Synthesis and antitumor activity of tropolone derivatives. 6. Structure-activity relationships of antitumor-active tropolone and 8-hydroxyquinoline derivatives

Organocatalytic Asymmetric Synthesis of Biologically Relevant 3,3- Dihydroxyphenyloxindoles via para-Quinone Methides Derived from Isatins

The first asymmetric synthetic approach to biologically relevant 3,3-diphenyloloxindoles was developed using para-quinone methides derived from isatins and phenols. Chiral phosphoric acid efficiently catalyzed the reaction and delivered 3,3-diphenyloloxindoles under mild conditions with up to an equivalent yield and excellent enantioselectivity (up to >99% ee). The chirality was maintained in further synthesis.

Crystal structure of 7,7'-[(pyridin-2-yl)methyl-ene]bis-(5-chloro-quinolin-8-ol)

In the title compound, C24H15Cl2N3O2, one quinoline ring system is essentially planar and the other is slightly bent. An intra-molecular O-H⋯N hydrogen bond involving the hy-droxy group and a pyridine N atom forms an S(5) ring motif. In the crystal, two mol-ecules are associated into an inversion dimer with two R 2 2(7) ring motifs through inter-molecular O-H⋯N and O-H⋯O hydrogen bonds. The dimers are further linked by an inter-molecular C-H⋯O hydrogen bond and four C-H⋯π inter-actions, forming a two-dimensional network parallel to (001).

Catalyst-free assembly of giant tris(heteroaryl)methanes: synthesis of novel pharmacophoric triads and model sterically crowded tris(heteroaryl/aryl)methyl cation salts

A series of giant tris(heteroaryl)methanes are easily assembled by one-pot three-component synthesis by simple reflux in ethanol without catalyst or additives. Diversely substituted indoles (Ar1) react with quinoline aldehydes, quinolone aldehydes, chromone aldehydes, and fluorene aldehydes (Ar2CHO) and coumarins (Ar3) in 1:1:1 ratio to form the corresponding tris(heteroaryl)methanes (Ar1Ar2Ar3)CH along with (Ar1Ar1Ar2)CH triads. A series of new 2:1 triads were also synthesized by coupling substituted indoles with Ar2CHO. The coupling reactions could also be carried out in water (at circa 80 °C) but with chemoselectivity favoring (Ar1Ar1Ar2)CH over (Ar1Ar2Ar3)CH. The molecular structure of a representative (Ar1Ar2Ar3)CH triad was confirmed by X-ray analysis. Model tris(heteroaryl/aryl)methylium salts were generated by reaction with DDQ/HPF6 and studied by NMR and by DFT and GIAO-DFT.

Identification of 4-isopropyl-thiotropolone as a novel anti-microbial: regioselective synthesis, NMR characterization, and biological evaluation

We have synthesized and separated tosylated thujaplicin isomers for the first time, and elucidated their structures using 1D, 2D-NMR techniques and X-ray crystallography. The tosylated isomers were used to synthesize 4-isopropyl–thiotropolone and 6-isopropyl–thiotropolone in a regioselective manner. ¹H and ¹³C Chemical shifts of synthesized isomers were fully assigned using several NMR experiments, and their isotropic magnetic shielding was calculated using the GIAO (Gauge Including Atomic Orbitals) method and the B3LYP def2-TZVPP level of theory. The calculated chemical shift values were in a good agreement with the experimental results. The biological activity of all synthesized compounds was evaluated against the fungal pathogen Cryptococcus neoformans and four different bacterial strains (Staphylococcus aureus (ATCC 29213), E. coli (ATCC 35218), Acinetobacter baumannii and Pseudomonas aeruginosa (ATCC 27853)). 4-Isopropyl–thiotropolone was found to inhibit Staphylococcus aureus in a low micro molar range and exhibit good therapeutic index and ADME properties. This compound can be used for future lead optimization to design inhibitors against Staphylococcus aureus (ATCC 29213).

4-Isopropyl–thiotropolone was identified as a novel anti-microbial agent with good therapeutic index and ADME properties.

Additional synthesis on thiophene-containing trisubstituted methanes (TRSMs) as inhibitors of M. tuberculosis and 3D-QSAR studies

We earlier reported thiophene-containing trisubstituted methanes (TRSMs) as novel cores carrying anti-tubercular activity, and identified S006-830 as the phenotypic lead with potent bactericidal activity against single- and multi-drug resistant clinical isolates of Mycobacterium tuberculosis (M. tb). In this work, we carried out additional synthesis of several TRSMs. The reaction scheme essentially followed the Grignard reaction and Friedel-Crafts alkylation, followed by insertion of a dialkylaminoethyl chain. We also performed microbiological evaluations including in vitro screening against the virulent strain M. tb H37Rv, cytotoxicity assessment in the Vero C-1008 cell line, and 3D-QSAR studies with comparative molecular field analysis (CoMFA) and comparative molecular similarity index analysis (CoMSIA). CoMFA and CoMSIA models yielded good statistical results in terms of q² and r² values, suggesting the validity of the models. It was concluded that a para-substituted benzene ring with bulkier electron-donating groups and aminoalkyl chains are required for higher inhibitory capacity against M. tuberculosis. We believe that these insights will rationally guide the design of newer, optimal, TRSMs.

Synthesis, crystal structures, photoluminescence properties and DNA binding of triazine-nickel(II) complexes for DNA detection

We report here the synthesis of three new nickel(II) complexes: [Ni(PzTA)2CO3]·5H2O (PzTA=2,4-diamino-6-(2'-pyrazin)-1,3,5-triazine) in 1, [NiQ(PyTA)(H2O)2]Cl·H2O (HQ=8-hydroxyquinoline, PyTA=2,4-diamino-6-(2'-pyridyl)-1,3,5-triazine) in 2, [NiQ(PzTA)(H2O)2]Cl·H2O in 3, and they were characterized by UV spectroscopy, elemental analysis, molar conductivity and X-ray single crystal diffraction. Binding of the complexes to ct-DNA was investigated with electronic spectroscopy, ethidium bromide displacement from DNA, viscometry and cyclic voltammetry. The results depicted the DNA binding mode of the three complexes was intercalation, and complex 1 together with external static-electricity. Moreover, the three complexes also presented potential anti-oxidant activity. Interestingly, we found 1 was sensitive to oxygen and to the polarity of nonaqueous solvents in fluorescence spectroscopy. Fluorescence of 2 and 3 is weak in neutral aqueous solvents, but is greatly enhanced by addition of ct-DNA. Thus, 2 and 3 can be used to DNA detection as DNA fluorescence probes with a LOD of 1.61 ng mL(-1), 4.90 ng mL(-1) for the relative wide linear range of 0.01-20 μg mL(-1), 0.02-30 μg mL(-1), respectively. These findings indicate that 1 may be a potential optical probe for oxygen-free environments in nonaqueous form, while 2 and 3 were DNA-targeted probes.

Investigation of aromatase inhibitory activity of metal complexes of 8-hydroxyquinoline and uracil derivatives

PURPOSE

Estrogens play important roles in the pathogenesis and progression of breast cancer as well as estrogen-related diseases. Aromatase is a key enzyme in the rate-limiting step of estrogen production, in which its inhibition is one strategy for controlling estrogen levels to improve prognosis of estrogen-related cancers and diseases. Herein, a series of metal (Mn, Cu, and Ni) complexes of 8-hydroxyquinoline (8HQ) and uracil derivatives (4-9) were investigated for their aromatase inhibitory and cytotoxic activities.

METHODS

The aromatase inhibition assay was performed according to a Gentest™ kit using CYP19 enzyme, wherein ketoconazole and letrozole were used as reference drugs. The cytotoxicity was tested on normal embryonic lung cells (MRC-5) using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay.

RESULTS

Only Cu complexes (6 and 9) exhibited aromatase inhibitory effect with IC50 0.30 and 1.7 μM, respectively. Cytotoxicity test against MRC-5 cells showed that Mn and Cu complexes (5 and 6), as well as free ligand 8HQ, exhibited activity with IC50 range 0.74-6.27 μM.

CONCLUSION

Cu complexes (6 and 9) were found to act as a novel class of aromatase inhibitor. Our findings suggest that these 8HQ-Cu-uracil complexes are promising agents that could be potentially developed as a selective anticancer agent for breast cancer and other estrogen-related diseases.

Novel kojic acid-polymer-based magnetic nanocomposites for medical applications

Iron oxide magnetic nanoparticles (MNPs) were synthesized by the coprecipitation of iron salts in sodium hydroxide followed by coating separately with chitosan (CS) and polyethylene glycol (PEG) to form CS-MNPs and PEG-MNPs nanoparticles, respectively. They were then loaded with kojic acid (KA), a pharmacologically bioactive natural compound, to form KA-CS-MNPs and KA-PEG-MNPs nanocomposites, respectively. The MNPs and their nanocomposites were characterized using powder X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, vibrating sample magnetometry, and scanning electron microscopy. The powder X-ray diffraction data suggest that all formulations consisted of highly crystalline, pure magnetite Fe₃O₄. The Fourier transform infrared spectroscopy and thermogravimetric analysis confirmed the presence of both polymers and KA in the nanocomposites. Magnetization curves showed that both nanocomposites (KA-CS-MNPs and KA-PEG-MNPs) were superparamagnetic with saturation magnetizations of 8.1 emu/g and 26.4 emu/g, respectively. The KA drug loading was estimated using ultraviolet–visible spectroscopy, which gave a loading of 12.2% and 8.3% for the KA-CS-MNPs and KA-PEG-MNPs nanocomposites, respectively. The release profile of the KA from the nanocomposites followed a pseudo second-order kinetic model. The agar diffusion test was performed to evaluate the antimicrobial activity for both KA-CS-MNPs and KA-PEG-MNPs nanocomposites against a number of microorganisms using two Gram-positive (methicillin-resistant Staphylococcus aureus and Bacillus subtilis) and one Gram-negative (Salmonella enterica) species, and showed some antibacterial activity, which could be enhanced in future studies by optimizing drug loading. This study provided evidence for the promise for the further investigation of the possible beneficial biological activities of KA and both KA-CS-MNPs and KA-PEG-MNPs nanocomposites in nanopharmaceutical applications.

8-Hydroxyquinolines: a review of their metal chelating properties and medicinal applications

Metal ions play an important role in biological processes and in metal homeostasis. Metal imbalance is the leading cause for many neurodegenerative diseases such as Alzheimer’s disease, Parkinson’s disease, and multiple sclerosis. 8-Hydroxyquinoline (8HQ) is a small planar molecule with a lipophilic effect and a metal chelating ability. As a result, 8HQ and its derivatives hold medicinal properties such as antineurodegenerative, anticancer, antioxidant, antimicrobial, anti-inflammatory, and antidiabetic activities. Herein, diverse bioactivities of 8HQ and newly synthesized 8HQ-based compounds are discussed together with their mechanisms of actions and structure–activity relationships.

Synthesis of 2,2'-dihydroxybisphenols and antiviral activity of some bisphenol derivatives

New diphenylmethane-type 2,2'-dihydroxybisphenols (5a-d) were prepared regioselectively in good yields. We evaluated the antiviral activity of some bisphenol derivatives synthesized by the plaque reduction assay. Most of the compounds showed significant antiviral activity and the 4,4'-dihydroxybisphenol derivative (10) showed higher activity than 2,2'-bisphenol derivatives. This compound had EC50 value of 1.8 microg/ml.

A New Approach for Oxygenation Using Nitric Oxide under the Influence of N-Hydroxyphthalimide

An approach for partial oxygenation through a carbocation as an intermediate was successfully developed by using nitric oxide under the influence of N-hydroxyphthalimide. Thus, a variety of benzylic ethers were converted into the corresponding partially oxidized compounds, which are difficult to prepare by conventional methods, in high yields. For example, the reaction of phthalane with NO in the presence of a catalytic amount of NHPI at 60 degrees C gave phthalaldehyde in 80% yield. The reaction was found to proceed through the formation of a hemiacetal, such as 1-hydroxyphthalane. In addition, 1,3-di-tert-butoxymethyl benzene afforded 1,3-benzenedicarbaldehyde in good yield. On the other hand, isochroman was converted into 1,1'-oxodiisochromane under these reaction conditions. The reaction of ethers with NO in the presence of a NHPI catalyst is thought to proceed via the formation of a carbocation as an intermediate. A possible reaction path was suggested.

Anti-proliferative effects and phenotypic alterations induced by 8-hydroxyquinoline in melanoma cell lines

The effect of the transition metal chelator, 8-hydroxyquinoline (8-HQ), was examined on the growth and phenotype expression of B16 mouse melanoma cells. Micromolar concentrations of 8-HQ inhibited the growth of B16 cells as well as human melanoma cell lines. Removal of 8-HQ from the culture medium restored normal cell growth. Growth inhibition by 8-HQ was accompanied by phenotypic alterations that included changes in cell morphology, increased production of melanin and enhanced activities of the enzymes gamma-glutamyl transpeptidase and NADPH cytochrome c reductase. These changes might be associated with a better differentiated phenotype.