Monthly Archives: September 2023

Antibacterial Compound Isolation and Characterization from the Plant Cynotis axillaris Schult

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Antibacterial Compound Isolation and Characterization from the Plant Cynotis axillaris Schult


Abstract

A novel flavone glycoside was isolated from the methanolic extract of Cynotis axillaris Schult. Various analysis and characterization techniques were used to determine its structure and properties. The compound exhibited a melting point range of 231–232 °C and had a molecular formula of C27H30O14. Several spectral characterization techniques were employed to establish the isolated compound's structure. These included UV-visible spectroscopy, FT-IR, LC-ESI-MS, and NMR spectroscopy. Based on these analyses, the structure of the isolated compound was determined to be 5,7,4’-trihydroxyflavone-8-α-L-rhamnopyranoside-4’-O-β-D-galactopyranosyl. This structure indicates that it is a flavone glycoside consisting of a flavone (5,7,4’-trihydroxyflavone) moiety attached to a sugar molecule (galactopyranosyl) at position 4’, which further bears a rhamnose group at position 8 of the flavone. In addition, to the structural characterization, the compound also demonstrated significant antibacterial efficacy against various bacterial pathogens, including Gram-positive bacteria such as Bacillus subtilis MTCC441 and Gram-negative bacteria such as Escherichia coli MTCC1098, Proteus vulgarize MTCC426, and Salmonella Typhimurium MTCC3224. The antimicrobial activity was evaluated by measuring the zone of inhibition in millimetres, which provides an indication of the compound's ability to inhibit bacterial growth. The study successfully identified and characterized a novel flavone glycoside from Cynotis axillaris Schult. and its antimicrobial activity.

Chloride‐Bridged Dimeric SalphenZr(IV) Cobaltate Catalyst Unleashes the Potential of Base‐Free Carbonylative Polymerization for Biodegradable PHAs

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Chloride-Bridged Dimeric SalphenZr(IV) Cobaltate Catalyst Unleashes the Potential of Base-Free Carbonylative Polymerization for Biodegradable PHAs†

Poly(3-hydroxyalkanoates) (PHA), promising biodegradable polymers, are hindered by the lack of efficient catalytic systems for competitive commercialization. Addressing this, we introduce a chloro-bridged dimeric salphen zirconium cobaltate complex. Under mild conditions under base-free conditions, it achieves full monomer conversion, 92% PHA selectivity, and challenges the prevailing β-lactone pathway. Instead, direct epoxide and carbon monoxide co-polymerization emerges as a unique and efficient PHA synthesis mechanism


Comprehensive Summary

Poly(3-hydroxyalkanoates) (PHAs) are a promising class of biodegradable polymers, exhibiting properties comparable to traditional petroleum-based counterparts. Nonetheless, the widespread commercialization of PHAs is hindered by the absence of an efficient and economically viable catalytic system, impeding their competitiveness against non-biodegradable polymers. In an effort to address this challenge, we present a study on a newly developed chloro-bridged dimeric salphen zirconium cobaltate complex for the direct synthesis of PHAs via carbonylative polymerization of epoxides. The catalytic system demonstrates favorable activity under mild reaction conditions, enabling complete monomer conversion and an impressive 92% selectivity towards PHA formation. Through meticulous control experiments and mechanistic studies, we have gained crucial insights into the polymerization process. Remarkably, our findings challenge the prevailing notion of sequential ring-opening polymerization of in-situ generated β-lactones as the primary pathway. Instead, we demonstrate that the polymerization predominantly proceeds through direct co-polymerization of epoxide and carbon monoxide, unveiling a unique and efficient mechanism for PHA synthesis.

Liquid‐Liquid Phase Equilibrium of Glycerolysis Precursors: Experimental and Modeling Study

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Liquid-Liquid Phase Equilibrium of Glycerolysis Precursors: Experimental and Modeling Study

Glycerol and oleic acid are mutually immiscible components. Their rigorous reaction produces glycerol esters and water. Such mutual immiscibility of glycerol and free fatty acids limits glycerolysis, a reaction capable of upgrading waste-derived oils. The glycerol solubility in the fatty phase increases when glycerol esters are added to the immiscible mixture of glycerol and oleic acid.


Abstract

The mutual immiscibility of glycerol and free fatty acids limits glycerolysis, a reaction capable of upgrading waste-derived oils. In the present work, the liquid-liquid phase equilibrium data for the glycerol-water-oleic acid and glycerol-monoolein-oleic acid ternary systems were determined experimentally and compared with predictions of the UNIFAC-LLE and COSMO-SAC models. Monoolein was found to affect the glycerol solubility in oleic acid strongly. None of the models investigated adequately determined phase equilibria for the glycerol-monoolein-oleic acid system. COSMO-SAC predictions showed the best trend for glycerol solubility in the fatty phase. For the glycerol-water-oleic acid system, UNIFAC-LLE predictions were in good agreement with experimental data.

Divergent Total Syntheses of 2, 6‐Dioxabicyclo[3.3.1]nonan‐3‐one Styryllactones: (−)‐Goniopypyrone, (+)‐Goniochelienlactone and (+)‐7‐Acetylgoniochelienlactone

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Divergent Total Syntheses of 2, 6-Dioxabicyclo[3.3.1]nonan-3-one Styryllactones: (−)-Goniopypyrone, (+)-Goniochelienlactone and (+)-7-Acetylgoniochelienlactone

The stereoselective syntheses of three 2,6-dioxabicyclo[3.3.1]nonan-3-one styryllactones, goniopypyrone, goniochelienlactone and 7-acetylgoniochelienlactone, has been accomplished based on chiron approach. In particular, (+)-goniochelienlactone and (+)-7-acetylgoniochelienlactone, which are the first total syntheses so far, were achieved in 5 steps (longest linear sequence) with a 28.3 % overall yield and in 8 steps (longest linear sequence) with a 22.2 % overall yield, respectively. The feature of this work involved a sequential reaction of Bernet-Vasella-type reductive elimination and nucleophilic addition by a one-pot sequence, sequential crossing metathesis (CM)/intramolecular oxa-Michael addition, and one-pot tandem deprotection/lactonization.


Abstract

Stereoselective total syntheses of (+)-goniochelienlactone, (+)-7-acetylgoniochelienlactone and (−)-goniopypyrone were accomplished by divergent strategies starting from readily available chiral pool methyl α-D-mannopyranoside. The present work provided an efficient strategy for the stereoselective construction of highly functionalized dioxabicyclo[3.3.1]nonan-3-one ring system through a sequential Bernet-Vasella-type reductive elimination/nucleophilic addition and a sequential cross-metathesis/intramolecular oxa-Michael addition in a one-pot process.

Promoting Electrocatalytic CO2 Reduction to CO via Sulfur‐Doped Co‐N‐C Single‐Atom Catalyst

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Promoting Electrocatalytic CO2 Reduction to CO via Sulfur-Doped Co-N-C Single-Atom Catalyst†

S doping can promote H2O activation and adjust Co active site. As a result, Co1-SNC catalyst exhibits a greatly enhanced CO2RR to CO performance compared to Co1-NC.


Comprehensive Summary

Electrocatalytic reduction of CO2 to fuels and chemicals possesses huge potential to alleviate current environmental crisis. Heteroatom doping in metal-nitrogen-carbon (M-N-C) single-atom catalysts (SACs) has been found to be capable to promote the electrocatalytic CO2 reduction reaction (CO2RR). However, the origin of the enhanced activity is still elusive. Here, we report that sulfur-doped cobalt-nitrogen-carbon single-atom catalyst (Co1-SNC) exhibits superior CO2RR performance compared to sulfur-free counterpart (Co1-NC). On the basis of in situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS), kinetic isotope effect (KIE) and theoretical calculation, it is demonstrated that sulfur doping can promote water activation, elevate the d-band center of Co active site, and reduce the free energy of *COOH intermediate formation. This work deepens the understanding of the CO2RR chemistry over heteroatom-doped SACs for designing efficient CO2RR processes.

Asymmetric Hydrogenation of Tetrapyridine‐Type N‐Heteroarenes Using Phosphine‐Free Ruthenium Diamine Catalysts

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Asymmetric Hydrogenation of Tetrapyridine-Type N-Heteroarenes Using Phosphine-Free Ruthenium Diamine Catalysts†

The first asymmetric hydrogenation of tetrapyridine-type N-heteroarenes, catalyzed by phosphine-free chiral cationic ruthenium diamine complexes, was successfully developed. With this methodology, a broad range of enantiopure tetradentate pyridine-amine-type ligands were obtained in high yields (up to 93%) with excellent stereoselectivities (up to 92 : 8 dl/meso and >99% ee) under mild conditions. Furthermore, the resulting tetradentate nitrogen-donor ligands were successfully applied in the Cu-catalyzed asymmetric Friedel–Crafts alkylation of indoles.


Comprehensive Summary

Chiral ruthenium-catalyzed enantioselective hydrogenation of tetrapyridine-type N-heteroarenes was firstly developed. The partial reduction of adjacent tetraheteroaromatic substrates proceeded smoothly in the presence of phosphine-free chiral cationic ruthenium diamine complexes, affording unprecedented high reactivity, enantioselecitivity and diastereoselectivity (up to 93% yield, >99% ee and 92 : 8 dr). The potential application of chiral tetradentate pyridine-amine products as chiral ligands has been demonstrated in the Cu-catalyzed asymmetric Friedel–Crafts alkylation reaction between indoles and nitroalkenes.

Carbon‐sulfur Coupling Reactions Catalyzed by Nickel(II) N‐Heterocyclic Carbene Complexes

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Abstract: The synthesis and characterization of Nickel(II) complexes with novel pincer-type N-heterocyclic carbene complexes were investigated. Nickel(II)-NHC complexes, 7 and 8, were characterized using HR ESI-MS, IR, UV-Visible, and elemental analysis. The complex 7 with less sterically demanding pincer ligand was investigated in the catalytic one pot synthesis of thioethers via coupling reactions of a series of aryl and alkyl halides in the presence of thiourea. In a mixture of water and ethanol, 5 mol% of 7 catalyzed the C-S bond coupling reaction in high yields.

Anticancer Properties of Ru and Os Half‐Sandwich Complexes of N,S Bidentate Schiff Base Ligands Derived from Phenylthiocarbamide

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The versatile coordinating nature of N,S bidentate ligands is of great importance in medicinal chemistry imparting stability and enhancing biological properties of the metal complexes. Phenylthiocarbamide-based N,S donor Schiff bases converted into RuII/OsII(cymene) complexes and characterized by spectroscopic techniques and elemental analysis. The hydrolytic stability of metal complexes to undergo metal-halido ligand exchange reaction was confirmed both by the DFT and NMR experimentation. The ONIOM (QM/MM) study confirmed the histone protein targeting nature of aqua/hydroxido complex 2aH with an excellent binding energy of -103.19 kcal/mol. The antiproliferative activity against a panel of cancer cells A549, MCF-7, PC-3, and HepG2 revealed that ruthenium complexes 1a–3a were more cytotoxic than osmium complexes and their respective ligands 1–3 as well. Among these ruthenium cymene complex bearing sulfonamide moiety 2a proved a strong cytotoxic agent and showed excellent correlation of cellular accumulation, lipophilicity, and drug-likeness to the anticancer activity. Moreover, the favorable physiochemical properties such as bioavailability and gastrointestinal absorption of ligand 2 also supported the development of Ru complex 2a as an orally active anticancer metallodrug.

Metallaphotoredox‐catalyzed three‐component couplings for the practical synthesis of ureas and carbamates

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Comprehensive Summary

Ureas are widely used in drugs, materials and catalysts because of their diamide structure, which can form strong hydrogen bonds. Therefore, it is of great scientific significance to develop efficient and green methods for the synthesis of urea compounds, especially unsymmetrical ureas. Here, we have disclosed novel and highly efficient three-component coupling reactions of organic halides, sodium cyanate and amines enabled by nickel/photoredox dual catalysis for the preparation of unsymmetrical ureas. The reaction features simple and safe operations, broad substrate scopes, and product diversities. It allows the facile synthesis of N-aryl/vinyl ureas from readily available, user-friendly feedstocks under mild conditions (27 examples, 36-98% yields). In addition, this method is further derived to alcohols as nucleophiles to synthesize a series of carbamates (15 examples, 40-95% yields). The mechanism experiment shows that the isocyanate produced by the coupling of halide and sodium cyanate may be the key intermediate in this reaction.

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