Electrochemical characteristics of nitroheterocyclic compounds of biological interest. VIII. Stability of nitro radical anions from cyclic voltammetric studies

Reduction Potential Predictions for Some 3-Aryl-Quinoxaline-2-Carbonitrile 1,4-Di-N-Oxide Derivatives with Known Anti-Tumor Properties

The ability for DFT: B3LYP calculations using the 6-31g and lanl2dz basis sets to predict the electrochemical properties of twenty (20) 3-aryl-quinoxaline-2-carbonitrile 1,4-di-N-oxide derivatives with varying degrees of cytotoxic activity in dimethylformamide (DMF) was investigated. There was a strong correlation for the first reduction and moderate-to-low correlation of the second reduction of the diazine ring between the computational and the experimental data, with the exception of the derivative containing the nitro functionality. The four (4) nitro group derivatives are clear outliers in the overall data sets and the derivative E4 is ill-behaved. The remaining three (3) derivatives containing the nitro groups had a strong correlation between the computational and experimental data; however, the computational data falls substantially outside of the expected range.

Voltammetric Study of Some 3-Aryl-quinoxaline-2-carbonitrile 1,4-di-N-oxide Derivatives with Anti-Tumor Activities

The electrochemical properties of twenty 3-aryl-quinoxaline-2-carbonitrile 1,4-di-N-oxide derivatives with varying degrees of cytotoxic activity were investigated in dimethylformamide (DMF) using cyclic voltammetry and first derivative cyclic voltammetry. With one exception, the first reduction of these compounds was found to be reversible or quasireversible and is attributed to reduction of the N-oxide moiety to form a radical anion. The second reduction of the diazine ring was found to be irreversible. Compounds containing a nitro group on the 3-phenyl ring also exhibited a reduction process that may be attributed to that group. There was good correlation between molecular structure and reduction potential, with reduction being facilitated by an enhanced net positive charge at the electroactive site created by electron withdrawing substituents. Additionally, the reduction potential was calculated using two common basis sets, 6-31g and lanl2dz, for five of the test molecules. There was a strong correlation between the computational data and the experimental data, with the exception of the derivative containing the nitro functionality. No relationship between the experimentally measured reduction potentials and reported cytotoxic activities was evident upon comparison of the data.

A study on the formation of the nitro radical anion by ornidazole and its significant decrease in a structurally characterized binuclear Cu(II)-complex: impact in biology

An acetate-bridged binuclear Cu^(II)complex of the antiparasitic drug ornidazole is able to decrease the formation of the nitro radical anion.

Indazoles: a new top seed structure in the search of efficient drugs against Trypanosoma cruzi

For years, Chagas disease treatment has been limited to only two drugs of highly questionable and controversial use (Nifurtimox® and Benznidazole®). In the search of effective drugs, many efforts have been made, but only a few structures have emerged as actual candidates. Heading into this, the multitarget-directed approach appears as the best choice. In this framework, indazoles were shown to be potent Trypanosoma cruzi growth inhibitors, being able to lead both the formation of reactive oxygen species and the inhibition of trypanothione reductase. Herein, we discuss the main structural factors that rule the anti-T. cruzi properties of indazoles, and how they would be involved in the biological properties as well as in the action mechanisms, attempting to make parallels between the old paradigms and current evidences in order to outline what could be the next steps to follow in regard to the future drug design for Chagas disease treatment.

5-Deazaflavin derivatives as inhibitors of p53 ubiquitination by HDM2

Based on previous reports of certain 5-deazaflavin derivatives being capable of activating the tumour suppressor p53 in cancer cells through inhibition of the p53-specific ubiquitin E3 ligase HDM2, we have conducted an structure–activity relationship (SAR) analysis through systematic modification of the 5-deazaflavin template. This analysis shows that HDM2-inhibitory activity depends on a combination of factors. The most active compounds (e.g., 15) contain a trifluoromethyl or chloro substituent at the deazaflavin C9 position and this activity depends to a large extent on the presence of at least one additional halogen or methyl substituent of the phenyl group at N10. Our SAR results, in combination with the HDM2 RING domain receptor recognition model we present, form the basis for the design of drug-like and potent activators of p53 for potential cancer therapy.

Supramolecular structures of metronidazole and its copper(II), cobalt(II) and zinc(II) coordination compounds

In this work we present the synthesis and structural and spectroscopic characterization of Cu(II), Co(II) and Zn(II) coordination compounds with the antibiotic metronidazole ([double bond]emni). Coordination to metal ions is through its imidazolic nitrogen, while the hydroxyethyl and nitro groups act as supramolecular synthons. [Co(emni)(2)Br(2)], and [Zn(emni)(2)X(2)] (X(-)=Cl, Br) stabilize zig-zag chains, and a 2D supramolecular structure is formed by inter-chain contacts through inter-molecular hydrogen-bonding. Pleated sheet or layers are formed by [Co(emni)(2)Cl(2)] and [Cu(emni)(2)Cl(H(2)O)](2)Cl(2), respectively. The dinuclear Cu(II) compound [Cu(emni)mu(O(2)CMe)(2)](2) gives a one-dimensional zig-zag arrangement. The contribution of metal ions in metronidazole coordination compounds is shown in the stabilization of the different aggregate structures.

Metronidazole resistance in Helicobacter pylori

Modern triple drug regimens are highly effective for treating Helicobacter pylori infection, but bacterial resistance to one of the most effective antibiotics, metronidazole, is a serious and increasing problem. The activity of metronidazole in H. pylori is dependent on reduction of its nitro moiety to highly reactive compounds that cause DNA strand breakage. The acquisition of resistance is highly associated with mutational inactivation of the rdxA gene, which encodes an oxygen-insensitive NADPH nitroreductase. Recent evidence has suggested that inactivation of frxA (NADPH flavin oxidoreductase), fdxB (ferredoxin-like protein) and possibly other reductase-encoding genes may also contribute to the resistant phenotype. Improved understanding of the mechanisms of metronidazole resistance in H. pylori is essential for the development and validation of biopsy-based tests for detection of resistance in clinical practice.

Synthesis and evaluation of nitro 5-deazaflavin-pyrrolecarboxamide(s) hybrid molecules as novel DNA targeted bioreductive antitumor agents

A series of 6-nitro-5-deazaflavins bearing at N(3) or N(10) position the pyrrolecarboxamide(s) group as DNA minor groove binder has been synthesized. These hybrid molecules show similar redox properties to those of 6-nitro-5-deazaflavins with no pyrrolecarboxamide(s) group, suggesting that they generate stable one- and two-electron reduction product(s). Electrolytic reductions of the hybrid molecules were carried out at a controlled potential under anaerobic conditions in the presence of plasmid pBR322 DNA. Significant conversions of the supercoiled circular pBR322 DNA (form I) to the open circular DNA (form II) have been found by treatment with the reductively activated 6-nitro-5-deazaflavin derivatives. Their DNA damaging effects have been found to be enhanced as the number of pyrrolecarboxamide group as the DNA binder increases. Antitumor activities of the hybrid molecules towards KB and L1210 cells were evaluated in vitro. It has been found that the antitumor effects of the compounds on KB cells slightly change and those on L1210 cells decrease as the number of the pyrrolecarboxamide group increases. These results reveal that the combination of 6-nitro-5-deazaflavin molecule with the pyrrolecarboxamide(s) group increase the DNA binding properties of the compounds, giving rise to promoted DNA damaging effects, and also suggest that the combination would affect the capacity of the compounds to act as the substrate for intracellular reductases and/or the cellular uptake of the compounds.

Redox behaviour of nifuroxazide: generation of the one-electron reduction product

The electrochemical properties of nifuroxazide have been investigated in aqueous and aqueous-DMF mixed solvents. In aqueous media, a single, irreversible four-electron reduction occurs to give the hydroxylamine derivative. In mixed media, a reversible one-electron reduction to form a nitro radical anion takes place. Cyclic voltammetric studies show that the anion radical product is stable, although the nitro radical anion intermediate shows a tendency to undergo further chemical reactions. A comparison with the voltammetric behaviour of other nitrofurans such as nifurtimox, nitrofurazone and furazolidone is made. The electrochemically-obtained parameters are correlated with the in vivo studies of oxygen consumption on Trypanosoma cruzi cell suspensions.

A nitro radical anion formation from nifedipine: an electrochemical approach

The cyclic voltammetric behaviour of nifedipine was studied. The addition of three aprotic solvents to nifedipine in an aqueous citrate buffer system was examined. Qualitatively they result in separation of the initial irreversible 4 electron reduction into two stages, the NO2/RNO2.- and RNO2.-, 4H/RNHOH, H2O couples, respectively. Particular attention was directed to the 1-electron RNO2/RNO2.- couple as measured by the cyclic voltammetric mode in mixed media. Analysis of the cyclic voltammetric response as a function of scan rate and non-aqueous solvent content yields information on the stability of the radical anion. The chemical forward reaction of the radical anion follows a second order kinetics with a stability constant of 1.1 x 10(-3) l mol-1 s-1 and a half-life time of 0.09 s for 1 mM of nifedipine in aqueous citrate buffer, pH 7.4/DMF; 50:50.