aromatic nitrogen-containing ligands: antimicrobial activity in relation to the complex nuclearity

Dinuclear Au(iii) complexes with N-heterocycles have been synthesized and biologically evaluated.

Double helicity induction in chiral bis(triphenylacetamides)

Helicity induction in a highly flexible trityl chromophore is not only due to the presence of the neighboring stereogenic center(s).

Chalcogen analogues of nicotine lactam studied by NMR, FTIR, DFT and X-ray methods

The selenoanalogue of nicotine has been synthesized and characterized by spectroscopic and X-ray diffraction methods. The crystals of selenonicotine are isomorphic with the thionicotine homologue and consist of molecules engaged in columnar π⋯π stacking interactions between antiparallely arranged pyridine moieties. These interactions, absent in other crystals containing nicotine fragments, seem to be induced by the presence of a lactam group. The molecular structures in the vacuum of the oxo-, thio- and selenonicotine homologues have been calculated by the DFT method and compared with the available X-ray data. The delocalized structure of thionicotine is stabilized by intramolecular C-H⋯S hydrogen bond, which becomes weaker in the partial zwitterionic resonance structure of selenonicotine in favor of multiple C-H⋯Se intermolecular hydrogen-bonds. The calculated data allow a complete assignment of vibration modes in the solid state FTIR spectra. The (1)H and (13)C NMR chemical shifts were calculated by the GIAO method with B3LYP/6-311G(3df) level. A comparison between experimental and calculated theoretical results indicates that the density functional B3LYP method provided satisfactory results for predicting FTIR, (1)H, (13)C NMR spectra properties.

Synthesis, spectral and solid state characterization of a new bioactive hydrazine bridged cyclic diphosphonium compound

The facile preparation of a racemic hydrazine bridged diphosphonium compound possessing a ring system analogous to bicyclo[3.3.2]decane is reported. Although the reaction yield is low, the structure of the compound, which possesses an eight-membered ring, two phosphonium cationic centers, a biimino bridge, molecular chirality and two fused aromatic rings locked into roughly perpendicular planes is unusual. The compound displays substantial biological activity in the brine shrimp test and cleaves plasmid DNA.

Role of the gauche effect and local 1,3-dipole–dipole interactions in stabilizing an unusual conformation of tartarodinitriles

This paper reports the synthesis, X-ray and NMR investigations of chiral and meso dinitriles of tartaric acid (tartarodinitriles) and their O,O′-diacetyl and O,O′-dibenzoyl derivatives. While in chiral tartaric acid its esters and NH amides the four-atom carbon chain is overwhelmingly trans, it is gauche in chiral tartarodinitriles. Conversely, meso-tartaric acid, its esters and amides display a tendency for the gauche conformation, but meso-tartarodinitriles usually have the trans conformation. The NMR studies of tartarodinitriles reveal the presence of a conformational equilibrium in solution with a preference for those conformers found in crystals. The gauche conformation of meso-tartarodinitriles seems to be stabilized by local dipolar interactions, intramolecular C—H...O hydrogen bonds and by a tendency for maximization of the gauche effect, the latter effect also operating in chiral tartarodinitriles. Stabilization of the trans conformers of tartarodinitriles in the crystals seems to originate from specific intermolecular interactions.

Crystal engineering of analogous and homologous organic compounds: hydrogen bonding patterns in trimethoprim hydrogen phthalate and trimethoprim hydrogen adipate

BACKGROUND

Trimethoprim [2,4-diamino-5-(3',4',5'-trimethoxybenzyl)pyrimidine] is an antifolate drug. It selectively inhibits the bacterial dihydrofolate reductase (DHFR) enzyme.

RESULTS

In the crystal structures of trimethoprim (TMP)-hydrogen phthalate (1) and trimethoprim-hydrogen adipate (2), one of the N atoms of the pyrimidine ring is protonated and it interacts with the deprotonated carboxylate oxygens through a pair of nearly parallel N-H...O hydrogen bonds to form a fork-like interaction. In the compound 1, the pyrimidine moieties of the TMP cations are centrosymmetrically paired through a pair of N-H...N hydrogen bonds involving 4-amino group and the N (N3) atom of the pyrimidine rings to form a 8-membered hydrogen bonded ring [R2(2)(8)]. The 4-amino group of one TMP moiety and 2-amino group of another TMP moiety (both moieties are members of a base pair) are bridged by the carbonyl oxygen of the phthalate moiety through N-H...O hydrogen bonds forming 8-membered hydrogen-bonded ring [R2(2)(8)]. The characteristic hydrogen-bonded rings observed in the structure aggregate into a supramolecular ladder consisting of a pair of chains, each of which is built up of alternate TMP and hydrogen phthalate ions. In the compound 2, two TMP cations and two hydrogen adipate anions are arranged about an inversion center so that the complementary DDAA (D = donor, A = acceptor) arrays of quadruple hydrogen-bonding patterns are formed. The head-to-tail arrangement of the hydrogen adipate ions leads to a hydrogen-bonded supramolecular chain. From crystal engineering point of view, it is interesting to note that the compound 1 has a hydrogen-bonded network remarkably identical with its aliphatic analogue, trimethoprim hydrogen maleate. Similarly the compound 2, resembles its homolog trimethoprim hydrogen glutarate.

CONCLUSION

In the crystal structure of trimethoprim hydrogen phthalate, the hydrogen-bonded network is remarkably identical with its aliphatic analogue, trimethoprim hydrogen maleate. Similarly in the crystal structure of trimethoprim hydrogen adipate the hydrogen bonded network resembles its homolog trimethoprim hydrogen glutarate.