C2 Position Research Articles

Synthesis of Novel 3,4-Dihydropyrimidine Derivatives, Cytotoxic Activity Evaluation, Apoptosis, Molecular Docking Studies, and MD Simulations.

In this study, twelve 3,4-dihydropyrimidines derivatives were synthesized through Biginelli multi-component reaction. The efficacy of these compounds against MCF-7, A549, and HeLa cells was evaluated using the MTT method. The results showed that designed derivatives were more effective against A549 cancer cells than MCF-7 and HeLa cells. Compound 5l (bearing 4-Cl-phenyl at C4 of 3, 4-dihydropyrimidin-2(1H)-one ring) was the most potent analogue (A549: 18.65±1.87 μM, HeLa: 26.59±2.71 μM, MCF-7: 31.82±2.64 μM). The presence of an electron-withdrawing group with optimum lipophilicity at the C4 position of the phenyl ring increased the cytotoxic effect. The flow cytometry findings indicated that compound 5l induced apoptosis in A549 cancer cells in a dose-dependent manner. Eg5 and AKT1 were selected as molecular modeling target by applying pharmacology network analyses. The molecular docking results indicated that both enantiomers of compound 5l had significant interactions with key residues in both Eg5 (Gly117 and Glu116) and AKT1 (Ala123 and Glu121) active sites. However, MD simulation revealed that the R enantiomer had a more stable complex and a higher binding affinity to the Eg5 enzyme active site than the S-enantiomer. The affinity of 5l (R enantiomer) to Eg5 was predicted more than AKT1.

Au(I)-Catalyzed Regioselective Hydrogen Isotope Labeling of Indoles.

The gold(I)-catalyzed hydrogen isotope exchange reaction on indoles and related heterocycles is described under mild conditions and low catalyst loadings, using CD3OD and D2O as readily available deuterium sources. C3-unsubstituted indoles are labeled at the C3 position with exquisite regioselectivity, while C3-substituted indoles are labeled at the C2 position. The method is also applicable to the regioselective tritiation of indoles. Mechanistic studies revealed the involvement of aurated indoles as key intermediates.

Palladium‐Catalyzed C4,C5‐Diarylation of Isoxazole‐3‐carboxylate by Double C–H Bond Functionalization

The Pd‐catalyzed C4‐arylation of 3,5‐disubstituted isoxazoles via C‐H bond functionalization has been largely described. By contrast, the reactivity of isoxazoles in C‐H bond functionalization with both unsubstituted C4 and C5 positions remains largely unexplored. Herein, we report on the reactivity in Pd‐catalyzed double C‐H bond arylation of an isoxazole with unsubstituted C4 and C5 positions. Conditions for the palladium‐catalyzed direct C4,C5‐diarylation of ethyl isoxazole‐3‐carboxylate using aryl bromides as the aryl source are reported. This procedure tolerates several useful substituents on the aryl bromide such as nitrile, acetyl, formyl, benzoyl, alkoxycarbonyl, chloro, fluoro, trifluoromethyl, trifluoromethoxy, cyanomethyl,tertbutyl and methoxy at para‐ and meta‐positions. Conversely, with ortho‐substituted aryl bromides, mixtures of mono‐ and di‐arylated isoxazoles were generally obtained. This methodology provides a simple one pot access to a wide variety of C4,C5‐diarylated isoxazoles from commercially available substrates allowing to modify easily their biological properties.

Dual-function natural products: Farnesoid X receptor agonist/inflammation inhibitor for metabolic dysfunction-associated steatotic liver disease therapy

Metabolic dysfunction-associated steatotic liver disease (MASLD) is the most prevalent chronic liver disease globally, with only one Food and Drug Administration (FDA)-approved drug for its treatment. Given MASLD’s complex pathophysiology, therapies that simultaneously target multiple pathways are highly desirable. One promising approach is dual-modulation of the farnesoid X receptor (FXR), which regulates lipid and bile acid metabolism. However, FXR agonists alone are insufficient due to their limited anti-inflammatory effects. This study aimed to dto identify natural products capable of both FXR activation and inflammation inhibition to provide a comprehensive therapeutic approach for MASLD. Potential FXR ligands from the Natural Product Library were predicted via virtual screening using the Protein Preparation Wizard module in Schrodinger (2018) for molecular docking. Direct binding and regulation of candidate compounds on FXR were analyzed using surface plasmon resonance (SPR) binding assay, reporter gene analysis, and reverse transcription-polymerase chain reaction (RT-PCR). The anti-inflammatory properties of these compounds were evaluated in AML12 cells treated with tumor necrosis factor-alpha (TNF-α). Dual-function compounds with FXR agonism and inflammation inhibition were further identified in cells transfected with Fxr siRNA and treated with TNF-α. The effects of these dual-function compounds on lipid accumulation and inflammation were evaluated in cells treated with palmitic acid. Results revealed that 17 natural products were predicted via computational molecular docking as potential FXR agonists, with 15 exhibiting a strong affinity for FXR recombinant protein. Nine isoflavone compounds significantly enhanced FXR reporter luciferase activity and the mRNA expressions of Shp and Ostb. Structure-activity relationship analysis indicated that introducing isopropyl or methoxy groups at the C7 position or a methoxy group at the C6 position could enhance the agonistic efficacy of isoflavones. Three compounds (2, 6, and 8) were identified as dual-function natural products functioning as FXR agonists and inflammatory inhibitors, while one compound (12) acted as an FXR agonist to inhibit inflammation. These natural products protected hepatocytes against palmitic acid-induced lipid accumulation and inflammation. In conclusion, compounds 2, 6, and 8 (genistein, biochanin A, and 7-methoxyisoflavone, respectively) were identified as dual-function bioactive products that transactivate FXR and inhibit inflammation, serving as potential candidates or lead compounds for MASLD therapy.

Green synthesis of 2-trifluoromethylquinoline skeletons via organocatalytic N-[(α-trifluoromethyl)vinyl]isatins C-N bond activation

The Pfitzinger reaction has long served as a notable synthesis pathway for quinoline-4-carboxylic acids. Although recognized for its synthetic potential since its discovery more than 138 years ago, a truly catalytic variant has remained elusive until now. Herein, we present a novel 2-tert-butyl-1,1,3,3-tetramethylguanidine (BTMG)-catalyzed Pfitzinger reaction that employs N-[(α-trifluoromethyl)vinyl]isatins with amines and alcohols, providing direct routes to 2-CF3-quinoline-4-carboxamides and carboxylic esters. This method is not only green and environmentally benign but also accommodates the introduction of other functional groups like CF2H and CO2Me at the C2 position of quinoline skeleton. The utility of this methodology was demonstrated by the broad substrate scope, the late-stage modification of commercial drugs, and the diverse derivatization of quinoline framework. More importantly, this work not only opens up a new avenue for the activation of amide C-N bonds in catalytic reaction development, but also unlocks the huge potential of some 2-trifluoromethyl quinolines with strong inhibitory activity against PTP1B or optoelectronic application in organic light-emitting diodes.

New CYP154C4 from Streptomyces cavourensis YBQ59 performs regio- and stereo- selective 3β-hydroxlation of nootkatone

Nootkatone, a sesquiterpenoid widely used in the food and cosmetics industries, exhibits diverse biological activities and pharmaceutical prospects. Modification of nootkatone to create new derivatives with desirable activities has attracted significant attention. For this purpose, cytochrome P450 monooxygenases (P450 or CYP) are attractive candidates due to their ability to perform regio- and stereoselective hydroxylation at allylic C–H bonds. In this study, CYP154C4 from Streptomyces cavourensis YBQ59 was cloned and expressed in Escherichia coli. By screening 64 candidate substrates, this P450 was found to catalyze the regio- and stereoselective hydroxylation of nootkatone, yielding a single product, 3β-hydroxynootkatone. Using a whole-cell E. coli system expressing CYP154C4, supported by the heterologous redox partners YkuN from Bacillus subtilis and FdR from E. coli, 3β-hydroxynootkatone was produced on a preparative scale. The structure of this compound was determined by 1H NMR, 13C NMR, NOESY, HMBC, and HSQC. The kinetics of product formation were analyzed using HPLC, and the Km and Kcat values were calculated. Furthermore, structural insights into the selective hydroxylation of nootkatone were elucidated by molecular docking. 3β-Hydroxynootkatone, recently synthesized semi-synthetically from nootkatone, has been reported to exhibit a higher insecticidal activity than its parent compound. Additionally, the functionalization of nootkatone with N-acyl-2-aminothiazole at the C3 and C2 positions, yielding an α-glucosidase inhibitor, has also been previously described. Therefore, 3β-hydroxynootkatone has great potential for further research and for synthesizing new derivatives with valuable biological activities for agricultural and medicinal applications.

A Reactivity Study of 4-Hydroxy-2H-chromene-2-thione and 4-Hydroxy-2H-thiochromene-2-thione with tert-Butyl Nitrite and Aromatic Amines: An Environmentally Benign Synthesis of New Hydrazone Derivatives

AbstractThe synthesis of biologically active coumarin-based hydrazone derivatives is achieved through a one-pot, three-component reaction of 4-hydroxy-2H-chromene-2-thiones with aniline derivatives and tert-butyl nitrite under solvent- and catalyst-free conditions in yields of 76–86%. Similarly, the reactions of 4-hydroxydithiocoumarins with aniline derivatives and tert-butyl nitrite under identical conditions provided the corresponding hydrazone products in 79–85% yield through a four-component reaction. It is observed in both cases that the C=S group at the C2 position is converted into a C=O moiety. However, the intermediate products derived from 4-hydroxydithiocoumarin react further with another aniline molecule leading to thioesters. 4-Hydroxy-2H-chromene-2-thione and 4-hydroxydithiocoumarin exhibit distinct reactivity pathways, resulting in the formation of two different types of product. In addition, quantum chemical analysis of the mechanistic steps show that this reaction is exergonic. This protocol offers broad substrate scope and tolerates various functional groups, leading to high product yields in short reaction times.

A Facile and Regioselective Synthesis of 2‐Formamidothiazoles via the C−H Formamidation of Thiazole N‐oxides with Isocyanides

A facile, microwave‐promoted, regioselective C−H formamidation of thiazole N‐oxides with isocyanides in the presence of TBDPSCl was developed. Various 2‐(N‐substituted formamido)thiazoles were obtained in moderate to high yields. In the case of the C2‐substituted thiazole N‐oxides, the C‐H formamidation took place selectively at the C4 position of the thiazole ring. This transformation is also applicable to some other N‐containing heterocyclic derivatives such as pyridine, quinoline, and pyridazine N‐oxides and has advantages such as broad substrate tolerance, high regioselectivity, and mild reaction conditions.

Regiodivergent Functionalization of Protected and Unprotected Carbohydrates using Photoactive 4‐Tetrafluoropyridinylthio Fragment as an Adaptive Activating Group

AbstractThe selective functionalization of carbohydrates holds a central position in synthetic carbohydrate chemistry, driving the ongoing quest for ideal approaches to manipulate these compounds. In this study, we introduce a general strategy that enables the regiodivergent functionalization of saccharides. The use of electron‐deficient photoactive 4‐tetrafluoropyridinylthio (SPyf) fragment as an adaptable activating group, facilitated efficient functionalization across all saccharide sites. More importantly, this activating group can be directly installed at the C1, C5 and C6 positions of biomass‐derived carbohydrates in a single step and in a site‐selective manner, allowing for the efficient and precision‐oriented modification of unprotected saccharides and glycans.

A Novel A105Y Mutant of CYP17A1 Exhibits Almost Perfect Regioselectivity in the Production of 17α-Hydroxyprogesterone.

17α-Hydroxyprogesterone (17α-OHP) is a steroid hormone with significant biological activity that can be obtained by catalyzing progesterone (PROG), the main product of sitosterol, through CYP17A1. However, increasing the catalytic specificity of HCYP17A1 for C17 hydroxylation of progesterone (PROG) poses a formidable challenge due to the close proximity of the C16 and C17 positions. In this study, a rational design was utilized to alter the spatial configuration of the substrate channel, leading to the complete abolition of its 16-hydroxylation activity. Subsequent molecular dynamics simulations revealed that the A105Y mutation heightened the rigidity of the G95-I112 region of CYP17A1, consequently regulating the direction of the entry of PROG into the catalytic pocket. Moreover, the establishment of hydrogen bonding between Y105 and R239, coupled with Pi-stacking of A105Y with F114, effectively immobilizes the substrate PROG in a fixed position, explaining the practically perfect regioselectivity observed in A105Y. Finally, a multifaceted enzymatic cascade system, incorporating A105Y, cytochrome P450 reductase (CPR), and glucose-6-phosphate dehydrogenase (ZWF) for NADPH cofactor regeneration, was constructed in Pichia pastoris GS115. The resulting biocatalyst produced 106 ± 3.2 mg L-1 17α-OHP, a 4.6-fold increase compared with A105Y alone. Thus, this study provides valuable insights for improving the regioselectivity and activity of P450 enzymes.

Hydrogen-Bond-Assisted Catalysis: Hydroxylation of Paclitaxel by Human CYP2C8.

Paclitaxel (PTX, or Taxol), a chemotherapeutic agent widely employed in the treatment of various cancers, undergoes metabolic transformations through the cytochrome P450 enzymes CYP3A4 and CYP2C8. CYP3A4 catalyzes the aromatic hydroxylation reaction of PTX, whereas CYP2C8 demonstrates a distinct reactivity pattern, producing 6α-hydroxypaclitaxel via alkane hydroxylation. Despite the significant impact of PTX metabolism on its anticancer efficacy, the detailed mechanisms underlying these transformations have remained largely unclear. In this study, we employed hybrid quantum mechanics and molecular mechanics (QM/MM) calculations to elucidate the mechanism of PTX metabolism by human CYP2C8. Our QM/MM results reveal that the hydroxylation of PTX by CYP2C8 follows an atypical rebound mechanism. Either of the two hydrogen atoms at the C6 position of PTX can be abstracted, leading to a common radical intermediate. Although the subsequent rebound barrier is unusually high, stereochemical scrambling is unlikely, as the rebound barrier for the formation of the 6α-hydroxylated PTX─the actual product─is significantly lower than that for the 6β-hydroxylated metabolite. Thus, product selectivity is determined by the non-rate-determining rebound step. Furthermore, the hydroxyl group at the C7 position of PTX plays a catalytic role by facilitating the hydrogen abstraction and rebound steps. Our study also confirms a pronounced stability of the transition state in the high-spin sextet spin state, enabled by the enzyme's specific substrate positioning.

Tandem Knoevenagel‐Aldol Cyclization Towards Di and Trisubstituted Pyridines: Use of Malonaldehyde and Diethyl Malonate for the Synthesis of Indolizine

AbstractAn effective method for the construction of a multi‐functionalized pyridine motif of indolizine using the [4+2] annulation pathway involves tandem Knoevenagel‐aldol cyclization as a critical step in the process. The production of an indolizine scaffold with a hydroxy group at the C6 position and an ethyl ester/aldehyde group at the C7 position was successfully accomplished using this approach with an excellent yield, with the use of a reagent that contains active methylene and operates under mild conditions. This straightforward and simple protocol allows extensions of the core moiety in a quick and dependable manner.

Ru(II)-Catalyzed C7 Trifluoromethylthiolation and Thioarylation of Indolines Using Bench-Stable Reagents.

A Ru(II)-catalyzed C(sp2)-H trifluoromethylthiolation and thioarylation of indolines using bench-stable reagents have been explored. Diversely substituted indolines were functionalized at C7 position in good to excellent yields. Radical quenching, deuterium labeling, KIE, and reaction order determination experiments were performed to support the proposed reaction pathway. Gram-scale synthesis and post-transformation of the synthesized products have also been carried out to demonstrate the applicability of the developed catalytic protocol.

Convenient partial reduction of CO2 to a useful C1 building block: efficient access to 13C‐labelled N‐heterocyclic carbenes

The selective, transition metal‐free hydrosilylation of CO2 to CH2(OSiEt3)2 has been achieved under mild conditions and in high isolated yields (up to 90%) using Et3SiH and the simple, easily prepared borohydride catalyst Li+[HB(C6F5)3]−. The resulting CO2‐derived bis(silyl)acetal product – whose mechanism of formation has been interrogated through detailed computational and experimental studies – can be rapidly valorized through the facile synthesis of N‐heterocyclic carbenes, via their corresponding imidazolium salts. By using relatively inexpensive, isotopically enriched 13CO2 this protocol can be exploited to prepare NHC isotopologues that are selectively 13C labelled at the key, ligating C2 position. This provides an electronically responsive 13C NMR spectroscopic handle with dramatically enhanced sensitivity which can directly benefit reactivity studies in both organo‐ and organometallic catalysis, where NHC use is ubiquitous.

Dicarbatriphyrin(2.1.1) and its Carbacalix[1]phyrin Analogue: Structure-Property Relationships and Application as a Fe(III) Chemosensor.

The investigation of unsaturated or π-conjugated hydrocarbons, particularly within the macrocyclic framework, has garnered significant interest due to their fundamental properties and practical applications. This research focuses on the synthesis and characterization of a novel stable dicarbatriphyrin(2.1.1) which was constructed by amending the [14]triphyrin(2.1.1) framework by, replacing two pyrrole rings with meta-connected phenyl rings and introducing an o-benzene bridge at the C2 position. The structural modification resulted in a saddle-shaped macrocyclic core with negative Gaussian curvature, as confirmed by crystal structure analysis. This unique molecular topology offers acumens into the structure-property relationships in the curved locally π-conjugated contracted porphyrinoids. The macrocycle exhibits fluorescent emission in solution, which is selectively quenched by Fe(III) ions, highlighting its potential as a chemosensor for Fe(III) cations. Additionally, the formation of carbacalix[1]phyrin(2.1.1), a phlorin analogue of dicarbatriphyrin(2.1.1), which exhibits a chair conformation in contrast to the saddle-shaped structure of its oxidized counterpart. Remarkably, the emergence of a mono-pyrrolic calixbenziphyrin marks an unprecedented advancement in the field of calixphyrin chemistry. Moreover, theoretical studies provide strong support for the experimental findings, reinforcing the conclusions drawn from the structural and functional analyses.

Retinoids Molecular Probes by Late-stage Azide Insertion - Functional Tools to Decrypt Retinoid Metabolism.

Studying the complex and intricate retinoids metabolic pathways by chemical biology approaches requires design and synthesis of biologically functional molecular probes. Only few of such molecular retinoid probes could be found in literature, most of them bearing a molecular structure quite different from natural retinoids. To provide close-to-native retinoid probes, we have developed a versatile late-stage method for the insertion of azide function at the C4 position of several retinoids. This one-step process opens straightforward access to different retinoid and carotenoid probes from commercially available precursors. We have further demonstrated that the different molecular probes retain ability of the original compound to activate genes' transcription, despite azide insertion, highlighting biological activities that were further validated in zebrafish in vivo model. The present work paves the way to future studies on vitamin A's metabolism.

Optimization of the Introduction of 2,6-Dimethylphenol at the C4-Atom of 2’-Deoxythymidine for the Preparation of Modified Oligonucleotides

Nucleic acids, including DNA and RNA, are vital for genetic information storage and expression, finding applications in diverse fields. Chemical synthesis is commonly used for nucleic acid modification, utilizing protecting groups to selectively modify specific positions without disrupting the overall structure. This study focuses on optimizing the introduction of a 2,6-dimethylphenoxy group at the C4 position of a protected 2’-deoxythymidine, a modification for enhancing stability, binding affinity, and expanding chemical diversity for future applications in therapeutics, diagnostics, and nanomaterials. Silylation was used as the initial step for 2’-deoxythymidine protection, followed by the preparation of the modified nucleoside. Optimization of synthetic procedures involved adjustments of reaction parameters, such as solvent and reagent stoichiometry, using small- and large-scale reactions. Extensive experimentation revealed that changing the solvent from tetrahydrofuran to dichloromethane and using 1,8-diazabicyclo [5.4.0] undec-7-ene as the base provided significant progress in reaction efficiency. Analytical techniques, including thin-layer chromatography and 1H Nuclear Magnetic Resonance spectroscopy, were employed for monitoring and confirmation of compound identity and purity. Successful optimization of the synthetic protocol will contribute to nucleic acid modification chemistry advancement with potential applications in therapeutics or diagnostics.

Rational Molecular Design of Phenanthroimidazole-Based Fluorescent Materials toward High-Efficiency Deep-Blue OLEDs by Molecular Isomer Engineering.

Organic light-emitting diodes (OLEDs) have been extensively investigated in full-color displays and energy-saving lighting owing to their unique advantages. However, deep-blue OLEDs based on nondoped emitting layers with a satisfactory external quantum efficiency (EQE) are still rare for applications. In this work, six hot exciton materials, PPIM-12F, PPIM-22F, PPIM-13F, PPIM-23F, PPIM-1CN, and PPIM-2CN, are designed and synthesized via an isomer engineering design strategy and their photophysical properties and OLED performance are systematically investigated. These emitters all possess wide band gaps (3.53-3.69 eV), hybrid local and charge transfer (HLCT) characteristics, and good thermal stabilities. The C2 series compounds, PPIM-22F, PPIM-23F, and PPIM-2CN, all show redder emission peaks than the N1 series counterparts of PPIM-12F, PPIM-13F, and PPIM-1CN. In addition, the LUMO energy levels decrease consecutively in the sequence of PPIM-22F < PPIM-23F < PPIM-2CN and are all lower than their respective N1 series position isomers of PPIM-12F, PPIM-13F, and PPIM-1CN. The CV measurements indicate that such a design strategy renders the fine-tuning of LUMO energy levels, and the incorporation of electron acceptors at the extended C2 position of the PI unit is a better choice to improve the electron injection ability. Theoretical simulations indicate that they may harvest the triplet exciton through an upper-level reverse intersystem crossing process, which decreases the gathering of triplet excitons and allows the OLEDs to be fabricated by nondoping technology. Among them, PPIM-22F with a difluorobenzene substituent at the C2 position manifests the best performance in OLEDs, which exhibits the maximum EQE of 7.87% and Commission Internationale de ĺEclairage (CIE) coordinates of (0.16, 0.10). This work demonstrates an effective strategy for considerable improvement in device performance by a subtle change in the molecular structure through isomer engineering.

The Anticholinesterase Perspective of Dimethoxyindole Based Benzenesulfonamides: Synthesis, Biological Investigation and Molecular Docking Applications

AbstractDue to the well‐known biological potential of benzenesulfonamides for the inhibition of specific enzymes, here in, we propose to investigate anticholinesterase efficiencies of five newly synthesized benzenesulfonamides incorporating dimethoxyindole tails. The targeted compounds were synthesized through the C7 position of the methyl 4,6‐dimethoxy‐1H‐indole‐2‐carboxylate via Schiff‐base reaction. The biological study was directed to identify the acetylcholinesterase (ACh) and butyrylcholinesterase (BCh) enzyme inhibitions. The molecular docking studies were also carried out to determine the possible poses of ligands 8 a–e in binding sites of enzymes and ligand‐residue interactions. Molecular dynamics simulations, RMSD and RMSF plots, hydrogen bond analysis, per‐residue energy decomposition and MM‐PB(GB)/SA calculations were carried out investigate the potentials of the compounds towards the designated enzymes. It is important to note that all the synthesized compounds were found to be selective towards the BChE inhibition with a range of efficiencies. In addition to that the compound 8 a exhibited more potency than the standard Galanthamine with the value of 87.75 % for the same enzyme. The results could be valuable for the determination of new targets which are highly selective for BChE inhibition. The formation of hydrogen bonds and hydrophobic interactions with the residues located on the compounds were responsible for the binding free energy scores. The stability of all the compounds proved by molecular dynamics simulations were also promising for the further directions of the study.

Palladium-catalyzed ring-opening/defluorinative coupling of gem-DFCPs with pyranones/pyridones

The monofluoroalkenes are found widespread applications in areas such as bioactive molecules, materials science and synthetic organic chemistry, therefore, investigating efficient methodologies to construct monofluoroalkenes is still in demand. In this paper, we reported an efficient synthesis of monofluoroalkenyl substituted pyranones/pyridones by using the gem-difluorocyclopropanes (gem-DFCPs) as monofluoroalkenyl precursors. In the presence of Palladium catalyst, the monofluoroalkenyl group was introduced into the C3 positions of pyranones/pyridones successfully. The reaction was featured with high regioselectivity, mild conditions, broad substrate scope, easy to scale up synthesis, which provided a novel avenue for the late-stagy modification of pyranones/pyridones.