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10 pages, 1399 KiB

Open AccessArticle

Enzymatic Synthesis of New Acetoacetate–Ursodeoxycholic Acid Hybrids as Potential Therapeutic Agents and Useful Synthetic Scaffolds as Well

by Valentina Venturi, Elena Marchesi, Daniela Perrone, Valentina Costa, Martina Catani, Simona Aprile, Lindomar Alberto Lerin, Federico Zappaterra, Pier Paolo Giovannini and Lorenzo Preti

Molecules 2024, 29(6), 1305; https://doi.org/10.3390/molecules29061305 - 15 Mar 2024

Cited by 5 | Viewed by 2026

Abstract

Ursodeoxycholic acid (UDCA) and acetoacetate are natural compounds present in the human intestine and blood, respectively. A number of studies highlighted that besides their well-known primary biological roles, both compounds possess the ability to influence a variety of cellular processes involved in the [...] Read more.

Ursodeoxycholic acid (UDCA) and acetoacetate are natural compounds present in the human intestine and blood, respectively. A number of studies highlighted that besides their well-known primary biological roles, both compounds possess the ability to influence a variety of cellular processes involved in the etiology of various diseases. These reasons suggested the potential of acetoacetate–UDCA hybrids as possible therapeutic agents and prompted us to develop a synthetic strategy to selectively derivatize the hydroxyl groups of the bile acid with acetoacetyl moieties. 3α-acetoacetoxy UDCA was obtained (60% isolated yield) via the regioselective transesterification of methyl acetoacetate with UDCA promoted by the Candida antarctica lipase B (CAL-B). 3α,7β-bis-acetoacetoxy UDCA was obtained instead by thermal condensation of methyl acetoacetate and UDCA (80% isolated yield). This bis-adduct was finally converted to the 7β-acetoacetoxy UDCA (82% isolated yield) via CAL-B catalyzed regioselective alcoholysis of the ester group on the 3α position. In order to demonstrate the value of the above new hybrids as UDCA-based scaffolds, 3α-acetoacetoxy UDCA was subjected to multicomponent Biginelli reaction with benzaldehyde and urea to obtain the corresponding 4-phenyl-3,4-dihydropyrimidin-2-(1H)-one derivative in 65% isolated yield. Full article

(This article belongs to the Special Issue Small Molecule Hybrids for Anticancer and Antiviral Therapy)

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13 pages, 2464 KiB

Open AccessArticle

Efficient Propylene Carbonate Synthesis from Urea and Propylene Glycol over Calcium Oxide–Magnesium Oxide Catalysts

by Kavisha Dang, Navneet Kumar, Vimal Chandra Srivastava, Jinsub Park and Mu. Naushad

Materials 2023, 16(2), 735; https://doi.org/10.3390/ma16020735 - 11 Jan 2023

Cited by 3 | Viewed by 2289

Abstract

A series of calcium oxide–magnesium oxide (CaO–MgO) catalysts were prepared under the effects of different precipitating agents and using varied Mg/Ca ratios. The physiochemical characteristics of the prepared catalysts were analyzed using XRD, FE-SEM, BET, FTIR, and TG/DTA techniques. Quantification of basic active [...] Read more.

A series of calcium oxide–magnesium oxide (CaO–MgO) catalysts were prepared under the effects of different precipitating agents and using varied Mg/Ca ratios. The physiochemical characteristics of the prepared catalysts were analyzed using XRD, FE-SEM, BET, FTIR, and TG/DTA techniques. Quantification of basic active sites present on the surface of the CaO–MgO catalysts was carried out using the Hammett indicator method. The as-prepared mixed oxide samples were tested for propylene carbonate (PC) synthesis through the alcoholysis of urea with propylene glycol (PG). The effects of the catalyst composition, catalyst dose, reaction temperature, and contact time on the PC yield and selectivity were investigated. The maximum PC yield of 96%, with high PC selectivity of 99% and a urea conversion rate of 96%, was attained at 160 °C using CaO–MgO catalysts prepared using a Mg/Ca ratio of 1 and Na₂CO₃ as a precipitating agent. The best-performing catalysts also exhibited good reusability without any significant loss in PC selectivity. It is expected that the present study will provide useful information on the suitability of different precipitating agents with respect to the catalytic properties of the oxides of Ca and Mg and their application in the synthesis of organic carbonates. Full article

(This article belongs to the Section Advanced Nanomaterials and Nanotechnology)

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16 pages, 3355 KiB

Open AccessArticle

Polyurethane Recycling: Conversion of Carbamates—Catalysis, Side-Reactions and Mole Balance

by Shahab Zamani, Jean-Paul Lange, Sascha R. A. Kersten and M. Pilar Ruiz

Polymers 2022, 14(22), 4869; https://doi.org/10.3390/polym14224869 - 11 Nov 2022

Cited by 12 | Viewed by 3781

Abstract

Diisocyanates, a key monomer in polyurethane, are generally lost during recycling. Polyurethane alcoholysis to carbamate and subsequent cracking to isocyanate represents a promising, phosgene-free recycling route. This work reports the thermal and catalytic cracking of a model carbamate (Methyl N-phenyl carbamate, MPC) to [...] Read more.

Diisocyanates, a key monomer in polyurethane, are generally lost during recycling. Polyurethane alcoholysis to carbamate and subsequent cracking to isocyanate represents a promising, phosgene-free recycling route. This work reports the thermal and catalytic cracking of a model carbamate (Methyl N-phenyl carbamate, MPC) to isocyanate (Phenyl isocyanate). Multiple catalysts (ZnO, Bi₂O₃, Al₂O₃, and Montmorillonite K-10) were evaluated in a closed system (batch autoclaves) to decompose MPC at temperatures of 160–200 °C, with a thorough analysis of the products and high (≥90%) mole balance. The thermal reaction was very limited at these temperatures, whereas the catalytic reaction led mainly to aniline and urea and seemed to be dominated by water adsorbed on the catalyst surface. Full article

(This article belongs to the Section Circular and Green Sustainable Polymer Science)

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30 pages, 3749 KiB

Open AccessReview

Dimethyl Carbonate: Review of Synthesis Routes and Catalysts Used

by Kirtika Kohli, Brajendra K. Sharma and Chandrakant B. Panchal

Energies 2022, 15(14), 5133; https://doi.org/10.3390/en15145133 - 14 Jul 2022

Cited by 32 | Viewed by 9841

Abstract

This review summarizes the performance of potential catalysts for the synthesis of dimethyl carbonate (DMC) using CO₂ as a feedstock by two major processes—the direct route of carbonylation of alcohols and the indirect route of alcoholysis of urea. The reaction mechanisms and [...] Read more.

This review summarizes the performance of potential catalysts for the synthesis of dimethyl carbonate (DMC) using CO₂ as a feedstock by two major processes—the direct route of carbonylation of alcohols and the indirect route of alcoholysis of urea. The reaction mechanisms and corresponding catalysts that were previously investigated are discussed. The major challenges associated with the conversion of CO₂ to DMC are the low yields, low DMC selectivity, and thermodynamic limitations (alcohol carbonylation) of reversible reactions with low equilibrium constants. This occurs mainly due to the highly stable carbon dioxide molecules. The development of novel catalysts with high yields and high selectivity needs to be studied to overcome these technical challenges. In addition, to enhance the DMC yield, the use of dehydrating agents for water removal from the reaction mixture is recommended and discussed in detail in this article. This review critically examines the different catalysts used by investigators, along with their respective operating conditions and suitability in applications for the commercial synthesis of CO₂-based DMC. Full article

(This article belongs to the Section B3: Carbon Emission and Utilization)

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18 pages, 963 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Synthesis of Propylene Carbonate by Urea Alcoholysis—Recent Advances

by Łukasz Kotyrba, Anna Chrobok and Agnieszka Siewniak

Catalysts 2022, 12(3), 309; https://doi.org/10.3390/catal12030309 - 9 Mar 2022

Cited by 10 | Viewed by 7309

Abstract

Organic carbonates are considered the chemicals of the future. In particular, propylene carbonate is widely used as a non-reactive solvent, plasticizer, fuel additive, and reagent, especially in the production of environmentally friendly polymers that are not harmful to human health. This paper reviews [...] Read more.

Organic carbonates are considered the chemicals of the future. In particular, propylene carbonate is widely used as a non-reactive solvent, plasticizer, fuel additive, and reagent, especially in the production of environmentally friendly polymers that are not harmful to human health. This paper reviews recent literature findings regarding the development of propylene carbonate synthetic methods starting from propane-1,2-diol and urea. The ammonia formed during the synthesis is recycled to obtain urea from carbon dioxide. Full article

(This article belongs to the Special Issue Catalysis in Green Chemistry and Organic Synthesis)

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16 pages, 2890 KiB

Open AccessArticle

Deep Eutectic Solvents as New Reaction Media to Produce Alkyl-Glycosides Using Alpha-Amylase from Thermotoga maritima

by Alfonso Miranda-Molina, Wendy Xolalpa, Simon Strompen, Rodrigo Arreola-Barroso, Leticia Olvera, Agustín López-Munguía, Edmundo Castillo and Gloria Saab-Rincon

Int. J. Mol. Sci. 2019, 20(21), 5439; https://doi.org/10.3390/ijms20215439 - 31 Oct 2019

Cited by 16 | Viewed by 3995

Abstract

Deep Eutectic Solvents (DES) were investigated as new reaction media for the synthesis of alkyl glycosides catalyzed by the thermostable α-amylase from Thermotoga maritima Amy A. The enzyme was almost completely deactivated when assayed in a series of pure DES, but as cosolvents, [...] Read more.

Deep Eutectic Solvents (DES) were investigated as new reaction media for the synthesis of alkyl glycosides catalyzed by the thermostable α-amylase from Thermotoga maritima Amy A. The enzyme was almost completely deactivated when assayed in a series of pure DES, but as cosolvents, DES containing alcohols, sugars, and amides as hydrogen-bond donors (HBD) performed best. A choline chloride:urea based DES was further characterized for the alcoholysis reaction using methanol as a nucleophile. As a cosolvent, this DES increased the hydrolytic and alcoholytic activity of the enzyme at low methanol concentrations, even when both activities drastically dropped when methanol concentration was increased. To explain this phenomenon, variable-temperature, circular dichroism characterization of the protein was conducted, finding that above 60 °C, Amy A underwent large conformational changes not observed in aqueous medium. Thus, 60 °C was set as the temperature limit to carry out alcoholysis reactions. Higher DES contents at this temperature had a detrimental but differential effect on hydrolysis and alcoholysis reactions, thus increasing the alcoholyisis/hydrolysis ratio. To the best of our knowledge, this is the first report on the effect of DES and temperature on an enzyme in which structural studies made it possible to establish the temperature limit for a thermostable enzyme in DES. Full article

(This article belongs to the Special Issue Carbohydrate-Active Enzymes: Structure, Activity and Reaction Products)

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15 pages, 15341 KiB

Open AccessArticle

Controllable Acid/Base Propriety of Sulfate Modified Mixed Metal Oxide Derived from Hydrotalcite for Synthesis of Propylene Carbonate

by Zhongxie Ding, Wenlong Xu, Xingguang Zhang, Zhen Liu, Jiecan Shen, Jinhua Liang, Min Jiang and Xiaoqian Ren

Catalysts 2019, 9(5), 470; https://doi.org/10.3390/catal9050470 - 21 May 2019

Cited by 14 | Viewed by 4427

Abstract

Ammonium persulfate modified mixed metal oxide derived from hydrotalcite with tunable acid/base properties can be prepared via thermal decomposition of Mg-Al hydrotalcite-type precursors and ammonium persulfate. By controlling the ammonium persulfate content, these sulphur mutated samples, denoted as SMgAlO-y (y = 1; 3; [...] Read more.

Ammonium persulfate modified mixed metal oxide derived from hydrotalcite with tunable acid/base properties can be prepared via thermal decomposition of Mg-Al hydrotalcite-type precursors and ammonium persulfate. By controlling the ammonium persulfate content, these sulphur mutated samples, denoted as SMgAlO-y (y = 1; 3; 5; 7), were investigated in this research. The resulted materials were characterized by XRD, SEM, FT-IR spectra, Py-IR spectra, XPS, Hammett indicator, CO₂-TPD, as well as NH₃-TPD. Furthermore, the acid-base property of the sample surface was determined by inverse gas chromatography measurements (IGC). Among all the obtained outcomes, the target SMgAlO-5 demonstrated the maximal K_a/K_b value, and it presented the highest activity as a catalyst in the synthesis of propylene carbonate (PC) through 1,2-propylene glycol and urea, giving the yield of 97.2% at the optimized reaction condition, which indicated that the PC yield counted on the synergic effect of the acidity and basicity on catalysts. Full article

(This article belongs to the Special Issue Supported Metal Catalysts and Their Applications in Fine Chemicals)

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14 pages, 3133 KiB

Open AccessReview

Recent Advances in Dynamic Kinetic Resolution by Chiral Bifunctional (Thio)urea- and Squaramide-Based Organocatalysts

by Pan Li, Xinquan Hu, Xiu-Qin Dong and Xumu Zhang

Molecules 2016, 21(10), 1327; https://doi.org/10.3390/molecules21101327 - 14 Oct 2016

Cited by 30 | Viewed by 10489

Abstract

The organocatalysis-based dynamic kinetic resolution (DKR) process has proved to be a powerful strategy for the construction of chiral compounds. In this feature review, we summarized recent progress on the DKR process, which was promoted by chiral bifunctional (thio)urea and squaramide catalysis via [...] Read more.

The organocatalysis-based dynamic kinetic resolution (DKR) process has proved to be a powerful strategy for the construction of chiral compounds. In this feature review, we summarized recent progress on the DKR process, which was promoted by chiral bifunctional (thio)urea and squaramide catalysis via hydrogen-bonding interactions between substrates and catalysts. A wide range of asymmetric reactions involving DKR, such as asymmetric alcoholysis of azlactones, asymmetric Michael–Michael cascade reaction, and enantioselective selenocyclization, are reviewed and demonstrate the efficiency of this strategy. The (thio)urea and squaramide catalysts with dual activation would be efficient for more unmet challenges in dynamic kinetic resolution. Full article

(This article belongs to the Collection Recent Advances in Organocatalysis)

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