Synthesis of bis-1,3-(benz)azoles catalyzed by palladium-PEPPSI complex-based catalysts and the study of photophysical properties

Many biologically potent molecules have been identified to consist of benzo [b]azoles skeleton that are regarded to be the most important drug targets. Specifically, bis-benzo azoles have been the privileged conjugated structures due to their broad applications in environmental catalysis, and synthesis of various polymers, advanced materials, ligands, and natural products. Considering the significant features, different approaches have been attempted to synthesize such molecules via C-H activations by utilizing the transition metal complexes. In this study, we have developed facile and efficient Pd-based N-heterocyclic carbene (NHC) complexes, i.e., Pd-PEPPSI (Palladium-Pyridine Enhanced Pre-catalyst Preparation Stabilization and Initiation) catalysts that could successfully activate C-H bond and construct C-C bond between two 1,3-(benz)azoles via intermolecular oxidative homo-coupling reaction. The prepared Pd NHC catalysts were characterized by NMR and XPS. Pd NHCs concern about the special electronic and steric factors as the strong σ-donating and poor π-accepting properties of these nuclei renders great diversity in the field of transition metal catalysis as ancillary ligands and catalysts. Key factors of this methodology include low catalyst load, good substrate scope (even with sterically hindered substituted components), but no necessity of any extraneous ligands/oxidants and working at ambient reaction conditions with good to excellent yields of the products. Further, the targeted bis azole molecules have been characterized by single-crystal X-ray diffraction (XRD), nuclear magnetic resonance (NMR), and cyclic voltammetric (CV) studies. The fluorescence and absorption spectra of a few of the synthesized compounds revealed that the electron-donating groups present on N-substituent dictate the absorption and emission bands.

Synthesis of Novel Biocompatible Thienopyrimidine Chromophores with Aggregation-Induced Emission Sensitive to Molecular Aggregation

Biocompatible luminogens with aggregation-induced emission (AIE) have several applications in the biology field, such as in detecting biomacromolecules bioprobes and in bio-imaging. Due to their bioactivities and light-emitting properties, many heterocyclic compounds are good candidates for such applications. However, heterocyclic π-conjugated systems with AIE behavior remain rare as strong intermolecular π-π interactions usually quench their emission. In this work, new thienopyrimidine heterocyclic compounds were synthesized and their structures were verified by elemental analysis and Fourier transform infrared (FT-IR), 1H nuclear magnetic resonance (NMR), and 13C NMR spectra. The photophysical properties of some compounds were investigated in the solution and solid states. Density functional theory calculations were also performed to confirm the observed photophysical properties of the compounds. The studied dyes displayed AIE properties with spectral shapes related to the aggregate structure and a quantum yield up to 10.8%. The emission efficiency of the powder is attributed to the incorporation of multiply rotatable and twisted aryl groups to the fused heterocyclic moieties. The dyes also showed high thermal stability and potent antimicrobial activities against numerous bacterial and fungal strains. Additionally, the cytotoxicity of the new compounds was evaluated against the Caco-2 cell line, and molecular docking was used to investigate the binding conformation of the most effective compound with the MNK2 enzyme. Therefore, the presented structures may potentially be used for bioapplications.

Metal–organic framework mediated expeditious synthesis of benzimidazole and benzothiazole derivatives through an oxidative cyclization pathway

Herein, we report facile synthesis of various benzimidazoles and benzothiazoles by using the NH₂-MIL-125(Ti) MOF as an efficient oxidant-free heterogeneous catalyst with good yield.

Design and Synthesis of 2-(5-Phenylindol-3-yl)benzimidazole Derivatives with Antiproliferative Effects towards Triple-Negative Breast Cancer Cells by Activation of ROS-Mediated Mitochondria Dysfunction

Benzimidazole derivatives are widely studied because of their broad-spectrum biological activity, such as antitumor properties and excellent fluorescence performance. Herein, two types of 2-(5-phenylindol-3-yl)benzimidazole derivatives (1 a-1 h and 2 a-2 e) were rationally designed and synthesized. When these compounds were investigated in vitro anti-screening assays, we found that all of them possessed antitumor effect, in particular compound 1 b, which showed an outstanding antiproliferative effect on MDA-MB-231 cells (IC₅₀ ≈2.6 μm). A study of the drug action mechanisms in cells showed that the antitumor activity of the compounds is proportional to their lipophilicity and cellular uptake; the tested compounds all entered the lysosome of MDA-MB-231 cells and caused changes in the levels of reactive oxygen species (ROS), and then caused mitochondrial damage. Apparent differences in the ROS levels for each compound suggest that the lethality of these compounds towards MDA-MB-231 cells is closely related to the ROS levels. Taken together, this study not only provides a theoretical basis for 2-(5-phenylindol-3-yl)benzimidazole anticarcinogens but also offers new thinking on the rational design of next-generation antitumor benzimidazole derivatives.

One-pot tandem cyclisation to pyrrolo[1,2-a][1,4]benzodiazepines: a modified approach to the Pictet-Spengler reaction

We have reported a one-pot two-step methodology for the synthesis of highly condensed heterocycles, pyrrolo[1,2-a][1,4]benzodiazepines, by a modified Pictet-Spengler reaction under mild conditions in a short time. Our approach has a few advantages over the conventional two components synthesis as it is step and atom economic, environmentally benign and a convergent synthetic method. We have discussed here the broad substrate scope of this novel methodology.