Recent Advances in the Chemistry of Acridines

Experiments and Calculation on New N,N-bis-Tetrahydroacridines

Tetrahydroacridines arouse particular interest due to the potential possibilities of application in the medical field and protection against corrosion. Bis-tetrahydroacridines were newly synthesized by Pfitzinger condensation of 5,5'-(ethane-1,2-diyl) diindoline-2,3-dione with several cyclanones. NMR, MS, and FT-IR were used to prove their molecular structure. In addition, a computer-aided study was performed for the lowest energy conformers of each structure, in vacuum conditions, at ground state using DFT models to assess their electronic properties. UV-Vis and voltammetric methods (cyclic voltammetry, differential pulse voltammetry, and rotating disk electrode voltammetry) were used to investigate their optical and electrochemical properties. The results obtained for these π-conjugated heteroaromatic compounds lead to the conclusion that they have real potential in applications in different fields such as pharmaceuticals and especially as corrosion inhibitors.

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.

Research status and prospects of organic photocatalysts in algal inhibition and sterilization: a review

An increasing amount of sewage has been discharged into water bodies in the progression of industrialization and urbanization, causing serious water pollution. Meanwhile, the increase of nutrients in the water induces water eutrophication and rapid growth of algae. Photocatalysis is a common technique for algal inhibition and sterilization. To improve the utilization of visible light and the conversion efficiency of solar energy, more organic photocatalytic materials have been gradually developed. In addition to ultraviolet light, partial infrared light and visible light could also be used by organic photocatalysts compared with inorganic photocatalysts. Simultaneously, organic photocatalysts also exhibit favorable stability. Most organic photocatalysts can maintain a high degradation rate for algae and bacteria after several cycles. There are various organic semiconductors, mainly including small organic molecules, such as perylene diimide (PDI), porphyrin (TCPP), and new carbon materials (fullerene (C60), graphene (GO), and carbon nanotubes (CNT)), and large organic polymers, such as graphite phase carbon nitride (g-C3N4), polypyrrole (PPy), polythiophene (PTH), polyaniline (PANI), and polyimide (PI). In this review, the classification and synthesis methods of organic photocatalytic materials were elucidated. It was demonstrated that the full visible spectral response (400-750 nm) could be stimulated by modifying organic photocatalysts. Moreover, some problems were summarized based on the research status related to algae and bacteria, and corresponding suggestions were also provided for the development of organic photocatalytic materials.

Scaffold repositioning of spiro-acridine derivatives as fungi chitinase inhibitor by target fishing and in vitro studies

The concept of "one target, one drug, one disease" is not always true, as compounds with previously described therapeutic applications can be useful to treat other maladies. For example, acridine derivatives have several potential therapeutic applications. In this way, identifying new potential targets for available drugs is crucial for the rational management of diseases. Computational methodologies are interesting tools in this field, as they use rational and direct methods. Thus, this study focused on identifying other rational targets for acridine derivatives by employing inverse virtual screening (IVS). This analysis revealed that chitinase enzymes can be potential targets for these compounds. Subsequently, we coupled molecular docking consensus analysis to screen the best chitinase inhibitor among acridine derivatives. We observed that 3 compounds displayed potential enhanced activity as fungal chitinase inhibitors, showing that compound 5 is the most active molecule, with an IC50 of 0.6 ng/µL. In addition, this compound demonstrated a good interaction with the active site of chitinases from Aspergillus fumigatus and Trichoderma harzianum. Additionally, molecular dynamics and free energy demonstrated complex stability for compound 5. Therefore, this study recommends IVS as a powerful tool for drug development. The potential applications are highlighted as this is the first report of spiro-acridine derivatives acting as chitinase inhibitors that can be potentially used as antifungal and antibacterial candidates.

Photoredox-Catalyzed Cascade sp2 C-H Bond Functionalization to Construct Substituted Acridine with Diarylamine and Hypervalent Iodine(III) Reagents

A photocatalyzed cascade double C-C formation via sp² C-H bond activation of diarylamines with hypervalent iodine diazo reagents was developed. A variety of diarylamines and hypervalent iodine(III) reagents were tolerated well, and a range of substituted acridines with yields ranging from moderate to excellent was provided efficiently. The protocol introduces diazo groups onto diarylamines and enables subsequent late-stage assembly point functionalization with the diazonium structure, forming two new C-C bonds in a sequential fashion.

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.

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.

Synthesis and investigation on optical and electrochemical properties of 2,4-diaryl-9-chloro-5,6,7,8-tetrahydroacridines

A facile synthesis of 2,4-diaryl-9-chloro-5,6,7,8-tetrahydroacridine derivatives is reported which is based on POCl₃-mediated cyclodehydration followed by double Suzuki-Miyaura cross-coupling. The absorption and fluorescence properties of the obtained products were investigated and their HOMO/LUMO energy levels were estimated by cyclic voltammetry measurements. Besides, density functional theory calculations were carried out for further exploration of their electronic properties.

Vinyldiazo Compounds as 3-Carbon Radical Acceptors: Synthesis of 4-Fluoroacridines via Visible-Light-Promoted Cascade Radical Cyclization

Vinyldiazo reagents were developed as the radical acceptors in a visible-light-promoted sequential radical cyclization reaction, providing a mechanistically distinct pathway to achieve (3 + 3) cyclization. Using N-aryl chlorodifluoromethyl alkynyl ketoimines as the radical precursors, the reaction allows the introduction of a fluorine atom to the acridine skeleton during the construction of both the pyridine and benzene motifs from acyclic building blocks. The resulting 4-fluoroacridines exhibited pronounced fluorescent properties in the solid state.

Aza-aromatic polycycles based on triphenylene and acridine or acridone: synthesis and properties

Our attempts to N-arylate anilines with 2-iodotriphenylene and then cyclize with the adjacent carbonyl group are reported.

Sustainable Access to Acridin-9-(10H)ones with an Embedded m-Terphenyl Moiety Based on a Three-Component Reaction

A Ce(IV)-catalyzed three-component reaction between chalcones, anilines and β-ketoesters followed by a microwave-assisted thermal cyclization afforded 1,3-diaryl-1,2-dihydroacridin-9(10H)-ones. Their microwave irradiation in nitrobenzene, acting both as solvent and oxidant, afforded fully unsaturated 1,3-diarylacridin-9(10H)-ones, which combine acridin-9-(10H)one and m-terphenyl moieties. Overall, the route generates three C-C and one C-N bond and has the advantage of requiring a single chromatographic separation.

Acid-promoted synthesis and photophysical properties of substituted acridine derivatives

A simple and efficient synthetic protocol for the preparation of acridinium esters and amides through the cyclization and esterification or amidation of isatins with alcohols or amines as nucleophiles in the presence of CF3SO3H is established. A series of polycyclic acridine derivatives bearing large π-conjugated systems were obtained in high yields, including some key intermediates for the synthesis of biologically active molecules. The photophysical properties of these synthesized acridines were investigated, demonstrating that the sulfur heterocyclic acridine 9w was obtained in a high quantum yield.

Synthesis of acridone derivatives via heterologous expression of a plant type III polyketide synthase in Escherichia coli

BACKGROUND

Acridone alkaloids are heterocyclic compounds that exhibit a broad-range of pharmaceutical and chemotherapeutic activities, including anticancer, antiviral, anti-inflammatory, antimalarial, and antimicrobial effects. Certain plant species such as Citrus microcarpa, Ruta graveolens, and Toddaliopsis bremekampii synthesize acridone alkaloids from anthranilate and malonyl-CoA.

RESULTS

We synthesized two acridones in Escherichia coli. Acridone synthase (ACS) and anthraniloyl-CoA ligase genes were transformed into E. coli, and the synthesis of acridone was examined. To increase the levels of endogenous anthranilate, we tested several constructs expressing proteins involved in the shikimate pathway and selected the best construct. To boost the supply of malonyl-CoA, genes coding for acetyl-coenzyme A carboxylase (ACC) from Photorhabdus luminescens were overexpressed in E. coli. For the synthesis of 1,3-dihydroxy-10-methylacridone, we utilized an N-methyltransferase gene (NMT) to supply N-methylanthranilate and a new N-methylanthraniloyl-CoA ligase. After selecting the best combination of genes, approximately 17.3 mg/L of 1,3-dihydroxy-9(10H)-acridone (DHA) and 26.0 mg/L of 1,3-dihydroxy-10-methylacridone (NMA) were synthesized.

CONCLUSIONS

Two bioactive acridone derivatives were synthesized by expressing type III plant polyketide synthases and other genes in E. coli, which increased the supplement of substrates. This study showed that is possible to synthesize diverse polyketides in E. coli using plant polyketide synthases.

Organophosphorus chemistry based on elemental phosphorus: advances and horizons

The results of studies on the application of elemental phosphorus for the synthesis of important organophosphorus compounds are surveyed and summarized. Currently, this trend represents a synthetically, environmentally and technologically attractive alternative to classical organophosphorus chemistry based on toxic and corrosive phosphorus chlorides. Direct phosphination and phosphinylation of organic compounds with elemental phosphorus (discussed in the first part of the review) basically extend the range of available phosphines, phosphine chalcogenides and phosphinic acids and provides further development of their synthetic potential (discussed in the second part of the review). It is shown that the breakthrough in this area is largely due to the discovery of reactions of elemental phosphorus (white and red) with various electrophiles in superbasic suspensions and emulsions derived from alkali metal hydroxides and to the development of electrochemical, electrocatalytic and catalytic activation of white phosphorus.

The bibliography includes 299 references.

Alkene Synthesis by Photocatalytic Chemoenzymatically Compatible Dehydrodecarboxylation of Carboxylic Acids and Biomass

Direct conversion of renewable biomass and bioderived chemicals to valuable synthetic intermediates for organic synthesis and materials science applications by means of mild and chemoselective catalytic methods has largely remained elusive. Development of artificial catalytic systems that are compatible with enzymatic reactions provides a synergistic solution to this enduring challenge by leveraging previously unachievable reactivity and selectivity modes. We report herein a dual catalytic dehydrodecarboxylation reaction that is enabled by a crossover of the photoinduced acridine-catalyzed O-H hydrogen atom transfer (HAT) and cobaloxime-catalyzed C-H-HAT processes. The reaction produces a variety of alkenes from readily available carboxylic acids. The reaction can be embedded in a scalable triple-catalytic cooperative chemoenzymatic lipase-acridine-cobaloxime process that allows for direct conversion of plant oils and biomass to long-chain terminal alkenes, precursors to bioderived polymers.

High-Performance N-Type Carbon Nanotube Composites: Improved Power Factor by Optimizing the Acridine Scaffold and Tailoring the Side Chains

Single-walled carbon nanotubes (SWCNTs)/organic small molecules (OSMs) are promising candidates for application in thermoelectric (TE) modules; however, the development of n-type SWCNT/OSMs with high performance is lagging behind. Only a few structure-activity relationships of OSMs on SWCNT composites have been reported. Recently, we find that the n-type acridone/SWCNT composites display high power factor (PF) values at high temperature but suffer from low PFs at room temperature. Here, the performance of SWCNT composites containing an acridine derivative (AD) as well as its analogues with different counterions (Cl^-, SO₄^2- and F^-) and lengths of alkyl chains (ADLA1-2 and ADLA4-5) is reported. Among the composites, SWCNT/ADLA4 with no counterions exhibits the highest PF value of 195.2 μW m^-1 K^-2 at room temperature, which is 4.9 times higher than that of SWCNT/ADTAd (39.8 μW m^-1 K^-2), indicating that the acridine scaffold and the lengths of alkyl chains contribute to the dramatic changes in the TE performance. In addition, SWCNT/ADLA4 exhibits high PF values at all the temperatures we investigate, which range from 154.7 to 230.7 μW m^-1 K^-2. Furthermore, a TE device consisting of five pairs of p (the pristine SWCNTs)-n (SWCNT/ADLA4) junctions is assembled, generating a relatively high open-circuit voltage (41.7 mV) and an output power of 1.88 μW at a temperature difference of 74.8 K. Our results suggest that structural modifications might be an effective way to advance the development of TE materials.

Synergistic Catalysis: Highly Enantioselective Cascade Reaction for the Synthesis of Dihydroacridines

The first stereoselective synthesis of dihydroacridines through synergistic catalysis, achieving the final target compounds with good to excellent yields and good to excellent enantioselectivities and diastereoselectivities, is reported. The synergistic approach consists in the activation of substituted quinolines with a Lewis acid catalyst that react in a cascade fashion with activated enals in the iminium form. Mechanistic calculations support a consecutive Michael-aldol reaction, followed by dehydration.

Cationic and Betaine-Type Boronated Acridinium Dyes: Synthesis, Characterization, and Photocatalytic Activity

A series of isomeric boronated acridinium dyes were obtained by reactions of 10-(4'-octyloxyphenyl) functionalized 9(10H)-acridanone derivative with lithiated phenylboronic azaesters followed by aromatization with perchloric acid. The effect of the position of boronic group attached at ortho, meta, and para positions of the 9-phenyl ring on the photophysical properties was investigated. Conversion to related betaine trifluoroborato-substituted compounds was successfully performed, and the effect of this structural change on UV-vis absorption and fluorescence spectroscopy characteristics was established. Furthermore, cyclic voltammetry studies revealed that electrochemical behavior of cationic versus betaine structures is different in terms of redox potential values as well as stability. The theoretical calculations revealed a different scheme for molecular excitation processes in B(OH)₂ versus BF₃ ^--substituted compounds as charge transfer to acridinium core is observed from N-aryl or B-aryl moiety, respectively. Obtained compounds were active as photocatalysts in selected visible-light-promoted addition reactions to unsaturated substrates.

A novel acridine derivative, LS-1-10 inhibits autophagic degradation and triggers apoptosis in colon cancer cells

Autophagy promotes cancer cell survival and drug resistance by degrading harmful cellular components and maintaining cellular energy levels. Disruption of autophagy may be a promising approach to sensitize cancer cells to anticancer drugs. The combination of autophagic inhibitors, such as chloroquine (CQ) and lucanthone with conventional cancer therapeutics has been investigated in clinical trials, but adverse drug-drug interactions are a high possibility. Here we designed and synthesized a novel, small-molecule library based on an acridine skeleton and the CQ structure with various modifications and substitutions and screened the compounds for effective autophagy inhibition. We found that 9-chloro-2-(3-(dimethylamino)propyl)pyrrolo[2,3,4-kl]acridin-1(2H)-one (LS-1-10) was the most effective from our library at inhibiting autophagic-mediated degradation and could decrease the viability of multiple colon cancer cells. In addition, LS-1-10 induced DNA damage and caspase 8-mediated apoptosis. Overall, this small molecule was more efficient at reducing the viability of cancer cells than other conventional chemotherapeutic agents, such as CQ and amsacrine. The anticancer and autophagy-inhibiting activities of LS-1-10 were confirmed in vivo in a xenograft mouse model. Collectively, this study has identified a new and efficient single compound with both autophagy-inhibiting and anticancer activity, which may provide a novel approach for cancer therapy.

Aromatization of 9,10-Dihydroacridine Derivatives: Discovering a Highly Selective and Rapid-Responding Fluorescent Probe for Peroxynitrite

As part of an effort to develop generally applicable strategies for creating probes suitable for detecting important molecular and ionic species, the oxidative aromatization of nonfluorescent 9,10-dihydroacridine derivatives triggered by peroxynitrite (ONOO^-) led to the identification of compound 2H, 9-phenyl-9,10-dihydroacridine-4-carboxylic acid, as a rapid-responding fluorescent probe capable of detecting ONOO^- with an extraordinary selectivity. Adding a little more than 1 equiv of ONOO^- to a solution of 2H resulted in over 100-fold fluorescence enhancement. In sharp contrast, treating 2H with excessive amounts of other oxidants that often interfere with the detection of ONOO^- failed to lead to noticeable fluorescence increase. The reaction of ONOO^- with 2H shows a similar efficiency in the pH range of 2-8. Low cytotoxicity was observed for 2H and its aromatized product. Bioimaging experiments revealed the promising potential of 2H as a new fluorescent probe for the selective detection of intracellular ONOO^-.

A new acridine derivative induces cell cycle arrest and antiangiogenic effect on Ehrlich ascites carcinoma model

BACKGROUND

Acridine derivatives, including amsacrine, have antitumor activity. However, side effects, development of resistance and their low bioavailability, have limited their use. Herein, we described the synthesis, and evaluated the toxicity and antitumor activity of a new amsacrine analogous, the N'-(2-chloro-6-methoxy-acridin-9-yl)-2-cyano-3-(4-dimethylaminophenyl)-acrilohidrazida (ACS-AZ10).

METHODS

The compound was obtained in a linear pathway where the ASC-Az intermediate was obtained by coupling of 6,9-dichloro-3-methoxy-acridine and 2-ciany-acethohidrazide followed by condensation with the corresponding aldehyde. The toxicity of ACS-AZ10 was evaluated in mice using acute toxicity and micronucleus assays. Ehrlich ascites carcinoma model was used to investigate the antitumor activity and toxicity of ACS-AZ10 (7.5, 15 or 30mg/kg, i.p.), after nine days of treatment. Cell cycle and angiogenesis were also evaluated.

RESULTS

The ASC-AZ10 was obtained with satisfactory yields and its structure was confirmed by spectroscopic and spectrometric techniques. On acute toxicity study, ACS-AZ10 (2000mg/kg, i.p.) induced transient depressant effects on central nervous system. The LD₅₀ was approximately 2500mg/kg. ACS-AZ10 (15 or 30mg/kg) displayed significant antitumor activity considering the tumor weight and volume, cell viability, and total Ehrlich cell count. ACS-AZ10 (7.5mg/kg) induced an increase in sub-G1 peak, suggesting apoptosis. At 15mg/kg ACS-AZ10 induced cell cycle arrest in G2/M phase and a reduction in the percentage of cells in G0/G1 and S phases, suggesting a pre-mitotic blockade. ACS-AZ10 reduced the microvessel density, indicating an antiangiogenic effect. Weak hematological, biochemical and histopathological toxicity were observed. The compound doesn't show genotoxicity in micronucleus assay.

CONCLUSIONS

ACS-AZ10 has potent antitumor activity in vivo along with low toxicity.

A Cu-Catalysed Radical Cross-Dehydrogenative Coupling Approach to Acridanes and Related Heterocycles

The synthesis of acridanes and related compounds through a Cu-catalysed radical cross-dehydrogenative coupling of simple 2-[2-(arylamino)aryl]malonates is reported. This method can be further streamlined to a one-pot protocol involving the in situ fomation of the 2-[2-(arylamino)aryl]malonate by α-arylation of diethyl malonate with 2-bromodiarylamines under Pd catalysis, followed by Cu-catalysed cyclisation.