Enhanced Energetic Performance via the Combination of Furoxan and Oxa-[5,5]bicyclic Structures.

Three new compounds based on the combination of furoxan (1,2,5-oxadiazole N-oxide) and oxa-[5,5]bicyclic ring were synthesized. Among them, the nitro compound showed satisfactory detonation properties (Dv, 8565 m s-1; P, 31.9 GPa), which is comparable to the performance of RDX (a classic high-energy secondary explosive). Additionally, the introduction of the N-oxide moiety and oxidation of the amino group more effectively improved the oxygen balance and density (d, 1.81 g cm-3; OB%, +2.8%) of the compounds compared to furazan analogues. Combined with good density and oxygen balance as well as moderate sensitivity, this type of furoxan and oxa-[5,5]bicyclic structure will open up a platform for the synthesis and design of new high-energy materials.

Proteomics Studies Suggest That Nitric Oxide Donor Furoxans Inhibit In Vitro Vascular Smooth Muscle Cell Proliferation by Nitric Oxide-Independent Mechanisms.

Physiologically, smooth muscle cells (SMC) and nitric oxide (NO) produced by endothelial cells strictly cooperate to maintain vasal homeostasis. In atherosclerosis, where this equilibrium is altered, molecules providing exogenous NO and able to inhibit SMC proliferation may represent valuable antiatherosclerotic agents. Searching for dual antiproliferative and NO-donor molecules, we found that furoxans significantly decreased SMC proliferation in vitro, albeit with different potencies. We therefore assessed whether this property is dependent on their thiol-induced ring opening. Indeed, while furazans (analogues unable to release NO) are not effective, furoxans' inhibitory potency parallels with the electron-attractor capacity of the group in 3 of the ring, making this effect tunable. To demonstrate whether their specific block on G1-S phase could be NO-dependent, we supplemented SMCs with furoxans and inhibitors of GMP- and/or of the polyamine pathway, which regulate NO-induced SMC proliferation, but they failed in preventing the antiproliferative effect. To find the real mechanism of this property, our proteomics studies revealed that eleven cellular proteins (with SUMO1 being central) and networks involved in cell homeostasis/proliferation are modulated by furoxans, probably by interaction with adducts generated after degradation. Altogether, thanks to their dual effect and pharmacological flexibility, furoxans may be evaluated in the future as antiatherosclerotic molecules.

Mechanochemical Dimerization of Aldoximes to Furoxans.

Solvent-free mechanical milling is a new, environmentally friendly and cost-effective technology that is now widely used in the field of organic synthesis. The mechanochemical solvent-free synthesis of furoxans from aldoximes was achieved through dimerization of the in situ generated nitrile oxides in the presence of sodium chloride, Oxone and a base. A variety of furoxans was obtained with up to a 92% yield. The present protocol has the advantages of high reaction efficiency and mild reaction conditions.

Greener Synthesis of Antiproliferative Furoxans via Multicomponent Reactions.

Prostate and bladder cancers are commonly diagnosed malignancies in men. Several nitric oxide donor compounds with strong antitumor activity have been reported. Thus, continuing with our efforts to explore the chemical space around bioactive furoxan moiety, multicomponent reactions were employed for the rapid generation of molecular diversity and complexity. We herein report the use of Ugi and Groebke-Blackburn-Bienaymé multicomponent reactions under efficient, safe, and environmentally friendly conditions to synthesize a small collection of nitric-oxide-releasing molecules. The in vitro antiproliferative activity of the synthesized compounds was measured against two different human cancer cell lines, LNCaP (prostate) and T24 (bladder). Almost all compounds displayed antiproliferative activity against both cancer cell lines, providing lead compounds with nanomolar GI50 values against the cancer bladder cell line with selectivity indices higher than 10.

Synthesis of 3,4,5-trisubstituted isoxazoles in water via a [3 + 2]-cycloaddition of nitrile oxides and 1,3-diketones, ß-ketoesters, or ß-ketoamides.

Herein we report a method for the synthesis of 3,4,5-trisubstituted isoxazoles in water under mild basic conditions at room temperature via a [3 + 2]-cycloaddition of nitrile oxides and 1,3-diketones, ß-ketoesters, or ß-ketoamides. We optimized the reaction conditions to control the selectivity of the production of isoxazoles and circumvent other competing reactions, such as O-imidoylation or hetero [3 + 2]-cycloaddition. The reaction happens fast in water and completes within 1-2 hours, which provides an environmentally friendly access to 3,4,5-trisubstituted isoxazoles, an important class of structures found in numerous bioactive natural products and pharmaceuticals. Additionally, we optimized the reaction conditions to produce trifluoromethyl-substituted isoxazoles, a prevalent scaffold in biomedical research and drug discovery programs. We also proposed a plausible mechanism for the selectivity of the [3 + 2]-cycloaddition reaction to produce 3,4,5-trisubstituted isoxazoles. Not to be overlooked are our optimized reaction conditions for the dimerization of hydroximoyl chlorides to form furoxans also known as 1,2,5-oxadiazole 2-oxides, a class of structures with important biological activities due to their unique electronic nature and coordination ability.

Tuning NO release of organelle-targeted furoxan derivatives and their cytotoxicity against lung cancer cells.

We herein report a study on a set of hybrid compounds in which 3-R-substituted furoxan moieties (R = CH3, CONH2, CN, SO2C6H5), endowed with varying NO-releasing capacities, are joined to a mitochondrial probe, rhodamine B. Each product has been investigated for its ability to release NO both in physiological solution, in the presence of cysteine, and in A549 lung adenocarcinoma cancer cells. The cytotoxicity of all the products against the aforementioned cancer cells has been assessed, including the structurally related compounds with no mitochondrial targeting, which were taken as a reference. In the case of the models bearing the -CH3 and -CONH2 groups at the 3-position on the furoxan, only the targeted models showed a significant cytotoxic activity, and only at the highest concentrations, in accordance with their weak NO-releasing properties. On the contrary, the presence of the strong electron-withdrawing groups, as -CN and -SO2C6H5, at the 3-position gave rise to anticancer agents, likely because of the high NO-releasing and of their capability of inhibiting cellular proteins by covalent binding. In detail, the rhodamine hybrid containing the 3-SO2C6H5 substituted furoxan moiety emerged as the most interesting product as it showed high cytotoxicity over the entire concentration range tested. This substructure was also linked to a phenothiazine scaffold that is able to accumulate in lysosomes. Nevertheless, mitochondrial targeting for these NO-donor furoxan substructures was found to be the most efficient.

Recent Advances in the Synthesis and Biomedical Applications of Heterocyclic NO-Donors.

Nitric oxide (NO) is a key signaling molecule that acts in various physiological processes such as cellular metabolism, vasodilation and transmission of nerve impulses. A wide number of vascular diseases as well as various immune and neurodegenerative disorders were found to be directly associated with a disruption of NO production in living organisms. These issues justify a constant search of novel NO-donors with improved pharmacokinetic profiles and prolonged action. In a series of known structural classes capable of NO release, heterocyclic NO-donors are of special importance due to their increased hydrolytic stability and low toxicity. It is no wonder that synthetic and biochemical investigations of heterocyclic NO-donors have emerged significantly in recent years. In this review, we summarized recent advances in the synthesis, reactivity and biomedical applications of promising heterocyclic NO-donors (furoxans, sydnone imines, pyridazine dioxides, azasydnones). The synthetic potential of each heterocyclic system along with biochemical mechanisms of action are emphasized.

Synthesis and biological evaluations of novel isoxazoles and furoxan derivative as anti-inflammatory agents.

Novel isoxazoles (10, 12a&b, 15a-c) and the furoxan derivative (14) have been prepared as new safe anti-inflammatory agents from the hydroximoyl 9. All compounds were evaluated for COX-1\COX-2 and most of them showed promising selectivity. The furoxan derivative 14 gave 59% inhibitory activity using carrageenan induced paw rat edema model. Ulcer index experiment and histo-pathological study of stomach samples were also included. Also the proposed binding mode of certain newly synthesized compounds with COX-2 isoform was briefly discussed.

Anti-Pseudomonas activity of 3-nitro-4-phenylfuroxan.

Pseudomonas aeruginosa is a microorganism that is well adapted to both clinical and industrial settings, where it can form adherent communities that are difficult to eradicate. New anti-Pseudomonas compounds and strategies are necessary, as the current antimicrobial approaches for the inhibition of biofilm formation and, above all, the eradication of formed biofilms are ineffective. Compounds that belong to the furoxan family, which are well-known NO donors, have recently been shown to display anti-Pseudomonas activity. The present study investigates three furoxan compounds that are substituted at the hetero-ring with electron-withdrawing groups (NO2, CN, CONH2) for their effects on P. aeruginosa PAO1 growth and biofilm formation/dispersal. Of the furoxans tested, only 3-nitro-4-phenylfuroxan (KN455) inhibited the growth of suspended P. aeruginosa PAO1 cultures. Furthermore, KN455 inhibited the formation of both younger and older biofilms with very high yields and thus proved itself to be toxic to planktonic subpopulations. It also displayed moderate eradicating power. The activity of KN455 does not appear to be related to its capacity to release small amounts of NO. Interestingly, the isomer 4-nitro-3-phenylfuroxan (KN454), included for comparison, displayed a comparable antibiofilm rate, but did not show the same antimicrobial activity against suspended cells and planktonic subpopulations. While hypotheses as to the mechanism of action have been formulated, further investigations are necessary to shed light onto the antimicrobial activity of this furoxan.

Nucleophilic dearomatization of 4-aza-6-nitrobenzofuroxan by CH acids in the synthesis of pharmacology-oriented compounds.

4-Aza-6-nitrobenzofuroxan (ANBF) reacts with 1,3-dicarbonyl compounds and other CH acids to give carbon-bonded 1,4-adducts - 1,4-dihydropyridines fused with furoxan ring. In the case of most acidic ß-diketones, which exist mainly in the enol form in polar solvents, the reactions proceed in the absence of any added base emphasizing the highly electrophilic character of ANBF. The resulting compounds combine in one molecule NO-donor furoxan ring along with a pharmacologically important 1,4-dihydropyridine fragment and therefore can be considered as prospective platforms for the design of pharmacology-oriented heterocyclic systems.

Reaction Mechanism of 3,4-Dinitrofuroxan Formation from Glyoxime: Dehydrogenation and Cyclization of Oxime.

The reaction pathway of the formation of 3,4-dinitrofuroxan from glyoxime is theoretically investigated under experimental conditions with 25 % nitric acid and dinitrogentetroxide reagents to clarify the mechanism of formation of a furoxan ring by glyoxime. The geometric configurations of minima and transition-state species are optimized at the (U)B3LYP/6-311++G** level. The CCSD(T) and CASSCF(10e,8o)/CASSCF(9e,8o) single-point energy corrections at the same level are performed on top of the optimized geometries. A subsequent dynamic correlation by using NEVPT2/6-311++G**-level single-point energy calculations based on the CASSCF results is also performed to obtain accurate energy values. The formation reaction is analyzed from two processes: glyoxime nitration and 3,4-dinitroglyoxime (nitration product) oxidative cyclization. Calculation results indicate that the electrophilic substitution of nitronium ions from the protonated HNO3 and the abstraction of hydrogen ions by HNO3 molecules are requisites of glyoxime nitration. The formation of a furoxan ring from 3,4-dinitroglyoxime involves two possible mechanisms: 1) oxydehydrogenation by NO2 molecules and the subsequent torsion of NO radical groups to form a ring and 2) the alternation of dehydrogenation and cyclization. The intermediates and transition states in both routes exhibit monoradical and diradical characteristics. Singlet and triplet reactions are considered for the diradical species. Results show that the singlet reaction mechanism is more favorable for cyclization than the triplet reaction. The formation of a furoxan ring from oxime is in accordance with the stepwise intermolecular dehydrogenation and intramolecular torsion to the ring.

Potassium 4,5-Bis(dinitromethyl)furoxanate: A Green Primary Explosive with a Positive Oxygen Balance.

Potassium 4,5-bis(dinitromethyl)furoxanate was synthesized readily from cyanoacetic acid. It was characterized by IR spectroscopy, elemental analysis, NMR spectroscopy, and differential scanning calorimetry (DSC), and the structure was confirmed by X-ray single-crystal diffraction. Its positive oxygen balance, high density (2.130 g cm(-3)), sensitivity (IS=2 J, FS=5 N), and calculated heat of formation (-421.0 kJ mol(-1)), combined with its calculated superior detonation performance (D=7759.0 m s(-1), P=27.3 GPa), make it a competitive replacement as a green primary explosive.

Design, synthesis and anti-ovarian cancer activities of thieno[2,3-d]pyrimidine based chimeric BRD4 inhibitor/nitric oxide-donator.

Bromodomain protein 4 (BRD4) is an attractive epigenetic target that regulating diverse cellular processes, and the discovery of dual-target inhibitors including BRD4 is an effective approach in cancer treatment to increase potency and reduce drug resistance. Based on the multifunctional drug development strategy, a series of new derivatives of nitrooxy (ONO2) or furoxan (1,2,5-oxadiazole 2-oxide) with BRD4 inhibitor capable of inhibiting BRD4 and simultaneously releasing NO were designed and synthesized. When NO concentrations were measured with Griess reagent under physiological conditions, all compounds released NO at micromolar levels, reaching effective antitumor concentrations. Biological studies showed that the most potent BRD4/NO hybrid 11a exhibited good BRD4 inhibitory activity and selectivity. Further mechanistic studies revealed that 11a significantly decreased the expression of BRD4 and c-Myc, as well as induced cellular apoptosis and autophagic cell death both in vitro and in vivo. In summary, we optimized the chimeric BRD4-inhibitor/NO-donor based on our previous studies, and it should be a lead compound for targeted therapy of OC (ovarian cancer) in the future. This interesting strategy could expand the usage of BRDi in human malignancies and endogenous gastro-transmitters.

New Nitric Oxide-Releasing Compounds as Promising Anti-Bladder Cancer Drugs.

Bladder cancer is a worldwide problem and improved therapies are urgently needed. In the search for newer strong antitumor compounds, herein, we present the study of three nitric oxide-releasing compounds and evaluate them as possible therapies for this malignancy. Bladder cancer cell lines T24 and 253J were used to evaluate the antiproliferative, antimigratory, and genotoxic effects of compounds. Moreover, we determined the NF-κB pathway inhibition, and finally, the survivin downregulation exerted by our molecules. The results revealed that compounds 1 and 3 exerted a high antiproliferative activity against bladder cancer cells through DNA damage and survivin downregulation. In addition, compound 3 reduced bladder cancer cell migration. We found that nitric oxide donors are promising molecules for the development of a new therapeutic targeting the underlying mechanisms of tumorigenesis and progression of bladder cancer.

Tert-Butyl Nitrite-initiated C-N Bond Cleavage of 1-Nitromethyl-N-aryltetrahydroisoquinolines: Synthesis of Furoxans with N-NO Skeleton.

A series of furoxan derivatives with N-nitroso groups were synthesized in good yields by TBN initiated radical sp3 C-N bond cleavage of 1-nitromethyl-N-aryltetrahydroisoquinolines. This reaction grafts the biologically important furoxan skeleton and N-nitroso group into on molecule, greatly improving the molecular complexity in one step transformation. The mechanistic study shows that this reaction is mediated by the in situ generated α-carbonyl nitrile oxide, which is afforded by TBN promoted C-N bond cleavage.

Antiaggregant effects of (1,2,5-oxadiazolyl)azasydnone ring assemblies as novel antiplatelet agents.

A series of biheterocyclic assemblies comprising of 1,2,5-oxadiazole and azasydnone scaffolds were synthesized and biologically evaluated as novel nitric oxide (NO)-donor and antiplatelet agents. Depending on functional substituents at the biheterocyclic core, all studied compounds demonstrated good NO-donor profiles releasing NO in a wide range of concentrations (19.2%-195.1%) according to a Griess assay. (1,2,5-Oxadiazolyl)azasydnones showed excellent antiplatelet activity in the case of ADP and adrenaline used as inducers completely suppressing the aggregate formation even at the lowest test concentration of 0.0375 µmol/ml, which is a rather unique feature. Moreover, studied biheterocycles possess a selective mechanism of inhibition of platelet aggregation mediated only by ADP and adrenaline, which are considered to be the main inducers causing thrombus formation. In addition, (1,2,5-oxadiazolyl)azasydnones were found to be completely non-toxic to hybrid endothelial cells EaHy 926. Studies of hydrolytic degradation of the synthesized compounds afforded benzoic acid as a sole detectable decomposition product, which is considered advantageous in drug design. Therefore, (1,2,5-oxadiazolyl)azasydnones represent a novel class of promising drug candidates with improved antiplatelet profile and reduced toxicity enabling their huge potential in medicinal chemistry and drug design.

Bis(Nitroxymethylisoxazolyl) Furoxan: A Promising Standalone Melt-Castable Explosive.

The synthesis and crystal structure of the heterocyclic explosive bis(nitroxymethylisoxazolyl) furoxan, C10 H6 N6 O10 , are described. In addition, we report its physical properties and theoretical performance. This material was found to exhibit standalone melt-castable explosive properties, with a melting point of 89.8 °C and an onset decomposition temperature of 193.8 °C. Bis(nitroxymethylisoxazolyl) furoxan features an insensitive behavior to impact, friction, and electrostatic discharge, with a calculated detonation pressure about 25 % higher than the state-of-the-art melt-castable explosive TNT.

Molecular Hybridization Tools in the Development of Furoxan-Based NO-Donor Prodrugs.

The molecular hybridization of different compounds with known pharmacological activity is a particularly prominent approach for the design of potential drugs with improved pharmacokinetic profiles. Much attention over the last decade has been focused on the synthesis of hybrid structures with a nitric oxide (NO)-donor framework, as NO is a ubiquitous and crucial regulator of cellular metabolism, affecting various physiological and pathophysiological processes. 1,2,5-Oxadiazole 2-oxides (furoxans), which are capable of exogenous NO release in the presence of thiol cofactors, are an important class of prospective NO donors. As such, a wide range of hybrid compounds that combine a furoxan ring with various pharmacologically active structures have been created. This review focuses on recent results in the synthesis and pharmacological activity of furoxan-based hybrids. Special attention is given to chemo- and regioselective methods used in the preparation of these hybrid structures, and the role of synergistic effects on their pharmacological activity, associated with the furoxan fragment.

New praziquantel derivatives containing NO-donor furoxans and related furazans as active agents against Schistosoma mansoni.

A series of NO-donor praziquantel hybrid compounds was obtained by combining praziquantel (PZQ) and furoxan moieties in a single entity. NO-donor properties of the furoxan derivatives were evaluated by detecting nitrite after incubation of the products in 7.4 pH buffered solution in the presence of L-cysteine. Structurally-related furazans, devoid of NO release capacity, were also synthesized for control purposes. All products were studied for their ability to inhibit recombinant Schistosoma mansoni thioredoxin glutathione reductase (TGR). Mobility and death of adult Schistosoma mansoni worms cultured in the presence of the products were evaluated versus PZQ. Analysis of the results showed that some products were endowed with both PZQ and NO-dependent antiparasitic properties. Compounds 6, 7, 18, and 24 emerged as the most interesting balanced hybrids, worthy of additional study on PZQ-resistant parasites.