Ester of Quinoxaline-7-carboxylate 1,4-di-N-oxide as Apoptosis Inductors in K-562 Cell Line: An in vitro, QSAR and DFT Study.

BACKGROUND: Quinoxalines have shown a wide variety of biological activities including as antitumor agents. The aims of this study were to evaluate the activity of quinoxaline 1,4-di-N-oxide derivatives on K562 cells, the establishment of the mechanism of induced cell death, and the construction of predictive QSAR models. MATERIAL AND METHODS: Sixteen esters of quinoxaline-7-carboxylate 1,4-di-N-oxide were evaluated for antitumor activity on K562 chronic myelogenous leukemia cells and their IC50 values were determined. The mechanism of induced cell death by the most active molecule was assessed by flow cytometry and an in silico study was conducted to optimize and calculate theoretical descriptors of all quinoxaline 1,4-di-N-oxide derivatives. QSAR and QPAR models were created using genetic algorithms. RESULTS & CONCLUSIONS: Our results show that compounds C5, C7, C10, C12 and C15 had the lowest IC50 of the series. C15 was the most active compound (IC50= 3.02 µg/mL), inducing caspase-dependent apoptotic cell death via the intrinsic pathway. QSAR and QPAR studies are discussed.

Synthesis and in vitro evaluation of new ethyl and methyl quinoxaline-7-carboxylate 1,4-di-N-oxide against Entamoeba histolytica.

In our search for new antiamoebic agents, a new series of ethyl and methyl quinoxaline-7-carboxylate 1,4-di-N-oxide derivatives have been synthesized using the Beirut reaction. All compounds were characterized by spectroscopic techniques and elemental analysis. Antiamoebic activity was evaluated in vitro against Entamoeba histolytica strain HM1:IMSS by the microdilution method, and the structure-activity relationship was analyzed. We found that eleven quinoxaline derivatives showed greater activity than metronidazole and nitazoxanide with IC50 values in the range 1.99-0.35 µM. Compounds T-001 and T-016 shows IC50 values of 1.41 and 1.47 µM, respectively, with a value of selectivity index >60.

Structural relationships in the solid state of the anti-chagas agent (E)-phenylethenylbenzofuroxan.

The crystal structure and the vibrational spectrum of a potential drug for Chagas's disease treatment, the (E)-isomer of phenylethenylbenzofuroxan 1 (5(6)(E)-[(2-phenylethenyl)]benzo[1,2-c]1,2,5-oxadiazole N-oxide), are reported. In order to provide insights into structural relationships, quantum mechanical calculations were employed starting from crystal structure. These results have given theoretical support to state interesting structural features, such as the effect of some intermolecular contacts on the molecule conformation and the electronic delocalization decreasing through atoms of the benzofuroxan moiety. Furthermore, the MOGUL comparative analysis in the Cambridge Structural Database provided additional evidences on these structural behaviors of compound 1. Intermolecular contacts interfere on the intramolecular geometry, as, for instance, on the phenyl group orientation, which is twisted by 12.32(6)° from the ethenylbenzofuroxan plane. The experimental Raman spectrum of compound 1 presents unexpected frequency shift and also anomalous Raman activities. At last, the molecule skeleton deformation and the characteristic vibrational modes were correlated by matching the experimental Raman spectrum to the calculated one.

Heteroarylnitrones as drugs for neurodegenerative diseases: synthesis, neuroprotective properties, and free radical scavenger properties.

New 1,2,4-thiadiazolylnitrones and furoxanylnitrones were developed and evaluated as neuroprotective agents on a human neuroblastoma (SH-SY5Y) cells model. They inhibited at low micromolar concentrations the oxidative damage and the death induced by exposure to hydrogen peroxide. These heteroarylnitrones showed excellent peroxyl free radical absorbance capacities, analyzed by oxygen radical absorbance capacity (ORAC) assay with fluorescein as the fluorescent probe, ranging from 1.5- to 16.5-fold the value of the reference nitrone, alpha-phenyl-N-tert-butylnitrone (PBN). The electron spin resonance spectroscopy (ESR) demonstrated the ability of these derivatives to directly trap and stabilize oxygen, carbon, and sulfur-centered free radicals. These results demonstrated the potential use of these heteroarylnitrones as neuroprotective agents in preventing the death of cells exposed to enhanced oxidative stress and damage.

Pyrimido[1,2-a]quinoxaline 6-oxide and phenazine 5,10-dioxide derivatives and related compounds as growth inhibitors of Trypanosoma cruzi.

Two different families of N-oxide containing heterocycles were evaluated as in vitro growth inhibitors of T. cruzi. Both families of heterocycles were selected from our in-house library of compounds as analogues of active anti-T. cruzi N-oxide containing heterocycles. Derivatives from pyrimido[1,2-a]quinoxaline 6-oxide family were poorly active at the assayed doses. However, phenazine 5,10-dioxide derivatives displayed good to excellent anti-T. cruzi activities. The anti-T. cruzi activity of phenazine derivatives was related to substituent' electronic descriptors, sigma(p)(-). Derivatives 19, 20 and 23 were the most cytotoxic compounds against the protozoan and became excellent hit for further structural modifications.

2H-benzimidazole 1,3-dioxide derivatives: a new family of water-soluble anti-trypanosomatid agents.

Three series of benzimidazole N-oxide derivatives were developed and were examined for their activity against trypanosomatid parasites (Trypanosoma cruzi and Leishmania spp.). 2H-benzimidazole 1,3-dioxides displayed remarkable in vitro activities against both parasites, with derivatives 28, 29, and 32 being the most potent (IC50 < 5 microM) against the epimastigote form of T. cruzi and 28, 33, and 35 the most potent against the promastigote form of Leishmania spp. Unspecific cytotoxicity was evaluated using murine macrophages, and derivative 33 was not toxic at a concentration 30 times that of its IC50 against T. cruzi that was completely toxic for Leishmania spp., implying that the series of 2H-benzimidazole 1,3-dioxides is selective toward both trypanosomatid parasites. Derivatives 33 and 35 were submitted to an in vivo assay using an acute model of Chagas' disease and a short-term treatment (30 mg/kg/day orally administrated as aqueous solution, during 10 days). While in the control (untreated) and Benznidazole (50 mg/kg/day) groups survival fraction was 60.0% and 87.5%, respectively, none of the animals treated with derivatives 33 and 35 died. From the preliminary structure-activity relationship studies reduction potential and electrophilicity were found relevant to anti-T. cruzi activity. Active compounds are better electrophiles and more easily reduced than inactive ones.

Quinoxaline N,N'-dioxide derivatives and related compounds as growth inhibitors of Trypanosoma cruzi. Structure-activity relationships.

Quinoxaline derivatives presented good inhibitor activity of growth of Trypanosoma cruzi in in vitro assays. The 50% inhibitory doses were of the same order of that of Nifurtimox. Derivative 13, a quinoxaline N,N'-dioxide derivative, and the reduced derivatives 19 and 20 were the most cytotoxic compounds against the protozoan. Structural requirements for optimal activity were studied by computational methods. From statistical analysis we could establish a multiple correlation between activity and lipophilic properties and LUMO energy.

Novel antiprotozoal products: imidazole and benzimidazole N-oxide derivatives and related compounds.

The syntheses and biological evaluation of the first anti-protozoa imidazole N-oxide and benzimidazole N-oxide and their derivatives are reported. They were tested in vitro against two different protozoa, Trypanosoma cruzi and Trichomonas vaginalis. Derivative 7c, ethyl-1-(i-butyloxycarbonyloxy)-6-nitrobenzimid-azole-2-carboxylate, displayed activity on both protozoa. Lipophilicity and redox potential were experimentally determined in order to study the relationship with activity of the compounds. These properties are well related with the observed bioactivity. Imidazole and benzimidazole N-oxide derivatives are becoming leaders for further chemical modifications and advanced biological studies.

1, 2, 4-Triazine N-oxide derivatives: studies as potential hypoxic cytotoxins. Part II.

New 1, 2, 4-Triazine N-oxide and N, N'-dioxide derivatives were synthesized in order to obtain compounds as selective hypoxic cell cytotoxins. The starting heterocycles have been prepared using a standard microwave oven in a clean and good-yielded process. The reactivity of methyl-1, 2, 4-triazine N(4)-oxide and N(1), N(4)-dioxide with different electrophilic agents has been studied. The desired products were obtained only when iminium electrophiles were employed. The regioselectivity of this process has been studied by means of experimental and theoretical (at ab initio level) procedures. Theoretically was expected that the most stable intermediates where the benzylic-like anion from position 5. A fact which agreed with the experimental observed regioselectivity. The new compounds were tested for their cytotoxicity in oxia and hypoxia. Some of them proved to be less active in hypoxic conditions than tirapazamine, 3-amino-benzo[1, 2-e]1, 2, 4-triazine N(1), N(4)-dioxide. Derivative 19, 6-methyl-5-[2-(5-nitrothienyl)ethenyl)-1, 2, 4-triazine N(4)-oxide, was the most cytotoxic compound, but it was non-selective.

1, 2, 4-Triazine N-oxide derivatives: studies as potential hypoxic cytotoxins. Part III.

New 5-(2-arylethenyl)-1, 2, 4-triazine N-oxide and N, N'-dioxide derivatives were synthesized in order to obtain compounds as selective hypoxic cell cytotoxins. The desired products were obtained when the 5-methyl heterocycle reacted with the corresponding iminium electrophiles. The new compounds were tested for their cytotoxicity in oxia and hypoxia. Some of them proved to be less active in hypoxic conditions than Tirapazamine, 3-aminobenzo[1, 2-e]1, 2, 4-triazine N(1), N(4)-dioxide. Derivative 11, 6-methyl-5-[2-(5-nitrofuryl)ethenyl)-1, 2, 4-triazine N(4)-oxide, was the most cytotoxic compound, but it was non-selective. Some derivatives were studied as DNA-binding agents in oxic conditions showing poor affinity for this biomolecule. This result showed that the cytotoxic activity in oxia is DNA damage not dependent. Electrochemical and ESR spectroscopy studies were performed in order to determine the ability of compounds to produce radicals and the relation of these in the mechanism of cytotoxicity.

Benzo[1,2-c]1,2,5-oxadiazole N-oxide derivatives as potential antitrypanosomal drugs. Structure-activity relationships. Part II.

The preparation of new derivatives of benzo[1,2-c]1,2,5-oxadiazole N-oxide is described. These derivatives were chosen in order to investigate and confirm previous structural features found necessary to display an adequate antitrypanosomal activity. The compounds synthesized were tested in vitro against epimastigote forms of Trypanosoma cruzi. The presence of a bromine atom in the benzo system produced compounds less active than the corresponding de-halo analogues. However, 5-(bromomethyl)-7-bromobenzo[1,2-c]oxadiazole N-oxide (23) was the most cytotoxic compound against T. cruzi. For this, the 50% inhibitory dose (ID50) was determined, it was of the same order as that of Nifurtimox. From statistical analysis we could establish a relationship between lipophilic-hydrophilic balance of the derivatives with their effectiveness as antichagasic compounds.

1,2,5-Oxadiazole N-oxide derivatives and related compounds as potential antitrypanosomal drugs: structure-activity relationships.

The syntheses of a new series of derivatives of 1,2,5-oxadiazole N-oxide, benzo[1,2-c]1,2,5-oxadiazole N-oxide, and quinoxaline di-N-oxide are described. In vitro antitrypanosomal activity of these compounds was tested against epimastigote forms of Trypanosoma cruzi. For the most effective drugs, derivatives IIIe and IIIf, the 50% inhibitory dose (ID50) was determined as well as their cytotoxicity against mammalian fibroblasts. Electrochemical studies and ESR spectroscopy show that the highest activities observed are associated with the facile monoelectronation of the N-oxide moiety. Lipophilic-hydrophilic balance of the compounds could also play an important role in their effectiveness as antichagasic drugs.