Novel chloropyridazine sulfonamides as aromatase inhibitors and apoptotic inducers in breast cancer

Aromatase catalyzes the rate-limiting and final step in the biosynthesis of estrogen. Inhibitors of this enzyme are effective targeted therapy for breast cancer. Molecular hybridization is a promising strategy in drug discovery that combines two or more biologically active moieties in a single structure. In this work, we aim at combining sulfonamide, chloropyridazine and pyrrole in a single design as potential aromatase inhibitors for breast cancer. The synthesized compounds were subjected to in vitro cytotoxic screening against MCF-7 breast cancer cell line, then were assessed for their ability to inhibit aromatase enzyme. Compound 10 exhibited a promising cytotoxic activity (IC50 1.83 μM) that nearly equal to the reference drug (doxorubicin, IC50 1.94 μM) on MCF-7 cells. Also, compound 10 was the most potent aromatase inhibitor with the lowest IC50 (0.06 μM) compared to letrozole (IC50 0.05 μM). Based on the promising results of compound 10, it was selected to investigate its apoptotic effect that disclosed a marked increase in Bax level to 5.42 folds and down-regulation in Bcl-2 expression to 0.34 folds in MCF-7 cells compared to letrozole. Moreover, compound 10 increased caspase 9 level by 4.84 folds. Also, compound 10 arrested the cell cycle at G1 phase and caused induction of early and late apoptosis in an AnnexinV-FITC assay. Compound 10 had been evaluated to study its synergistic effect with γ-radiation by evaluating the cytotoxicity against MCF-7 after exposure to gamma rays (8 Gy). In addition, compound 10 showed low toxicity against human normal breast (MCF-10 A) cell line. Docking study of compound 10 was performed and showed binding with the key amino acids in aromatase active site.

Zinc(II)-catalysed cyclocondensation of oxime ethers triggered by polarity inversion: construction of fused pyrroles

An efficient approach for the synthesis of fused pyrroles such as indoles, thieno[3,2-b]pyrroles, and benzothieno[3,2-b]pyrroles possessing an N-alkoxy group was developed via the Zn(II)-catalysed cyclocondensation of α-hydroxy oxime ethers. Important features include the scalable synthesis with high yield achieved (up to 99%), environmentally benign, low-cost catalysts, and less hazardous reaction conditions.

Delineating the binding site of a series of gold(III) Schiff base chelates on HSA via experimentation and in silico methods

Human serum albumin (HSA) is crucial for drug transport, influencing pharmacokinetics and pharmacological activity. While drug binding to HSA is well-studied, precise identification of primary binding sites remains underexplored. Since unbound drug fractions impact distribution and receptor-site concentration, understanding HSA interactions is essential for evaluating pharmacokinetics and toxicity. This study presents a systematic workflow integrating fluorescence quenching, circular dichroism, and ligand-binding thermodynamics to map ligand binding on HSA. Using patented Schiff base Au (III) chelates, we validate our approach with experimental data, molecular dynamics simulations, and QM/MM TD-DFT methods. Results indicate all three chelates preferentially bind Sudlow's site I, with affinities following AuL3 > AuL1 > AuL1, with logka values ranging from 4.73 to 5.03. Thermodynamic analysis suggests endothermic, hydrophobic-driven binding. Competitive site displacement assays confirm these findings. Overall, our results highlight HSA's potential as a transporter for metal-based therapeutics and demonstrate the efficacy of our workflow in accurately determining drug-binding sites.

A transition metal-free [3 + 2] cycloaddition approach for the efficient synthesis of trisubstituted pyrrole derivatives from β-chlorovinyl aldehydes

A transition metal-free, Cs2CO3-promoted approach has been devised for the efficient synthesis of nitrile-substituted novel pyrrole derivatives from β-chlorovinyl aldehydes. Interestingly, the strategy was also found to be applicable to the synthesis of chromenone-fused pyrrole derivatives. The reaction proceeded through [3 + 2] cycloaddition between diversely substituted aryl propiolonitriles and toluenesulphonylmethyl isocyanide in DMF at ambient temperature. This approach offers several advantages including the use of inexpensive and readily available starting materials, wide substrate scope, operational simplicity, short reaction times (15 min-1.5 h), high atom economy, sustainable reaction conditions and high product yields. The strategy has been found to be amenable for gram-scale synthesis, and the scope of the strategy has been demonstrated for the synthesis of a diverse library of novel pyrrole derivatives with yields of up to 91%. The generated pyrrole derivatives are amenable for late-stage functionalisation and functional group interconversion.

Pyrrole dicarboxylate substituted porphyrazine, microwave assisted synthesis and properties

In this study, a new magnesium(II) porphyrazine derivative tetrasubstituted with dicarboxypyrrolyl moieties was synthesized. Two different approaches were used, utilizing conventional heating and microwave irradiation. The developed three-step processes were compared showing the superior performance of the microwave-assisted organic synthesis. The new macrocycle and the novel maleonitrile derivatives were characterized using spectral techniques (mass spectrometry, NMR spectroscopy, UV-Vis spectrophotometry) and the ability of the porphyrazine to generate singlet oxygen assessed using the method with 1,3-diphenylisobenzofuran. The singlet oxygen generation quantum yields were found to be moderate (ΦΔ = 0.23 and 0.22 in DMF and DMSO, respectively) and no aggregation behavior was noted in a series of dilutions. Additionally, the acute toxicity test using Microtox was performed showing almost no toxicity at the concentration of 10- 5 mol/L. The electrochemical studies revealed three redox processes of targeted porphyrazine with low first oxidation peak, whereas the spectroelectrochemistry showed the formation of both cationic and anionic species at proper potentials.

Quantum Chemical Studies on the Prototropic and Acid/Base Equilibria for 2-Aminopyrrole in Vacuo-Role of CH Tautomers in the Design of Strong Brønsted Imino N-Bases

In the quest of the pivotal origin of the very strong gas-phase proton basicity for some iminopyrrole derivatives, proposed in the literature on the basis of quantum chemical calculations, the full tautomeric and acid/base equilibria were investigated in vacuo for 2-aminopyrrole exhibiting enamino-imino tautomerism. Thermochemistry of these processes investigated at the Density Functional Theory (DFT) level indicates a lower stability for the imino than for the enamino tautomers. However, the imino N atom in the imino forms displays an exceptionally high basicity, particularly in the minor and rare tautomers containing at least one tautomeric proton at the pyrrole C atom. This explains why derivatives of CH tautomers (being free of prototropy) display exceptionally high gas-phase proton basicity. As predicted by the Maksić group using quantum chemical methods, these derivatives can be considered as good organic imino N-superbase candidates. Unfortunately, some other structures of iminopyrrole derivatives (proposed by the same group) possess labile protons, and, thus, exhibit prototropy, resulting in the transformation into the more stable but less basic aminopyrrole derivatives under synthesis conditions or acid/base equilibria measurements.

Finding of antibiotic compounds pyrrolo [1,2-a]pyrazine-1,4-dione, hexahydro and Cyclo(prolyl-tyrosyl) isolated from the degradation of epoxy

The investigation focused on the endophytic gram-positive microbial isolate KARE_P3, capable of degrading epoxy resin materials. This isolate produced bioactive secondary metabolic molecules with potent inhibitory effects against Staphylococcus aureus, Microbial Type Culture Collection and GenBank (MTCC 96). The study examined microbial growth and degradation mechanisms at various time points, with samples collected on the 35th and 70th days of fermentation. Three different solvents were used for extraction, and the crude metabolite was analysed using Thin Layer Chromatography (TLC), Gas Chromatography - Mass Spectrophotometry (GC-MS), Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC). These analyses revealed numerous secondary metabolites that help microbes adapt to changing environments. Further characterisation using bioautography and GC-MS identified 71 compounds, with 3-5 showing positive results. Important findings include compounds such as pyrrolo[1,2-a]pyrazine-1,4-dione, hexahydro 98% and Cyclo(prolyl-tyrosyl), which have diverse pharmaceutical applications. Antibacterial efficiency was studied using an in silico model, showing higher binding energy and inhibition rates of pyrrolo[1,2-a]pyrazine-1,4-dione and Cyclo(prolyl-tyrosyl) against Candida albicans compared to Staphylococcus epidermis. Challenges remain in the efficient sorting, recycling, and recovery of epoxy materials, crucial for future biotechnological progress.

Understanding nonlinear molecular responses in highly inhomogeneous electric fields: Insights from imidazole and pyrrole

The study of molecules subjected to highly inhomogeneous electric fields, whether static or time-dependent, is relatively unexplored. Advances in this area, as shown in condensed matter physics, could lead to new insights into molecular physics and offer novel ways to control molecules, driving technological innovations. In this work, we numerically investigate the properties of imidazole and pyrrole under the influence of highly inhomogeneous static and dynamic electric fields, modeled by a new procedure employing charge configurations, using density functional theory calculations with the DALTON software package. We analyze their dipole moments, highest occupied molecular orbital-lowest unoccupied molecular orbital gap energies, polarizability, and first and second hyperpolarizabilities across different field orientations. Our results show that inhomogeneous fields acting upon the molecule would induce changes in nonlinear optical properties, with the response depending on the nature of the inhomogeneity. These findings are relevant for fundamental research and practical applications. Tailored electric non-uniform fields can help unveil complex relationships among molecular orbitals that induce specific nonlinear optical phenomena. Moreover, they can enhance or suppress nonlinear responses, opening up new avenues for molecular engineering and device design.

Discovery of Conformationally Constrained Dihydro Benzo-Indole Derivatives as Metallo-β-Lactamase Inhibitors to Tackle Multidrug-Resistant Bacterial Infections

The discovery of metallo-β-lactamase (MBL) inhibitors is crucial in the fight against bacterial infections following the emergence and rapid spread of New Delhi metallo-β-lactamase-1 (NDM-1), as well as clinically relevant Verona integrin-encoded metallo-β-lactamase (VIM), and Imipenemase (IMP). The situation is alarming as there are insufficient antibiotics in the pipeline to combat critical multidrug-resistant infections. Here, we report the discovery of novel dihydrobenzo-indole (dBI) derivatives as a new class of potent metallo-β-lactamase inhibitors (MBLIs) by applying scaffold hopping, conformation constrained, and substituent-decorating strategies. Among them, compound 17u exhibited the best inhibitory activity against MBL with acceptable physicochemical and ADME properties. 17u exhibited remarkable enhancement of carbapenems' effectiveness against a range of MBL-producing clinical strains. This efficacy extended to in vivo settings when combined with the imipenem antibiotic, significantly reducing the bacterial load in a thigh infection model. Consequently, it qualifies as a prime candidate for further development as an MBLI.

Quantum Mechanical Spectral Analysis and Aldose Reductase Inhibition Evaluation of Synthetic New Pyrrolopyrazinones

The Maillard reaction, known as the condensation of reduced sugars with amino acids, can be a great source of pyrroles for the discovery of bioactive compounds. In the present study, using glucose and l-alanine, two new pyrrolopyrazinones (1a and 1b) were obtained. Subsequently, two more new pyrrolopyrazinones (2a and 2b) were prepared by further hydrolyzing the methyl ester into carboxylic acid. The structures of the pyrrolopyrazinones were determined by interpretation of 1D and 2D NMR and HRESIMS data as well as computational calculation of ECD Cotton effects. Moreover, the broad 1H NMR peak shapes observed in the pyrrolopyrazinones were accurately resolved to the presence of long-range couplings, including allylic 4 J and homoallylic 5 J couplings, by employing quantum mechanics-driven 1H iterative full spin analysis (QM-HiFSA). The four pyrrolopyrazinones were evaluated for their biological efficacy in the treatment of diabetes in terms of their structural elements, including carboxyl functional groups. As a result, all four compounds were found to be moderately effective in inhibiting aldose reductase and also in proliferating mesenchymal stem cells.

Cytotoxic pyrrole-based gold(III) chelates target human topoisomerase II as dual-mode inhibitors and interact with human serum albumin

Topoisomerase IIα (Top II) is a critical enzyme that resolves DNA topology during transcription and replication. Inhibitors of Top II are used as anticancer agents and are classified as interfacial poisons (IFPs) or catalytic inhibitors (CICs). Here, we report a novel class of cytotoxic, stable cationic gold(III) Schiff base chelates (AuL1, AuL2, and AuL3) with DNA-intercalating properties. In the NCI-60 screen, AuL1 and AuL3 exhibited potent cytotoxicity (mean GI50 values of 11 (7) μM and 14 (9) μM, respectively), whereas AuL2 showed minimal cytotoxicity. Cluster analysis aligned AuL1 and AuL3 with the Top II poison etoposide. Mechanistic studies revealed that AuL1 acts as an IFP at concentrations between 0.5 and 50 μM and as a CIC at concentrations between 50 and 500 μM. Further investigations demonstrated that all three gold(III) chelates bind to and intercalate DNA, the main substrate for Top II. Finally, binding studies with human serum albumin (HSA) indicated that the chelates have moderate affinity for the protein. Thermodynamic analysis indicates entropically driven binding, with minimal structural disruption observed via UV-CD spectroscopy. These findings highlight the dual mode Top II inhibition mechanism delineated for the gold(III) chelates and their favourable pharmacodynamic interactions with HSA, underscoring their potential as promising anticancer agents.

Five-membered heterocycles as promising platforms for molecular logic gate construction

The field of molecular logic gates began thirty years ago with the early pioneers de Silva et al. (A. P. de Silva, H. Q. N. Gunaratne and C. P. McCoy, Nature, 1993, 364, 42) laying the foundation for modern molecular-scale switches and devices. Recent reports of lab-on-a-molecule and molecular calculators (Moleculators) demonstrate the potential of this bottom-up approach. Five-membered heterocycles were central to the first reported logic gates in 1994 and remain valuable scaffolds in the present day. This review provides an overview of logic gate design using Boolean logic, introduces the work of the first pioneers, and highlights recently reported five-membered heterocycle logic gates.

Xiapyrroles A-F: N-Alkylpyrrole Alkaloids from the Marine-Derived Actinomycete Streptomyces xiamenensis 1310KO-148

Six new N-alkylpyrrole alkaloids (1-6) were isolated from the marine-derived actinomycete Streptomyces xiamenensis 1310KO-148 from a sponge sample. The structures of xiapyrroles A-F (1-6) were elucidated by detailed analysis of extensive spectroscopic data, including 1D, 2D NMR, and HRESIMS data. The absolute configurations of 2, 3, 4, and 6 were determined by a comparison of their calculated and experimental electronic circular dichroism (ECD) spectra. The position of the hydroxamate group in 6 was confirmed through NO-methylation and NOESY data analysis. All compounds (1-6) were tested for their anti-inflammatory effects in LPS-stimulated RAW 264.7 cells, a mouse macrophage cell line. The treatment of RAW 264.7 cells with 30 μM of 1-6 showed no significant cytotoxic effects. However, 1 dose-dependently suppressed the LPS-induced production of NO (IC50 = 29.5 μM) and interleukin-6 (IL-6) (IC50 = 10.9 μM). Compound 1 exhibited no potential cytotoxicity against six solid cancer cell lines and eight blood cancer cell lines at a concentration of 30 μM.

Tandem Synthesis of Polysubstituted Pyrroles via Cu(I)-Catalyzed Cyclization of Ketene N,S-Acetals with β-Ketodinitriles

A new approach to multifunctionalized pyrroles has been explored by the tandem cyclization of α-oxoketene-N,S-acetals with β-ketodinitriles using Cu(MeCN)4BF4 and Ag2CO3 in toluene under reflux conditions. The reaction involves C-C/C-N bond creation, and is assumed to proceed via enamine formation, intramolecular cyclization, and rearrangement. The potential of the methodology has also been demonstrated for a gram-scale reaction as well as for some useful organic transformations. The reaction offers a practical pathway to achieve polysubstituted pyrroles with broad substrate scope and good functional group tolerance.

Tunable Synthesis of 4-Acyl- and 4-Formyl Pyrroles by Rhodium-Catalyzed Ring-Expansion of Azirines with Enaminones

A rhodium-catalyzed annulation of 2H-azirines with enaminones is presented. This protocol affords a convenient approach to the diversity-oriented synthesis of 4-acyl- and 4-formyl pyrroles with good functional group tolerance. The utility of this reaction has been demonstrated by scale-up preparation, late-stage modification of natural molecules, and synthesis of diverse derivatives.

Urinary odor molecules in the Otassha Study can distinguish patients with sarcopenia: A pilot study

AIM

To identify sarcopenia markers in urinary odor.

METHODS

We performed solid-phase microextraction from the headspace and gas chromatography-mass spectrometry analysis of urinary volatile organic compounds (VOCs) in 71 healthy individuals and 68 patients diagnosed with sarcopenia according to the Asian Working Group on Sarcopenia 2019 criteria. The mass-to-charge ratios (m/z) of 10 VOCs with a significant difference in the total ion chromatogram of 220 VOCs detected in this study were compared by U-test. To calculate the predictive values for sarcopenia, binomial logistic regression analyses were conducted with sarcopenia (0, 1) as the dependent variable and the m/z values of each of the 10 VOCs and all 10 VOCs as independent variables. Receiver operating characteristic (ROC) curves for predictive values were generated to evaluate diagnostic accuracy. The correlations between the predictive value and handgrip strength, usual gait speed, and skeletal muscle mass were assessed using Pearson's r.

RESULTS

We identified 10 VOCs (p-xylene, 1-butanol, d-limonene, nonanal, pyrrole, γ-butyrolactone, texanol isomer, octanoic acid, nonanoic acid, and diisobutyl phthalate) as candidate biomarkers in urine. The ROC curve analysis showed high diagnostic accuracy of the predictive values of the 10 VOCs for sarcopenia (area under the curve = 0.866, 95% confidence interval: 0.829-0.942; sensitivity, 80.9%; specificity, 81.7%). Additionally, the predictive values significantly correlated with handgrip strength (male: r = -0.505, P < 0.0001; female: r = -0.568, P < 0.0001).

CONCLUSIONS

This study identified 10 urinary VOCs as possible non-invasive biomarkers for sarcopenia, offering insights into its onset mechanism and potential therapeutic targets. Geriatr Gerontol Int 2025; 25: 307-315.

Design, synthesis, and pharmacological evaluation of indazole carboxamides of N-substituted pyrrole derivatives as soybean lipoxygenase inhibitors

In this paper, we attempted to develop a novel class of compounds against lipoxygenase, a key enzyme in the biosynthesis of leukotrienes implicated in a series of inflammatory diseases. Given the absence of appropriate human 5-lipoxygenase crystallographic data, solved soybean lipoxygenase-1 and -3 structures were used as a template to generate an accurate pharmacophore model which was further used for virtual screening purposes. Eight compounds (1-8) have been derived from the in-house library consisting of N-substituted pyrroles conjugated with 5- or 6-indazole moieties through a carboxamide linker. This study led to the discovery of hit molecule 8 bearing a naphthyl group with the IC50 value of 22 μM according to soybean lipoxygenase in vitro assay. Isosteric replacement of naphthyl ring with quinoline moieties and reduction of carbonyl carboxamide group resulted in compounds 9-12 and 13, respectively. Compound 12 demonstrated the most promising enzyme inhibition. In addition, compounds 8 and 12 were found to reduce the carrageenan-induced paw edema in vivo by 52.6 and 49.8%, respectively. In view of the encouraging outcomes concerning their notable in vitro and in vivo anti-inflammatory activities, compounds 8 and 12 could be further optimized for the discovery of novel 5-lipoxygenase inhibitors in future.

Unlocking the Potential of Pyrrole: Recent Advances in New Pyrrole-Containing Compounds with Antibacterial Potential

Nitrogen heterocycles are valuable structural elements in the molecules of antibacterial drugs approved and used to treat bacterial infections. Pyrrole is a five-atom heterocycle found in many natural compounds with biological activity, including antibacterial activity. Numerous compounds are being develop based on the pyrrole heterocycle as new potential antibacterial drugs. Due to the phenomenon of antibacterial resistance, there is a continuous need to create new effective antibacterials. In the scientific literature, we have identified the most relevant studies that aim to develop new compounds, such as pyrrole derivatives, that are proven to have antibacterial activity. Nature is an endless reservoir of inspiration for designing new compounds based on the structure of pyrrole heterocycles such as calcimycin, lynamycins, marinopyrroles, nargenicines, phallusialides, and others. However, many other synthetic compounds based on the pyrrole heterocycle have been developed and can be optimized in the future. The identified compounds were classified according to the type of chemical structure. The chemical structure-activity relationships, mechanisms of action, and antibacterial effectiveness of the most valuable compounds were highlighted. This review highlights scientific progress in designing new pyrrole-containing compounds and provides examples of lead compounds that can be successfully optimized further.

Construction of axially chiral 2-arylpyrroles using catalytic asymmetric Suzuki-Miyaura cross-coupling: an efficient approach to esaxerenone

A general and efficient method has been developed to access axially chiral 2-arylpyrroles using catalytic asymmetric Suzuki-Miyaura cross-coupling. A wide range of axially chiral arylpyrroles were obtained in high yields with good to excellent enantioselectivities. The key to success is the use of a combined catalytic system involving a palladium catalyst and chiral ferrocene diphosphine ligand for achieving effective enantiocontrol. More importantly, this axially chiral CF3-substituted 2-arylpyrrole serves as a key intermediate in the preparation of the anti-hypertensive and diabetic nephropathy drug esaxerenone. It was directly asymmetrically synthesized with high enantioselectivity (92% ee). Thus, a new strategy is provided for the catalytic asymmetric synthesis of esaxerenone.

TCFH-NMI Ketone Synthesis Inspired by Nucleophilicity Scales

N,N,N',N'-Tetramethylchloroformamidinium hexafluorophosphate (TCFH) and N-methylimidazole (NMI) enable the facile and practical reaction of carboxylic acids with amines, alcohols, and thiols to form amides, esters, and thioesters. To develop a mild synthesis of ketones with TCFH-NMI directly from carboxylic acids at room temperature, the Mayr nucleophilicity scale was used to compare the N values of competent nucleophiles to potential carbon-centered nucleophiles, identifying pyrroles and indoles as successful substrates when N ≥ 10.

Humin-sulfuric acid as a novel recoverable biocatalyst for pyrrole synthesis in water

Humin-sulfuric acid (Humin-SO3H) as a novel efficient biobased sulfonic acid was easily prepared by adding chlorosulfuric acid (ClSO3H) to Humin and characterized by potentiometric titration and FT-IR spectrum. Humin-SO3H is an eco-friendly, heterogeneous biobased, and efficient catalyst for Paal-Knorr and Clauson-Kaas pyrrole synthesis. The catalyst is easily recovered by simple filtration and has excellent turnover efficiency even after 4 cycles. Besides, due to the clearance of the biocatalyst away from the reaction media, the desired highly pure products can be achieved in high to excellent yields. Due to high water dispersibility, Humin-SO3H can be utilized as a highly efficient green catalyst for pyrrole synthesis.

Neurotoxicity, Neuroprotection, In Vitro MAOA/MAOB Inhibitory Activity Assessment, Molecular Docking, and Permeability Assay Studies of Newly Synthesized Hydrazones Containing a Pyrrole Ring

Neurodegenerative diseases such as Parkinson's and Alzheimer's continue to be some of the most significant challenges in modern medicine. Recent research related to the molecular mechanisms of parkinsonism has opened up new approaches to antiparkinsonian therapy. In response to this, we present the evaluation of the potential neuroprotective and MAOA/MAOB inhibitory effects of newly synthesized hydrazones, containing a pyrrole moiety in the carboxyl fragment of the structure. The substances were studied on different brain subcellular fractions, including rat brain synaptosomes, mitochondria, and microsomes. The single application of 50 µM of each compound to the subcellular fractions showed that all substances exhibit a weak neurotoxic effect, with 7b, 7d, and 8d being the least neurotoxic representatives. The corresponding neuroprotective and antioxidant effects were also evaluated in different injury models on subcellular fractions, single out 7b, 7d, and 8d as the most prominent derivatives. A 1 µM concentration of each molecule from the series was also studied for potential hMAOA/hMAOB inhibitory effects. The results revealed a lack of hMAOA activity for all evaluated structures and the appearance of hMAOB effects, with compounds 7b, 7d, and 8d showing effects similar to those of selegiline. The best hMAOB selectivity index (>204) was determined for 7d and 8d, distinguishing these two representatives as the most promising molecules for further studies as potential selective MAOB inhibitors. The performed molecular docking simulations defined the appearance of selective MAOB inhibitory effects based on the interaction of the tested molecules with Tyr398, which is one of the components of the aromatic cage of MAOB and participated in π-π stabilization with the aromatic pyrrole ring. The preliminary PAMPA testing indicated that in relation to the blood-brain barrier (BBB) permeability, the tested pyrrole-based hydrazones may be considered as high permeable, except for 8a and 8e, which were established to be permeable in the medium range with -logP of 5.268 and 5.714, respectively, compared to the applied references.

Antimicrobial potential of Streptomyces sp. NP73 isolated from the forest soil of Northeast India against multi-drug resistant Escherichia coli

This study reports the isolation and characterization of a Streptomyces sp. from soil, capable of producing bioactive secondary metabolites active against a variety of bacterial human pathogens. We targeted the antimicrobial activity against Escherichia coli ATCC-BAA 2469, a clinically relevant strain of bacteria harbouring resistance genes for carbapenems, extended spectrum beta-lactams, tetracyclines, fluoroquinones, etc. Preliminary screening using the spot inoculation technique identified Streptomyces sp. NP73 as the potent strain among the 74 isolated Actinomycetia strain. 16S rRNA gene and whole genome sequencing (WGS) confirmed its taxonomical identity and helped in the construction of the phylogenetic tree. WGS revealed the predicted pathways and biosynthetic gene clusters responsible for producing various types of antibiotics including the isolated compound. Bioactivity guided fractionation and chemical characterization of the active fraction, carried out using liquid chromatography, gas chromatography-mass spectrometry, infra-red spectroscopy, and nuclear magnetic resonance spectroscopy, led to the tentative identification of the active compound as Pyrrolo[1,2-a] pyrazine-1,4-dione, hexahydro-, a diketopiperazine molecule. This compound exhibited excellent antimicrobial and anti-biofilm properties against E. coli ATCC-BAA 2469 with an MIC value of 15.64 µg ml-1, and the low cytotoxicity of the compound identified in this study provides hope for future drug development.

Photoredox Catalysis by 21-Thiaporphyrins: A Green and Efficient Approach for C-N Borylation and C-H Arylation

Photoredox catalysis provides a green and sustainable alternative for C-H activation of organic molecules that eludes harsh conditions and use of transition metals. The photocatalytic C-N borylation and C-H arylation mostly depend on the ruthenium and iridium complexes or eosin Y and the use of porphyrin catalysts is still in infancy. A series of novel 21-thiaporphyrins (A2B2 and A3B type) were synthesized having carbazole/phenothiazine moieties at their meso-positions and screened as catalysts for C-N borylation and C-H arylation. This paper demonstrates the 21-thiaporphyrin catalyzed C-N borylation and het-arylation of anilines under visible light. The method utilizes only 0.1 mol % of 21-thiaporphyrin catalyst under blue light for the direct C-N borylation and het-arylation reactions. A variety of substituted anilines were used as source for expensive and unstable aryl diazonium salts in the reactions. The heterobiaryls and aryl boronic esters were obtained in decent yields (up to 88 %). Versatility of the 21-thiaporphyrin catalyst was tested by thiolation and selenylation of anilines under similar conditions. Mechanistic insight was obtained from DFT studies, suggesting that 21-thiaporphyrin undergo an oxidative quenching pathway. The photoredox process catalyzed by 21-thiaporphyrins offers a mild, efficient and metal-free alternative for the formation of C-C, C-S, and C-Se bonds in aryl compounds; it can also be extended to borylation reaction.

Regioselective Synthesis of Highly Functionalized 2H-Pyrroles via Dearomative Chlorination of 1H-Pyrroles

An efficient protocol was developed for the synthesis of highly functionalized 2H-pyrroles. This synthetic approach involves the in situ generation of highly reactive 2,5-dichloro-substituted 2H-pyrroles through dearomative chlorination of the corresponding 1H-pyrroles. The resulting reaction mixture is then treated with various amines, leading to the formation of 2,5-diaminated 2H-pyrroles. Subsequent nucleophilic substitution of fluorine with different N-, O-, and S-nucleophiles allows us to introduce additional functionality into a 2H-pyrrole core. The overall outcome of this reaction sequence is the triple nucleophilic modification of pyrroles. All steps of the sequence were found to be highly efficient, regioselective in the preparation of desired di- and trisubstituted derivatives in up to 96% overall yield. In addition, the computational study of this reaction sequence was carried out using density functional theory (DFT). The results of calculations are in perfect agreement with experimental observations.

Evaluating Pigments as a Biosignature: Abiotic/Prebiotic Synthesis of Pigments and Pigment Mimics in Planetary Environments

Pigments serve a multitude of functions in biology including light harvesting for photosynthesis, radiation protection, membrane support, and defense. The ubiquity of pigments-especially within extremophiles found in high-radiation, high-salinity, and dry environments-and their detectability via mission-ready techniques have elevated these molecules as promising targets in the search for evidence of life elsewhere. Moreover, the detection of pigments has been proposed as a "smoking gun" for extraterrestrial life as it has been suggested that these molecules cannot be generated abiotically. However, while pigments may hold promise as a biosignature, current understanding of their possible prebiotic origins remains understudied and uncertain. Better understanding of the abiotic synthesis of pigments is critical for evaluating the biogenicity of any pigment detected during missions, including by the Mars Perseverance rover or from returned samples. Compounding this uncertainty is the broad definition of pigment as it includes any compound capable of absorbing visible light and by itself does not specify a particular chemical motif. While not experimentally verified, there are promising prebiotic routes for generating pigments including hemes, chlorophylls, and carotenoids. Herein, we review the biochemistry of pigments, the inherent assumptions made when searching for these molecules in the field, their abiotic synthesis in industry and prebiotic reactions, prebiotically relevant molecules that can mimic their spectral signatures, and implications/recommendations for future work.

Enal-azomethine ylides: application in the synthesis of functionalized pyrroles

Rhodium-catalyzed [3 + 2] annulation of diazoenals and N-alkyl imines resulted in N-alkyl-pyrrole-3-carbaldehyde derivatives. The reaction involves thermal 6π-electrocyclization and aromatization of a new class of enal-azomethine ylides (EAYs). The EAYs derived from dihydroisoquinoline and 2H-azirine gave fused-pyrrole and pyridine derivatives, respectively. The synthetic importance of pyrrole products has been demonstrated by one-step synthesis of the biologically relevant pyrrolo[3,2-c]quinoline scaffold as well as pyrrolo[2,1-a]isoquinoline which is a core structure of lamellarin alkaloids.

Pyrrole-containing hybrids as potential anticancer agents: An insight into current developments and structure-activity relationships

Cancer poses a significant threat to human health. Therefore, it is urgent to develop potent anti-cancer drugs with excellent inhibitory activity and no toxic side effects. Pyrrole and its derivatives are privileged heterocyclic compounds with significant diverse pharmacological effects. These compounds can target various aspects of cancer cells and have been applied in clinical settings or are undergoing clinical trials. As a result, pyrrole has emerged as a promising drug scaffold and has been further probed to get novel entities for the treatment of cancer. This article reviews recent research progress on anti-cancer drugs containing pyrrole. It focuses on the mechanism of action, biological activity, and structure-activity relationships of pyrrole derivatives, aiming to assist in designing and synthesizing innovative pyrrole-based anti-cancer compounds.

Design, Synthesis, and Antifungal Activities of Phenylpyrrole Analogues Based on Alkaloid Lycogalic Acid

Plant diseases caused by pathogenic fungi seriously affect the yield and quality of crops, cause huge economic losses, and pose a considerable threat to global food security. Phenylpyrrole analogues were designed and synthesized based on alkaloid lycogalic acid. All target compounds were characterized by 1H NMR, 13C NMR, and HRMS. Their antifungal activities against seven kinds of phytopathogenic fungi were evaluated. The results revealed that most compounds had broad-spectrum fungicidal activities at 50 μg/mL; 14 compounds displayed more than 60% fungicidal activities against Rhizoctonia cerealis and Sclerotinia sclerotiorum, and in particular, the fungicidal activities of compounds 8g and 8h against Rhizoctonia cerealis were more than 90%, which could be further developed as lead agents for water-soluble fungicides. The molecular docking results indicate that compounds 8g and 8h can interact with 14α-demethylase (RcCYP51) through hydrogen bonding with strong affinity.

Unpredictable Dynamic Behaviour of Ruthenium Chelate Pyrrole Derivatives

Reaction of [Ru(H)2(CO)(PPh3)3] 1 with an equimolar amount of pyrrole-2-carboxylic acid (H2L1) leads to the homoleptic chelate derivative k2(O,O)-[RuH(CO)(HL1)(PPh3)2] 2. Prolonged acetonitrile refluxing promotes an unusual k2(O,O)- → k2(N,O)- dynamic chelate conversion, forming a neutral, stable, air- and moisture- insensitive, solvento-species k2(N,O)-[Ru(MeCN)(CO)(L1)(PPh3)2] 3. Analogously, reaction of 1 with the pyrrole-2-carboxyaldehyde (HL2) affords k2(N,O)-[RuH(CO)(HL2)(PPh3)2] 4, 5, as a couple of functional isomers. Optimized reaction conditions such as temperature and solvent polarity allow the isolation of dominant configurations. Structure 5 is a pyrrolide Ru-carbaldehyde, obtained from cyclization of the pendant CHO function, whereas species 4 can be viewed as an ethanoyl-conjugated Ru-pyrrole. Derivatives 3-5 were characterized by single crystal X-ray diffraction, ESI-Ms, IR, and NMR spectroscopy, indicating distinct features for the Ru-bonded pyrrolyl groups. DFT computational results, coplanarity, bond equalization, and electron delocalization along the fused five-membered rings support aromatic features. In accordance with the antisymbiotic trans-influence, both the isolated isomers 4 and 5 disclose CO ligands opposite to N- or O-anionic groups. The quantitative Mayer bond order evidences a stabilizing backbonding effect. Antibacterial and antifungal trials on Gram-positive (Staphylococcus aureus), Gram-negative (Escherichia coli), and Candida albicans were further carried out.

Kinetic resolution of 1-(1-alkynyl)cyclopropyl ketones via gold-catalyzed divergent (4 + 4) cycloadditions: stereoselective access to furan fused eight-membered heterocycles

Chiral eight-membered heterocycles comprise a diverse array of natural products and bioactive compounds, yet accessing them poses significant challenges. Here we report a gold-catalyzed stereoselective (4 + 4) cycloaddition as a reliable and divergent strategy, enabling readily accessible precursors (anthranils and ortho-quinone methides) to be intercepted by in situ generated gold-furyl 1,4-dipoles, delivering previously inaccessible chiral furan/pyrrole-containing eight-membered heterocycles with good results (56 examples, all >20 : 1 dr, up to 99% ee). Moreover, we achieve a remarkably efficient kinetic resolution (KR) process (s factor up to 747). The scale-up synthesis and diversified transformations of cycloadducts highlight the synthetic potential of this protocol. Computational calculations provide an in-depth understanding of the stereoselective cycloaddition process.

Elucidation of Chalkophomycin Biosynthesis Reveals N-Hydroxypyrrole-Forming Enzymes

Reactive functional groups, such as N-nitrosamines, impart unique bioactivities to the natural products in which they are found. Recent work has illuminated enzymatic N-nitrosation reactions in microbial natural product biosynthesis, motivating interest in discovering additional metabolites constructed using such reactivity. Here, we use a genome mining approach to identify over 400 cryptic biosynthetic gene clusters (BGCs) encoding homologues of the N-nitrosating biosynthetic enzyme SznF, including the BGC for chalkophomycin, a CuII-binding metabolite that contains a C-type diazeniumdiolate and N-hydroxypyrrole. Characterizing chalkophomycin biosynthetic enzymes reveals previously unknown enzymes responsible for N-hydroxypyrrole biosynthesis, including the first prolyl-N-hydroxylase, and a key step in the assembly of the diazeniumdiolate-containing amino acid graminine. Discovery of this pathway enriches our understanding of the biosynthetic logic employed in constructing unusual heteroatom-heteroatom bond-containing functional groups, enabling future efforts in natural product discovery and biocatalysis.

Cp*Ir(III) complexes catalyzed solvent-free synthesis of quinolines, pyrroles and pyridines via an ADC strategy

A trio of Ir(III) complexes that are held together by a picolinamidato moiety were created. In our earlier research, we demonstrated the catalytic activity of the complexes for producing alpha-alkylated ketones from a ketone or secondary alcohol with a primary alcohol in the presence of a catalytic amount of a Cp*Ir(III) catalyst and tBuOK in toluene at 110 °C using the hydrogen-borrowing technique. Earlier many research groups had synthesized quinoline, pyrrole, and pyridine derivatives using 2-amino alcohol and ketone or secondary alcohol derivatives as starting materials, but in all those cases the reaction conditions are not suitable in terms of green synthesis like more catalyst loading, base loading, long reaction time, and high temperature. In addition, most of the reactions contain phosphine a hazardous by-product, along with the catalyst. Keeping in mind these shortcomings, we tried to expand the use of our catalysts after achieving an excellent result in our previous work, and we were successful in producing quinoline, pyrrole, and pyridine derivatives through acceptor-less dehydrogenative coupling (ADC) procedures at 90-110 °C under neat/solvent-free conditions and achieved good to exceptional yields of those nitrogen-containing heterocycles. This methodology is attractive because it is environmentally benign and allows for the "green" synthesis of nitrogen-containing heterocycles. All that is required is a modest quantity of catalyst and base, and the by-products are merely H2O and H2.

Mechanosynthesis of Pyrrole-2-carboxylic Acids via Copper-Catalyzed Spiroannulation/Ring-Opening Aromatization of 4-Arylidene Isoxazol-5-ones with Enamino Esters

An efficient and practical tandem reaction of 4-arylidene isoxazol-5-ones with enamino esters catalyzed by an inexpensive copper salt has been established in a ball mill. This innovative approach yields a diverse array of structurally novel pyrrole-2-carboxylic acids, showing excellent tolerance toward different functional groups. By integrating spiroannulation and ring-opening aromatization processes, this protocol introduces a facile and cost-effective strategy for synthesizing highly functionalized pyrrole derivatives.

Cobalt(II)-Catalyzed Synthesis of γ-Diketones from Aryl Alkenes and Its Utilization in the Synthesis of Various Heterocyclic Compounds

An earth-abundant Co(II) salt-catalyzed mild and affordable synthetic route has been developed for the synthesis of industrially relevant 1,4-dicarbonyl compounds (or γ-diketones) via oxidative coupling between aryl alkenes and ketones (both cyclic and acyclic) using TBHP and DBU as the oxidant and base, respectively. 1,4-Dicarbonyl compounds are known to be synthesized using expensive metal catalysts, dual catalysts, or low-cost metal complexes combined with an additive or ligand template, which further needs to be synthesized. Herein, we report the synthesis of 1,4-dicarbonyl compounds using cobalt(II) acetate as a catalyst without any expensive co-catalyst or ligand templates. This methodology has a broad substrate scope with significant yields and good functional group tolerance. Generation of unsymmetrical 1,4-dicarbonyls at room temperature and its versatile synthetic expansion to produce synthetically and biologically valuable heterocyclic compounds are salient features of this novel methodology. In addition, various controlled experiments such as primary kinetic isotope effect study, Hammett analysis with variation of the nature of the substituents on the styrene ring, and theoretical calculations (density functional theory) unravel the mechanistic intricacies involved in this new, simple, and atom-economic methodology.

Design, Synthesis, Biological Evaluation and in Silico Studies of Curcumin Pyrrole Conjugates

Curcumin conjugated heterocyclic compounds are potent candidates with drug likeness against various bacterial pathogens. A set of curcumin-based pyrrole conjugates (CPs) were synthesized and characterized by FT-IR, 1H and 13C NMR and HR-MS techniques. The results of free radical scavenging activity of the synthesized CPs, evaluated by FRAP and CUPRAC assays, showed the potency of these compounds as effective antioxidants. CP3 exhibits the highest antioxidant activity amongst the CPs. The bactericidal efficacy of CPs was screened against ESKAP bacterial pathogens, and CPs were found to possess better antibacterial property than curcumin, specifically against staphylococcus aureus bacteria. In addition, serum albumin (BSA and HSA) binding interaction of these CPs were determined by UV-visible and fluorescence spectrophotometric techniques. In-silico molecular docking study was performed to determine the binding patterns of molecular targets against Staphylococcus aureus tyrosyl tRNA synthetase, and serum albumin proteins. The structure-activity relationship showed that the presence of multiple phenolic hydroxyl groups, and electron withdrawing groups on the structure of CP molecule, enhances its antioxidant and antibacterial activity, respectively.

Elucidation of chalkophomycin biosynthesis reveals N-hydroxypyrrole-forming enzymes

Reactive functional groups, such as N-nitrosamines, impart unique bioactivities to the natural products in which they are found. Recent work has illuminated enzymatic N-nitrosation reactions in microbial natural product biosynthesis, motivating an interest in discovering additional metabolites constructed using such reactivity. Here, we use a genome mining approach to identify over 400 cryptic biosynthetic gene clusters (BGCs) encoding homologs of the N-nitrosating biosynthetic enzyme SznF, including the BGC for chalkophomycin, a CuII-binding metabolite that contains a C-type diazeniumdiolate and N-hydroxypyrrole. Characterizing chalkophomycin biosynthetic enzymes reveals previously unknown enzymes responsible for N-hydroxypyrrole biosynthesis, including the first prolyl-N-hydroxylase, and a key step in assembly of the diazeniumdiolate-containing amino acid graminine. Discovery of this pathway enriches our understanding of the biosynthetic logic employed in constructing unusual heteroatom-heteroatom bond-containing functional groups, enabling future efforts in natural product discovery and biocatalysis.

Reaction Pattern and Mechanistic Aspects of Iodine and Iodine-Based Reagents in Selenylation of Aliphatic, Aromatic, and (Hetero)Cyclic Systems

Organoselenium compounds have been the subject of extensive research since the discovery of the biologically active compound ebselen. Ebselen has recently been found to show activity against the main protease of the virus responsible for COVID-19. Other organoselenium compounds are also well-known for their diverse biological activities, with such compounds exhibiting interesting physical properties relevant to the fields of electronics, materials, and polymer chemistry. In addition, the incorporation of selenium into various organic molecules has garnered significant attention due to the potential of selenium to enhance the biological activity of these molecules, particularly in conjunction with bioactive heterocycles. Iodine and iodine-based reagents play a prominent role in the synthesis of organoselenium compounds, being valued for their cost-effectiveness, non-toxicity, and ease of handling. These reagents efficiently selenylate a broad range of organic substrates, encompassing alkenes, alkynes, and cyclic, aromatic, and heterocyclic molecules. They serve as catalysts, additives, inducers, and oxidizing agents, facilitating the introduction of different functional groups at alternate positions in the molecules, thereby allowing for regioselective and stereoselective approaches. Specific iodine reagents and their combinations can be tailored to follow the desired reaction pathways. Here, we present a comprehensive review of the progress in the selenylation of organic molecules using iodine reagents over the past decade, with a focus on reaction patterns, solvent effects, heating, microwave, and ultrasonic conditions. Detailed discussions on mechanistic aspects, such as electrophilic, nucleophilic, radical, electrochemical, and ring expansion reactions via selenylation, multiselenylation, and difunctionalization, are included. The review also highlights the formation of various cyclic, heterocyclic, and heteroarenes resulting from the in situ generation of selenium intermediates, encompassing cyclic ketones, cyclic ethers, cyclic lactones, selenophenes, chromones, pyrazolines, pyrrolidines, piperidines, indolines, oxazolines, isooxazolines, lactones, dihydrofurans, and isoxazolidines. To enhance the reader's interest, the review is structured into different sections covering the selenylation of aliphatic sp2/sp carbon and cyclic sp2 carbon, and then is further subdivided into various heterocyclic molecules.

B(C6F5)3-Catalyzed Dehydrogenation of Pyrrolidines to Form Pyrroles

Pyrroles are important N-heterocycles found in medicines and materials. The formation of pyrroles from widely accessible pyrrolidines is a potentially attractive strategy but is an underdeveloped approach due to the sensitivity of pyrroles to the oxidative conditions required to achieve such a transformation. Herein, we report a catalytic approach that employs commercially available B(C6F5)3 in an operationally simple procedure that allows pyrrolidines to serve as direct synthons for pyrroles. Mechanistic studies have revealed insights into borane-catalyzed dehydrogenative processes.

Mn(II) Promoted Divergent-Convergent Domino Reaction Giving Dinuclear Tetrasubstituted Pyrrole Complex

Domino reaction of benzo[d]thiazole-2-methylamine (S1) has been developed in the presence of MnCl2 ⋅ 4H2O, leading to tetrasubstituted pyrrole coordinated dinuclear Mn(II) complex 1 ([MnClP]2, P-=2,3,4,5-tetrakis(benzo[d]thiazol-2-yl)pyrrol-1-ide). The reaction process has been studied by assigning a series of intermediates based on time-dependent mass spectrometry, control experiments, crystallography, and density functional theory (DFT) theoretical calculation. A plausible mechanism involving an unprecedented divergent-convergent domino sequence has been proposed. Compound S1 could be activated by MnCl2 ⋅ 4H2O via coordination, which divergently produces two intermediates imine II (1-(benzo[d]thiazol-2-yl)-N-(benzo[d]thiazol-2-ylmethyl)methanimine) and alkene C (1,2-bis(benzo[d]thiazol-2-yl)ethene) through oxidative self-condensation and free radical coupling followed by elimination, respectively. They could then react with each other convergently via formal [3+2] cycloaddition to give deprotonated tetrasubstituted pyrrole coordinated intermediate [MnClP] after aromatization. Dimerization of [MnClP] produces the final product 1. Three C-C bonds and one C-N bond are formed through this six-step domino sequence. The corresponding organic skeleton (HP: 2,2',2'',2'''-(1H-pyrrole-2,3,4,5-tetrayl)tetrakis(benzo[d]thiazole)) has been obtained from 1 and shows a higher fluorescent quantum yield (52 %) than the reported 3,4-diphenyl substituted analogue 2,2'-(3,4-diphenyl-1H-pyrrole-2,5-diyl)bis(benzo[d]thiazole) (DPB) (42 %).

Chiral Au(III) chelates exhibit unique NCI-60 cytotoxicity profiles and interactions with human serum albumin

Au(III) bis(pyrrolide-imine) chelates are emerging as a class of versatile, efficacious metallodrug candidates. Here, we synthesised two enantiopure chiral ligands H2L1 and H2L2 (tetradentate cyclohexane-1,2-diamine-bridged bis(pyrrole-imine) derivatives). Metallation of the ligands with Au(III) afforded the chiral cationic complexes AuL1 and AuL2. The in vitro cytotoxicities of AuL1 and AuL2 determined in the NCI-60 single-dose drug screen were 56.5% and 89.1%, respectively. AuL1 was subsequently selected for a five-dose NCI-60 screen, attaining GI50, IC50, and LC50 values of 4.7, 9.3 and 39.8 μM, respectively. Hierarchical cluster analysis of the NCI-60 data indicated that the profile for AuL1 was similar to that of vinblastine sulfate, a microtubule-targeting vinca alkaloid. Reactions of AuL1 with glutathione (GSH) in vitro confirmed its susceptibility to reduction, Au(III) → Au(I), by intracellular thiols. Because human serum albumin (HSA) is responsible for transporting clinically deployed and investigational drugs, we studied the uptake of AuL1 and AuL2 by HSA to delineate how chirality impacts their protein-binding affinity. Steady-state fluorescence quenching data acquired on the native protein and data from site-specific probes showed that the compounds bind at sites close enough to Trp-214 (subdomain IIA) of HSA to quench the fluorophore. The bimolecular quenching rate constants, Kq, were ca. 102 times higher than the maximum diffusion-controlled collision constant of a biomolecule in water (1010 M-1 s-1), confirming that static fluorescence quenching was the dominant mechanism. The Stern-Volmer constants, KSV, were ∼104 M-1 at 37 °C, while the affinity constants, Ka (37 °C), measured ∼2.1 × 104 M-1 (AuL1) and ∼1.2 × 104 M-1 (AuL2) for enthalpy-driven ligand uptake targeting Sudlow's site I. Although far- and near-UV CD spectroscopy indicated that both complexes minimally perturb the secondary and tertiary structure of HSA, substantial shifts in the CD spectra were recorded for both protein-bound ligands. This study highlights the role of chirality in determining the cytotoxicity profiles and protein binding behaviour of enantiomeric Au(III) chelates.

Trifluoromethyl-β-dicarbonyls as Versatile Synthons in Synthesis of Heterocycles

Trifluoromethyl group relishes a privileged position in the realm of medicinal chemistry because its incorporation into organic molecules often enhances the bioactivity by altering pharmacological profile of molecule. Trifluoromethyl-β-dicarbonyls have emerged as pivotal building blocks in synthetic organic chemistry due to their facile accessibility, stability and remarkable versatility. Owing to presence of nucleophilic and electrophilic sites, they offer multifunctional sites for the reaction. This review covers a meticulous exploration of their multifaceted role, encompassing an in-depth analysis of mechanism, extensive scope, limitations and wide-ranging applications in diverse organic synthesis, covering the literature from the 21st century. This comprehensive review encapsulates the applications of trifluoromethyl-β-dicarbonyls and their synthetic equivalents as precursors of complex and diverse heterocyclic scaffolds, fused heterocycles and spirocyclic compounds having medicinal and material importance. Their potent synthetic utility in cyclocondensation reactions with binucleophiles, cycloaddition reactions, C-C bond formations, asymmetric multicomponent reactions using classical/solvent-free/catalytic synthesis have been presented. Influence of unsymmetrical trifluoromethyl-β-diketones on regioselectivity of transformation is also reviewed. This review will benefit the synthetic and pharmaceutical communities to explore trifluoromethyl-β-dicarbonyls as trifluoromethyl building blocks for fabrication of heterocyclic scaffolds having implementation into drug discovery programs in the imminent future.

Crystal structure and Hirshfeld surface analysis of (2E)-1-phenyl-3-(1H-pyrrol-2-yl)propen-1-one

The title com-pound, C13H11NO, adopts an E configuration about the C=C double bond. The pyrrole ring is inclined to the phenyl ring at an angle of 44.94 (8)°. In the crystal, mol-ecules are linked by N-H⋯O hydrogen bonds, forming ribbons parallel to (020) in zigzag C(7) chains along the a axis. These ribbons are connected via C-H⋯π inter-actions, forming a three-dimensional network. No significant π-π inter-actions are observed.

Site-selective chlorination of pyrrolic heterocycles by flavin dependent enzyme PrnC

Halogenation of pyrrole requires strong electrophilic reagents and often leads to undesired polyhalogenated products. Biocatalytic halogenation is a highly attractive approach given its chemoselectivity and benign reaction conditions. While there are several reports of enzymatic phenol and indole halogenation in organic synthesis, corresponding reports on enzymatic pyrrole halogenation have been lacking. Here we describe the in vitro functional and structural characterization of PrnC, a flavin-dependent halogenase that can act on free-standing pyrroles. Computational modeling and site mutagenesis studies identified three key residues in the catalytic pocket. A moderate resolution map using single-particle cryogenic electron microscopy reveals PrnC to be a dimer. This native PrnC can halogenate a library of structurally diverse pyrrolic heterocycles in a site-selective manner and be applied in the chemoenzymatic synthesis of a chlorinated analog of the agrochemical fungicide Fludioxonil.

Ag(I)-Mediated Annulation of 2-(2-Enynyl)pyridines and Propargyl Amines to Access 1-(2H-Pyrrol-3-yl)indolizines

An effective Ag(I)-mediated annulation of 2-(2-enynyl)pyridines and propargyl amines was developed, unexpectedly affording a broad range of functionalized 1-(2H-pyrrol-3-yl)indolizines in moderate to excellent yields. The developed method is characterized by operational simplicity, ready availability of starting materials, high regioselectivity, and broad substrate scope under mild reaction conditions. The Ag(I)-promoted cyclization of 2-(2-enynyl)pyridines and propargyl amines possibly results in the formation of the spiroindolizine, the ring-opening rearrangement of which may give the 1-(2H-pyrrol-3-yl)indolizine. Furthermore, a gram-scale reaction and synthetic transformations are also studied.

Visible Light-Induced Hydroacylation of Benzylidenemalononitriles with Aroyl Chlorides Using Silane as a Hydrogen Donor

A novel photoredox-catalyzed direct hydroacylation of benzylidenemalononitriles is described. In this method, aroyl chlorides are employed as a readily available and affordable source of acyl groups, while commercially available tris(trimethylsilyl)silane acts as both the hydrogen atom donor and electron donor. By eliminating the requirement for complex synthesis of acyl precursors and hydrogen atom-transfer (HAT) reagents, this approach offers a convenient and efficient strategy for the hydroacylation of benzylidenemalononitriles.

Self-Assembly of 4,4'-Linked Dipyrromethanes from Unconventional Reactants─Propargylamines, 2-(Vinyloxy)ethyl Isothiocyanate, and Alkylating Agents under Basic Conditions

Self-assembly of 4,4'-linked dipyrromethanes from 2-(vinyloxy)ethyl isothiocyanate, tertiary propargylamines, and alkylating agents has been discovered. The plausible reaction mechanism, the major stages of which have been confirmed experimentally, includes (1) the lithiation of propargylamine (with n-BuLi); (2) the formation of lithium N-[2-(vinyloxy)ethyl]but-2-ynimidothioate (product of the addition of monolithiated propargylamine to isothiocyanate); (3) isomerization of the latter in the corresponding allenylimidothioate (under the action of the t-BuOK/t-BuOH system); (4) low-temperature (<15 °C) intramolecular cyclization of the latter into potassium N-(5-amino-2-thienyl)-N-[2-(vinyloxy)ethyl]amide; (5) the base-induced cleavage of the C-O bond of the N-[2-(vinyloxy)ethyl] group and removal of vinyloxide-anion leading to acetaldehyde; (6) interaction of acetaldehyde with two molecules of N-(5-amino-2-thienyl)-N-[2-(vinyloxy)ethyl]amide-anion resulting in dithienomethane N-anionic intermediate; (7) recyclization of the latter into dipyrromethane S-anionic intermediate. Final S-alkylation affords synthetically challenging 4,4'-dipyrromethanes in a yield of 22-51%. The whole process is carried out in a single synthetic operation in a very short time (∼10-15 min, excluding alkylation time).

Gold-Catalyzed Cyclization of Yndiamides with Isoxazoles via α-Imino Gold Fischer Carbenes

Gold catalysis is an important method for alkyne functionalization. Here we report the gold-catalyzed formal [3+2] aminative cyclization of yndiamides and isoxazoles in a direct synthesis of polysubstituted diaminopyrroles, which are important motifs in drug discovery. Key to this process is the formation, and subsequent cyclization, of an α-imino gold Fischer carbene, which represents a new type of gold carbene intermediate. The reaction proceeds rapidly under mild conditions, with high regioselectivity being achieved by introducing a subtle steric bias between the nitrogen substituents on the yndiamide. DFT calculations revealed that the key to this regioselectivity was the interconversion of isomeric gold keteniminiun ions via a low-barrier π-complex transition state, which establishes a Curtin-Hammett scenario for isoxazole addition. By using benzisoxazoles as substrates, the reaction outcome could be switched to a formal [5+2] cyclization, leading to 1,4-oxazepines.

Dipyrrolonaphthyridinedione - (still) a mysterious cross-conjugated chromophore

Dipyrrolonaphthyridinediones (DPNDs) entered the chemical world in 2016. This cross-conjugated donor-acceptor skeleton can be prepared in two steps from commercially available reagents in overall yield ≈15-20% (5 mmol scale). DPNDs can be easily and regioselectively halogenated which opens an avenue to numerous derivatives as well as to π-expansion. Although certain synthetic limitations exist, the current derivatization possibilities provided impetus for numerous explorations that use DPNDs. Structural modifications enable bathochromic shift of the emission to deep-red region and reaching the optical brightness 30 000 M-1 cm-1. Intense absorption and strong emission of greenish-yellow light attracted the interest which eventually led to the discovery of their strong two-photon absorption, singlet fission in the crystalline phase and triplet sensitization. Dipyrrolonaphthyridinedione-based twistacenes broadened our knowledge on the influence of twisting angle on the fate of the molecule in the excited state. Collectively, these findings highlight the compatibility of DPNDs with various applications within organic optoelectronics.

Synthesis, Hydrolytic Stability and In Vivo Biological Study of Bioconjugates of the Tetrapeptides FELL Containing Pyrrole Moiety

BACKGROUND

Bioconjugates are promising alternatives for the multiple targeting of any disease. Pyrrole heterocycle is well known with many activities and is a building block of a lot of medical drugs. On the other hand, peptides are short molecules with many advantages such as small size, ability to penetrate the cell membrane and bond-specific receptors, vectorizing potential, etc. Thus, hybrid molecules between peptide and pyrrole moiety could be a promising alternative as an anti-pain tool.

METHODS

New bioconjugates with a general formula Pyrrole (α-/β-acid)-FELL-OH (NH2) were synthesized using Fmoc/OtBu peptide synthesis on solid support. HPLC was used to monitor the purity of newly synthesized bioconjugates. Their structures were proven by electrospray ionization mass spectrometry. The Paw Pressure test (Randall-Selitto test) was used to examinate the analgesic activity. Hydrolytic stability of targeted structures was monitored in three model systems with pH 2.0, 7.4 and 9.0, including specific enzymes by means of the HPLC-UV method.

RESULTS

The obtained results reveal that all newly synthesized bioconjugates have analgesic activity according to the used test but free pyrrole acids have the best analgesic activity.

CONCLUSIONS

Although free pyrrole acids showed the best analgesic activity, they are the most unstable for hydrolysis. Combination with peptide structure leads to the hydrolytic stabilization of the bioconjugates, albeit with slightly reduced activity.