New trypanocidal hybrid compounds from the association of hydrazone moieties and benzofuroxan heterocycle

Synthesis, X-ray Structure, Hirshfeld, DFT Conformational, Cytotoxic, and Anti-Toxoplasma Studies of New Indole-Hydrazone Derivatives

The hydrazones 3a-c, were synthesized from the reaction of indole-3-carbaldehyde and nicotinic acid hydrazide, isonicotinic acid hydrazide, and benzoic acid hydrazide, respectively. Their structures were confirmed using FTIR, 1HNMR, and 13CNMR spectroscopic techniques. Exclusively, hydrazones 3b and 3c were confirmed using single crystal X-ray crystallography to exist in the Eanti form. With the aid of DFT calculations, the most stable configuration of the hydrazones 3a-c in gas phase and in nonpolar solvents (CCl4 and cyclohexane) is the ESyn form. Interestingly, the DFT calculations indicated the extrastability of the EAnti in polar aprotic (DMSO) and polar protic (ethanol) solvents. Hirshfeld topology analysis revealed the importance of the N…H, O…H, H…C, and π…π intermolecular interactions in the molecular packing of the studied systems. Distribution of the atomic charges for the hydrazones 3a-c was presented. The hydrazones 3a-c showed a polar character where 3b has the highest polarity of 5.7234 Debye compared to the 3a (4.0533 Debye) and 3c (5.3099 Debye). Regarding the anti-toxoplasma activity, all the detected results verified that 3c had a powerful activity against chronic toxoplasma infection. Compound 3c showed a considerable significant reduction percent of cyst burden in brain homogenates of toxoplasma infected mice representing 49%.

Hybrid-Compounds Against Trypanosomiases

Neglected tropical diseases (NTDs) are a global public health problem associated with approximately 20 conditions. Among these, Chagas disease (CD), caused by Trypanosoma cruzi, and human African trypanosomiasis (HAT), caused by T. brucei gambiense or T. brucei rhodesiense, affect mainly the populations of the countries from the American continent and sub- Saharan Africa. Pharmacological therapies used for such illnesses are not yet fully effective. In this context, the search for new therapeutic alternatives against these diseases becomes necessary. A drug design tool, recently recognized for its effectiveness in obtaining ligands capable of modulating multiple targets for complex diseases, concerns molecular hybridization. Therefore, this review aims to demonstrate the importance of applying molecular hybridization in facing the challenges of developing prototypes as candidates for the treatment of parasitic diseases. Therefore, studies involving different chemical classes that investigated and used hybrid compounds in recent years were compiled in this work, such as thiazolidinones, naphthoquinones, quinolines, and others. Finally, this review covers several applications of the exploration of molecular hybridization as a potent strategy in the development of molecules potentially active against trypanosomiases, in order to provide information that can help in designing new drugs with trypanocidal activity.

The Reactivity of Azidonitrobenzofuroxans towards 1,3-Dicarbonyl Compounds: Unexpected Formation of Amino Derivative via the Regitz Diazo Transfer and Tautomerism Study

Herein, we report on the reaction of nitro-substituted azidobenzofuroxans with 1,3-dicarbonyl compounds in basic media. The known reactions of benzofuroxans and azidofuroxans with 1,3-dicarbonyl compounds in the presence of bases are the 1,3-dipolar cycloaddition and the Beirut reaction. In contrast with this, azidonitrobenzofuroxan reacts with 1,3-carbonyl compounds through Regitz diazo transfer, which is the first example of this type of reaction for furoxan derivatives. This difference is seemingly due to the strong electron-withdrawing effect of the superelectrophilic azidonitrobenzofuroxan, which serves as the azido transfer agent rather than 1,3-dipole in this case.

Predictive Global Models of Cruzain Inhibitors with Large Chemical Coverage

Chagas disease affects 8-11 million people worldwide, most of them living in Latin America. Moreover, migratory phenomena have spread the infection beyond endemic areas. Efforts for the development of new pharmacological therapies are paramount as the pharmacological profile of the two marketed drugs currently available, nifurtimox and benznidazole, needs to be improved. Cruzain, a parasitic cysteine protease, is one of the most attractive biological targets due to its roles in parasite survival and immune evasion. In this work, we compiled and curated a database of diverse cruzain inhibitors previously reported in the literature. From this data set, quantitative structure-activity relationship (QSAR) models for the prediction of their pIC50 values were generated using k-nearest neighbors and random forest algorithms. Local and global models were calculated and compared. The statistical parameters for internal and external validation indicate a significant predictability, with q loo 2 values around 0.66 and 0.61 and external R 2 coefficients of 0.725 and 0.766. The applicability domain is quantitatively defined, according to QSAR good practices, using the leverage and similarity methods. The models described in this work are readily available in a Python script for the discovery of novel cruzain inhibitors.

Polymer-supported triphenylphosphine: application in organic synthesis and organometallic reactions

This comprehensive review highlights the diverse chemistry and applications of polymer-supported triphenylphosphine (PS-TPP) in organic synthesis since its inception. Specifically, the review describes applications of the preceding reagent in functional group interconversions, heterocycle synthesis, metal complexes and their application in synthesis, and total synthesis of natural products. Many examples are provided from the literature to show the scope and selectivity (regio, stereo, and chemo) in these transformations.

Rational Design of Benzylidenehydrazinyl-Substituted Thiazole Derivatives as Potent Inhibitors of Human Dihydroorotate Dehydrogenase with in Vivo Anti-arthritic Activity

Human dihydroorotate dehydrogenase (hDHODH) is an attractive therapeutic target for the treatment of rheumatoid arthritis, transplant rejection and other autoimmune diseases. Based on the X-ray structure of hDHODH in complex with lead compound 7, a series of benzylidenehydrazinyl-substituted thiazole derivatives as potent inhibitors of hDHODH were designed and synthesized, of which 19 and 30 were the most potent with IC₅₀ values in the double-digit nanomolar range. Moreover, compound 19 displayed significant anti-arthritic effects and favorable pharmacokinetic profiles in vivo. Further X-ray structure and SAR analyses revealed that the potencies of the designed inhibitors were partly attributable to additional water-mediated hydrogen bond networks formed by an unexpected buried water between hDHODH and the 2-(2-methylenehydrazinyl)thiazole scaffold. This work not only elucidates promising scaffolds targeting hDHODH for the treatment of rheumatoid arthritis, but also demonstrates that the water-mediated hydrogen bond interaction is an important factor in molecular design and optimization.

The study of NADPH-dependent flavoenzyme-catalyzed reduction of benzo[1,2-c]1,2,5-oxadiazole N-oxides (benzofuroxans)

The enzymatic reactivity of a series of benzo[1,2-c]1,2,5-oxadiazole N-oxides (benzofuroxans; BFXs) towards mammalian single-electron transferring NADPH:cytochrome P-450 reductase (P-450R) and two-electron (hydride) transferring

NAD(P)H

quinone oxidoreductase (NQO1) was examined in this work. Since the =N+ (→O)O- moiety of furoxan fragments of BFXs bears some similarity to the aromatic nitro-group, the reactivity of BFXs was compared to that of nitro-aromatic compounds (NACs) whose reduction mechanisms by these and other related flavoenzymes have been extensively investigated. The reduction of BFXs by both P-450R and NQO1 was accompanied by O2 uptake, which was much lower than the NADPH oxidation rate; except for annelated BFXs, whose reduction was followed by the production of peroxide. In order to analyze the possible quantitative structure-activity relationships (QSARs) of the enzymatic reactivity of the compounds, their electron-accepting potency and other reactivity indices were assessed by quantum mechanical methods. In P-450R-catalyzed reactions, both BFXs and NACs showed the same reactivity dependence on their electron-accepting potency which might be consistent with an "outer sphere" electron transfer mechanism. In NQO1-catalyzed two-electron (hydride) transferring reactions, BFXs acted as more efficient substrates than NACs, and the reduction efficacy of BFXs by NQO1 was in general higher than by single-electron transferring P-450R. In NQO1-catalyzed reactions, QSARs obtained showed that the reduction efficacy of BFXs, as well as that of NACs, was determined by their electron-accepting potency and could be influenced by their binding mode in the active center of NQO1 and by their global softness as their electronic characteristic. The reductive conversion of benzofuroxan by both flavoenzymes yielded the same reduction product of benzofuroxan, 2,3-diaminophenazine, with the formation of o-benzoquinone dioxime as a putative primary reductive intermediate, which undergoes a further reduction process. Overall, the data obtained show that by contrast to NACs, the flavoenzyme-catalyzed reduction of BFXs is unlikely to initiate their redox-cycling, which may argue for a minor role of the redox-cycling-type action in the cytotoxicity of BFXs.

Optimization of antitrypanosomatid agents: identification of nonmutagenic drug candidates with in vivo activity

Chagas disease, caused by Trypanosoma cruzi parasite, was described thousands of years ago. Currently, it affects millions of people, mostly in Latin America, and there are not suitable drugs for treating it. As an attempt to find appropriate drugs to deal with this problem, we report here on the design, synthesis, and characterization of 82 new compounds. Trypanosomicidal behavior in vitro showed more than 20 outstanding derivatives with anti-Trypanosoma cruzi activity. Furthermore, we studied the nonspecific toxicity against mammalian cells determining their selectivity and also performed mutagenicity studies. Proof of concept, in vivo studies, was conducted with two of the most promising derivatives (77 and 80). They were identified as candidates because they have (i) very simple and cost-effective syntheses; (ii) activity against different stages and strains of the parasite showing excellent in vivo behavior during the acute phase of Chagas disease; and (iii) neither nonspecific toxicity nor mutagenic activity.

A review exploring biological activities of hydrazones

The development of novel compounds, hydrazones has shown that they possess a wide variety of biological activities viz. antimicrobial, anticonvulsant, antidepressant, anti-inflammatory, analgesic, antiplatelet, antimalarial, anticancer, antifungal, antitubercular, antiviral, cardio protective etc., Hydrazones/azomethines/imines possess-NHN = CH- and constitute an important class of compounds for new drug development. A number of researchers have synthesized and evaluated the biological activities of hydrazones. This review aims at highlighting the diverse biological activities of hydrazones.

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.

Ligand-based design, synthesis, and experimental evaluation of novel benzofuroxan derivatives as anti-Trypanosoma cruzi agents

A set of substituted-[N'-(benzofuroxan-5-yl)methylene]benzohydrazides (4a-t), previously designed and synthesized, was experimentally assayed against Trypanosoma cruzi, the etiological agent of Chagas' disease, one of the most neglected tropical diseases. Exploratory data analysis, Hansch approach and VolSurf formalism were applied to aid the ligand-based design of novel anti-T. cruzi agents. The best 2D-QSAR model showed suitable statistical measures [n = 18; s = 0.11; F = 42.19; R(2) = 0.90 and Q(2) = 0.77 (SDEP = 0.15)], and according to the optimum 3D-QSAR model [R(2) = 0.98, Q(2) = 0.93 (SDEP = 0.08)], three latent variables explained 62% of the total variance from original data. Steric and hydrophobic properties were pointed out as the key for biological activity. Based upon the findings, six novel benzofuroxan derivatives (4u-z) were designed, synthesized, and in vitro assayed to perform the QSAR external prediction. Then, the predictability for the both models, 2D-QSAR (Rpred(2) = 0.91) and 3D-QSAR (Rpred(2) = 0.77), was experimentally validated, and compound 4u was identified as the most active anti-T. cruzi hit (IC50 = 3.04 μM).

Induction of oxidative stress in Trypanosoma brucei by the antitrypanosomal dihydroquinoline OSU-40

Dihydroquinoline derivative OSU-40 (1-benzyl-1,2-dihydro-2,2,4-trimethylquinolin-6-yl acetate) is selectively potent against Trypanosma brucei rhodesiense in vitro (50% inhibitory concentration [IC(50)], 14 nM; selectivity index, 1,700) and has been proposed to cause the formation of reactive oxygen species (ROS) in African trypanosomes (J. Fotie et al., J. Med. Chem. 53:966-982, 2010). In the present study, we sought to provide further support for the hypothesis that OSU-40 kills trypanosomes through oxidative stress. Inducible RNA interference (RNAi) was applied to downregulate key enzymes in parasite antioxidant defense, including T. brucei trypanothione synthetase (TbTryS) and superoxide dismutase B (TbSODB). Both TbTryS RNAi-induced and TbSODB RNAi-induced cells showed impaired growth and increased sensitivity toward OSU-40 by 2.4-fold and 3.4-fold, respectively. Decreased expression of key parasite antioxidant enzymes was thus associated with increased sensitivity to OSU-40, consistent with the hypothesis that OSU-40 acts through oxidative stress. Finally, the dose-dependent formation of free radicals was observed after incubation of T. brucei with OSU-40 utilizing electron spin resonance (ESR) spectroscopy. These data support the notion that the mode of antitrypanosomal action for this class of compounds is to induce oxidative stress.

3-Trifluoromethylquinoxaline N,N'-dioxides as anti-trypanosomatid agents. Identification of optimal anti-T. cruzi agents and mechanism of action studies

For a fourth approach of quinoxaline N,N'-dioxides as anti-trypanosomatid agents against T. cruzi and Leishmania, we found extremely active derivatives. The present study allows us to state the correct requirements for obtaining optimal in vitro anti-T. cruzi activity. Derivatives possessing electron-withdrawing substituents in the 2-, 3-, 6-, and 7-positions were the most active compounds. With regard to these features and taking into account their mammal cytotoxicity, some trifluoromethylquinoxaline N,N'-dioxides have been proposed as candidates for further clinical studies. Consequently, mutagenicity and in vivo analyses were performed with the most promising derivatives. In addition, with regard to the mechanism of action studies, it was demonstrated that mitochondrial dehydrogenases are involved in the anti-T. cruzi activity of the most active derivatives.

New heteroaryl nitrones with spin trap properties: Identification of a 4-furoxanyl derivative with excellent properties to be used in biological systems

A new series of heteroaryl nitrones, 1-7, bearing furoxanyl and thiadiazolyl moieties, were evaluated for their free radical-trapping properties. The physicochemical characterization by electron paramagnetic resonance (EPR) demonstrated its capability to trap and stabilize oxygen-, carbon-, sulfur-, and nitrogen-centered free radicals. The 4-furoxanyl nitrone 3 (FxBN), alpha(Z)-(3-methylfuroxan-4-yl)-N-tert-butylnitrone, showed appropriate solubility in aqueous solution and taking into account that this physicochemical property is very important for biological applications, we studied it deeply in terms of its trapping and kinetic behaviors. For this, kinetic studies of the hydroxyl adduct decay gave rate constants k(ST) of 1.22x10(10)dm(3)mol(-1)s(-1) and half-live up to 7200s at physiological pH, without any artifactual signals. The ability of FxBN to directly traps and stabilizes superoxide free radical, with a half-life of 1620s at physiological pH, was also demonstrated. Besides, FxBN-hydroxyl and -superoxide adducts exhibited distinct and characteristic EPR spectral patterns. Finally, we confirmed the ability of FxBN to act as spin trap in a specific biological system, that is, in the free radical production of experimental anti-trypanosomatid drugs using Trypanosoma cruzi microsomes as biological system. Moreover, previous observations of low FxBN toxicity transform it in a good candidate for in vivo spin trapping.

Anti-trypanosomatid benzofuroxans and deoxygenated analogues: synthesis using polymer-supported triphenylphosphine, biological evaluation and mechanism of action studies

Hybrid vinylthio-, vinylsulfinyl-, vinylsulfonyl- and vinylketo-benzofuroxans developed as anti-trypanosomatid agents, against Trypanosoma cruzi and Leishmania spp., have showed low micromolar IC(50) values. The synthetic route to access to these derivatives was an efficient Wittig reaction performed in mild conditions with polymer-supported triphenylphosphine (PS-TPP). Additionally, the benzofurozan analogues, deoxygenated benzofuroxans, were prepared using PS-TPP as reductive reagent in excellent yields. The trypanosomicidal and leishmanocidal activities of the benzofuroxan derivatives were measured and also some aspects of their mechanism of action studied. In this sense, inhibition of mitochondrial dehydrogenases activities, production of intra-parasite free radicals and cruzipain inhibition were studied as biological target for the anti-trypanosomatid identified compounds. The trypanosomicidal activity could be the result of both the parasite-mitochondrion function interference and production of oxidative stress into the parasite.

Design, synthesis, antimicrobial activity and molecular modeling studies of novel benzofuroxan derivatives against Staphylococcus aureus

Molecular modification is a quite promising strategy in the design and development of drug analogs with better bioavailability, higher intrinsic activity and less toxicity. In the search of new leads with potential antimicrobial activity, a new series of 14 4-substituted [N'-(benzofuroxan-5-yl)methylene]benzohydrazides, nifuroxazide derivatives, were synthesized and tested against standard and multidrug-resistant Staphylococcus aureus strains. The selection of the substituent groups was based on physicochemical properties, such as hydrophobicity and electronic effect. These properties were also evaluated through the lipophilic and electrostatic potential maps, respectively, considering the compounds with better biological profile. Twelve compounds exhibited similar bacteriostatic activity against standard and multidrug-resistant strains. The most active compound was the 4-CF(3) substituted derivative, which presented a minimum inhibitory concentration (MIC) value of 14.6-13.1 microg/mL, and a ClogP value of 1.87. The results highlight the benzofuroxan derivatives as potential leads for designing new future antimicrobial drug candidates.