Bioactive pyrrole-based compounds with target selectivity

Zr-Catalyzed Synthesis of Tetrasubstituted 1,3-Diacylpyrroles from N-Acyl α-Aminoaldehydes and 1,3-Dicarbonyls

A Zr-catalyzed synthesis of tetrasubstituted 1,3-diacylpyrroles is reported that employs the direct use of N-acyl α-aminoaldehydes with 1,3-dicarbonyl compounds. The products were formed in up to 88% yield and shown to be hydrolytically and configurationally stable under the reaction conditions (THF/1,4-dioxane and H₂O). The N-acyl α-aminoaldehydes were readily prepared from the corresponding α-amino acids. The reaction tolerates a wide array of substrate types including alkyl-, aryl-, heteroaryl-, and heteroatom-containing groups on the aminoaldehyde side chain. A variety of 1,3-dicarbonyls proved amenable to the reaction along with an aldehyde derived from a l,l-dipeptide, an aldehyde generated in situ, and an N-acylated glucosamine.

Cytotoxic and immunomodulatory potential of a novel [2-(4-(2,5-dimethyl-1H-pyrrol-1-yl)-1H-pyrazol-3-yl)pyridine] in myeloid leukemia

Cancer ranks among the leading causes of mortality worldwide. However, the efficacy of commercially available anticancer drugs is compromised by the emerging challenge of drug resistance. This study aimed to investigate the anticancer and immunomodulatory potential of a recently developed a novel [2-(4-(2,5-dimethyl-1 H-pyrrol-1-yl)- 1 H-pyrazol-3-yl) pyridine]. The cytotoxic potential of the compound was assessed using the MTT assay on both cancerous HL60 (acute myeloid leukemia) and K562 (chronic myeloid leukemia) cell lines, as well as non-cancerous Vero cells and human peripheral blood mononuclear cells (PBMCs). A clonogenic assay was employed to evaluate the anticancer efficacy of the compound, while flow cytometry was utilized to investigate its effect on cell cycle arrest. Furthermore, the immunomodulatory potential of the compound was assessed by quantifying inflammatory and anti-inflammatory biomarkers in the supernatant of PBMCs previously treated with the compound. Our study revealed that the novel pyridine ensemble exhibits selective cytotoxicity against HL60 (IC₅₀ = 25.93 µg/mL) and K562 (IC₅₀ = 10.42 µg/mL) cell lines, while displaying no significant cytotoxic effect on non-cancerous cells. In addition, the compound induced a decrease of 18% and 19% in the overall activity of COX-1 and COX-2, respectively. Concurrently, it upregulated the expression of cytokines including IL4, IL6, IL10, and IL12/23p40, while downregulating INFγ expression. These findings suggest that the compound has the potential to serve as a promising candidate for the treatment of acute and chronic myeloid leukemias due to its effective antiproliferative and immunomodulatory activities, without causing cytotoxicity in non-cancerous cells.

Hydrazone-Tethered 5-(Pyridin-4-yl)-4H-1,2,4-triazole-3-thiol Hybrids: Synthesis, Characterisation, in silico ADME Studies, and in vitro Antimycobacterial Evaluation and Cytotoxicity

Compounds containing arylpyrrole-, 1,2,4-triazole- and hydrazone structural frameworks have been widely studied and demonstrated to exhibit a wide range of pharmacological properties. Herein, an exploratory series of new 1,2,4-triazole derivatives designed by amalgamation of arylpyrrole and 1,2,4-triazole structural units via a hydrazone linkage is reported. The synthesised compounds were tested in vitro for their potential activity against Mycobacterium tuberculosis (MTB) H₃₇ Rv strain. The most promising compound 13 - the derivative without the benzene ring appended to the pyrrole unit displayed acceptable activity (MIC₉₀ =3.99 μM) against MTB H₃₇ Rv, while other compounds from the series exhibited modest to weak antimycobacterial activity with MIC₉₀ values in the range between 7.0 and >125 μM. Furthermore, in silico results, predicated using the SwissADME web tool, show that the prepared compounds display desirable ADME profile with parameters within acceptable range.

Compilation of the Antimicrobial Compounds Produced by Burkholderia Sensu Stricto

Due to the increase in multidrug-resistant microorganisms, the investigation of novel or more efficient antimicrobial compounds is essential. The World Health Organization issued a list of priority multidrug-resistant bacteria whose eradication will require new antibiotics. Among them, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacteriaceae are in the "critical" (most urgent) category. As a result, major investigations are ongoing worldwide to discover new antimicrobial compounds. Burkholderia, specifically Burkholderia sensu stricto, is recognized as an antimicrobial-producing group of species. Highly dissimilar compounds are among the molecules produced by this genus, such as those that are unique to a particular strain (like compound CF66I produced by Burkholderia cepacia CF-66) or antimicrobials found in a number of species, e.g., phenazines or ornibactins. The compounds produced by Burkholderia include N-containing heterocycles, volatile organic compounds, polyenes, polyynes, siderophores, macrolides, bacteriocins, quinolones, and other not classified antimicrobials. Some of them might be candidates not only for antimicrobials for both bacteria and fungi, but also as anticancer or antitumor agents. Therefore, in this review, the wide range of antimicrobial compounds produced by Burkholderia is explored, focusing especially on those compounds that were tested in vitro for antimicrobial activity. In addition, information was gathered regarding novel compounds discovered by genome-guided approaches.

1,3 Dipolar Cycloaddition of Münchnones: Factors behind the Regioselectivity

The 1,3 dipolar cycloaddition reactions of münchnones and alkenes provide an expedite synthetic way to substituted pyrroles, an exceedingly important structural motif in the pharmaceutical and material science fields of research. The factors governing their regioselectivity rationalization are not well understood. Using several approaches, we investigate a set of 14 reactions (featuring two münchnones, 12 different alkenes, and two alkynes). The Natural Bond Theory and the Non-Covalent Interaction Index analyses of the noncovalent interaction energies fail to predict the experimental major regioisomer. Employing global cDFT descriptors or local ones such as the Fukui function and dual descriptor yields similarly inaccurate predictions. Only the local softness pairing, within Pearson's Hard and Soft Acids and Bases principle, constitutes a reliable predictor for the major reaction product. By taking into account an estimator for the steric effects, the correct regioisomer is predicted. Steric effects play a major role in driving the regioselectivity, as was corroborated by energy decomposition analysis of the transition states.

Recent Progress in Cyclic Aryliodonium Chemistry: Syntheses and Applications

Hypervalent aryliodoumiums are intensively investigated as arylating agents. They are excellent surrogates to aryl halides, and moreover they exhibit better reactivity, which allows the corresponding arylation reactions to be performed under mild conditions. In the past decades, acyclic aryliodoniums are widely explored as arylation agents. However, the unmet need for acyclic aryliodoniums is the improvement of their notoriously low reaction economy because the coproduced aryl iodides during the arylation are often wasted. Cyclic aryliodoniums have their intrinsic advantage in terms of reaction economy, and they have started to receive considerable attention due to their valuable synthetic applications to initiate cascade reactions, which can enable the construction of complex structures, including polycycles with potential pharmaceutical and functional properties. Here, we are summarizing the recent advances made in the research field of cyclic aryliodoniums, including the nascent design of aryliodonium species and their synthetic applications. First, the general preparation of typical diphenyl iodoniums is described, followed by the construction of heterocyclic iodoniums and monoaryl iodoniums. Then, the initiated arylations coupled with subsequent domino reactions are summarized to construct polycycles. Meanwhile, the advances in cyclic aryliodoniums for building biaryls including axial atropisomers are discussed in a systematic manner. Finally, a very recent advance of cyclic aryliodoniums employed as halogen-bonding organocatalysts is described.

One-Pot Synthesis of Unprotected 2-Acylpyrroles from 1,2,3-Triazoles and 2-Hydroxymethylallyl Carbonates

An efficient, tandem one-pot approach to synthesize multisubstituted 2-acylpyrroles from readily prepared N-tosyl triazoles and 2-hydroxymethylallyl carbonates is reported. The reaction proceeds via Rh(II)-catalyzed O-H insertion, [3,3]-sigmatropic rearrangement, Pd(0)-catalyzed oxidative addition, intramolecular cyclization, DBU-promoted E1cB elimination, double bond isomerization, and aromatization, enabling the disconnection and formation of multiple bonds in one reactor. The approach represents a highly regioselective way to access di-, tri-, and tetra-substituted NH pyrroles with high efficiency.

Modular Synthesis of Highly Substituted 3-Azapyrroles by Rh(II)-Catalyzed N-H Bond Insertion and Cyclodehydration

A modular synthesis of highly substituted 3-azapyrroles has been developed using a three-step sequence comprising copper-catalyzed alkyne-azide cycloaddition (CuAAC), N-H bond insertion, and cyclodehydration. 1-Sulfonyl-1,2,3-triazoles (1-STs) can be accessed from common alkyne and sulfonyl azide building blocks by CuAAC using CuTC. Rhodium(II)-acetate-promoted 1-ST denitrogenation results in highly electrophilic rhodium azavinyl carbenes that, here, underwent insertion into the N-H bond of secondary α-aminoketones to form 1,2-aminoalkenes. These products were cyclized and dehydrated using BF₃·OEt₂ into highly substituted 3-azapyrroles. The three steps (CuAAC, N-H bond insertion, and cyclodehydration) could be telescoped into a one-pot process. The method proved to be highly efficient and tolerated a wide range of substituents.

Substituent-Dependent Divergent Synthesis of 2-(3-Amino-2,4-dicyanophenyl)pyrroles, Pyrrolyldienols and 3-Amino-1-acylethylidene-2-cyanopyrrolizines via Reaction of Acylethynylpyrroles with Malononitrile

An efficient method for the synthesis of pharmaceutically and high-tech prospective 2-(3-amino-2,4-dicyanophenyl)pyrroles (in up to 88% yield) via the reaction of easily available substituted acylethynylpyrroles with malononitrile has been developed. The reaction proceeds in the KOH/MeCN system at 0 °C for 2 h. In the case of 2-acylethynylpyrroles without substituents in the pyrrole ring, the reaction changes direction: instead of the target 2-(3-amino-2,4-dicyanophenyl)pyrroles, the unexpected formation of pyrrolyldienols and products of their intramolecular cyclization, 3-amino-1-acylethylidene-2-cyanopyrrolizines, is observed.

Pyrrolidine derivatives as antibacterial agents, current status and future prospects: a patent review

Bacterial infections are increasingly epitomizing major global health concerns, with rising death rates. Since the most complete assessment of the worldwide impact of antimicrobial resistance to date, with over 1.2 million people dead in 2019 as a direct result of antibiotic-resistant bacterial infections. The majority of antimicrobial drugs have been associated with a multitude of adverse effects including financial costs as well. Pyrrolidine derivatives have sparked the interest of researchers to create novel synthetic molecules with minimal side effect and drawbacks. To close the research gap, the current review discusses the synthetic compounds with active pyrrolidine scaffolds, critical findings and most crucially the structure-activity relationship that affects the activity of the ring over the last one and half decade.

Bisphosphonylallenes as Suitable Scaffolds for Unprecedented 4,5-Diphosphonyldihydropyridazines and 3,4-Diphosphonylpyrroles Displaying Antimelanoma Activity

An efficient and simple approach has been developed for the synthesis of unprecedented 4,5-diphosphonyldihydropyridazines and 3,4-diphosphonylpyrroles, through the condensation of bisphosphonylallenes with hydrazines and primary amines, respectively. The reactions proceed under operationally simple, mild, and catalyst-free conditions, for a wide substrate scope. The synthesized compounds were screened for their antiproliferative activity against melanoma cancer cells, and they showed promising growth inhibition.

Coupled Natural Fusion Enzymes in a Novel Biocatalytic Cascade Convert Fatty Acids to Amines

Tambjamine YP1 is a pyrrole-containing natural product. Analysis of the enzymes encoded in the Pseudoalteromonas tunicata “tam” biosynthetic gene cluster (BGC) identified a unique di-domain biocatalyst (PtTamH). Sequence and bioinformatic analysis predicts that PtTamH comprises an N-terminal, pyridoxal 5′-phosphate (PLP)-dependent transaminase (TA) domain fused to a NADH-dependent C-terminal thioester reductase (TR) domain. Spectroscopic and chemical analysis revealed that the TA domain binds PLP, utilizes l-Glu as an amine donor, accepts a range of fatty aldehydes (C₇–C₁₄ with a preference for C₁₂), and produces the corresponding amines. The previously characterized PtTamA from the “tam” BGC is an ATP-dependent, di-domain enzyme comprising a class I adenylation domain fused to an acyl carrier protein (ACP). Since recombinant PtTamA catalyzes the activation and thioesterification of C₁₂ acid to the holo-ACP domain, we hypothesized that C₁₂ ACP is the natural substrate for PtTamH. PtTamA and PtTamH were successfully coupled together in a biocatalytic cascade that converts fatty acids (FAs) to amines in one pot. Moreover, a structural model of PtTamH provides insights into how the TA and TR domains are organized. This work not only characterizes the formation of the tambjamine YP1 tail but also suggests that PtTamA and PtTamH could be useful biocatalysts for FA to amine functional group conversion.

Therapeutic potential of pyrrole and pyrrolidine analogs: an update

The chemistry of nitrogen-containing heterocyclic compound pyrrole and pyrrolidine has been a versatile field of study for a long time for its diverse biological and medicinal importance. Biomolecules such as chlorophyll, hemoglobin, myoglobin, and cytochrome are naturally occurring metal complexes of pyrrole. These metal complexes play a vital role in a living system like photosynthesis, oxygen carrier, as well storage, and redox cycling reactions. Apart from this, many medicinal drugs are derived from either pyrrole, pyrrolidine, or by its fused analogs. This review mainly focuses on the therapeutic potential of pyrrole, pyrrolidine, and its fused analogs, more specifically anticancer, anti-inflammatory, antiviral, and antituberculosis. Further, this review summarizes more recent reports on the pyrrole, pyrrolidine analogs, and their biological potential.

Direct C-H Trifluoromethylation of (Hetero)Arenes in Water Enabled by Organic Photoredox-Active Amphiphilic Nanoparticles

Photoredox-catalyzed chemical conversions are predominantly operated in organic media to ensure good compatibility between substrates and catalysts. Yet, when conducted in aqueous media, they are an attractive, mild, and green way to introduce functional groups into organic molecules. We here show that trifluoromethyl groups can be readily installed into a broad range of organic compounds by using water as the reaction medium and light as the energy source. To bypass solubility obstacles, we developed robust water-soluble polymeric nanoparticles that accommodate reagents and photocatalysts within their hydrophobic interior under high local concentrations. By taking advantage of the high excited state reduction potential of N-phenylphenothiazine (PTH) through UV light illumination, the direct C-H trifluoromethylation of a wide array of small organic molecules is achieved selectively with high substrate conversion. Key to our approach is slowing down the production of CF3 radicals during the chemical process by reducing the catalyst loading as well as the light intensity, thereby improving effectiveness and selectivity of this aqueous photocatalytic method. Furthermore, the catalyst system shows excellent recyclability and can be fueled by sunlight. The method we propose here is versatile, widely applicable, energy efficient, and attractive for late-stage introduction of trifluoromethyl groups into biologically active molecules.

The Effect of 1,2,4-Triazole-3-thiol Derivatives Bearing Hydrazone Moiety on Cancer Cell Migration and Growth of Melanoma, Breast, and Pancreatic Cancer Spheroids

4-Phenyl-3-[2-(phenylamino)ethyl]-1H-1,2,4-triazole-5(4H)-thione was used as a starting compound for the synthesis of the corresponding 1,2,4-triazol-3-ylthioacetohydrazide, which reacts with isatins and various aldehydes bearing aromatic and heterocyclic moieties provided target hydrazones. Their cytotoxicity was tested by the MTT assay against human melanoma IGR39, human triple-negative breast cancer (MDA-MB-231), and pancreatic carcinoma (Panc-1) cell lines. The selectivity of compounds towards cancer cells was also studied. In general, the synthesized compounds were more cytotoxic against the melanoma cell line. N′-(2-oxoindolin-3-ylidene)-2-((4-phenyl-5-(2-(phenylamino)ethyl)-4H-1,2,4-triazol-3-yl)thio)acetohydrazide, N′-((1H-pyrrol-2-yl)methylene)-2-((4-phenyl-5-(2-(phenylamino)ethyl)-4H-1,2,4-triazol-3-yl)thio)acetohydrazide and N′-(2-hydroxy-5-nitrobenzylidene)-2-((4-phenyl-5-(2-(phenylamino)ethyl)-4H-1,2,4-triazol-3-yl)thio)acetohydrazide were identified as the most active among all synthesized compounds in 3D cell cultures. N′-(4-(dimethylamino)benzylidene)-2-((4-phenyl-5-(2-(phenylamino)ethyl)-4H-1,2,4-triazol-3-yl)thio)acetohydrazide inhibited all cancer cell migration, was characterized as relatively more selective towards cancer cells, and could be further tested as an antimetastatic candidate.

New Pyrrole Derivatives as Promising Biological Agents: Design, Synthesis, Characterization, In Silico, and Cytotoxicity Evaluation

The current study describes the synthesis, physicochemical characterization and cytotoxicity evaluation of a new series of pyrrole derivatives in order to identify new bioactive molecules. The new pyrroles were obtained by reaction of benzimidazolium bromide derivatives with asymmetrical acetylenes in 1,2-epoxybutane under reflux through the Huisgen [3 + 2] cycloaddition of several ylide intermediates to the corresponding dipolarophiles. The intermediates salts were obtained from corresponding benzimidazole with bromoacetonitrile. The structures of the newly synthesized compounds were confirmed by elemental analysis, spectral techniques (i.e., IR, 1H-NMR and 13C-NMR) and single-crystal X-ray analysis. The cytotoxicity of the synthesized compounds was evaluated on plant cells (i.e., Triticum aestivum L.) and animal cells using aquatic crustaceans (i.e., Artemia franciscana Kellogg and Daphnia magna Straus). The potential antitumor activity of several of the pyrrole derivatives was studied by performing in vitro cytotoxicity assays on human adenocarcinoma-derived cell lines (i.e., LoVo (colon), MCF-7 (breast), and SK-OV-3 (ovary)) and normal human umbilical vein endothelial cells (HUVECs). The obtained results of the cytotoxicity assessment indicated that the tested compounds had nontoxic activity on Triticum aestivum L., while on Artemia franciscana Kellogg nauplii, only compounds 2c and 4c had moderate toxicity. On Daphnia magna, 4b and 4c showed high toxicity; 2a, 2b, and 2c moderate to high toxicity; only 4a and 4d were nontoxic. The compound-mediated cytotoxicity assays showed that several pyrrole compounds demonstrated dose- and time-dependent cytotoxic activity against all tested tumor cell lines, the highest antitumor properties being achieved by 4a and its homologue 4d, especially against LoVo colon cells.

Synthesis and evaluation of novel almazole D analogs as anticancer agents

Novel almazole D-amide conjugates, esters, and N-alkylated analogs were synthesized and investigated for their anticancer activity against seven cancer cell lines. Among the series, compounds 5g and 5m showed significant anticancer activities against multiple cell lines with moderate selectivity indices. Compound 5g had IC₅₀ values of 5.86 ± 0.31, 9.94 ± 0.06, 12.74 ± 0.12, and 9.40 ± 0.03 μM against the B16-F10, DU145, HeLa, and LC-540 cell lines, respectively, while compound 5m showed IC₅₀ values of 6.35 ± 0.09, 9.17 ± 0.11, 9.00 ± 0.011, 19.65 ± 0.63, 8.13 ± 0.04, and 11.56 ± 0.01 μM against B16-F10, DU145, HeLa, HepG2, LC-540, and SK-BR-3 cells, respectively. Compared to almazole D, which only showed significant activity against B16-F10 cells (IC₅₀  = 9.05 ± 0.008 μM), the synthesized analogs showed improved anticancer activity against multiple cell lines. The kinase inhibition assay coupled with the docking studies revealed that epidermal growth factor receptor (EGFR) kinase inhibition via interaction with amino acid residue T790 on the EGFR is one of the possible mechanisms by which 5g exerts its anticancer potential. The ADMET prediction and drug-likeness of the analogs project the synthesized analogs as promising agents, which can be further developed for application in cancer therapy.

Recent advances in cascade reactions and their mechanistic insights: a concise strategy to synthesize complex natural products and organic scaffolds

The beauty of cascade reactions to bestow us with cumbersome organic scaffolds has made them a cutting-edge area of research. Although the planning of cascades may require intuition, their results can be highly impactful. The development of cascades to provide specific targeted molecules of an appropriate structural and stereochemical framework poses a significant challenge but can serve as one of the most impressive tools in organic synthesis. This review shares a broad interest in compiling cascade transformations towards the construction of polycyclic frameworks, induction of chirality/asymmetry in the protocol, etc. to solve diverse challenges in organic synthesis pursuits, as cascades enable the rapid and efficient construction of complex architectures from simple molecules. The studies highlighted herein manifest the utilization of a range of cascade reactions under various classifications for generating natural product skeletons such as palau'amine, benzosimuline, arcutinine, and others from simple building blocks, with emphasis on breakthroughs and potential for asymmetric synthesis. The exquisite synthetic designs of recently completed total synthesis of natural products with a focus on strategic concerns are also highlighted in this review.

Computational-Based Discovery of the Anti-Cancer Activities of Pyrrole-Based Compounds Targeting the Colchicine-Binding Site of Tubulin

Despite the tubulin-binding agents (TBAs) that are widely used in the clinic for cancer therapy, tumor resistance to TBAs (both inherited and acquired) significantly impairs their effectiveness, thereby decreasing overall survival (OS) and progression-free survival (PFS) rates, especially for the patients with metastatic, recurrent, and unresectable forms of the disease. Therefore, the development of novel effective drugs interfering with the microtubules' dynamic state remains a big challenge in current oncology. We report here about the novel ethyl 2-amino-1-(furan-2-carboxamido)-5-(2-aryl/tert-butyl-2-oxoethylidene)-4-oxo-4,5-dihydro-1H-pyrrole-3-carboxylates (EAPCs) exhibiting potent anti-cancer activities against the breast and lung cancer cell lines in vitro. This was due to their ability to inhibit tubulin polymerization and induce cell cycle arrest in M-phase. As an outcome, the EAPC-treated cancer cells exhibited a significant increase in apoptosis, which was evidenced by the expression of cleaved forms of PARP, caspase-3, and increased numbers of Annexin-V-positive cells. By using the in silico molecular modeling methods (e.g., induced-fit docking, binding metadynamics, and unbiased molecular dynamics), we found that EAPC-67 and -70 preferentially bind to the colchicine-binding site of tubulin. Lastly, we have shown that the EAPCs indicated above and colchicine utilizes a similar molecular mechanism to inhibit tubulin polymerization via targeting the T7 loop in the β-chain of tubulin, thereby preventing the conformational changes in the tubulin dimers required for their polymerization. Collectively, we identified the novel and potent TBAs that bind to the colchicine-binding site and disrupt the microtubule network. As a result of these events, the compounds induced a robust cell cycle arrest in M-phase and exhibited potent pro-apoptotic activities against the epithelial cancer cell lines in vitro.

Computational-Based Discovery of the Anti-Cancer Activities of Pyrrole-Based Compounds Targeting the Colchicine-Binding Site of Tubulin

Despite the tubulin-binding agents (TBAs) that are widely used in the clinic for cancer therapy, tumor resistance to TBAs (both inherited and acquired) significantly impairs their effectiveness, thereby decreasing overall survival (OS) and progression-free survival (PFS) rates, especially for the patients with metastatic, recurrent, and unresectable forms of the disease. Therefore, the development of novel effective drugs interfering with the microtubules' dynamic state remains a big challenge in current oncology. We report here about the novel ethyl 2-amino-1-(furan-2-carboxamido)-5-(2-aryl/tert-butyl-2-oxoethylidene)-4-oxo-4,5-dihydro-1H-pyrrole-3-carboxylates (EAPCs) exhibiting potent anti-cancer activities against the breast and lung cancer cell lines in vitro. This was due to their ability to inhibit tubulin polymerization and induce cell cycle arrest in M-phase. As an outcome, the EAPC-treated cancer cells exhibited a significant increase in apoptosis, which was evidenced by the expression of cleaved forms of PARP, caspase-3, and increased numbers of Annexin-V-positive cells. By using the in silico molecular modeling methods (e.g., induced-fit docking, binding metadynamics, and unbiased molecular dynamics), we found that EAPC-67 and -70 preferentially bind to the colchicine-binding site of tubulin. Lastly, we have shown that the EAPCs indicated above and colchicine utilizes a similar molecular mechanism to inhibit tubulin polymerization via targeting the T7 loop in the β-chain of tubulin, thereby preventing the conformational changes in the tubulin dimers required for their polymerization. Collectively, we identified the novel and potent TBAs that bind to the colchicine-binding site and disrupt the microtubule network. As a result of these events, the compounds induced a robust cell cycle arrest in M-phase and exhibited potent pro-apoptotic activities against the epithelial cancer cell lines in vitro.

Tandem construction of biological relevant aliphatic 5-membered N-heterocycles

Nature often uses cascade reactions in a highly stereocontrolled manner for assembly structurally diverse nitrogen-containing heterocyclic scaffolds, i.e. secondary metabolites, important for medicinal chemistry and pharmacy. Five-membered nitrogen-containing heterocycles as standalone rings, as well as spiro and polycyclic systems are pharmacophores of drugs approved in various therapies, i.a. antibacterial or antiviral, antifungal, anticancer, antidiabetic, as they target many key enzymes. Furthermore, a large number of pyrrolidine derivatives are currently considered as drug candidates. Cascade transformations, also known as domino or tandem reactions, offer straightforward methods to build N-heterocyclic libraries of the great structural variety desired for drawing SAR conclusions. The tandem transformations are often atom economic and time-saving because they are performed as the one-pot, so no need for purification after each 'virtual' step and the limited necessity of protective groups are characteristic for these processes. Thus, the same results as in classical multistep synthesis can be achieved at markedly lower costs and shorter time, which is in line with modern green chemistry rules. Great advantage of cascade reactions is often reflected in their high regio- and stereoselectivities, enabling the preparing of the heterocyclic compound better fitted to the expected target in cells. This review reveals the biological relevance of N-heterocyclic scaffolds based on saturated 5-membered rings since we showed a number of examples of approved drugs together with the recent biologically attractive leading structures of drug candidates. Next, novel cascade synthetic procedures, taking into account the structure of the reactants and reaction mechanisms, enabling to obtain biological-relevant heterocyclic frameworks with good yields and relatively high stereoselectivity, were reviewed and compared. The review covers the advances of designing biological active N-heterocycles mainly from 2018 to 2021, whereas the synthetic part is focused on the last 7 years.

Silver-Catalyzed Asymmetric Desymmetrization of Cyclohexadienones via Van Leusen Pyrrole Synthesis

A catalytic asymmetric desymmetrization of cyclohexadienones was accomplished via Van Leusen pyrrole synthesis in the presence of a chiral silver catalyst. The ready access to chiral-fused pyrrole derivatives is attributed to the identification of a suitable isocyanomethyl sulfone surrogate, NasMIC. The current Ag(I)-chiral phosphino-carboamide ligand system can be extended to the kinetic resolution of racemic cyclohexadienones, capitalizing on the differentiated reactivity of chiral quaternary complexes from AgSbF₆, chiral ligand (L*), cyclohexadienone, and NasMIC.

Lights on 2,5-diaryl tetrazoles: applications and limits of a versatile photoclick reaction

Recently, photoclick chemistry emerged as a powerful tool employed in several research fields, from medicinal chemistry and biology to material sciences. The growing interest in this type of chemical process is justified by the possibility to produce complex molecular systems using mild reaction conditions. However, the elevated spatio-temporal control offered by photoclick chemistry is highly intriguing, as it expands the range of applications. In this context, the light-triggered reaction of 2,5-diaryl tetrazoles with dipolarophiles emerged for its interesting features: excellent stability of the substrates, fast reaction kinetic, and the formation of a highly fluorescent product, fundamental for sensing applications. In the last years, 2,5-diaryl tetrazoles have been extensively employed, especially for bioorthogonal ligations, to label biomolecules and nucleic acids. In this review, we summarized recent applications of this interesting photoclick reaction, with a particular focus on biological fields. Moreover, we described the main limits that affect this system and current strategies proposed to overcome these issues. The general discussion here presented could prompt further optimization of the process and pave the way for the development of new original structures and innovative applications.

Graphical abstract

Synthesis of 3-Aroyl-4-heteroarylpyrrole Derivatives by the Van Leusen Method

The synthesis and structural diversification of N-heterocycles systems have attracted much attention because of their potential applications. Three 6-aryl-3-methyl-1-phenyl-1H-pyrazolo[3,4-b]pyridine-5-carbaldehyde 4 derivatives, in reaction with acetophenones 5, via conventional Claisen–Schmidt condensation reactions, generated the respective enones. The enones were used as electron-deficient olefins in a “formal” [2+3] cycloaddition reaction using p-tosylmethyl isocyanide—TosMIC 7. This protocol allows access to 3-(substituted aroyl)-4-heteroaryl pyrrole derivatives by the Van Leusen method.

Chiral Calcium Phosphate Catalyzed Enantioselective Synthesis of All-Carbon Quaternary Center by Friedel–Crafts Alkylation Reaction of Pyrroles and Trifluoromethylated Nitrostyrenes

A chiral calcium phosphate-catalyzed enantioselective Friedel–Crafts alkylation reaction of pyrroles and α-trifluoromethyl-β-nitrostyrenes has been developed. Pyrroles bearing an all-carbon quaternary center at 2-position were obtained with high to excellent enantioselectivity. Use of 4,7-dihydroindole as a nucleophile and subsequent oxidation resulted in the formation a 2-substituted indole derivative with excellent enantioselectivity. A 3,4-dihydropyrrolo[1,2-c]pyrimidine derivative was successfully synthesized by reduction followed by benzoylation of the product without loss of enantioselectivity. Application to a 1 mmol scale reaction was successfully achieved.

Assembly of 1,2,3,4-Tetrahydropyrrolo[1,2-a]pyrazines via the Domino Reaction of 2-Imidazolines and Terminal Electron-Deficient Alkynes

The transformation of 2-imidazolines into 1,2,3,4-tetrahydropyrrolo[1,2-a]pyrazines has been realized. A pseudo-three-component reaction of 2-imidazolines with terminal electron-deficient alkynes (2 equiv) first generates imidazolidines, containing an N-vinylpropargylamine fragment. The latter can then undergo a base-catalyzed domino aza-Claisen rearrangement/cyclization reaction sequence, simultaneously constructing pyrrole and pyrazine rings. The process works in a broad substrate scope, delivering pyrrolo[1,2-a]pyrazines in good to excellent yields (45-90%). This two-step approach can be carried out in a one-pot fashion without a noticeable decrease in yield. Remarkably, a three-component protocol for the introduction of two different alkynes has been also developed.

Divergent Conversion of Double Isocyanides with Alkenyl Bromide to Polysubstituted Pyrroles and 4-Imino-4,5-dihydropyrrolo[3,4-b]pyrrol-6(1H)-one Derivatives by Pd-Catalyzed Tandem Cyclization Reactions

Herein a novel and concise approach to pyrrole skeletons via Pd-catalyzed tandem cyclization reactions is investigated. The substrates for the transformation could be readily prepared by phosphoric acid-catalyzed Ugi reactions with available starting materials. In this strategy, two isocyanides participate in sequential isocyanide insertion reactions, and the chemoselectivity of the products is regulated by the steric hindrance of the isocyanide. A plausible mechanism for the formation of the corresponding adducts is proposed.

Palladium-catalyzed denitrative N-arylation of nitroarenes with pyrroles, indoles, and carbazole

We have developed an efficient palladium-catalyzed denitrative N-arylation via cross-coupling of N–H heteroarenes with nitroarenes, one of the most inexpensive and fundamental feedstocks in the chemical industry. A variety of...

Synthesis and Anti-Cancer Applications of Benzimidazole Derivatives - Recent Studies

BACKGROUND

Cancer is a life-threatening disease. Anti-cancer drugs are the focus of research. The heterocyclic molecules like benzimidazole occupy a central position in searching for novel and effective anti-cancer drugs. The medicinal chemists designed and synthesized several benzimidazole derivatives and conjugates to evaluate them as potential anti-cancer agents.

OBJECTIVE

The purpose of this compilation of literature is to cover the progress of benzimidazole-based anti-cancer agents, their synthesis, and their evaluation for cancer disease treatment.

METHODS

The recent literatures have been collected from various search engines and peer-reviewed journals.

RESULTS

The compounds like benzimidazole derivatives of dehydroabietic acid, piperidyl benzimidazole carboxamide, benzimidazole-quinazolinone hybrids, benzimidazole-thiazole conjugate, and benzimidazole pendant cyanopyrimidine derivatives have been discussed in detail.

CONCLUSION

This review article will help the medicinal chemists to design and synthesize benzimidazole-based molecules and evaluate them as anti-cancer agents.

An expeditious and highly efficient synthesis of substituted pyrroles using a low melting deep eutectic mixture

An expeditious green method for the synthesis of diverse valued substituted pyrroles through a Paal-Knorr condensation reaction, using a variety of amines and 2,5-hexanedione/2,5-dimethoxytetrahydrofuran in the presence of a low melting mixture of N,N'-dimethylurea and L-(+)-tartaric acid (which acts as a dual catalyst/solvent system), has fruitfully been revealed. Herein, we have disclosed the applicability of this simple yet effective strategy for the generation of mono- and dipyrroles in good to excellent yields. Moreover, C₃-symmetric tripyrrolo-truxene derivatives have also been assembled by means of cyclotrimerization, Paal-Knorr and Clauson-Kaas reactions as crucial steps. Interestingly, the melting mixture was recovered and reused with only a gradual decrease in the catalytic activity (over four cycles) without any significant drop in the yield of the product. This particular methodology is simple, rapid, environmental friendly, and high yielding for the generation of a variety of pyrroles. To the best of our knowledge, the present work reveals the fastest greener method reported up to this date for the construction of substituted pyrroles by utilizing the Paal-Knorr synthetic protocol, achieving impressive yields under operationally simple reaction conditions without involving any precarious/dangerous catalysts or unsafe volatile organic solvents.