A simple protocol for the synthesis of perylene bisimides from perylene tetracarboxylic dianhydride.

Perylene bisimides are highly attractive polycyclic aromatic hydrocarbons due to their photostability associated to unique and characteristic photochemical properties. They have been widely used for analytical purposes, despite the hydrophobicity of most of these compounds. The ring substitution pattern plays an important role in fine-tuning the physicochemical properties that govern solubility and aggregation. In this work, a selection of perylene bisimides were prepared from the reaction of perylenetetracarboxylic dianhydride with α-amino acids or primary aliphatic and aromatic amines. These molecules were obtained in good yield by a simple synthetic protocol based on the use of imidazole as a green solvent and avoiding the need for complex purification methods, a major advantage for future applications. Functionalization of the exocyclic substituent can also be performed and was exemplified by the incorporation of the maleimide and anthraquinone moieties.

Discovery of 2,9-diaryl-6-carbamoylpurines as a novel class of antitubercular agents.

A series of novel 9-alkyl/aryl-2-aryl-6-carbamoylpurines were synthesized, and their activity against Mycobacterium tuberculosis strain H37Rv was assessed. The SAR analysis on the first set of derivatives, with an alkyl or aryl unit at N-9 and a phenolic unit at C-2, showed that the activity depends on the purine ring substituents at N-9 and C-2. A phenyl group at N-9 combined with a 3-hydroxyphenyl or 4-hydroxyphenyl at C-2 improve the activity. The most active compound of this set has a phenyl group at N-9 and a 4-hydroxyphenyl group at C-2, displaying an IC90 = 1.2 µg/mL and a selectivity index higher than 25.5. This compound served as a Hit to design the second set of derivatives. A phenyl group at N-9 was maintained, and the group at C-2 was diversified. The SAR analysis showed that the aryl unit at C-2 must have an oxygen or nitrogen atom bonded in the para position. A proton, a small alkyl or a substituted aryl group may also be bonded to the oxygen. The compound with the 4-methoxyphenyl group at C-2, 1Bd, exhibits the highest activity with an IC90 < 0.19 µg/mL. This compound is highly potent against M. tuberculosis strain H37Rv and non-toxic for VERO mammalian cells with an SI > 153.8. Compound 1Bd was also non-cytotoxic against primary macrophage cultures at IC90, 2xIC90, and 10xIC90 and significantly reduced the bacterial load in M. tuberculosis-infected macrophages at the same concentrations. Compound 1Bd showed a favorable pharmacokinetic profile when administered orally, with major lung and liver accumulation. In vivo antimycobacterial efficacy of 1Bd was tested at 25 mg/kg. At the tested regimen, a decrease in bacterial burden was observed in the liver. Optimization of the treatment regimen should be performed to fully potentiate the in vivo efficacy of our lead molecule, particularly in the lung, the main target organ of M. tuberculosis.

Regioselective Synthesis of 2-Aryl-5-cyano-1-(2-hydroxyaryl)-1H-imidazole-4-carboxamides Self-Assisted by a 2-Hydroxyaryl Group.

The reactivity of the diaminomaleonitrile-based imines containing hydroxyphenyl substituents with diverse aromatic aldehydes has been explored for the synthesis of novel highly substituted nitrogen heterocycles, which are considered privileged scaffolds in drug discovery. We report here a simple and efficient method for the regiocontrolled synthesis of a variety of 2-aryl-5-cyano-1-(2-hydroxyaryl)-1H-imidazole-4-carboxamides from 2-hydroxybenzylidene imines and aromatic aldehydes. Computational studies on the reaction path revealed that the regioselectivity of the reaction toward the formation of imidazole derivatives instead of 1,2-dihydropyrazines, most likely via a diaza-Cope rearrangement, is driven by the 2-hydroxyaryl group in the scaffold. The latter group promotes the intramolecular abstraction and protonation process in the cycloadduct intermediate, triggering the evolution of the reaction toward the formation of imidazole derivatives.

A Simple Method for Anchoring Silver and Copper Nanoparticles on Single Wall Carbon Nanotubes.

Single walled carbon nanotubes (SWCNT) were functionalized using the 1,3-dipolar cycloaddition reaction of an azomethine ylide under solvent-free conditions, a one-pot procedure that yields pyrrolidine type of groups at the nanotubes surface. The functionalized SWCNT were further decorated with Ag and Cu nanoparticles by reduction of the corresponding metal salts in dimethylformamide. The extensive reduction of silver from its nitrate was observed, as well as the partial reduction of copper from its acetate. X-ray photoelectron spectroscopy (XPS) confirmed the functionalization of SWCNT with pyrrolidine that provided anchoring sites for the metal nanoparticles. Metal nanoparticles (NP) were formed at the surface of the organically functionalized SWCNT in higher yields as compared to the same procedure carried out with pristine SWCNT. This was observed using scanning electron microscopy (SEM) and quantified by XPS. Raman spectroscopy demonstrated that functionalization and metal decoration of the SWCNT did not induce structural damage to the SWCNT.

2-Aryladenine derivatives as a potent scaffold for A1, A3 and dual A1/A3 adenosine receptor antagonists: Synthesis and structure-activity relationships.

From a collection containing more than 1500 academic compounds, in silico screening identified a hit for the human A1 adenosine receptor containing a new purine scaffold. To study the structure activity relationships of this new chemical series for adenosine receptors, a library of 24 purines was synthesized and tested in radioligand binding assays at human A1, A2A, A2B and A3 adenosine receptor subtypes. Fourteen molecules showed potent antagonism at A1, A3 or dual A1/A3 adenosine receptors. This purine scaffold is an important source for novel biochemical tools and/or therapeutic drugs.

New Nitrogen Compounds Coupled to Phenolic Units with Antioxidant and Antifungal Activities: Synthesis and Structure⁻Activity Relationship.

A selection of 1-amino-2-arylidenamine-1,2-(dicyano)ethenes 3 was synthesized and cyclized to 2-aryl-4,5-dicyano-1H-imidazoles 4 upon reflux in ethyl acetate/acetonitrile, in the presence of manganese dioxide. These compounds were tested for their antioxidant capacity by cyclic voltammetry, 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical and deoxyribose degradation assays. The minimum inhibitory concentration of all compounds was evaluated against two yeast species, Saccharomyces cerevisiae and Candida albicans. Their toxicity was tested in mammal fibroblasts. Among the synthesised compounds, two presented dual antioxidant/antifungal activity without toxic effects in fibroblasts. The new compounds synthesized in this work are potential biochemical tools and/or therapeutic drugs.

Synthesis and antimicrobial activity of novel 5-aminoimidazole-4-carboxamidrazones.

A mild and simple method was developed to prepare a series of fifteen 5-aminoimidazole 4-carboxamidrazones, starting from the easily accessible 5-amino-4-cyanoformimidoyl imidazoles. The antimicrobial activity of these novel amidrazones was screened against Gram positive (Staphylococcus aureus) and Gram negative (Escherichia coli, Pseudomonas aeruginosa) bacteria and Candida sp. (Candida albicans, Candida krusei, Candida parapsilosis). Only a subset of compounds displayed fair-moderate activity against S. aureus and E. coli but all exhibited activity against Candida sp. The three most potent antifungal compounds were further tested against Cryptococcus neoformans, Aspergillus fumigatus and three dermatophytes (Trichophyton rubrum, Trichophyton mentagrophytes, Microsporum gypseum). These three hit compounds strongly inhibited C. krusei and C. neoformans growth, although their activity on filamentous fungi was very weak when compared to the activity on yeasts.

Synthesis and radical scavenging activity of phenol-imidazole conjugates.

Novel hydroxylated benzylideneamino imidazole derivatives were synthesized and their radical scavenging activity was assessed against DPPH and hydroxyl radicals. In the DPPH assay, most of the synthesized compounds showed an IC50 in the range 3.2µM⩽IC50⩽8.4µM, lower than the reference compound trolox (IC50=9.5µM) or the parent aldehydes (5.4µM⩽IC50⩽11.6µM). The activity depends mainly on the phenolic subunit (number and position of the hydroxyl groups) and the extent of conjugation with the imidazole ring. In the deoxyribose assay, all the compounds, including parent imidazoles and aldehydes, showed high activity against the hydroxyl radical and the ability to chelate iron ions. At 5µM concentration, the compounds protected the deoxyribose from degradation by hydroxyl radical between 62% and 38%.

Superior anticancer activity of halogenated chalcones and flavonols over the natural flavonol quercetin.

A series of chalcone and flavonol derivatives were synthesized in good yield by an eco-friendly approach. A pharmacological evaluation was performed with the human colorectal carcinoma cell line HCT116 and revealed that the anticancer activity of flavonols was higher when compared with that of the respective chalcone precursors. The antiproliferative activity of halogenated derivatives increases as the substituent in the 3- or 4-positon of the B-ring goes from F to Cl and to Br. In addition, halogens in position 3 enhance anticancer activity in chalcones whereas for flavonol derivatives the best performance was registered for the 4-substituted derivatives. Flow cytometry analysis showed that compounds 3p and 4o induced cell cycle arrest and apoptosis as demonstrated by increased S, G2/M and sub-G1 phases. These data were corroborated by western blot and fluorescence microscopy analysis. In summary, halogenated chalcones and flavonols were successfully prepared and presented high anticancer activity as shown by their cell growth and cell cycle inhibitory potential against HCT116 cells, superior to that of quercetin, used as a positive control.

New chromene scaffolds for adenosine A(2A) receptors: synthesis, pharmacology and structure-activity relationships.

In silico screening of a collection of 1584 academic compounds identified a small molecule hit for the human adenosine A(2A) receptor (pK(i) = 6.2) containing a novel chromene scaffold (3a). To explore the structure-activity relationships of this new chemical series for adenosine receptors, a focused library of 43 2H-chromene-3-carboxamide derivatives was synthesized and tested in radioligand binding assays at human adenosine A(1), A(2A), A(2B) and A(3) receptors. The series was found to be enriched with bioactive compounds for adenosine receptors, with 14 molecules showing submicromolar affinity (pK(i) ≥ 6.0) for at least one adenosine receptor subtype. These results provide evidence that the chromene scaffold, a core structure present in natural products from a wide variety of plants, vegetables, and fruits, constitutes a valuable source for novel therapeutic agents.

Controlled functionalization of carbon nanotubes by a solvent-free multicomponent approach.

The present work reports the solvent-free, one-pot functionalization of multiwall carbon nanotubes (CNTs) based on the 1,3-dipolar cycloaddition of azomethine ylides using N-benzyloxycarbonyl glycine and formaldehyde. The surface morphology of the functionalized CNTs was investigated by scanning tunneling microscopy. The effect of temperature on the reaction was studied by thermogravimetry and X-ray photoelectron spectroscopy (XPS). XPS was a key technique for the detailed chemical analysis of the CNT surface. The formation of two major reaction products was observed, namely a cyclic benzyl carbamate and a pyrrolidine. The concentration of the two products varied with reaction temperature and time. At 180 °C, the main product was the cyclic benzyl carbamate, while at 250 °C the major product was the pyrrolidine. This simple, solvent-free chemical procedure yields CNTs with fine-tuned surface functionality.

In silico directed chemical probing of the adenosine receptor family.

One of the grand challenges in chemical biology is identifying a small-molecule modulator for each individual function of all human proteins. Instead of targeting one protein at a time, an efficient approach to address this challenge is to target entire protein families by taking advantage of the relatively high levels of chemical promiscuity observed within certain boundaries of sequence phylogeny. We recently developed a computational approach to identifying the potential protein targets of compounds based on their similarity to known bioactive molecules for almost 700 targets. Here, we describe the direct identification of novel antagonists for all four adenosine receptor subtypes by applying our virtual profiling approach to a unique synthesis-driven chemical collection composed of 482 biologically-orphan molecules. These results illustrate the potential role of in silico target profiling to guide efficiently screening campaigns directed to discover new chemical probes for all members of a protein family.

Unzipping of functionalized multiwall carbon nanotubes induced by STM.

Carbon nanotubes (CNTs), functionalized by a cycloaddition reaction, were studied by ultrahigh vacuum scanning tunneling microscopy (STM). The STM images provided evidence for partial or total unzipping of the outer CNT layer. The formation of graphene ribbons was triggered by the STM tip, under specific operating conditions. A model for the unzipping is proposed, based on the perturbation of the pi-conjugation along the CNT surface induced by the cycloaddition reaction.

Synthesis and in vitro evaluation of substituted pyrimido[5,4-d]pyrimidines as a novel class of anti-Mycobacterium tuberculosis agents.

Novel pyrimido[5,4-d]pyrimidines were efficiently synthesized and evaluated for antibacterial activity against Mycobacterium tuberculosis strain H(37)Rv. This new structural class of compounds showed high activity against the bacilli. The activity depends on the substituents present in N-3 and C-8 of the pyrimido[5,4-d]pyrimidine core. Compounds having a 4-MeOC(6)H(4), a Ph or a 4-FC(6)H(4) group as the substituent on C-8 and a 4'-pyridinyl, a Ph or 2'-furyl group as the substituent on N-3 were active. The highest activity was registered for compounds having 4-FC(6)H(4) or 4-MeOC(6)H(4) as substituents in C-8 and a heteroaryl group as substituent in N-3. The new compounds showed high potency and promising antitubercular activity, as is the case of N-[8-[(4-fluorophenyl)amino]-4-iminopyrimido[5,4-d]pyrimidin-3(4H)-yl]isonicotinamide with an IC(90)=3.58 microg/mL, and should be regarded as new hits for further development as a novel class of Antimycobacterium tuberculosis agents.

The Diels-Alder cycloaddition reaction in the functionalization of carbon nanofibers.

Carbon nanofibres were functionalized by a Diels-Alder cycloaddition reaction of 1,3-butadiene, generated in situ from sulfolene. The experimental conditions were selected on the basis of a differential scanning calorimetry (DSC) study on the reagents and the functionalization was confirmed by thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Analysis performed on the surface of the functionalized material by X-ray photoelectron spectroscopy (XPS) and FT-IR using the Attenuated Total Reflectance (ATR) technique indicates that the carbonyl and sulfoxide groups are present on the surface of the functionalized material. The acidic surface of the functionalized nanofiber suggests the presence of carboxylic acid and possibly sulfonic acid groups.

Synthesis of novel 6-enaminopurines.

Two different approaches have been used for the synthesis of 6-enaminopurines 6 from 5-amino-4-cyanoformimidoyl imidazoles. In the first approach imidazoles 1 were reacted with ethoxymethylenemalononitrile or ethoxymethylenecyanoacetate under mild experimental conditions and this led to 9-substituted-6-(1-amino-2,2-dicyanovinyl) purines 6a-f or 9-substituted-6-(1-amino-2-cyano-2-methoxycarbonylvinyl) purines 6g-k. These reactions are postulated to occur through an imidazo-pyrrolidine intermediate 7, which rapidly rearranges to the 6-enaminopurine 6. In the second approach 6-methoxyformimidoyl purines 3, prepared in two efficient steps from 5-amino-4-cyanoformimidoyl imidazoles 1, were reacted with malononitrile and methylcyanoacetate with a mild acid catalysis (ammonium acetate or piperidinium acetate) to give 6-enaminopurines 6a, 6d, 6f, 6g and 6k in very good yields. Only low yields were obtained for the 6-enaminopurine 6j, as competing nucleophilic attack on C-8 of either 3d or 6jcauses ring opening with formation of pyrimido-pyrimidines 11 and 10a respectively.

Efficient conversion of 6-cyanopurines into 6-alkoxyformimidoylpurines.

An extremely simple method for the selective synthesis of 9-aryl and 9-alkyl 6-alkoxy or 6-alkoxyformimidoylpurines from the corresponding 6-cyanopurines is described. The reaction is carried out with methanol or ethanol in the presence of DBU. At room temperature, nucleophilic attack by the primary alcohol occurs selectively on the cyano carbon atom, leading to 6-alkoxyformimidoylpurines in good yields. Heating the reaction mixture at a temperature greater than or equal to 78 degrees C leads to nucleophilic substitution of the substituent in the 6-position by the alkoxy group, generating the corresponding 6-alkoxypurines, also in excellent yields. The 6-alkoxyformimidoylpurines were used as intermediates in the synthesis of 6-carboxamidinopurines by reaction with methylamine (for 9-methylpurine 5a) or methyl ammonium chloride (for 9-arylpurines and 5b and 5c).

Efficient synthesis of 3H-imidazo[4,5-b]pyridines from malononitrile and 5-amino-4-(cyanoformimidoyl)imidazoles.

1-Aryl-5-amino-4-(cyanoformimidoyl)imidazoles 2 were reacted with malononitrile under mild experimental conditions and led to 3-aryl-5,7-diamino-6-cyano-3H-imidazo[4,5-b]pyridines 5, when the reaction was carried out in the presence of DBU, or to 3-aryl-5-amino-6,7-dicyano-3H-imidazo[4,5-b]pyridines 3, in its absence. Both reactions evolved from the adduct formed by nucleophilic attack of the malononitrile anion to the carbon of the cyanoformimidoyl substituent. A 5-amino-1-aryl-4-(1-amino-2,2-dicyanovinyl)imidazole 4 was isolated when this reaction was carried out in the presence of DBU. The structure of compound 4 was confirmed by spectroscopic methods and by reaction with triethyl orthoformate and with acetic anhydride, leading respectively to 9-aryl-6-(cyanomethylidene)purines 11 and 12. Imidazole 2b was also reacted with ethyl acetoacetate, a carbon acid with a pK(a) comparable to that of malononitrile. Similar reaction conditions were used and the product isolated was a 6-carbamoyl-1,2-dihydropurine 10, showing that a different mechanism was operating in this case.

Efficient synthesis of 4,4'-bi-1H-imidazol-2-ones from 5-amino-alpha-imino-1H-imidazole-4-acetonitriles and isocyanates.

Reactions of 5-amino-alpha-imino-1H-imidazole-4-acetonitriles 1 with alkyl and aryl isocyanates led to efficient syntheses of 5'-amino-5-imino-4,4'-bi-1H-imidazol-2-ones 3 formed by intramolecular cyclization of the corresponding 5-amino-alpha-(N-alkyl/arylcarbamoyl)imino-1H-imidazole-4-acetonitriles 2. The cyclization occurs only slowly in solution but is considerably accelerated by the addition of a catalytic amount of DBU (1,8-diazabicyclo[5.4.0]undec-7-ene). The reaction of the N-arylamidine 6b, the synthetic precursor of the imidazole 1b, with benzyl isocyanate also led to the formation of 4,4'-bi-1H-imidazol-2-one 3b in quantitative yield. The imidazole intermediate 2b has been isolated and found to be identical with the compound obtained by reaction of the imidazole 1b and benzyl isocyanate. The N-arylamidine 6c (R = 4-NCC(6)H(4)) reacted with benzyl isocyanate in a similar way, but the electrophilicity of the amidine carbon atom resulted in rapid hydrolysis of the intermediate 7c leading ultimately to the isolation of the urea 9. The N-alkylamidines 6a and 6d behaved differently in their reaction with benzyl isocyanate, and the major product isolated in these reactions is again the urea 9.