C2 Position Research Articles

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.

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±1.87μM, 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.

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.

Amino acid based natural deep eutectic solvents: An efficient catalyst and solvent for N-acetyl-d-glucosamine conversion into organonitrogen chemicals

Organonitrogen chemicals are widely used and in great demand in the food, pharmaceutical and chemical industries. Hence, it is important to develop green and efficient synthesis paths to organonitrogen chemicals for their use as new resources. Herein, we propose the preparation of organonitrogen chemicals from chitin biomass monomer N-acetyl-d-glucosamine (GlcNAc) promoted by natural deep eutectic solvents (NADESs). The selective generation of 3-acetamido-5-(1′,2′-dihydroxyethyl) furan (Chromogen III) and 3-acetamido-5-acetylfuran (3A5AF) from GlcNAc was achieved by the design of NADESs components. GlcNAc reacts in binary NADES proline-glycerol (Pro-Gly) to generate 26 % of Chromogen III and 39 % of 3A5AF in ternary NADES proline-glycerol-lactic acid (Pro-Gly-LA). In addition, the intermolecular hydrogen bonds in NADESs were confirmed through 1H diffusion-ordered spectroscopy (DOSY) NMR technology. And the results of 13C NMR chemical shift titration indicated interaction between NADESs and the C3 and C6 position of GlcNAc. Based on the NMR experiments a mechanism is proposed.

Biochemical and structural insights of a recombinant AA16 LPMO from the marine and sponge-symbiont Peniophora sp

Lytic polysaccharide monooxygenases (LPMOs) are copper-dependent enzymes that oxidize polysaccharides, leading to their cleavage. LPMOs are classified into eight CAZy families (AA9-11, AA13-17), with the functionality of AA16 being poorly characterized. This study presents biochemical and structural data for an AA16 LPMO (PnAA16) from the marine sponge symbiont Peniophora sp. Phylogenetic analysis revealed that PnAA16 clusters separately from previously characterized AA16s. However, the structural modelling of PnAA16 showed the characteristic immunoglobulin-like fold of LPMOs, with a conserved his-brace motif coordinating a copper ion. The copper-bound PnAA16 showed greater thermal stability than its apo-form, highlighting copper's role in enzyme stability. Functionally, PnAA16 demonstrated oxidase activity, producing 5 μM H₂O₂ after 30 min, but showed 20 times lower peroxidase activity (0.27 U/g) compared to a fungal AA9. Specific activity assays indicated that PnAA16 acts only on cellohexaose, generating native celloligosaccharides (C3 to C5) and oxidized products with regioselective oxidation at C1 and C4 positions. Finally, PnAA16 boosted the activity of a cellulolytic cocktail for cellulose saccharification in the presence of ascorbic acid, hydrogen peroxide, or both. In conclusion, the present work provides insights into the AA16 family, expanding the understanding of their structural and functional relationships and biotechnological potential.

An arabinan from Citrus grandis fruits alleviates ischemia/reperfusion-induced myocardial cell apoptosis via the Nrf2/Keap1 and IRE1/GRP78 signaling pathways

Citrus grandis fruit is a famous traditional Chinese medicine with various bioactivities, including cardioprotective effects. Polysaccharides are one of the key active ingredients responsible for its cardioprotective effects. This study aimed to investigate the structure and cardioprotective effect of a homogeneous polysaccharide from C. grandis fruit (CGP80-1) and explore its mechanism against myocardial ischemia-reperfusion (MI/R) injury. Structure analysis showed that CGP80-1 (11,917 Da) is an arabinan with compact coil chain conformation, containing →5)-α-L-Araf-(1→, →3,5)-α-L-Araf-(1→, and →2,3,5)-α-L-Araf-(1→ as the backbone, as well as →5)-α-L-Araf-(1→ and t-α-L-Araf as side-chains substituted at the C2 and C3 positions. Pharmacological experiments showed that pre-treatment with CGP80-1 could effectively alleviate MI/R injury by improving endogenous antioxidant enzymes and cardiac enzymes, reducing reactive oxygen species levels, and regulating apoptosis-related proteins such as caspase-3, Bax, and Bcl-2. The protective effects were correlated with the Nrf2/Keap1 and IRE1/GRP78 signaling pathways. Further analysis of structure-activity relationships revealed that the myocardial protection effects of CGP80-1 might be attributed to its appropriate molecular weight, high arabinose content, and unique compact coil chain conformation. Overall, our results provide insight into the chemical structure of CGP80-1 and its mechanism of action, suggesting that CGP80-1 could be a candidate drug for myocardial protection.

Chemoenzymatic Modification of Daptomycin: Aromatic Group Installation on Trp1.

Daptomycin is a cyclic lipodepsipeptide antibiotic used to treat infections caused by Gram-positive pathogens, including multi-drug resistant strains such as methicillin-resistant Staphylococcus au-reus (MRSA) and vancomycin-resistant enterococci (VRE). The emergence of daptomycin-resistant bacterial strains has renewed interest in generating daptomycin analogs. Previous studies have shown that replacing the tryptophan of daptomycin with aromatic groups can generate analogs with enhanced potency. Additionally, we have demonstrated that aromatic prenyltransferases can attach diverse groups to the tryptophan of daptomycin. Here, we report the use of the prenyltransferase CdpNPT to derivatize the tryptophan of daptomycin with a library of benzylic and heterocyclic pyrophosphates. An analytical-scale study revealed that CdpNPT can transfer various aromatic groups onto daptomycin. Subsequent scaled-up and purified reactions indicated that the enzyme can attach aromatic groups to N1, C2, C5 and C6 positions of Trp1 of daptomycin. In vitro antibacterial activity assays using six of these purified compounds identified aromatic substituted daptomycin analogs show potency against both daptomycin-susceptible and resistant strains of Gram-positive bacteria. These findings suggest that installing aromatic groups on the Trp1 of daptomycin can lead to the generation of potent daptomycin analogs.

Sydnone-based prosthetic groups for radioiodination

The potential of Strained-Promoted Sydnone-Alkyne Cycloaddition (SPSAC) for radioiodination was evaluated with model cyclooctyne-conjugated peptides. Starting with a series of sydnones with varying N3 and C4 substitution, a preliminary kinetic study with non-radioactive iodinated compounds highlighted the superiority of an arylsydnone substituted by a chlorine atom in C4 position. Interestingly, reaction rate up to 11 times higher than using an azide was achieved with the best system. Access to 125I-labelled sydnones was granted with high efficiency from arylboronic acid precursors by copper catalyzed nucleophilic substitution. Application of SPSAC on the model peptide in radiotracer conditions showed the same trend than in non-radioactive kinetic study and complete reactions could be achieved within less than an hour for the best systems. These results are favorable for use in the production of radiopharmaceuticals with heavy halogens and increase the diversity of available bioorthogonal reaction for nuclear imaging and therapy.

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

The 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.