Red-shifted and pH-responsive imidazole-based azo dyes with potent antimicrobial activity

Domino synthesis of a new class of red-shifted and antimicrobial imidazole-based azo dyes from 5-aminoimidazole-4-carboxamidrazones

Combining antimicrobial activity with halochromic properties offers an enticing opportunity to both combat and detect microbial infection in the medical field. Previous research has identified a class of compounds that demonstrate potent antimicrobial activity, particularly against pathogenic yeasts. Notably, these compounds also exhibit vibrant pink-blue colours and a halochromic behaviour within the therapeutic pH range. Aiming at developing a more sustainable synthetic method and to generate better red-shifted and pH-responsive imidazole-based azo dyes, a new domino reaction was discovered yielding a novel class of green-coloured 2-aminoimidazole azo-dyes. A strategy based on circular chemistry was achieved by introducing the accessible and environmentally benign O2/KI oxidant system, which is able not only to regenerate the oxidants but also minimize side reactions. The isolation of two key intermediates was also an important achievement in comprehending the underlying mechanisms. As expected, this new class of 2-aminoimidazole dyes also presented significant solvatochromism and pronounced halochromism with colours changing from green to purple as the pH decreases. Ab initio molecular quantum mechanics calculations supported the data obtained experimentally. A great number of compounds (12 in 18 compounds) showed potent fungicidal activity against C. neoformans and moderate activity against C. krusei.

Mass Spectrometry Directed Structural Elucidation of Isomeric [2 + 2] Photocycloadducts

[2 + 2] Photocycloaddition reactions are powerful tools for synthetic chemistry. However, analysis of the head-to-head or head-to-tail conformation of the resulting cycloadducts is often challenging by conventional spectroscopic methods. Herein, we report the analysis of coumarin and styrylpyrene cycloadducts by cyclic ion-mobility tandem mass spectrometry (cIM-MS/MS) to characterize the regioisomeric products of this important class of photoresponsive groups. Photodissociation (PD) and collision-induced dissociation (CID) of the cycloadduct ions in the gas phase gave similar products to photodissociation in solution with regiospecific fragmentation of the core cyclobutane ring. The styrylpyrene cycloadduct ion was observed to be more stable than the coumarin analog under CID conditions, reflecting the impact of different substituents on the stability of the cyclobutane ring. Exploiting the difference in cyclobutane fragmentation for head-to-head and head-to-tail styrylpyrene cycloadduct isomers, ion mobility enabled CID-MS/MS was applied successfully to differentiate and identify these isomers. The developed method proved to be robust even to complex molecular structures and enabled the identification and separation of photocycloadducts resulting from styrylpyrene terminated peptides, providing access to a rapid analysis of challenging cycloadduct isomers.

Unveiling the structural aspects of novel azo-dyes with promising anti-virulence activity against MRSA: a deep dive into the spectroscopy via integrated experimental and computational approaches

A novel series of azo dyes was successfully synthesized by combining amino benzoic acid and amino phenol on the same molecular framework via azo linkage. The structural elucidation of these dyes was carried out using various spectroscopic techniques, including UV-vis, FT-IR, NMR spectroscopy, and HRMS. Surprisingly, the aromatic proton in some dyes exhibited exchangeability in D2O, prompting a 2D NMR analysis to confirm this phenomenon. Furthermore, comprehensive density functional theory (DFT) calculations were conducted to unravel synthetic dyes' geometrical and electronic properties. Meanwhile, the reactivity of various sites was further investigated through Frontier Molecular Orbitals (FMOs) analysis and molecular electrostatic potential mapping. Besides, the experimental NMR spectra were interpreted by incorporating theoretically computed NMR spectrum and reduced density gradient (RDG) function. These computations revealed a pronounced intramolecular hydrogen bond through O-H⋯N interaction that significantly influenced the proton chemical shift. The dyes were assessed for their antimicrobial activities using agar diffusion, micro broth dilution, and biofilm inhibition assays. Interestingly, one of the synthetic dyes showed promising antibacterial effects against S. aureus (ATCC-6538) as well as against a multidrug-resistant MRSA clinical isolate with a MIC (minimum inhibitory concentration) of 78.12 μg mL-1. Moreover, that dye inhibited biofilm formation of the strong biofilm former clinical MRSA isolate with a concentration as low as 0.25 MIC (19.53 μg mL-1). Indeed, our qPCR data suggest that inhibiting the SaeS/SaeR system is another potential mechanism by which D4 exerts its antibacterial and anti-virulence effects. Altogether, this shows these synthetic azo dyes' promising antibacterial and anti-virulence activities concerning MRSA clinical infections.

Synthesis of 6,8-diaminopurines via acid-induced cascade cyclization of 5-aminoimidazole precursors and preliminary anticancer evaluation

Inspired by the pharmacological interest generated by 6-substituted purine roscovitine for cancer treatment, 5-aminoimidazole-4-carboxamidine precursors containing a cyanamide unit were prepared by condensation of 5-amino-N-cyanoimidazole-4-carbimidoyl cyanides with a wide range of primary amines. When these amidine precursors were combined with acids, a fast cascade cyclization occurred at room temperature, affording new 6,8-diaminopurines with the N-3 and N-6 substituents changed relatively to the original positions they occupied in the amidine and imidazole moieties of precursors. The efficacy and wide scope of this method was well demonstrated by an easy and affordable synthesis of 22 6,8-diaminopurines decorated with a wide diversity of substituents at the N-3 and N-6 positions of the purine ring. Preliminary in silico and in vitro assessments of these 22 compounds were carried out and the results showed that 13 of these tested compounds not only exhibited IC50 values between 1.4 and 7.5 μM against the colorectal cancer cell line HCT116 but also showed better binding energies than known inhibitors in docking studies with different cancer-related target proteins. In addition, good harmonization observed between in silico and in vitro results strengthens and validates this preliminary evaluation, suggesting that these novel entities are good candidates for further studies as new anticancer agents.

Imidazoles as Serotonin Receptor Modulators for Treatment of Depression: Structural Insights and Structure-Activity Relationship Studies

Serotoninergic signaling is identified as a crucial player in psychiatric disorders (notably depression), presenting it as a significant therapeutic target for treating such conditions. Inhibitors of serotoninergic signaling (especially selective serotonin reuptake inhibitors (SSRI) or serotonin and norepinephrine reuptake inhibitors (SNRI)) are prominently selected as first-line therapy for the treatment of depression, which benefits via increasing low serotonin levels and norepinephrine by blocking serotonin/norepinephrine reuptake and thereby increasing activity. While developing newer heterocyclic scaffolds to target/modulate the serotonergic systems, imidazole-bearing pharmacophores have emerged. The imidazole-derived pharmacophore already demonstrated unique structural characteristics and an electron-rich environment, ultimately resulting in a diverse range of bioactivities. Therefore, the current manuscript discloses such a specific modification and structural activity relationship (SAR) of attempted derivatization in terms of the serotonergic efficacy of the resultant inhibitor. We also featured a landscape of imidazole-based development, focusing on SAR studies against the serotoninergic system to target depression. This study covers the recent advancements in synthetic methodologies for imidazole derivatives and the development of new molecules having antidepressant activity via modulating serotonergic systems, along with their SAR studies. The focus of the study is to provide structural insights into imidazole-based derivatives as serotonergic system modulators for the treatment of depression.

Synergistic Antimicrobial Activity of Silver Nanoparticles with an Emergent Class of Azoimidazoles

The combination of two or more agents capable of acting in synergy has been reported as a valuable tool to fight against pathogens. Silver nanoparticles (AgNPs) present a strong antimicrobial action, although their cytotoxicity for healthy cells at active concentrations is a major concern. Azoimidazole moieties exhibit interesting bioactivities, including antimicrobial activity. In this work, a class of recently described azoimidazoles with strong antifungal activity was conjugated with citrate or polyvinylpyrrolidone-stabilized AgNPs. Proton nuclear magnetic resonance was used to confirm the purity of the compounds before further tests and atomic absorption spectroscopy to verify the concentration of silver in the prepared dispersions. Other analytical techniques elucidate the morphology and stability of AgNPs and corresponding conjugates, namely ultraviolet–visible spectrophotometry, scanning transmission electron microscopy and dynamic light scattering analysis. The synergistic antimicrobial activity of the conjugates was assessed through a checkerboard assay against yeasts (Candida albicans and Candida krusei) and bacteria (Staphylococcus aureus and Escherichia coli). The conjugates showed improved antimicrobial activity against all microorganisms, in particular towards bacteria, with concentrations below their individual minimal inhibitory concentration (MIC). Furthermore, some combinations were found to be non-cytotoxic towards human HaCaT cells.