Harnessing the benzyne insertion consequence to enable π-extended pyrido-acridine and quinazolino-phenanthridine

Distinct protocols have been devised for the preparation of hybrid heterocyclic scaffolds like π-extended pyrido-acridines and quinazolino-phenanthridines duly materialized through Rh(III)- and Pd(II)-mediated catalytic courses commencing from acridine and quinazolimine scaffolds. Interestingly, the parent compounds (acridines and quinazolimines) are actualized from 2-aminobenzonitrile and anthranilic acid, where 2-aminobenzonitrile acts as the 1,4-dipolarophilic species and anthranilic acid as the benzyne precursor. The molecular assembly of acridine suggests the participation of two benzyne units. In addition, the structural motif of the quinazolimine ring features one benzyne unit. Further, indolizine ring containing the enaminonitrile skeleton upon exposure to benzyne forms an indolizine fused quinoline ring, decorated with three benzyne units.

Facile and Novel Synthetic Approach, Molecular Docking, Molecular Dynamics, and Drug-Likeness Evaluation of 9-Substituted Acridine Derivatives as Dual Anticancer and Antimicrobial Agents

In the present study, numerous acridine derivatives A1-A20 were synthesized via aromatic nucleophilic substitution (SNAr) reaction of 9-chloroacridine with carbonyl hydrazides, amines, or phenolic derivatives depending upon facile, novel, and eco-friendly approaches (Microwave and ultrasonication assisted synthesis). The structures of the new compounds were elucidated using spectroscopic methods. The title products were assessed for their antimicrobial, antioxidant, and antiproliferative activities using numerous assays. Promisingly, the investigated compounds mainstream revealed promising antibacterial and anticancer activities. Thereafter, the investigated compounds' expected mode of action was debated by using an array of in silico studies. Compounds A2 and A3 were the most promising antimicrobial agents, while compounds A2, A5, and A7 revealed the most cytotoxic activities. Accordingly, RMSD, RMSF, Rg, and SASA analyses of compounds A2 and A3 were performed, and MMPBSA was calculated. Lastly, the ADMET (absorption, distribution, metabolism, excretion, and toxicity) analyses of the novel acridine derivatives were investigated. The tested compounds' existing screening results afford an inspiring basis leading to developing new compelling antimicrobial and anticancer agents based on the acridine scaffold.

Acridine-Isoxazole and Acridine-Azirine Hybrids: Synthesis, Photochemical Transformations in the UV/Visible Radiation Boundary Region, and Anticancer Activity

Easy-to-handle N-hydroxyacridinecarbimidoyl chloride hydrochlorides were synthesized as convenient nitrile oxide precursors in the preparation of 3-(acridin-9/2-yl)isoxazole derivatives via 1,3-dipolar cycloaddition with terminal alkynes, 1,1-dichloroethene, and acrylonitrile. Azirines with an acridin-9/2-yl substituent attached directly or via the 1,2,3-triazole linker to the azirine C2 were also synthesized. The three-membered rings of the acridine-azirine hybrids were found to be resistant to irradiation in the UV/visible boundary region, despite their long-wave absorption at 320-420 nm, indicating that the acridine moiety cannot be used as an antenna to transfer light energy to generate nitrile ylides from azirines for photoclick cycloaddition. The acridine-isoxazole hybrids linked at the C9-C3 or C2-C3 atoms under blue light irradiation underwent the addition of such hydrogen donor solvents, such as, toluene, o-xylene, mesitylene, 4-chlorotoluene, THF, 1,4-dioxane, or methyl tert-butyl ether (MTBE), to the acridine system to give the corresponding 9-substituted acridanes in good yields. The synthesized acridine-azirine, acridine-isoxazole, and acridane-isoxazole hybrids exhibited cytotoxicity toward both all tested cancer cell lines (HCT 116, MCF7, and A704) and normal cells (WI-26 VA4).

Improved synthesis of antiplasmodial 4-aminoacridines and 4,9-diaminoacridines

Acridines are one of the most important nitrogen-containing heterocycle systems and have many applications in the therapeutic field. However, the synthesis of acridine-based scaffolds is not always straightforward. Herein, we report the optimization of two multi-step synthetic routes towards 4,9-diaminoacridines and 4-aminoacridines, which have shown promising antiplasmodial properties. The improved synthesis pathways make use of greener, simpler, and more efficient methods, with less reaction steps and increased overall yields, which were doubled in some cases. These are impactful results towards future approaches to the chemical synthesis of acridine-based compounds.

Metal-free C(sp3)-H functionalization (C-C and C-N bond formation) of 1,2,3,4-tetrahydroacridines using deep eutectic solvents as catalyst and reaction medium

Herein, we report a metal-free and efficient method for the C(sp3)-H functionalization of 1,2,3,4-tetrahydroacridines at the C4-position by the addition of azodicarboxylates (C-N bond) and maleimides (C-C bond) using deep eutectic solvents (DESs) at 80 °C. The C4-functionalized 1,2,3,4-tetrahydroacridines were achieved with high atom efficiency, precise regioselectivity, and yields ranging from 70-96%. The practicality of the developed method has been demonstrated through gram-scale synthesis. Also the green-metrics were calculated for the developed method and it was found that the metrics are near to the ideal values.

Influence of N-protonation on electronic properties of acridine derivatives by quantum crystallography

Applications of 9-aminoacridine (9aa) and its derivatives span fields such as chemistry, biology, and medicine, including anticancer and antimicrobial activities. Protonation of such molecules can alter their bioavailability as weakly basic drugs like aminoacridines exhibit reduced solubility at high pH levels potentially limiting their effectiveness in patients with elevated gastric pH. In this study, we analyse the influence of protonation on the electronic characteristics of the molecular organic crystals of 9-aminoacridine. The application of quantum crystallography, including aspherical atom refinement, has enriched the depiction of electron density in the studied systems and non-covalent interactions, providing more details than previous studies. Our experimental results, combined with a topological analysis of the electron density and its Laplacian, provided detailed descriptions of how protonation changes the electron density distribution around the amine group and water molecule, concurrently decreasing the electron density at bond critical points of N/O-H bonds. Protonation also alters the molecular architecture of the systems under investigation. This is reflected in different proportions of the N⋯H and O⋯H intermolecular contacts for the neutral and protonated forms. Periodic DFT calculations of the cohesive energies of the crystal lattice, as well as computed interaction energies between molecules in the crystal, confirm that protonation stabilises the crystal structure due to a positive synergy between strong halogen and hydrogen bonds. Our findings highlight the potential of quantum crystallography in predicting crystal structure properties and point to its possible applications in developing new formulations for poorly soluble drugs.

Metal-free synthesis of functionalized tacrine derivatives and their evaluation for acetyl/butyrylcholinesterase and α-glucosidase inhibition

A mild and greener protocol was developed for C-C (C(sp3)-H functionalization) and C-N bond formation to synthesize functionalized tacrine derivatives using a biodegradable and reusable deep eutectic solvent [(DES) formed from N,N'-dimethyl urea and L-(+)-tartaric acid in a 3 : 1 ratio at 80 °C]. The condensation of 9-chloro-1,2,3,4-tetrahydroacridines with a variety of aromatic aldehydes gave unsaturated compounds via C(sp3)-H functionalization (at the C-4 position) with good yields. The substituted N-aryl tacrine derivatives were obtained from the condensed products of 9-chloro-1,2,3,4-tetrahydroacridine with substituted anilines via the nucleophilic substitution reaction (SN2 type) in the DES with good yields. This is the first example of C4-functionalized tacrine derivatives, highlighting the dual capacity of the DES to serve as both a catalyst and a solvent for facilitating C-N bond formation on acridine. The generated compounds were evaluated for acetyl/butyrylcholinesterase (AChE/BChE) and α-glucosidase inhibitory activity. It was found that the majority of the compounds reported here were significantly more potent inhibitors than the standard inhibitor tacrine (AChE IC50 = 203.51 nM; BChE IC50 = 204.01 nM). Among the compounds screened, 8m was found to be more potent with IC50 = 125.06 nM and 119.68 nM towards AChE and BChE inhibition respectively. The α-glucosidase inhibitory activity of the compounds was tested using acarbose as a standard drug (IC50 = 23 100 nM) and compound 8j was found to be active with IC50 = 19 400 nM.

Acridones as promising drug candidates against Oropouche virus

Oropouche virus (OROV) is an emerging vector-borne arbovirus found in South America that causes Oropouche fever, a febrile infection similar to dengue fever. It has a high epidemic potential, causing illness in over 500,000 cases diagnosed since the virus was first discovered in 1955. Currently, the prevention of human viral infection depends on vaccination, but availability for many viruses is limited, and they are classified as neglected viruses. At present, there are no vaccines or antiviral treatments available. An alternative approach to limiting the spread of the virus is to selectively disrupt viral replication mechanisms. Here, we demonstrate the inhibitory effect of acridones, which efficiently inhibited viral replication by 99.9 % in vitro. To evaluate possible mechanisms of action, we conducted tests with dsRNA, an intermediate in virus replication, as well as MD simulations, docking, and binding free energy analysis. The results showed a strong interaction between FAC21 and the OROV endonuclease, which possibly limits the interaction of viral RNA with other proteins. Therefore, our results suggest a dual mechanism of antiviral action, possibly caused by ds-RNA intercalation. In summary, our findings demonstrate that a new generation of antiviral drugs could be developed based on the selective optimization of molecules.

A sequential Friedländer and anionic benzannulation strategy for the regiodefined assembly of unsymmetrical acridines

An efficient sequential double-annulation strategy has been developed to afford a series of unsymmetrical acridines with high yield and regioselectivity for the first time. This simple protocol enables the sequential assembly of two aromatic rings from simple starting materials. The reaction proceeds via modified Friedländer annulation and subsequent base-mediated benzannulation with acrylates as Michael acceptors. A range of substrate scope and functional group tolerance is observed. Late-stage synthetic modification is also explored to access novel unsymmetrical acridines in good yield.

In silico design of bio-marker detection fluorescent probes

Fluorescent probes capable of sensing the biological medium are of utmost importance in medical diagnostics. However, the optical spectrum of such probes needs to be tuned with care for compatibility with living tissues. More specifically, fluorescent bioprobes must be adjusted so as to avoid light interference with pigments (e.g. hemoglobin), tissue photodamage, scattering of the emitted light, and autofluorescence. This leads to two important conditions on the optical spectrum of the probes. On the one hand, the emission wavelength must be in an optical window of 650 to 950 nm. On the other hand, the Stokes shift must be large, ideally greater than 150 nm. In this paper, we showcase the in-silico design of potential fluorescent biomarkers fulfilling these two conditions by means of heteroatomic substitution and conjugation on a 1,2,4-triazole core initially far away from biological standards.

Biochemical investigation of the tryptophan biosynthetic enzyme anthranilate phosphoribosyltransferase in plants

While mammals require the essential amino acid tryptophan (Trp) in their diet, plants and microorganisms synthesize Trp de novo. The five-step Trp pathway starts with the shikimate pathway product, chorismate. Chorismate is converted to the aromatic compound anthranilate, which is then conjugated to a phosphoribosyl sugar in the second step by anthranilate phosphoribosyltransferase (PAT1). As a single-copy gene in plants, all fixed carbon flux to indole and Trp for protein synthesis, specialized metabolism, and auxin hormone biosynthesis proceeds through PAT1. While bacterial PAT1s have been studied extensively, plant PAT1s have escaped biochemical characterization. Using a structure model, we identified putative active site residues that were variable across plants and kinetically characterized six PAT1s (Arabidopsis thaliana (thale cress), Citrus sinensis (sweet orange), Pistacia vera (pistachio), Juglans regia (English walnut), Selaginella moellendorffii (spike moss), and Physcomitrium patens (spreading earth-moss)). We probed the catalytic efficiency, substrate promiscuity, and regulation of these six enzymes and found that the C. sinensis PAT1 is highly specific for its cognate substrate, anthranilate. Investigations of site-directed mutants of the A. thaliana PAT1 uncovered an active site residue that contributes to promiscuity. While Trp inhibits bacterial PAT1 enzymes, the six plant PAT1s that we tested were not modulated by Trp. Instead, the P. patens PAT1 was inhibited by tyrosine, and the S. moellendorffii PAT1 was inhibited by phenylalanine. This structure-informed biochemical examination identified variations in activity, efficiency, specificity, and enzyme-level regulation across PAT1s from evolutionarily diverse plants.

K2CO3-Catalyzed Dual C-C-Coupled Cyclization to 3-Amino-4-benzoylbiphenyls and In Situ I2-Catalyzed C-N Bond Forming Annulation: A Metal-Free Synthesis of Arylacridones

Unprecedented metal-free cyclization catalysis reactions are developed in a highly regioselective fashion to synthesize 3-amino-4-benzoyl biphenyls and arylacridones with high atom economy. Catalytic K2CO3 is utilized as the only reagent for the unusual rapid dual C-C-coupled cyclization between β-keto enamines and cinnamaldehydes to furnish the functionalized biphenyls. Its C(sp2)-H functionalized C-N bond-forming cyclization was performed in situ using molecular I2 as a catalyst to furnish valuable arylacridones. Plausible mechanisms for the new cyclization reactions are predicted by conducting various control experiments and ESI-MS analyses.

New antibacterial hydrogels based on sodium alginate

Nowadays, the combined knowledge and experience in biomedical research and material sciences results in the innovation of smart materials that could efficiently overcome the problems of microbial contaminations. Herein, a new drug delivery platform prepared by grafting sodium alginate with β-carboxyethyl acrylate and acrylamide was described and characterized. 9-Aminoacridine (9-AA), and kanamycin sulfate (KS) were separately loaded into the hydrogel in situ during graft polymerization. The grafting efficiency for the resulting hydrogels was 70.01-78.08 %. The chemical structure of the hydrogels, thermogravimetric analysis, and morphological features were investigated. The swelling study revealed that the hydrogel without drugs achieved a superior swelling rate compared to drug-loaded hydrogels. The hydrogel tuned the drug-release rate in a pH-dependent manner. Furthermore, the antibacterial study suggested that the hydrogels encapsulating 9-AA (88.6 %) or KS (89.3 %) exhibited comparable antibacterial activity against Gram-positive and Gram-negative bacterial strains. Finally, the cytocompatibility study conducted on normal lung cell line (Vero cells) demonstrated neglectable to tolerable toxicity for the drug-loaded hydrogel. More interestingly, the cell viability for the blank hydrogel was 92.5 %, implying its suitability for biomedical applications.

Molecular Hybridization as a Strategy for Developing Artemisinin-Derived Anticancer Candidates

Artemisinin is a natural compound extracted from Artemisia species belonging to the Asteraceae family. Currently, artemisinin and its derivatives are considered among the most significant small-molecule antimalarial drugs. Artemisinin and its derivatives have also been shown to possess selective anticancer properties, however, there are several limitations and gaps in knowledge that retard their repurposing as effective anticancer agents. Hybridization resulting from a covalent combination of artemisinin with one or more active pharmacophores has emerged as a promising approach to overcome several issues. The variety of hybridization partners allows improvement in artemisinin activity by tuning the ability of conjugated artemisinin to interact with various molecule targets involved in multiple biological pathways. This review highlights the current scenario of artemisinin-derived hybrids with potential anticancer activity. The synthetic approaches to achieve the corresponding hybrids and the structure-activity relationships are discussed to facilitate further rational design of more effective candidates.

Evaluation of N 10 -substituted acridone-based derivatives as AKT inhibitors against breast cancer cells: in vitro and molecular docking studies

A series of N 10 -substituted acridone-2-carboxamide derivatives were synthesized and evaluated for their potent anti-cancer agents targeting AKT kinase. In vitro cytotoxicity activity of the target compounds was tested against breast cancer cell lines (MCF-7 and MDA-MB-231). Among the tested compounds, four compounds (7f, 8d, 8e, and 8f) exhibited promising anti-cancer activity against both cancer cell lines. Notably, compound 8f demonstrated the highest activity against MCF-7 and MDA-MB-231 at IC50 values of 4.72 and 5.53 μM, respectively. In vitro AKT kinase activity revealed that compounds 7f and 8f were the most potent AKT inhibitors with IC50 values of 5.38 and 6.90 μM, respectively. In addition, the quantitative ELISA method of testing confirmed that compound 8f effectively inhibited cell proliferation by suppressing the activation of p-AKT Ser473. Furthermore, molecular docking studies revealed that compound 8f can bind well to the active site of the AKT enzyme. The in silico ADME studies suggested that all synthesized molecules showed good oral bioavailability with a low-toxicity profile and can be used for further optimization as AKT kinase inhibitors in the treatment of breast cancer.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03524-z.

Structure-Activity Relationship Studies of 9-Alkylamino-1,2,3,4-tetrahydroacridines against Leishmania (Leishmania) infantum Promastigotes

Leishmaniasis is one of the most neglected diseases in modern times, mainly affecting people from developing countries of the tropics, subtropics and the Mediterranean basin, with approximately 350 million people considered at risk of developing this disease. The incidence of human leishmaniasis has increased over the past decades due to failing prevention and therapeutic measures-there are no vaccines and chemotherapy, which is problematic. Acridine derivatives constitute an interesting group of nitrogen-containing heterocyclic compounds associated with numerous bioactivities, with emphasis to their antileishmanial potential. The present work builds on computational studies focusing on a specific enzyme of the parasite, S-adenosylmethionine decarboxylase (AdoMet DC), with several 1,2,3,4-tetrahydro-acridines emerging as potential inhibitors, evidencing this scaffold as a promising building block for novel antileishmanial pharmaceuticals. Thus, several 1,2,3,4-tetrahydroacridine derivatives have been synthesized, their activity against Leishmania (Leishmania) infantum promastigotes evaluated and a structure-activity relationship (SAR) study was developed based on the results obtained. Even though the majority of the 1,2,3,4-tetrahydroacridines evaluated presented high levels of toxicity, the structural information gathered in this work allowed its application with another scaffold (quinoline), leading to the obtention of N¹,N¹²-bis(7-chloroquinolin-4-yl)dodecane-1,12-diamine (12) as a promising novel antileishmanial agent (IC₅₀ = 0.60 ± 0.11 μM, EC₅₀ = 11.69 ± 3.96 μM and TI = 19.48).

Acridine/Acridone-Carborane Conjugates as Strong DNA-Binding Agents with Anticancer Potential

Synthesis of acridine derivatives that act as DNA-targeting anticancer agents is an evolving field and has resulted in the introduction of several drugs into clinical trials. Carboranes can be of importance in designing biologically active compounds due to their specific properties. Therefore, a series of novel acridine analogs modified with carborane clusters were synthesized. The DNA-binding ability of these analogs was evaluated on calf thymus DNA (ct-DNA). Results of these analyses showed that 9-[(1,7-dicarba-closo-dodecaborane-1-yl)propylamino]acridine (30) interacted strongly with ct-DNA, indicating its ability to intercalate into DNA, whereas 9-[(1,7-dicarba-closo-dodecaborane-1-yl)propanamido]acridine (29) changed the B-form of ct-DNA to the Z form. Compound 30 demonstrated cytotoxicity, was able to inhibit cell proliferation, arrest the cell cycle in the S phase in the HeLa cancer cell line, and induced the production of reactive oxygen species (ROS). In addition, it was specifically localized in lysosomes and was a weak inhibitor of Topo IIα.

Synthesis, Structures, and Complexation with Phenolic Guests of Acridone-Incorporated Arylene-Ethynylene Macrocyclic Compounds

Acridone units were incorporated into the arylene-ethynylene structure as polar arene units. Cyclic trimers consisting of three acridone-2,7-diyl units and three 1,3-phenylene units were synthesized by Sonogashira couplings via stepwise or direct route. X-ray analysis revealed that the trimer had a nearly planar macrocyclic framework with a cavity surrounded by three carbonyl groups. In contrast, the corresponding tetramer had a nonplanar macrocyclic framework. ¹ H NMR measurements showed that the trimer formed a 1 : 1 complex as a macrocyclic host with dihydric phenol guests, and the association constants were determined to be ca. 1.0×10³  L mol^-1 for hydroquinone or resorcinol guests in CDCl₃ at 298 K. The calculated structures of these complexes by the DFT method supported the presence of two sets of OH⋅⋅⋅O=C hydrogen bonds between the host and guest molecules. The spectroscopic data of the cyclic trimers and tetramers are compared with those of reference acridone compounds.

Synthesis of acridines via copper-catalyzed amination/annulation cascades between arylboronic acids and anthranils

Copper-catalyzed tandem cyclization reactions between arylboronic acids and anthranils have been established, providing new approaches for one-pot assembly of azacycle acridines. This one-pot protocol features simple operation, precious-metal-free conditions and good functional group compatibility, thus providing an efficient approach for the synthesis of a variety of acridines in moderate to good yields.

Synthesis, computational study and biological evaluation of 9-acridinyl and 1-coumarinyl-1,2,3-triazole-4-yl derivatives as topoisomerase II inhibitors

Topoisomerase (IIB) inhibitors have been involved in the therapies of tumour progression and have become a major focus for the development of anticancer agents. New three-component hybridised ligands, 1,4-disubstituted-1,2,3-triazoles (8-17), were synthesised via a 1,3-dipolar cycloaddition reaction of 9-azidoacridine/3-azidocoumarin with N/O-propargyl small molecules under click reaction conditions. Cancer cell growth inhibition of the synthesised triazoles was tested against human cell-lines in the NCI-60-cell-panel, and the most active compounds tested against topoisomerase (IIB)-enzymes. The acridinyl ligands (8-10) revealed 60-97% cell growth inhibition in six cancer cell-panels. Cell-cycle analysis of MCF7 and DU-145 cells treated with the active acridinyl ligands exhibited cell-cycle arrest at G2/M phase and proapoptotic activity. In addition, compound 8 displayed greater inhibitory activity against topoisomerase (IIB) (IC50 0.52 µM) compared with doxorubicin (IC50 0.83 µM). Molecular dynamics simulation studies showed the acridine-triazole-pyrimidine hybrid pharmacophore was optimal with respect to protein-ligand interaction and fit within the binding site, with optimal orientation to allow for intercalation with the DNA bases (DG13, DC14, and DT9).

Acridine and Its Derivatives: Synthesis, Biological, and Anticorrosion Properties

The phenomenon of corrosion threatens metallic components, human safety, and the economy. Despite being eco-friendly and promising as a corrosion inhibitor, acridine has not been explored to its full potential. In this review, we have discussed multiple biological activities that acridines have been found to show in a bid to prove that they are environmentally benign and much less toxic than many inhibitors. Some synthetic routes to acridines and substituted acridines have also been discussed. Thereafter, a multitude of acridines and substituted acridines as corrosion inhibitors of different metals and alloys in various corrosive media have been highlighted. A short mechanistic insight into how acridine-based compounds function as corrosion inhibitors have also been included. We believe this review will generate an impression that there is still much to learn about previously reported acridines. In the wake of recent surges to find efficient and non-toxic corrosion inhibitors, acridines and their analogs could be an appropriate answer.

Development and validation of a high-performance thin-layer chromatography densitometric method for the simultaneous determination of novel 1-acridinyl-1,2,3-triazole derivatives

High-performance thin-layer chromatographic (HPTLC) method provides a simple, sensitive, and accurate analytical method for the simultaneous determination of certain synthesized 1-acridinyl-1,2,3-triazole derivatives without interference from starting materials and intermediates. Separation was carried out on Merck HPTLC silica gel 60F254 plates, using chloroform‒methanol (9:1, V/V) and hexane‒ethyl acetate (3:2, V/V) as mobile phases. Validation of the method was performed based on the basis of the International Council for Harmonisation (ICH) guidelines in terms of linearity, sensitivity, limit of detection, limit of quantification, precision, selectivity, and specificity. Least-square equations were calculated for the studied compounds in the ranges of 25–500 and 10–500 ng/spot for ultraviolet (UV) and fluorescence measurements, respectively. Correlation coefficients (r) values were found ranging from 0.9913 to 0.9992 for analytes. The method provides selectivity and specificity which ensure that synthesized compounds are in the pure form without the interference of starting materials and intermediates. The detection limits for the studied compounds ranged from 11.02 to 51.09 ng/spot and 3.84 to 31.95 ng/spot and quantification limits were 33.39–154.82 ng/spot and 11.63–73.67 ng/spot for both spectrophotometric and spectrofluorimetric methods, respectively, indicating applicability for good qualitative and quantitative determination of members of this series at the nanogram concentration levels in biological fluids.

A comprehensive review on acridone based derivatives as future anti-cancer agents and their structure activity relationships

The development of drug resistance and severe side-effects has reduced the clinical efficacy of the existing anti-cancer drugs available in the market. Thus, there is always a constant need to develop newer anti-cancer drugs with minimal adverse effects. Researchers all over the world have been focusing on various alternative strategies to discover novel, potent, and target specific molecules for cancer therapy. In this direction, several heterocyclic compounds are being explored but amongst them one promising heterocycle is acridone which has attracted the attention of medicinal chemists and gained huge biological importance as acridones are found to act on different therapeutically proven molecular targets, overcome ABC transporters mediated drug resistance and DNA intercalation in cancer cells. Some of these acridone derivatives have reached clinical studies as these heterocycles have shown huge potential in cancer therapeutics and imaging. Here, the authors have attempted to compile and make some recommendations of acridone based derivatives concerning their cancer biological targets and in vitro-cytotoxicity based on drug design and novelty to increase their therapeutic potential. This review also provides some important insights on the design, receptor targeting and future directions for the development of acridones as possible clinically effective anti-cancer agents.

General electrochemical Minisci alkylation of N-heteroarenes with alkyl halides

Herein, we report, a general, facile and environmentally friendly Minisci-type alkylation of N-heteroarenes under simple and straightforward electrochemical conditions using widely available alkyl halides as radical precursors. Primary, secondary and tertiary alkyl radicals have been shown to be efficiently generated and coupled with a large variety of N-heteroarenes. The method presents a very high functional group tolerance, including various heterocyclic-based natural products, which highlights the robustness of the methodology. This applicability has been further proved in the synthesis of various interesting biologically valuable building blocks. In addition, we have proposed a mechanism based on different proofs and pieces of electrochemical evidence.

Apoptotic and antioxidant effects in HCT-116 colorectal carcinoma cells by a spiro-acridine compound, AMTAC-06

BACKGROUND

Acridine compounds have been described as promising anticancer agents. Previous studies showed that (E)-1'-((4-chlorobenzylidene)amino)-5'-oxo-1',5'-dihydro-10H-spiro[acridine-9,2'-pyrrole]-4'-carbonitrile (AMTAC-06), a spiro-acridine compound, has antitumor activity on Ehrlich tumor and low toxicity. Herein, we investigated its antitumor effect against human cells in vitro.

METHODS

MTT assay was used to assess cytotoxicity of AMTAC-06 (3.125-200 µM) against tumor and non-tumor cells, and the half-maximal inhibitory concentration (IC₅₀) and the selectivity index (SI) were calculated. The effects on the cell cycle (propidium iodide-PI-staining), apoptosis (Annexin V-FITC/PI double staining by flow cytometry), and production of reactive oxygen species, ROS (DCFH assay) were also evaluated. Statistical analysis was achieved using ANOVA followed by Tukey's post-test.

RESULTS

AMTAC-06 showed higher cytotoxicity against colorectal carcinoma HCT-116 cells (IC₅₀: 12.62 µM). The SI showed that AMTAC-06 was more selective for HCT-116 cells (HaCaT SI: 1.41; PBMC SI: 0.62) than doxorubicin (HaCaT SI: 0.10; PBMC SI: 0.01). AMTAC-06 (15 and 30 µM) induced an increase in the sub-G1 peak (p < 0.000001) and cell cycle arrest in S phase (p = 0.003547). Moreover, treatment with this compound (15 and 30 µM) resulted in increased early (p < 0.000001) and late apoptotic cells (p < 0.000001). In addition, there was a reduction on ROS production (p < 0.000001).

CONCLUSIONS

AMTAC-06 presents anticancer activity against HCT-116 cells by regulating the cell cycle, inducing apoptosis and an antioxidant action.

Major Achievements in the Design of Quadruplex-Interactive Small Molecules

Organic small molecules that can recognize and bind to G-quadruplex and i-Motif nucleic acids have great potential as selective drugs or as tools in drug target discovery programs, or even in the development of nanodevices for medical diagnosis. Hundreds of quadruplex-interactive small molecules have been reported, and the challenges in their design vary with the intended application. Herein, we survey the major achievements on the therapeutic potential of such quadruplex ligands, their mode of binding, effects upon interaction with quadruplexes, and consider the opportunities and challenges for their exploitation in drug discovery.

Preparation and characterization of Gum Arabic Schiff's bases based on 9-aminoacridine with in vitro evaluation of their antimicrobial and antitumor potentiality

The conjugation between drug and biopolymers through an easily hydrolysable bond such as ester linkage, disulfide linkage, or imine-bond have been extensively employed to control the drug release pattern and improve its bioavailability. This work described the conjugation of 9-aminoacridine (9-AA) to Gum Arabic (GA) via Schiff's base, as a pH-responsive bond. First, GA was oxidized to Arabic Gum dialdehyde (AGDA), then a different amount of 9-AA (10, 25, and 50 mg 9-AA) was coupled to defined amount of AGDA, the coupling was confirmed by elemental analysis and different spectroscopic tools. In addition, the physical features of Schiff's base conjugates including surface morphology, thermal stability, and crystalline structure were examined. The thermogravimetric analysis revealed that the incorporation of 9-AA slightly improved the thermal stability. The coupling of 9-AA to AGDA dramatically enhanced its in vitro antimicrobial and antitumor activities. All conjugates exhibited broad-spectrum activity against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Bacillus subtilis, and Candida albicans. Moreover, AGA 25 and AGA 50 demonstrated promising capability to suppress the proliferation of human colon cancer cell line (Caco-2), with IC₅₀ 190.10 and 180.80 μg/mL respectively.

Evolution of Acridines and Xanthenes as a Core Structure for the Development of Antileishmanial Agents

Nowadays, leishmaniasis constitutes a public health issue in more than 88 countries, affecting mainly people from the tropics, subtropics, and the Mediterranean area. Every year, the prevalence of this infectious disease increases, with the appearance of 1.5–2 million new cases of cutaneous leishmaniasis and 500,000 cases of visceral leishmaniasis, endangering approximately 350 million people worldwide. Therefore, the absence of a vaccine or effective treatment makes the discovery and development of new antileishmanial therapies one of the focuses for the scientific community that, in association with WHO, hopes to eradicate this disease shortly. This paper is intended to highlight the relevance of nitrogen- and oxygen-containing tricyclic heterocycles, particularly acridine and xanthene derivatives, for the development of treatments against leishmaniasis. Thus, in this review, a thorough compilation of the most promising antileishmanial acridine and xanthene derivatives is performed from both natural and synthetic origins. Additionally, some structure–activity relationship studies are also depicted and discussed to provide insight into the optimal structural features responsible for these compounds’ antileishmanial activity.

Recent developments in the synthesis and anti-cancer activity of acridine and xanthine-based molecules

Cancer is the uncontrolled growth and development of abnormal cells which is a major cause of death in both advanced and emerging countries. Although currently chemotherapy is most broadly used among an extensive range of anti-cancer therapies, it includes many demerits, such as highly toxic, side-effects, expensive and partial lack of targeting specificity. So the design and synthesis of new molecules that perform specifically on target proteins in tumor cells is a focus of contemporary research. So many researchers aim for new drugs that will be more efficient, more selective, and less toxic. Because of the interesting structures and significant biological profile, naturally occurring acridines and xanthines as well as their analogues have attracted considerable interest in researchers and technologists. Natural and synthetic acridine derivatives form a significant category of heterocycles having nitrogen that is of considerable interest for organic chemists and biological communities due to their attractive anti-cancer activity. Another important class of therapeutic agents with diverse biological properties including cytotoxic effects is xanthine derivatives which are collectively called xanthines (a group of alkaloids). Among many significant molecules based on the structure of the purine, there is a group of natural xanthines, involving theobromine, caffeine, and theophylline and analogues of xanthine display anti-cancer activity. Hence the present chapter wishes to concentrate the attention on the synthesis and anti-cancer activity of acridine and xanthine-based compounds brilliantly.

Direct benzylic C–H difluoroalkylation with difluoroenoxysilanes by transition metal-free photoredox catalysis

A visible light promoted direct benzylic C–H difluoroalkylation with difluoroenoxysilanes catalyzed by Na2-eosin Y via a HAT-ORPC pathway has been developed, providing an efficient and atom-economic method for production of α-benzyl-α,α-difluoroketones.

A practical route to arylated dihydroacridine derivatives via nickel boride mediated intramolecular reductive cyclization-concomitant dehydration

A facile and highly efficient route towards 3-aryl-1,2-dihydroacridine derivatives from an aldol adduct of o-nitrobenzaldehyde and cyclohexenone derivatives has been described.

Studies Directed towards the Synthesis of the Acridone Family of Natural Products: Total Synthesis of Acronycines and Atalaphyllidines

A modular and flexible three-step synthetic strategy has been developed for the synthesis of acridone natural products of biological significance. The tetracyclic core of acridone derivatives has been achieved efficiently in high yield from commercially available anthranilic acid and phenol derivatives via condensation reaction, followed by regioselective annulation. Acridone alkaloids acronycine and noracronycine are synthesized in improved overall yields in fewer steps than the previously reported approaches. The method has further been used for the synthesis of atalaphyllidine and 5-hydroxynoracronycine in excellent yields for the first time. Moreover, the synthetic utility of the present strategy has been showcased by the synthesis of oxa and thia analogues of acronycine alkaloid.

Access to acridones by tandem copper(I)-catalyzed electrophilic amination/Ag(I)-mediated oxidative annulation of anthranils with arylboronic acids

An efficient and practical approach for the synthesis of medicinally important acridones was developed from anthranils and commercially available arylboronic acids by a tandem copper(I)-catalyzed electrophilic amination/Ag(I)-mediated oxidative annulation strategy. This new and straightforward protocol displayed a broad substrate scope (25 examples) and high functional group tolerance. What's more, a possible mechanistic proposal was also presented.

Mitochondria-targeted acridine-based dual-channel fluorescence chemosensor for detection of Sn4+ and Cr2O72- ions in water and its application in discriminative detection of cancer cells

The goal of the present work was to fabricate a new low-cost, easy-to-prepare, dual-channel fluorescence chemosensor comprised of acridine-diphenylacetyl moieties (NDA) to enable remarkable Sn⁴⁺ detection in water and biological medium. The resulting NDA-Sn⁴⁺ complex was utilized for the distinguished identification of Cr₂O₇^2- ions from other anions and biomolecules. These investigations involve the absorption, fluorescence, and electrochemical methods for the detection of Sn⁴⁺ and Cr₂O₇^2- ions in pure water. The mechanism for NDA-mediated Sn⁴⁺ detection was experimentally determined by FT-IR, NMR titrations, mass (ESI) analyses, and DFT calculations. The obtained results indicate that the NDA chemosensor possessed excellent performance characteristics including good water solubility and compatibility, quick response time (less than 10 s), high sensitivity (Sn⁴⁺ = 0.268 μM and Cr₂O₇^2- = 0.160 μM), and selectivity against coexisting metals, anions, amino acids, and peptides. The chemosensor NDA induced negligible toxicity in live cells and was successfully utilized as a biomarker for the tracking of Sn⁴⁺ in human normal and cancer cells. More importantly, NDA demonstrates distinguished recognition of Sn⁴⁺ in human cancer cells rather than in normal live cells. Additionally, NDA was shown to act as a mitochondria-targeted probe in FaDu cells.

Synthesis of Novel Biologically Active Proflavine Ureas Designed on the Basis of Predicted Entropy Changes

A novel series of proflavine ureas, derivatives 11a–11i, were synthesized on the basis of molecular modeling design studies. The structure of the novel ureas was obtained from the pharmacological model, the parameters of which were determined from studies of the structure-activity relationship of previously prepared proflavine ureas bearing n-alkyl chains. The lipophilicity (LogP) and the changes in the standard entropy (ΔS°) of the urea models, the input parameters of the pharmacological model, were determined using quantum mechanics and cheminformatics. The anticancer activity of the synthesized derivatives was evaluated against NCI-60 human cancer cell lines. The urea derivatives azepyl 11b, phenyl 11c and phenylethyl 11f displayed the highest levels of anticancer activity, although the results were only a slight improvement over the hexyl urea, derivative 11j, which was reported in a previous publication. Several of the novel urea derivatives displayed GI₅₀ values against the HCT-116 cancer cell line, which suggest the cytostatic effect of the compounds azepyl 11b–0.44 μM, phenyl 11c–0.23 μM, phenylethyl 11f–0.35 μM and hexyl 11j–0.36 μM. In contrast, the novel urea derivatives 11b, 11c and 11f exhibited levels of cytotoxicity three orders of magnitude lower than that of hexyl urea 11j or amsacrine.

Room Temperature Phosphorescence vs Triplet-Triplet Annihilation in N-Substituted Acridone Solids

Organic room temperature phosphorescent (ORTP) compounds have recently emerged as a promising class of emissive materials with a multitude of potential applications. However, the number of building blocks that give rise to efficient ORTP materials is still limited, and the rules for engineering phosphorescent properties in organic solids are not well understood. Here, we report ORTP in a series of N-substituted acridone derivatives with electron-donating, electron-withdrawing, and sterically bulky substituents. X-ray crystallography shows that the solid-state packing varies progressively between coparallel and antiparallel π-stacking and separated π-dimers, depending on the size of the substituent. The detailed photophysical studies supported by DFT calculations reveal complex dynamics of singlet and triplet excited states, depending on the electronic effects of substituents and solid-state packing. The programmable molecular packing provides a lever to control the triplet-triplet annihilation that is manifested as delayed fluorescence in acridone derivatives with continuous (both parallel and antiparallel) π-stacking.

Microwave-assisted multicomponent reactions in heterocyclic chemistry and mechanistic aspects

Microwave-assisted (MWA) multicomponent reactions (MCRs) have successfully emerged as one of the useful tools in the synthesis of biologically relevant heterocycles. These reactions are strategically employed for the generation of a variety of heterocycles along with multiple point diversifications. Over the last few decades classical MCRs such as Ugi, Biginelli, etc. have witnessed enhanced yield and efficiency with microwave assistance. The highlights of MWA-MCRs are high yields, reduced reaction time, selectivity, atom economy and simpler purification techniques, such an approach can accelerate the drug discovery process. The present review focuses on the recent advances in MWA-MCRs and their mechanistic insights over the past decade and shed light on its advantage over the conventional approach.