Significant facilitation of metal-free aerobic oxidative cyclization of imines with water in synthesis of benzimidazoles

A mild and convenient protocol for the synthesis of quinoxalin-2(1H)-ones and benzimidazoles

We present a mild and simple method for the cyclization of N-protected o-phenylenediamines with carbonyl compounds in the presence of trifluoroacetic acid. This method reliably provides various substrates of benzimidazoles and quinoxalin-2(1H)-ones, with all reactions conducted at room temperature, demonstrating excellent substrate adaptability and a broad substrate scope.

Difluoroboron Complexes Based on Benzimidazole-Phenolates as Blue Emitters

Novel four-coordinated boron complexes (1-5) were synthesized via a reaction between BF3·CH3OH and benzimidazole-phenolate ligands (L1-L5), which are N,O-donors. These complexes exhibit intense blue emission in the solution and solid states accompanied by notable fluorescence quantum yields (ΦF). The study of the structure-property relation, through theoretical and experimental approaches, revealed a distinctive trend where compounds incorporating electron-donating substituents (methyl and ethoxy groups) in the phenolate moiety manifest shifts in emission wavelengths across the blue spectrum, concomitant with an increase in ΦF. Furthermore, the incorporation of an aromatic ring into the benzimidazole moiety considerably intensifies the rate of radiative relaxation from excited states. Notably, in the solid phase, either as a crystalline powder or loaded into polymer films, these modified complexes maintain or even surpass ΦF values observed in molecular solutions, ranging from 0.18 to 0.57, depending on the substitution. This characteristic makes these compounds attractive for applications in optoelectronics. All of the compounds were characterized using 1H, 13C, 11B, and 19F NMR, elemental analysis, and the molecular structures were corroborated through single-crystal X-ray diffraction analysis. Computational calculations via time-dependent density functional theory further elucidate the tunability of optical bandgaps through group substitution on ligands, aligning well with experimental observations.

Synthesis, structural study and antitumor activity of novel alditol-based imidazophenanthrolines (aldo-IPs)

A series of 1H-imidazo [4,5-f][1,10] phenanthroline derivatives functionalized at 2-position with chiral, and conformationally flexible polyhydroxy alkyl chains derived from carbohydrates (alditol-based imidazophenanthrolines, aldo-IPs) is presented herein. These novel glycomimetics showed relevant and differential cytotoxic activity against several cultured tumor cell lines (PC3, HeLa and HT-29), dependent on the nature and stereochemistry of the polyhydroxy alkyl chain. The mannose-based aldo-IP demonstrated the higher cytotoxicity in the series, substantially better than cisplatin metallo-drug in all cell lines tested, and better than G-quadruplex ligand 360A in HeLa and HT29 cells. Cell cycle experiments and Annexin V-PI assays revealed that aldo-IPs induce apoptosis in HeLa cells. Initial study of DNA interactions by DNA FRET melting assays proved that the aldo-IPs produce only a slight thermal stabilization of DNA secondary structures, more pronounced in the case of quadruplex DNA. Viscosity titrations with CT dsDNA suggest that the compounds behave as DNA groove binders, whereas equilibrium dialysis assays showed that the compounds bind CT with Ka values in the range 104-105 M-1. The aldo-IP derivatives were obtained with synthetically useful yields through a feasible one-pot multistep process, by aerobic oxidative cyclization of 1,10-phenanthroline-5,6-diamine with a selection of unprotected aldoses using (NH4)2SO4 as promoter.

Sensitizer-Free Photochemical Regeneration of Benzimidazoline Organohydride

Organohydrides are an important class of organic compounds that can provide hydride anions for chemical and biochemical reactions, as demonstrated by reduced nicotinamide adenine dinucleotides serving as important natural redox cofactors. The coupling of hydride transfer from the organohydride to the substrate and subsequent regeneration of the organohydride from its oxidized form can realize organohydride-catalyzed reduction reactions. Depending on the structure of the organohydride, its hydridicity and ease of regeneration vary. Benzimidazoline (BIH) is one of the strongest synthetic C-H hydride donors; however, its reductive regeneration requires highly reducing conditions. In this study, we synthesized various oxidized and reduced forms of BIH derivatives with aryl groups at the 2-position and investigated their photophysical and electrochemical properties. 4-(Dimethylamino)phenyl-substituted BIH exhibited salient red-shifted absorption compared with other synthesized BIH derivatives, and visible-light-driven regeneration without using an external photosensitizer was achieved. This knowledge has significant implications for the future development of solar-energy-based catalytic photoreduction technologies that utilize organohydride regeneration strategies.

Recent advances in the application of magnetic nanocatalysts in multicomponent reactions

Recently, the preparation and applications of magnetic nanostructures have attracted increasing attention in nanocatalysis studies, and magnetic nanoparticle (MNP) functionalized catalysts have been applied in important reactions such as Suzuki-Miyaura and Heck couplings. The modified nanocomposites demonstrate significant catalytic efficiency and excellent benefits in the context of catalyst recovery methods. This review discusses the recent modified magnetic nanocomposites in the field of catalytic applications along with the synthetic processes that are usually employed.

2D Covalent Organic Frameworks Based on Heteroacene Units

Covalent organic frameworks (COFs) are a unique new class of porous materials that arrange building units into periodic ordered frameworks through strong covalent bonds. Accompanied with structural rigidity and well-defined geometry, heteroacene-based COFs have natural advantages in constructing COFs with high stability and crystallinity. Heteroacene-based COFs usually have high physical and chemical properties, and their extended π-conjugation also leads to relatively low energy gap, effectively promoting π-electron delocalization between network units. Owing to excellent electron-withdrawing or -donating ability, heteroacene units have incomparable advantages in the preparation of donor-acceptor type COFs. Therefore, the physicochemical robust and fully conjugated heteroacene-based COFs solve the problem of traditional COFs lacking π-π interaction and chemical stability. In recent years, significant breakthroughs are made in this field, the choice of various linking modes and building blocks has fundamentally ensured the final applications of COFs. It is of great significance to summarize the heteroacene-based COFs for improving its complexity and controllability. This review first introduces the linkages in heteroacene-based COFs, including reversible and irreversible linkages. Subsequently, some representative building blocks are summarized, and their related applications are especially emphasized. Finally, conclusion and perspectives for future research on heteroacene-based COFs are presented.

Design, Synthesis, and Biological Evaluation of Benzo[cd]indol-2(1H)-ones Derivatives as a Lysosome-Targeted Anti-metastatic Agent

Lysosomes have become a hot topic in tumor therapy; targeting the lysosome is therefore a promising strategy in cancer therapy. Based on our previous lysosome-targeted bio-imaging agent, homospermine-benzo[cd]indol-2(1H)-one conjugate (HBC), we further developed three novel series of polyamine- benzo[cd]indol-2(1H)-one conjugates. Among them, compound 15f showed potent inhibitory activity in hepatocellular carcinoma migration both in vitro and in vivo. Our study results showed that compound 15f entered the cancer cells via the polyamine transporter localized in the lysosomes and caused autophagy and apoptosis. The mechanism of action revealed that the crosstalk between autophagy and apoptosis induced by 15f was mutually reinforcing patterns. Besides, 15f also targeted lysosomes and exhibited stronger green fluorescence than HBC, which indicated its potential as an imaging agent. To summarize, compound 15f could be used as a valuable dual-functional lead compound for future development against liver-cancer metastasis and lysosome imaging.

Peroxide-mediated synthesis of benzimidazo[2,1-a]isoquinoline-6(5H)-ones via cascade methylation/ethylation and intramolecular cyclization

A metal-free oxidative radical methylation/arylation of 2-arylbenzoimidazoles with DTBP as the oxidant and methyl radical source was developed. The reaction proceeds through a sequential methyl radical addition/cyclization pathway and affords a series of methyl functionalized benzimidazo[2,1-a]isoquinoline-6(5H)-ones in moderate to good yields. Besides, the ethylation/arylation of 2-arylbenzoimidazoles was also achieved with DTAP.

Ultrafine Pt nanoparticles supported on a dendrimer containing thiol groups: an efficient catalyst for the synthesis of benzimidazoles and benzothiazoles from benzyl alcohol derivatives in water

A novel and unique platform was prepared based on a dendrimer containing thiol groups supported on nanosilica (nSTDP), and ultrafine platinum nanoparticles were synthesized and immobilized on the thiol decorated branches of nSTPD. The new catalyst, (Ptnp@nSTDP), was characterized by different techniques such as FE-SEM, TEM, ICP, XPS and DR UV-vis. This heterogeneous catalyst presented an outstanding performance for the synthesis of benzimidazole and benzothiazole derivatives through a reaction between benzyl alcohol derivatives and 2-aminothiophenol or 1,2-phenylenediamine. No requirement for the pre-reduction of catalysts and using water as a green solvent make it an individual catalyst for these reactions. Furthermore, the catalyst can be easily recovered and reused five consecutive times in the production of benzimidazoles and benzothiazoles without significant leaching of Pt and loss of its activity which illustrated the chemical stability of the catalyst during the reaction.

Quantifying the nitrogen effect on CO2 capture using isoporous network polymers

The impact of nitrogen atoms on CO₂ binding was evaluated for two isostructural porous bisimidazole-linked polymers (BILPs), which serendipitously had identical surface areas and pore size distributions, a very rare observation. The two structures differ only in the core of the trialdehyde component, the nitrogen atom (BILP-19) versus benzene ring (BILP-5). Such a slight difference, however, has brought about a stronger CO₂ capture capacity of BILP-19 and hence increased CO₂/N₂ separation capability.

Design, synthesis and biological evaluation of a series of CNS penetrant HDAC inhibitors structurally derived from amyloid-β probes

To develop novel CNS penetrant HDAC inhibitors, a new series of HDAC inhibitors having benzoheterocycle were designed, synthesized, and biologically evaluated. Among the synthesized compounds, benzothiazole derivative 9b exhibited a remarkable anti-proliferative activity (GI₅₀ = 2.01 μM) against SH-SY5Y cancer cell line in a dose and time-dependent manner, better than the reference drug SAHA (GI₅₀ = 2.90 μM). Moreover, compound 9b effectively promoted the accumulation of acetylated Histone H3 and α-tubulin through inhibition of HDAC1 and HDAC6 enzymes, respectively. HDAC enzyme assay also confirmed that compound 9b efficiently inhibited HDAC1 and HDAC6 isoforms with IC₅₀ values of 84.9 nM and 95.9 nM. Furthermore, compound 9b inhibited colony formation capacity of SH-SY5Y cells, which is considered a hallmark of cell carcinogenesis and metastatic potential. The theoretical prediction, in vitro PAMPA-BBB assay, and in vivo brain pharmacokinetic studies confirmed that compound 9b had much higher BBB permeability than SAHA. In silico docking study demonstrated that compound 9b fitted in the substrate binding pocket of HDAC1 and HDAC6. Taken together, compound 9b provided a novel scaffold for developing CNS penetrant HDAC inhibitors and therapeutic potential for CNS-related diseases.

Formation of Amidinyl Radicals via Visible-Light-Promoted Reduction of N-Phenyl Amidoxime Esters and Application to the Synthesis of 2-Substituted Benzimidazoles

We have developed a new method for the synthesis of 2-substituted benzimidazoles via amidinyl radicals generated by visible-light-promoted reduction of N-phenyl amidoxime esters in the presence of an iridium photocatalyst. This is the first report of the use of N-phenyl amidoxime esters as amidinyl radical precursors, and the first use of substituted benzene rings as amidinyl radical acceptors. This method widens the application range of substrates and overcomes the shortcomings of the traditional methods for the synthesis of 2-substituted benzimidazoles, which requires harsh reaction conditions, involves difficult-to-prepare substituted o-phenylenediamine substrates, and produces acidic waste.

Synthesis of benzimidazoles by CuI-catalyzed three-component reaction of 2-haloaniline, ammonia and aldehyde in water

An efficient copper-catalyzed three-component reaction of 2-haloaniline, ammonia and aldehyde for the synthesis of benzimidazoles with 1,10-phenanthroline as the ligand has been developed. A variety of substituted benzimidazole derivatives can be obtained in yields up to 95%.

Platinum(ii)-catalyzed dehydrative C3-benzylation of electron-deficient indoles with benzyl alcohols

A synthetic strategy for the water-promoted direct dehydrative coupling of indoles with benzyl alcohols catalyzed by PtCl₂(PhCN)₂ in 1,2-dichloroethane has been developed.

A modern and practical laccase-catalysed route suitable for the synthesis of 2-arylbenzimidazoles and 2-arylbenzothiazoles

Heterocyclic aromatic compounds containing an imine (C[double bond, length as m-dash]N) bond such as benzimidazoles and benzothiazoles are important active pharmaceutical ingredients. The synthesis of 2-aryl-1H-benzimidazoles and 2-arylbenzothiazoles in good to excellent yields was achieved by reacting 2-aminoaromatics with various benzaldehyde derivatives catalysed by the commercial laccases Novoprime and Suberase® at room temperature and in the presence of atmospheric oxygen.

Chemistry of Cyanide Adducts of Aldimines from Aniline Derivatives

The chemistry of hydrogen cyanide adducts of imines is well-developed, but that of cyanide adducts remains unexplored. This is presumably because these cyanide adducts are not stable and thus not readily available in their isolated forms. In this personal account, we present the progress made in our research program towards the development of novel organic transformations utilizing cyanide adducts of imines as key intermediates. We also report the application of these methodologies to the total synthesis of natural products including indole alkaloids.

The synthesis of benzimidazoles via a recycled palladium catalysed hydrogen transfer under mild conditions

An efficient synthesis of benzimidazoles was developed by virtue of a recycled palladium catalyzed hydrogen transfer.

I2-Mediated Intramolecular C-H Amidation for the Synthesis of N-Substituted Benzimidazoles

A practical intramolecular C-H amidation methodology has been developed using molecular iodine under basic conditions. The required imine substrates were readily obtained by condensation of simple o-phenylenediamine derivatives and aldehydes. The transition-metal-free cyclization reaction described here works well with crude imines and allows for the sequential synthesis of N-protected benzimidazoles without purification of the less stable condensation intermediates. This operationally simple synthetic approach is broadly applicable to a variety of aromatic, aliphatic, and cinnamic aldehydes to produce diverse 1,2-disubstituted benzimidazole derivatives in an efficient and scalable fashion.

Metal-Free Oxidative Coupling of Benzylamines to Imines under an Oxygen Atmosphere Promoted Using Salicylic Acid Derivatives as Organocatalysts

The oxidative coupling of benzylamines proceeds efficiently using salicylic acid derivatives as organocatalysts under an oxygen atmosphere, affording the corresponding N-benzylidenebenzylamines in high yields. Electron-rich salicylic acid derivatives such as 4,6-dimethoxysalicylic acid and 4,6-dihydroxysalicylic acid exhibit excellent catalytic activities for the oxidative coupling of benzylamines to give the corresponding imines. This amine oxidation can also be applied to the synthesis of nitrogen-containing heterocycles such as benzimidazole derivatives. Furthermore, to recycle the catalyst, silica gel supported with 4.7 wt % of 4,6-dihydroxysalicylic acid is prepared, which acts as a recyclable catalyst, oxidizing benzylamine to imine four times successfully.

Lithium Hexamethyldisilazane Transformation of Transiently Protected 4-Aza/Benzimidazole Nitriles to Amidines and their Dimethyl Sulfoxide Mediated Imidazole Ring Formation

Trimethylsilyl-transient protection successfully allowed the use of lithium hexamethyldisilazane to prepare benzimidazole (BI) and 4-azabenzimidazole (azaBI) amidines from nitriles in 58-88% yields. This strategy offers a much better choice to prepare BI/azaBI amidines than the lengthy, low-yielding Pinner reaction. Synthesis of aza/benzimidazole rings from aromatic diamines and aldehydes was affected in dimethyl sulfoxide in 10-15 min, while known procedures require long time and purification. These methods are important for the BI/azaBI-based drug industry and for developing specific DNA binders for expanded therapeutic applications.