Synthesis and Antimycobacterial Evaluation of Novel Pyrazole-Isoxazolines and Pyrazole-Isoxazoles.

This study reports the synthesis of a new series of pyrazole-isoxazolines, at very good yields, from the cyclocondensation reaction of pyrazole-enaminones with hydroxylamine hydrochloride. Dehydration of the pyrazole-isoxazolines furnished another new series of the respective pyrazole-isoxazoles, at excellent yields. Both series of the obtained compounds were screened for antimycobacterial activity, and compounds 4f and 5c showed significant inhibition of bacterial growth with a time- and concentration-dependent bactericidal effect. Cytotoxicity tests in VERO cell line did not indicate toxicity of compounds 4f and 5c regarding cellular prediction, NO production or dsDNA release. However, both compounds were associated with an increase in total ROS levels, providing induction of oxidative stress, but without compromising cellular targets. These results highlight compounds 4f and 5c as promising candidates for antimycobacterial treatment with a favorable safety profile.

1,2,3-Triazolo[4,5-b]aminoquinolines: Design, synthesis, structure, acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibitory activity, and molecular docking of novel modified tacrines.

An efficient [4 + 2] cyclization protocol to synthesize a series of twelve examples of 1,2,3-triazolo[4,5-b]aminoquinolines (5) as novel structurally modified tacrines was obtained by reacting readily accessible precursors (i.e., 3-alky(aryl)-5-amino-1,2,3-triazole-4-carbonitriles (3)) and selected cycloalkanones (4) of five-, six-, and seven-membered rings. We evaluated the AChE and BChE inhibitory activity of the novel modified tacrines 5, and the compound derivatives from cyclohexanone (4b) showed the best AChE and BChE inhibitory activities. Specifically, 1,2,3-triazolo[4,5-b]aminoquinolines 5bb obtained from 3-methyl-carbonitrile (3b) showed the highest AChE (IC50 = 12.01 µM), while 5ib from 3-sulfonamido-carbonitrile (3i) was the most significant inhibitor for BChE (IC50 = 1.78 µM). In general, the inhibitory potency of compound 5 was weaker than the pure tacrine reference, and our findings may help to design and develop novel anticholinesterase drugs based on modified tacrines.

Bromo-Substituted Diazenyl-pyrazolo[1,5-a]pyrimidin-2-amines: Sonogashira Cross-Coupling Reaction, Photophysical Properties, Bio-interaction and HSA Light-Up Sensor.

A convenient synthesis of a broad series of thirteen examples of alkyne-spacer derivatives 2 from the well-known Sonogashira cross-coupling reaction on diazenyl-pyrazolo[1,5-a]pyrimidin-2-amine compounds 1 is reported. The reactivity of heterocycles 1 due the presence of selected electron-donor (EDG) and electron-withdrawing (EWG) groups attached to different alkynes was evaluated. Also, the reactional versatility due the position variation of the bromo atom at the scaffolds 1 was also investigated. In general, derivatives presented strong absorption bands at the 250-500 nm optical window and UV to cyan emission properties. Also, the redox analysis was recorded by electrochemical cyclic voltammetry technique. For HSA biomacromolecule assays, spectroscopic studies by UV-Vis, steady-state and time-resolved emission fluorescence, and molecular docking calculations evidenced the ability of each compound to establish interactions with human serum albumin (HSA). Finally, the behavior presented for this new class of heterocycles makes them a promising tool as optical sensors for albumins.

Hybridized 4-Trifluoromethyl-(1,2,3-triazol-1-yl)quinoline System: Synthesis, Photophysics, Selective DNA/HSA Bio-interactions and Molecular Docking.

The synthesis, structural analysis, and evaluation of the photophysical properties of twelve novel 2-aryl(heteroaryl)-6-(4-alkyl(aryl)-1H-1,2,3-triazol-1-yl)-4-(trifluoromethyl)quinolines (6-8), where aryl(heteroaryl)=Ph, 4-Me-C6 H4 , 4-F-C6 H4 and 2- furyl; 4-alkyl(aryl)=-CH2 OH, -(CH2 )5 CH3 and Ph, are reported. Hybrid scaffolds 6-8 were synthesized at 77-95 % yields by regioselective copper-catalysed azide-alkyne cycloaddition (CuAAC) reaction of unpublished 6-azido-4-(trifluoromethyl)quinolines (2) with selected terminal alkynes (3-5). Azido intermediates 2 were obtained from the reaction of 6-amino-4-(trifluoromethyl)quinolines (1) and sodium azide at good yields (78-87 %). Compounds 6-8 were structurally fully characterized by 1 H-, 13 C- and 19 F- and 1 H-13 C 2D-NMR (HSQC, HMBC) spectroscopy, X-ray diffraction (SC-XRD) and HRMS analysis. Moreover, the photophysical properties, DNA- and HSA-binding experiments (bio-interactions), and molecular docking studies for compounds 6-8 were performed. These are discussed and compared with similar compounds from recent research.

Substituent-Driven Selective N-/O-Alkylation of 4-(Trihalomethyl)pyrimidin-2(1H)-ones Using Brominated Enones.

The selective N- or O-alkylation of 4-(trihalomethyl)pyrimidin-2(1H)-ones, using 5-bromo enones/enaminones as alkylating agents, is reported. It was found that the selectivity toward the N- or O-regioisomer is driven by the substituent present at the 6-position of the pyrimidine ring, thus enabling the preparation of each isomer as the sole product, in 60-95% yields. Subsequent cyclocondensation of the enaminone moiety with nitrogen dinucleophiles led to pyrimidine-azole conjugates in 55-83% yields.

7-Amine-spiro[chromeno[4,3-b]quinoline-6,1'-cycloalkanes]: Synthesis and cholinesterase inhibitory activity of structurally modified tacrines.

Five new examples of 9,10-chloro(bromo)-7-amine-spiro[chromeno[4,3-b]quinoline-6,1'-cycloalkanes] - in which cycloalkanes = cyclopentane, cyclohexane, and cycloheptane - were synthesized at yields of 42-56%, using a sequential one-pot two-step cyclocondensation reaction of three different scaffolds of 2-aminobenzonitriles and the respective spiro[chroman-2,1'-cycloalkan]-4-ones, and using AlCl3 as the catalyst in a solvent-free method. Subsequently, the five new spirochromeno-quinolines and nine quinolines previously published by us (14 modified tacrine scaffolds) were subjected to AChE and BChE inhibitory activity evaluation. The molecule containing a spirocyclopentane derivative had the highest AChE and BChE inhibitory activity (IC50 = 3.60 and 4.40 µM, respectively), and in general, the non-halogenated compounds were better inhibitors of AChE and BChE than the halogenated molecules. However, the inhibitory potency of compounds 3a-n was weaker than that of tacrine. By molecular docking simulations, it was found that the size of the spirocarbocyclic moieties is inversely proportional to the inhibitory activity of the cholinesterases, probably because an increase in the size of the spirocyclic component sterically hindered the interaction of tacrine derivatives with the active site of tested cholinesterases. The findings obtained here may help in the design and development of new anticholinesterase drugs.

Photophysical, photostability, and ROS generation properties of new trifluoromethylated quinoline-phenol Schiff bases.

A new series of ten examples of Schiff bases, namely (E)-2-(((2-alkyl(aryl/heteroaryl)-4-(trifluoromethyl)quinolin-6-yl)imino)methyl)phenols 3, was easily synthesized with yields of up to 91% from the reactions involving a series of 2-(R-substituted) 6-amino-4-(trifluoromethyl)quinolines 1 and 4(5)-R1-substituted salicylaldehydes 2 - in which alkyl/aryl/heteroaryl for 2-R-substituents are Me, Ph, 4-MeC6H4, 4-FC6H4, 4-NO2C6H4, and 2-furyl, and R1-substituents are 5-NEt2, 5-OCH3, 4-Br, and 4-NO2. Complementarily, the Schiff bases showed low to good quantum fluorescence yield values in CHCl3 (Φf = 0.12-0.80), DMSO (Φf = 0.20-0.75) and MeOH (Φf = 0.13-0.85). Higher values of Stokes shifts (SS) were observed in more polar solvents (DMSO; 65-150 nm and MeOH; 65-130 nm) than in CHCl3 (59-85 nm). Compounds 3 presented good stability under white-LED irradiation conditions and moderate ROS generation properties were observed.

Copper-Linked Rotaxanes for the Building of Photoresponsive Metal Organic Frameworks with Controlled Cargo Delivery.

We have prepared a photoresponsive metal-organic framework by using an amide-based [2]rotaxane as linker and copper(II) ions as metal nodes. The interlocked linker was obtained by the hydrogen bond-directed approach employing a fumaramide thread as template of the macrocyclic component, this latter incorporating two carboxyl groups. Single crystal X-ray diffraction analysis of the metal-organic framework, prepared under solvothermal conditions, showed the formation of stacked 2D rhombohedral grids forming channels decorated with the interlocked alkenyl threads. A series of metal-organic frameworks differing in the E/Z olefin ratio were prepared either by the previous isomerization of the linker or by postirradiation of the reticulated materials. By dynamic solid state 2H NMR measurements, using deuterium-labeled materials, we proved that the geometry of the olefinic axis of the interlocked struts determined the obtention of materials with different independent local dynamics as a result of the strength of the intercomponent noncovalent interactions. Moreover, the usefulness of these novel copper-rotaxane materials as molecular dosing containers has also been assayed by the diffusion and photorelease of p-benzoquinone, evaluated in different solvents and temperatures.

Synthesis of N-Pyrrolyl(furanyl)-Substituted Piperazines, 1,4-Dizepanes, and 1,4-Diazocanes.

The synthetic potential of 5-bromo-1,1,1-trifluoro-4-methoxypent-3-en-2-one toward the catalyst-free synthesis of N-pyrrolyl(furanyl)-piperazines, 1,4-diazepanes, and 1,4-diazocanes through a telescoped protocol is reported. This three-component one-pot method provided 23 examples with high chemo- and regioselectivity at yields up to 96%.

Chemo- and regioselective reactions of 5-bromo enones/enaminones with pyrazoles.

Reaction of 5-bromo enones with pyrazoles provided a series of unexpected N,O-aminal derivatives, through a 1,4-conjugated addition at the ß-carbon of the 5-bromo enones instead of the expected nucleophilic substitution of the bromine. This reaction also furnished the 1,3-regioisomer of the pyrazole. A similar reaction of pyrazoles using 5-bromo enaminones furnished only N-alkylated pyrazoles-with high regioselectivity and at good yields-through nucleophilic substitution of the bromine.

Effect of slight structural changes on the gelation properties of N-phenylstearamide supramolecular gels.

Supramolecular gels present several applications in which the gelator properties are closely dependent on their structure and solvent. Despite this, there are few studies on the effect of the gelation ability of gelators with slight molecular changes. Therefore, N-arylestearamides (in which aryl = phenyl (1), 4-tolyl (2) and 4-acetylphenyl (3)) were evaluated in different solvents. The critical gelefication concentration (CGC) values indicated that the substituents can significantly affect the concentration at which the supramolecular gels are formed, mainly in non-aromatic solvents (e.g. cyclohexane, acetonitrile and DMSO). From UV-Vis and DSC data, we verified that the gel-sol and sol-gel transitions (Tgel-sol and Tsol-gel) increase in the order of 1 < 2 < 3. Organogel strength was evaluated for 1-3 as a function of concentration and solvent type using rheology data. Gel strength is concentration-dependent and a strength order was found in acetonitrile, cyclohexane and DMSO, in which: 1 ∼ 2 > 3. Dynamic viscoelastic measurements as a function of temperature sweeps indicate a predominantly enthalpic contribution to the elasticity of the organogels formed from 1-3. Temperature-dependent 1H NMR indicates that NHO interactions may be responsible for the molecular association of molecules into 1D fibers, while 3D fibers were formed from van der Waals interactions.

Synthesis, Crystal Structure, and Supramolecular Understanding of 1,3,5-Tris(1-phenyl-1H-pyrazol-5-yl)benzenes.

Understanding the supramolecular environment of crystal structures is necessary to facilitate designing molecules with desirable properties. A series of 12 novel 1,3,5-tris(1-phenyl-1H-pyrazol-5-yl)benzenes was used to assess the existence of planar stacking columns in supramolecular structures of pyrazoles. This class of molecules with different substituents may assist in understanding how small structural changes affect the supramolecular environment. The obtained compounds did not present the formation of planar stacking interactions between benzenes in solid or liquid states. This supposition was indicated by single crystal diffraction, Density Functional Theory (DFT) and quantum theory of atoms in molecules (QTAIM) calculations, and concentration-dependent liquid-state ¹H nuclear magnetic resonance (NMR). NMR showed that chemical shifts of benzene and pyrazole hydrogens confirm that planar stacking interactions are not formed in solution. The crystalline structures presented different molecular conformations. The molecular structures of 5 and 9b are in a twisted conformation, while compound 7 showed a conformation analogous to a calyx form.

Regiochemistry of cyclocondensation reactions in the synthesis of polyazaheterocycles.

The syntheses of several polyazaheterocycles are demonstrated. The cyclocondensation reactions between ß-enaminodiketones [CCl3C(O)C(=CNMe2)C(O)-CO2Et] and aromatic amidines resulted in glyoxalate-substituted pyrido[1,2-a]pyrimidinone, thiazolo[3,2-a]pyrimidinone and pyrimido[1,2-a]benzimidazole. Pyrazinones and quinoxalinones were obtained through the reaction of these glyoxalates with ethylenediamine and 1,2-phenylenediamine derivatives. On the other hand, the reaction of glyoxalates with amidines did not lead to the formation of imidazolones, but rather N-acylated products were obtained. All the products were isolated in good yields. DFT-B3LYP calculations provided HOMO/LUMO coefficients, charge densities, and the stability energies of the intermediates, and from these data it was possible to explain the regiochemistry of the products obtained. Additionally, the data were a useful tool for elucidating the reaction mechanisms.

Synthesis, effect of substituents on the regiochemistry and equilibrium studies of tetrazolo[1,5-a]pyrimidine/2-azidopyrimidines.

An efficient synthesis methodology for a series of tetrazolo[1,5-a]pyrimidines substituted at the 5- and 7-positions from the cyclocondensation reaction [CCC + NCN] was developed. The NCN corresponds to 5-aminotetrazole and CCC to ß-enaminone. Two distinct products were observed in accordance with the ß-enaminone substituent. When observed in solution, the compounds can be divided into two groups: (a) precursor compounds with R = CF3 or CCl3, which leads to tetrazolo[1,5-a]pyrimidines in high regioselectivity with R at the 7-position of the heterocyclic ring; and (b) precursor compounds with R = aryl or methyl, which leads to a mixture of compounds, tetrazolo[1,5-a] pyrimidines (R in the 5-position of the ring) and 2-azidopyrimidines (R in the 4-position of the ring), which was attributed to an equilibrium of azide-tetrazole. In the solid state, all compounds were found as 2-azidopyrimidines. The regiochemistry of the reaction and the stability of the products are discussed on the basis of the data obtained by density functional theory (DFT) for energetic and molecular orbital (MO) calculations.

Regioselectively Controlled Synthesis of N-Substituted (Trifluoromethyl)pyrimidin-2(1H)-ones.

A simple and regioselectively controlled method for the preparation of both 1,4- and 1,6-regioisomers of 1-substituted 4(6)-trifluoromethyl-pyrimidin-2(1H)-ones is described. Both regioisomers were synthesized from the cyclocondensation reaction of 4-substituted 1,1,1-trifluoro-4-methoxybut-3-en-2-ones: with nonsymmetric ureas for the 1-substituted 4-(trifluoromethyl)pyrimidin-2(1H)-ones (1,4-isomer) and with nonsymmetric 1-substituted 2-methylisothiourea sulfates for the synthesis of 1-substituted 6-(trifluoromethyl)pyrimidin-2(1H)-ones (1,6-isomer). Each method furnished only the respective isomer in very good yields. The structure of the products was assigned based on the (1)H and (13)C NMR as well as 2D HMBC spectral analysis.

Dethreading of Tetraalkylsuccinamide-Based [2]Rotaxanes for Preparing Benzylic Amide Macrocycles.

The dethreading of a series of succinamide-based [2]rotaxanes bearing benzylic amide macrocycles is reported herein. These transformations proceeded quantitatively either under flash vacuum pyrolysis, conventional heating, or microwave irradiation. Studying the size complementarity of the stoppers at the ends of the thread and the cavity of the macrocycle allowed us to set up the best substituents for implementing the extrusion of the thread from the interlocked precursors. A variety of (1)H NMR kinetic experiments were carried out in order to evaluate the rate constants of the dethreading process, the half-life times of the rotaxanes, and the influence of temperature and solvents on these processes. The use of dibutylamino groups as stoppers yielded the rotaxane precursor in a reasonable yield and allowed the quantitative deslipping of the rotaxane. The overall process, including the rotaxane formation and its further dethreading, has been exploited for preparing benzylic amide macrocycles enhancing, in most cases, the results of the classical (2 + 2) condensation and other reported stepwise syntheses. The kinetics of the dethreading process is fairly sensitive to the electronic effects of the substituents on the isophthalamide unit or to the electronic nature of the pyridine rings through a conformational equilibrium expanding or contracting the cavity of the interlocked precursor.

Chemoselective Synthesis of 1-Substituted 4-Amino-2-(trifluoromethyl)-1H-pyrroles through the Heterocyclization Reaction of 4-Methoxy-5-bromo-1,1,1-trifluoropent-3-en-2-ones with Amines.

A concise method to synthesize 1-substituted 4-amino-2-(trifluoromethyl)-1H-pyrroles from the heterocyclization reaction of 5-bromo-4-methoxy-1,1,1-trifluoropent-3-en-2-ones with amines is described. This method has the following advantages: it uses a wide range of primary amines, starting materials are easily available, it is simple to perform, the reaction conditions are mild, it is environmentally friendly, and it furnishes yields of up to 98%.

Antitumoral activity of a trichloromethyl pyrimidine analogue: molecular cross-talk between intrinsic and extrinsic apoptosis.

Acute lymphoblastic leukemia (ALL) is a malignant disorder caused by the proliferation of lymphoid progenitor cells and is the most common cancer in children. Cytotoxic nucleoside analogues are important chemotherapeutic agents, which are used in many cancers, including leukemias. In this study, we investigated the effects of the synthetic nucleoside analogue 1-(5,5,5-trichloro-2-methoxy-4-oxopenten-2-yl)-4-trichloromethyl-pyrimidin-2(1H)-one, named compound 3 or C3, on leukemia cell lines. The compound stimulated cell death by apoptosis, evidenced by DNA fragmentation, phosphatidylserine externalization, and caspase-3 activation. Compound 3 seemed to trigger several cell death pathways. The mitochondrial pathway was evidenced through a disturbance of mitochondrial membrane potential, strong cytochrome c liberation, decrease of antiapoptotic Bcl-2 protein expression, and caspase-9 activation. The C3 also induced caspase-8 and -12 activation, an increase in the intracellular calcium level, and an overproduction of reactive oxygen species. Increased caspase 8 activity suggests that the extrinsic pathway was activated and that the ROS production and enzyme activity alteration (glutathione S-transferase, glutathione peroxidase, catalase, and glutathione reductase) might be related to oxidative stress. Finally, the increase in calcium release, CHOP expression, and caspase-12 activity might characterize endoplasmic reticulum stress. Compound 3 was likewise cytotoxic to leukemic and melanoma human cell lines. Taken together, the results contribute to further understanding the new pyrimidine analogue as a potential chemotherapeutic drug or lead molecule.

The Persistence of Hydrogen Bonds in Pyrimidinones: From Solution to Crystal.

Pyrimidinone scaffolds are present in a wide array of molecules with synthetic and pharmacological utility. The inherent properties of these compounds may be attributed to intermolecular interactions analogous to the interactions that molecules tend to establish with active sites. Pyrimidinones and their fused derivatives have garnered significant interest due to their structural features, which resemble nitrogenous bases, the foundational building blocks of DNA and RNA. Similarly, pyrimidinones are predisposed to forming N-H···O hydrogen bonds akin to nitrogenous bases. Given this context, this study explored the supramolecular features and the predisposition to form hydrogen bonds in a series of 18 substituted 4-(trihalomethyl)-2(1H)-pyrimidinones. The formation of hydrogen bonds was observed in solution via nuclear magnetic resonance (NMR) spectroscopy experiments, and subsequently confirmed in the crystalline solid state. Hence, the 18 compounds were crystallized through crystallization assays by slow solvent evaporation, followed by single-crystal X-ray diffraction (SC-XRD). The supramolecular cluster demarcation was employed to evaluate all intermolecular interactions, and all crystalline structures exhibited robust hydrogen bonds, with an average energy of approximately -21.64 kcal mol-1 (∼19% of the total stabilization energy of the supramolecular clusters), irrespective of the substituents at positions 4, 5, or 6 of the pyrimidinone core. To elucidate the nature of these hydrogen bonds, an analysis based on the quantum theory of atoms in molecules (QTAIM) revealed that the predominant intermolecular interactions are N-H···O (average of -16.55 kcal mol-1) and C-H···O (average of -6.48 kcal mol-1). Through proposing crystallization mechanisms based on molecular stabilization energy data and contact areas between molecules and employing the supramolecular cluster and retrocrystallization concepts, it was determined that altering the halogen (F/Cl) at position 4 of the pyrimidinone nucleus modifies the crystallization mechanism pathway. Notably, the hydrogen bonds present in the initial proposed steps were confirmed by 1H NMR experiments using concentration-dependent techniques.

Regiocontrolled Synthesis of 1-Substituted-3(5)-carboxyalkyl-1H-pyrazoles Using Trichloromethyl Enones.

In this work, we present a regiocontrolled methodology to prepare 1-substituted-3(5)-carboxyalkyl-1H-pyrazoles using trichloromethyl enones as starting materials. It was found that the selectivity of the reaction depends on the nature of the hydrazine: when using arylhydrazine hydrochlorides, synthesis of the 1,3-regioisomer was achieved (22 examples, 37-97% yields), while the corresponding free hydrazine led exclusively to the 1,5-regioisomer (12 examples, 52-83% yields). The trichloromethyl group was used as a precursor for the carboxyalkyl moiety, furnishing a one-pot three-component regioselective protocol suitable for preparing both isomers at moderate to excellent yields. The selectivity of the reaction was investigated through NMR analyses and the structures of the products were unambiguously determined by SCXR analyses.