Carbazole Derivatives as Potential Antimicrobial Agents

Design, synthesis and biological evaluation of multitarget hybrid molecules containing NHC-Au(I) complexes and carbazole moieties

N-heterocyclic carbenes (NHCs) represent suitable ligands for rapid and efficient drug design, because they offer the advantage of being easily chemically modified and can bind several substituents, including transition metals as, for instance, gold derivatives. Gold-NHC complexes possess various biological activities and were demonstrated good candidates as anticancer drugs. Besides, carbazole derivatives are characterized by various pharmacological properties, such as anticancer, antibacterial, anti-inflammatory, and anti-psychotropic. Amongst the latter, N-thioalkyl carbazoles were proved to inhibit cancer cells damaging the nuclear DNA, through the inhibition of human topoisomerases. Herein, we report the design, synthesis and biological evaluation of nine new hybrid molecules in which NHC-Au(I) complexes and N-alkylthiolated carbazoles are linked together, in order to obtain novel biological multitarget agents. We demonstrated that the lead hybrid complexes possess anticancer, anti-inflammatory and antioxidant properties, with a high potential as useful tools for treating distinct aspects of several diseases, amongst them cancer.

Synthesis of biscarbazole derivative, detection of the "on-off" sensor property of Cu2+ by fluorimetry, and anti-cancer evaluation

Biscarbazole derivative probe (6) (Z)-2-(3-(((9-heptyl-9H-carbazol-3-yl)methylene)amino)-9H-carbazol-9-yl)ethan-1-ol containing an imine group, which is a sensitive and selective fluorescence chemosensor, was designed and synthesized for the effective evaluation of Cu2+ metal ion levels. The synthesized compounds were characterized using 1H NMR, 13C NMR, FT-IR, and MALDI-TOF MS (for compound 6) spectroscopic data. The interaction model between probe 6 and Cu2+ was determined by combining fluorescence methods, 1H NMR titration, Job's plot, and theoretical calculations. For probe 6, the fluorogenic recognition of Cu2+ was investigated by fluorescence spectroscopy, and the optical changes caused by Cu2+ ions were carried out in ACN/H2O (50:50) solution at pH 7.0. Fluorescence probe 6 was found to "turn-off" its fluorescence in the presence of paramagnetic Cu2+ ions. Probe 6 was determined to have a rapid response within 40s and showed a fluorescence response to Cu2+ with a low detection limit of 0.16 μM. Additionally, in vitro anticancer activity and cell imaging studies of probe 6 against the prostate cell line (PC-3) were performed.

Antifungal Tetrahydrocarbazole Compound CAR-8 Induces Endoplasmic Reticulum Stress in Candida albicans

The development of new effective antifungal agents is essential to combat fungal infections. Tetrahydrocarbazole has been exploited as a promising skeleton against various pathogenic microorganisms and is used to search for novel active antifungal compounds. In this study, a library composed of small tetrahydrocarbazole compounds was screened, and a potent antifungal agent, CAR-8, was identified with a minimum inhibitory concentration of 2-4 μg/mL against Candida albicans. CAR-8 showed strong fungicidal activities and killed almost all C. albicans within 3 h at a concentration of 16 μg/mL. At concentrations of 2 and 8 μg/mL, CAR-8 significantly inhibited the formation of hyphae and biofilms. Moreover, CAR-8 at 10 and 20 mg/kg reduced the fungal load and improved the survival in the C. albicans infection model in the invertebrate Galleria mellonella. Transcriptome analysis revealed significant changes in the expression of genes associated with protein processing in the endoplasmic reticulum (ER), ER-associated degradation, and unfolded protein response (UPR), which suggested that CAR-8 treatment induced ER stress. Moreover, CAR-8 treatment resulted in various phenotypes similar to tunicamycin, a classical ER stress inducer. These included nonconventional splicing of HAC1 mRNA, the fragmented morphology of ER, the distribution changes of GFP-Snc1 in Saccharomyces cerevisiae, and cell apoptosis probably caused by ER stress. More importantly, the disruption of IRE1 or HAC1 increased the sensitivity of C. albicans to CAR-8, confirming that the UPR signaling pathway was critical for CAR-8 resistance. Overall, our study identifies a potent ER stress-induced antifungal compound that will help the discovery of new antifungal drugs.

An Overview of the Structure-Activity Relationship in Novel Antimicrobial Thiazoles Clubbed with Various Heterocycles (2017-2023)

Antimicrobial resistance is an increasing problem for global public health. One of the strategies to combat this issue is the synthesis of novel antimicrobials through rational drug design based on extensive structure-activity relationship studies. The thiazole nucleus is a prominent feature in the structure of many authorized antimicrobials, being clubbed with different heterocycles. The purpose of this review is to study the structure-activity relationship in antimicrobial thiazoles clubbed with various heterocycles, as reported in the literature between 2017 and 2023, in order to offer an overview of the last years in terms of antimicrobial research and provide a helpful instrument for future research in the field.

Design of N-heterocycle based-phthalonitrile/metal phthalocyanine-silver nanoconjugates for cancer therapies

This study reports the anticancer properties of carbazole-containing phthalonitrile/phthalocyanine-modified silver nanoparticles for the first time. In this study, a new mono-substituted phthalonitrile namely 3-[9H-carbazole-9-ethoxy]phthalonitrile and its metal phthalocyanines {M = Zn, Co, and Mn(Cl)} were synthesized by template cyclotetramerization of phthalonitrile derivatives. The newly synthesized compounds were characterized using UV-vis, FT-IR, 1H NMR, 13C NMR, and mass spectroscopy. The resultant compounds were successfully linked to the surface of silver nanoparticles. The characterization of the surficial modification was carried out by applying the TEM technique. The cytotoxic activities of the studied nanoconjugates were tested against A549, DLD-1, and Wi38 cell lines by performing a (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) (MTT) assay with/without irradiation. Although the functionalization of silver nanoparticles increased the solubility of phthalocyanines in aqueous media, the presence of phthalonitrile/phthalocyanine derivatives on the silver nanoparticles' surface improved their biological properties. All the studied biological candidates exhibited antiproliferative activities against the cell lines. The IC50 values calculated were between 6.80 and 97.99 μM against the studied cell lines in the dark. However, the IC50 values determined were between 3.11 and 88.90 μM with irradiation. The highest IC50 values obtained were 3.11 and 3.52 μM against the DLD-1 cell line for nanoconjugates 1-AgNP and 3-AgNP, respectively. The findings indicated that the compounds may be utilized as anticancer agents after further studies.

Antimicrobial Activity and Toxicity of Newly Synthesized 4-[4-(benzylamino)butoxy]-9H-carbazole Derivatives

One of the main challenges of medicinal chemistry is the search for new substances with antimicrobial potential that could be used in the fight against pathogenic microorganisms. Therefore, the antimicrobial activity of newly synthesized compounds is still being investigated. Carbazole-containing compounds appear to be promising antibacterial, antifungal, and antiviral agents. The aim of this study was to examine the antimicrobial potential and toxicity of newly synthesized isomeric fluorinated 4-[4-(benzylamino)butoxy]-9H-carbazole derivatives. Their antimicrobial activity against bacteria and fungi was tested according to CLSI guidelines. Similarly to previously studied carbazole-containing compounds, the tested derivatives showed the ability to effectively inhibit the growth of Gram-positive bacteria. The addition of carbazole derivatives 2, 4, and 8 at the concentration of 16 µg/mL caused the inhibition of S. aureus growth by over 60%. The MIC value of compounds 2-5 and 7-10 was 32 µg/mL for Staphylococcus strains. Gram-negative strains of E. coli and P. aeruginosa were found to be more resistant to the tested carbazole derivatives. E. coli cells treated with compounds 3 and 8 at a concentration of 64 µg/mL resulted in a greater-than-40% reduction in bacterial growth. In the case of the P. aeruginosa strain, all compounds in the highest concentration that we tested limited growth by 35-42%. Moreover, an over-60% inhibition of fungal growth was observed in the cultures of C. albicans and A. flavus incubated with 64 µg/mL of compounds 2 or 7 and 1 or 4, respectively. The hemolysis of red blood cells after their incubation with the tested carbazole derivatives was in the range of 2-13%. In the case of human fibroblast cells, the toxicity of the tested compounds was higher. Derivative 1, functionalized with fluorine in position 2 and its hydrobromide, was the least toxic. The obtained results indicated the antimicrobial potential of the tested 4-[4-(benzylamino)butoxy]-9H-carbazole derivatives, especially against S. aureus strains; therefore, it is worth further modifying these structures, in order to enhance their activity against pathogenic microorganisms.

Programming Positive Mechanofluorescence in Liquid Crystalline Elastomers

Liquid single crystal elastomers (LSCEs) containing organic fluorophores within their polymeric network are attractive materials to detect forces with simple spectroscopic measurements. Hitherto, all mechanoluminescent LSCEs decrease their emission intensity upon mechanical stimulation; that is, they display negative mechanofluorescence. Such behavior is governed by the mechanically induced approximation of the quenching mesogenic units and the fluorophores. In this work, we propose the integration of fluorescent molecular rotors (FMRs), whose luminescence is not quenched by the mesogens, in LSCEs as a valuable strategy to conceive elastomeric materials programmed with exactly the opposite behavior, i.e., their fluorescence increases upon deformation (positive mechanofluorescence). Specifically, carbazole-indolenine dyes are interesting candidates for this purpose since their luminescence depends mainly on the degree of intramolecular rotation allowed by the local environment. On this basis, the uniaxial deformation of an LSCE, along its anisotropic direction, incorporating such FMRs will place the fluorophores in a more restricted medium, leading to the desired enhanced emission at the macroscale.

9-(4-Meth-oxy-phen-yl)-9H-carbazole

In the title compound, C19H15NO, the dihedral angle between the benzene rings of the carbazole moiety is 1.73 (12)° and the meth-oxy-substituted phenyl ring deviates from the mean plane of the carbazole grouping (r.m.s. deviation = 0.020 Å) by 56.78 (8)°. In the crystal, weak C-H⋯π inter-actions link the mol-ecules. The two-dimensional fingerprint plots derived from the Hirshfeld surface indicate that H⋯H (51.2%) and C⋯H/H⋯C (39.9%) contacts dominate the packing.

Synthetic Pathways to Non-Psychotropic Phytocannabinoids as Promising Molecules to Develop Novel Antibiotics: A Review

Due to the rapid emergence of multi drug resistant (MDR) pathogens against which current antibiotics are no longer functioning, severe infections are becoming practically untreatable. Consequently, the discovery of new classes of effective antimicrobial agents with novel mechanism of action is becoming increasingly urgent. The bioactivity of Cannabis sativa, an herbaceous plant used for millennia for medicinal and recreational purposes, is mainly due to its content in phytocannabinoids (PCs). Among the 180 PCs detected, cannabidiol (CBD), Δ⁸ and Δ⁹-tetrahydrocannabinols (Δ⁸-THC and Δ⁹-THC), cannabichromene (CBC), cannabigerol (CBG), cannabinol (CBN) and some of their acidic precursors have demonstrated from moderate to potent antibacterial effects against Gram-positive bacteria (MICs 0.5-8 µg/mL), including methicillin-resistant Staphylococcus aureus (MRSA), epidemic MRSA (EMRSA), as well as fluoroquinolone and tetracycline-resistant strains. Particularly, the non-psychotropic CBG was also capable to inhibit MRSA biofilm formation, to eradicate even mature biofilms, and to rapidly eliminate MRSA persiter cells. In this scenario, CBG, as well as other minor non-psychotropic PCs, such as CBD, and CBC could represent promising compounds for developing novel antibiotics with high therapeutic potential. Anyway, further studies are necessary, needing abundant quantities of such PCs, scarcely provided naturally by Cannabis plants. Here, after an extensive overture on cannabinoids including their reported antimicrobial effects, aiming at easing the synthetic production of the necessary amounts of CBG, CBC and CBD for further studies, we have, for the first time, systematically reviewed the synthetic pathways utilized for their synthesis, reporting both reaction schemes and experimental details.

Oral Delivery of Anti-Parasitic Agent-Loaded PLGA Nanoparticles: Enhanced Liver Targeting and Improved Therapeutic Effect on Hepatic Alveolar Echinococcosis

Background

Alveolar echinococcosis (AE) is a lethal parasitic disease caused by infection with the metacestode of the dog/fox tapeworm Echinococcus multilocularis, which primarily affects the liver. Although continued efforts have been made to find new drugs against this orphan and neglected disease, the current treatment options remain limited, with drug delivery considered a likely barrier for successful treatment.

Methods

Nanoparticles (NPs) have gained much attention in the field of drug delivery due to their potential to improve delivery efficiency and targetability. In this study, biocompatible PLGA nanoparticles encapsulating a novel carbazole aminoalcohol anti-AE agent (H1402) were prepared to promote the delivery of the parent drug to liver tissue for treating hepatic AE.

Results

H1402-loaded nanoparticles (H1402-NPs) had a uniform spherical shape and a mean particle size of 55 nm. Compound H1402 was efficiently encapsulated into PLGA NPs with a maximal encapsulation efficiency of 82.1% and drug loading content of 8.2%. An in vitro uptake assay demonstrated that H1402-NPs rapidly penetrated the in vitro cultured pre-cyst wall and extensively accumulated in the pre-cysts of E. multilocularis within only 1 h. The biodistribution profile of H1402-NPs determined through ex vivo fluorescence imaging revealed significantly enhanced liver distribution compared to unencapsulated H1402, which translated to improved therapeutic efficacy and reduced systemic toxicity (especially hepatotoxicity and cytotoxicity) in a hepatic AE murine model. Following a 30-day oral regimen (100 mg/kg/day), H1402-NPs significantly reduced the parasitic burden in both the parasite mass (liver and metacestode total weight, 8.8%) and average metacestode size (89.9%) compared to unmedicated infected mice (both p-values < 0.05); the treatment outcome was more effective than those of albendazole- and free H1402-treated individuals.

Conclusion

Our findings demonstrate the advantages of encapsulating H1402 into PLGA nanoparticles and highlight the potential of H1402-NPs as a promising liver-targeting therapeutic strategy for hepatic AE.

9-Methoxyellipticine: Antibacterial Bioactive Compound Isolated from Ochrosia elliptica Labill. Roots

Antibacterial resistance bears a major threat to human health worldwide, causing about 1.2 million deaths per year. It is noteworthy that carbazole derivatives have shown a potential antibacterial activity, for example, 9-methoxyellipticine, which was isolated from Ochrosia elliptica Labill. roots (Apocynaceae) in the present study. An in vitro screening of the antibacterial activity of 9-methoxyellipticine was investigated against four multidrug-resistant (MDR) Klebsiella pneumoniae and Shiga toxin-producing Escherichia coli (STEC O157) as Gram-negative bacteria, in addition to Methicillin-resistant Staphylococcus aureus (MRSA) with Bacillus cereus as Gram-positive bacteria. The compound had significant antibacterial activity against the two Gram-negative isolates and lower activity against the Gram-positive ones. The synergistic use of 9-methoxyellipticine and antibiotics was successfully effective in reducing the MDR microorganisms. Lung pneumonia and kidney infection mice models were used to investigate the compound's efficacy in vivo for the first time. Noteworthy reductions in K. pneumoniae and STEC shedding and the colonization were observed, with a reduction in pro-inflammatory factors and immunoglobulin levels. Other related lesions such as inflammatory cell infiltration, alveolar interstitial congestion, and edema were noticed to occur, lessened to different limits. The anti-STEC and anti-K. pneumoniae activities of 9-methoxyellipticine were revealed, providing a new alternative against MDR nosocomial infections.

Site-Selective C-H Functionalization of Carbazoles

Carbazole alkaloids hold great potential in pharmaceutical and material sciences. However, the current approaches for C1 functionalization of carbazoles rely on the use of a pre-installed directing group, severely limiting their applicability and hindering their overall efficiency. Herein, we report for the first time the development of direct Pd-catalyzed C-H alkylation and acylation of carbazoles assisted by norbornene (NBE) as a transient directing mediator. Notably, the involvement of a six-membered palladacycle intermediate was suggested in this case, representing the first example of such intermediacy within the extensively studied Pd/norbornene reactions realm.

Synergy between Genome Mining, Metabolomics, and Bioinformatics Uncovers Antibacterial Chlorinated Carbazole Alkaloids and Their Biosynthetic Gene Cluster from Streptomyces tubbatahanensis sp. nov., a Novel Actinomycete Isolated from Sulu Sea, Philippines

In this study, a novel actinomycete strain, DSD3025T, isolated from the underexplored marine sediments in Tubbataha Reefs Natural Park, Sulu Sea, Philippines, with the proposed name Streptomyces tubbatahanensis sp. nov., was described using polyphasic approaches and characterized using whole-genome sequencing. Its specialized metabolites were profiled using mass spectrometry and nuclear magnetic resonance analyses, followed by antibacterial, anticancer, and toxicity screening. The S. tubbatahanensis DSD3025T genome was comprised of 7.76 Mbp with a 72.3% G+C content. The average nucleotide identity and digital DNA-DNA hybridization values were 96.5% and 64.1%, respectively, compared with its closest related species, thus delineating the novelty of Streptomyces species. The genome encoded 29 putative biosynthetic gene clusters (BGCs), including a BGC region containing tryptophan halogenase and its associated flavin reductase, which were not found in its close Streptomyces relatives. The metabolite profiling unfolded six rare halogenated carbazole alkaloids, with chlocarbazomycin A as the major compound. A biosynthetic pathway for chlocarbazomycin A was proposed using genome mining, metabolomics, and bioinformatics platforms. Chlocarbazomycin A produced by S. tubbatahanensis DSD3025T has antibacterial activities against Staphylococcus aureus ATCC BAA-44 and Streptococcus pyogenes and showed antiproliferative activity against colon (HCT-116) and ovarian (A2780) human cancer cell lines. Chlocarbazomycin A exhibited no toxicity to liver cells but moderate and high toxicity to kidney and cardiac cell lines, respectively. IMPORTANCE Streptomyces tubbatahanensis DSD3025T is a novel actinomycete with antibiotic and anticancer activities from Tubbataha Reefs Natural Park, a United Nations Educational, Scientific and Cultural Organization World Heritage Site in Sulu Sea and considered one of the Philippines' oldest and most-well-protected marine ecosystems. In silico genome mining tools were used to identify putative BGCs that led to the discovery of genes involved in the production of halogenated carbazole alkaloids and new natural products. By integrating bioinformatics-driven genome mining and metabolomics, we unearthed the hidden biosynthetic richness and mined the associated chemical entities from the novel Streptomyces species. The bioprospecting of novel Streptomyces species from marine sediments of underexplored ecological niches serves as an important source of antibiotic and anticancer drug leads with unique chemical scaffolds.