Reduction Of Esters Research Articles

Ruthenium-Catalyzed Selective Reduction of Carboxylic Esters and Carboxamides

Amines and alcohols are important classes of building blocks in organic synthesis. The synthesis of these compounds has been a topic of interest. A straightforward method for their synthesis is the reduction of esters and amides to alcohols and amines, respectively. Various transition-metal catalysts have been developed for the homogeneous hydrogenation of esters and amides to alcohols and amines. In this review, an overview of the ruthenium-catalyzed selective hydrogenation of esters and amides is provided.1 General Introduction2 Ru-Catalyzed Reduction of Esters3 Ru-Catalyzed Selective Reduction of Amides4 Conclusions

Peach Carboxylesterase PpCXE1 Is Associated with Catabolism of Volatile Esters.

Peach fruit volatile acetate esters impact consumer sensory preference and contribute to defense against biotic stresses. Previous studies showed that alcohol acyltransferase (AAT) family PpAAT1 is correlated with volatile ester formation in peach fruits. However, fruits also contain carboxylesterase (CXE) enzymes that hydrolyze esters. The functions of this family with regard to volatile ester content has not been explored. Here, we observed that content of acetate ester was negatively correlated with expression of PpCXE1. Recombinant PpCXE1 protein exhibited hydrolytic activity toward acetate esters present in peach fruit. Kinetic analysis showed that PpCXE1 showed the highest catalytic activity toward E-2-hexenyl acetate. Subcellular localization demonstrated that PpCXE1 is present in the cytoplasm. Transient expression in peach fruit and stable overexpression in tomato fruit resulted in significant reduction of volatile esters in vivo. Taken together, the results indicate that PpCXE1 expression is associated with catabolism of volatile acetate esters in peach fruit.

Asymmetric transfer hydrogenations of β-N-substituted enamino esters with ammonia borane

Optically active β-amino acids and their derivatives are very useful building blocks in synthetic and medicinal chemistry. The catalytic asymmetric reduction of β-enamino esters is one of the most efficient approaches for their synthesis. Ammonia borane with low molecular weight, high hydrogen capacity, and good stability, is an ideal hydrogen source for the transfer hydrogenation. However, only a few successful examples have been reported for the asymmetric reduction with ammonia borane. In this work, an asymmetric metal-free transfer hydrogenation of β-N-substituted enamino esters with ammoinia borane was successfully realized by using a frustrated Lewis pair of Piers’ borane and (S)-tert-butylsulfinamide as a chiral catalyst. A variety of β-amino acid derivatives were obtained in 51–90% yields with up to 91% ee.

A Concise Enantioselective Synthesis of (S)-Preclamol via Asymmetric Catalytic Negishi Cross-Coupling Reaction

A novel, concise, and efficient enantioselective synthesis of (S)-preclamol (87% ee, 51% total yield) has been developed. The key steps of this synthetic approach included cobalt-catalyzed asymmetric catalytic cross-coupling of α-bromo ester with arylzinc and the reduction of chiral ester to diol with a tertiary carbon atom. Moreover, it was demonstrated that our enantioselective Negishi cross-coupling was a powerful tool to construct stereogenic benzylmethyl center in chiral drugs on a gram scale.

Interconverting Lanthanum Hydride and Borohydride Catalysts for C=O Reduction and C−O Bond Cleavage

AbstractThe high catalytic reactivity of homoleptic tris(alkyl) lanthanum La{C(SiHMe2)3}3 is highlighted by C−O bond cleavage in the hydroboration of esters and epoxides at room temperature. The catalytic hydroboration tolerates functionality typically susceptible to insertion, reduction, or cleavage reactions. Turnover numbers (TON) up to 10 000 are observed for aliphatic esters. Lanthanum hydrides, generated by reactions with pinacolborane, are competent for reduction of ketones but are inert toward esters. Instead, catalytic reduction of esters requires activation of the lanthanum hydride by pinacolborane.

Towards practical earth abundant reduction catalysis: design of improved catalysts for manganese catalysed hydrogenation

Rational design using kinetic studies has led to a 3-fold-increase in the reaction-rates compared to an already-promising lead catalyst for the reduction of ketones and esters.

Microbial Production of Chiral Hydroxy Esters and Their Analogs: Biocatalytic Reduction of Carbonyl Compounds by Actinobacteria, <i>Agromyces</i> and <i>Gordonia</i> Strains

We screened 15 Agromyces strains from the Microbacteriaceae family and 16 Gordonia strains from the Gordoniaceae family to investigate their biocatalytic ability to reduce carbonyl compounds. Two Agromyces strains (A. soli NBRC109063 and A. humatus NBRC109085) and two Gordonia strains (G. hydrophobica NBRC16057 and G. malaquae NBRC108250) grew well in 230 medium. The stereoselective reduction of various carbonyl compounds using these four strains was investigated. We discovered that these strains can reduce aliphatic and aromatic α-keto esters and an aromatic α-keto amide. On the basis of the conversion rate and stereoselectivity of the alcohols produced, G. hydrophobica NBRC16057 is a potential biocatalyst for the stereoselective reduction of α-keto esters and an aromatic α-keto amide to the corresponding chiral alcohols. Our results also suggest that the reduction of ethyl 2-methylacetoacetate by wet G. hydrophobica NBRC16057 cells in the presence of L-glutamate is useful for the production of chiral ethyl 3-hydroxy-2-methylbutanoate.

Iron catalysed selective reduction of esters to alcohols.

The reaction of (dppBIAN)FeCl2 with 3 equivalents of n-BuLi affords a catalytically active anionic Fe complex; the nature of the anionic complex was probed using EPR and IR experiments and is proposed to involve a dearomatized, radical, ligand scaffold. This complex is an active catalyst for the hydrosilylation of esters to afford alcohols; loadings as low as 1 mol% were employed.

First total synthesis of ampullosine, a unique isoquinoline alkaloid isolated from Sepedonium ampullosporum, and of the related permethylampullosine.

A straightforward and convenient approach toward the first total synthesis of ampullosine, a structurally unique 3-methylisoquinoline alkaloid isolated from Sepedonium ampullosporum, is reported. Access to the related O-methyl ampullosine methyl ester from a common intermediate is also disclosed. The synthetic sequence toward the natural product comprised a Kolbe-type carboxylation of 3,5-dihydroxybenzoic acid and further esterification of the diacid, followed by masking of one of the phenols through selective ester reduction and subsequent acetonide formation. Installation of the three-carbon atom required for the 3-methylpyridine ring was performed by triflation of the remaining free phenol and a Pd-catalyzed Suzuki–Miyaura reaction with potassium E-propenyltrifluoroborate. Deprotection of the acetonide, followed by partial oxidation of the benzylic alcohol to the salicylaldehyde, O-methylation of the free phenol and hydrazonation of the resulting ortho-anisaldehyde derivative gave a hydrazone-based 1-azatriene. This was further subjected to 6π-azaelectrocyclization to afford permethylampullosine (11 steps, 14% overall yield), whereas exhaustive demethylation with AlI3 generated in situ gave ampullosine (12 steps, 3.2% global yield).

Ir-catalyzed chemoselective reduction of β-amido esters: A versatile approach to β-enamino esters

The conversion of β-amido esters to β-enamino esters is an indispensable step for some synthetic approaches to alkaloids and related medicines. Known methods for such transformation are not only stepwise, but also proceed with low atom-efficiency. Herein, we report a direct and versatile approach that features the Ir-catalyzed chemoselective reduction of β-amido esters with 1,1,3,3-tetramethyldisiloxane (TMDS). In addition, a lack of some signals was observed in the 13C NMR spectra of some alicyclic β-enamino esters. This revealed a longstanding existing but being ignored phenomenon in the literature.

Fatty Acid–Derived Aliphatic Long Chain Polyethers by a Combination of Catalytic Ester Reduction and ADMET or Thiol‐Ene Polymerization

AbstractAliphatic long‐chain polyesters are a common class of renewable polymers and can be obtained by various synthetic routes, most notably from renewable fatty acids. In contrast, for aliphatic long chain polyethers only a few examples are known. Recently, the GaBr3‐catalyzed reduction of esters to ethers has been introduced as convenient post‐polymerization modification to obtain polyethers directly from polyesters. Here, this reduction is applied to synthesize fatty acid–based ω,ω′‐unsaturated diene diether monomers, which are polymerized afterward by thiol‐ene or acyclic diene metathesis (ADMET) polymerizations in the “green” solvents methyl‐THF (2‐methyltetrahydrofuran) and polarclean. After polymerization, the thiol‐ene or ADMET polymers are modified by either oxidation or hydrogenation, respectively.

Chiron approach towards optically pure γ-valerolactone from alanine

A concise synthesis of both enantiomers of γ-valerolactone has been developed from commercially available Alanine. The key steps in the synthesis of these γ-Lactones are DIBAL-H reduction of ester (9) followed by in situ Wittig reaction with EtO2CCH = PPh3 ylide (13) (Z/E = 1: 3.5) and one pot lactonization triggered by deprotection of O-TBS ether (14).

Synthesis of (3-Hydroxyadamantan-1-yl)methanols

A convenient procedure has been developed for the synthesis of (3-hydroxyadamantan-1-yl)-methanols on the basis of nitroxylation of adamantan-1-ylmethanols with fuming nitring acid and subsequent reduction of intermediate nitric acid esters with hydrazine hydrate. The title diols have also been obtained by the reduction of 1-nitroxy-3-(nitroxymethyl)adamantanes. The nitroxylation process is accompanied by oxidation with the formation of substituted adamantane-1-carboxylic acids.

Design and Synthesis of Chiral oxa-Spirocyclic Ligands for Ir-Catalyzed Direct Asymmetric Reduction of Bringmann's Lactones with Molecular H2.

We herein present a facile and column-free synthetic route toward a structurally unique oxa-spirocyclic diphenol, termed as O-SPINOL. Features of the synthesis include the construction of the all-carbon quaternary center at an early stage, a key double intramolecular SNAr step to introduce the spirocycles and the feasibility of operating on >100 g scale. Both enantiomers of O-SPINOL can be easily accessed through optical resolution with l-proline by control of the solvent. The chiral tridentate ligand O-SpiroPAP derived from O-SPINOL has been successfully synthesized and applied in the iridium-catalyzed asymmetric hydrogenation of bridged biaryl lactones under mild reaction conditions, providing valuable and enantioenriched axially chiral molecules in excellent yields and enantioselectivities (up to 99% yield and >99% ee). This method represents a rare example of constructing axially chiral molecules by direct reduction of esters with H2.

Elimination of 3-MCPD fatty acid esters and glycidyl esters during palm oil hydrogenation and wet fractionation

Palm oil is the vegetable oil refined and modified in the largest amount. In this study, we present the effect of wet fractionation and hydrogenation of RBD palm oil on the removal of 3-MCPD and glycidyl esters. Fractionated palmstearins had significantly decreased contents of 3-MCPD esters (71–74%) and glycidyl esters (21–26%), whereas top olein contained the highest levels of processing-induced contaminants accompanied by polar compounds. Exhaustive hydrogenation conditions caused rapid degradation of 3-MCPD esters (51–70%) in high melting palm oil products. Reduction of glycidyl esters (1–42%) was dependent on the type of nickel catalyst. The effect of iodine value drop on the contaminant degradation was shown to be linear. The combined action of dry-reduced, supported, 22% Ni and Raney nickel catalysts was found to be an optimal. Adsorptive bleaching and deodorization of hydrogenated palm stearin impacted particularly repeated formation of glycidyl esters up to 1.01–1.76 mg/kg, while 3-MCPD esters remained under the input RBD palm oil level. The mechanism of the catalyst action was investigated with glycidyl-d5 palmitate, 3-MCPD-d5-1,2-dipalmitate. They were transformed into non-carcinogenic and non-genotoxic products by hydrogenolysis and deoxygenation reactions.

Co-Immobilization of Ketoreductase and Glucose Dehydrogenase

A two-enzyme system composed of immobilized ketoreductase (Hansenula polymorpha) and glucose dehydrogenase (Bacillus megaterium) was developed for the asymmetric reduction of keto esters to optically active hydroxy esters via immobilization in polyvinyl alcohol (PVA) gel particles. The concentration of enzymes was optimized, and the final particles were used 18 times in a row in a batch mode to achieve minimal loss of activity and complete conversion of the model substrate, β-ketoester ethyl-2-methylacetoacetate. Excellent stability was also achieved using new storage conditions of PVA particles, with 80% of activity being retained after almost 10 months.

Novel Approach to Synthesizing Carbide Materials from a Cellulosic Precursorposter Format

Carbides are an important class of materials given their high melting temperature, abrasion resistance, and compressive strength. Carbides are obtained through the reaction of carbon and other elements such as silicon, titanium and tungsten. In particular, porous carbides find application in high temperature filters, membranes, and catalysts thanks to their lower density and a higher surface area to volume ratio compared to classically manufactured solid carbide materials. The use of templates is a common way to derive porous carbides. For example, in industry when carbides are being formed in a specific shape or morphology, the use of polymers which have a more controllable structure are used as a precursor for the production of porous carbides. Here we postulate the use of cellulosic paper as a carbon precursor. If the paper is infiltrated with precursors for silicon, titanium or tungsten, then a carbide is derived upon heat treatment. Origami techniques can then be used to shape the infiltrated paper into different geometries, which remain throughout heat treatment. Hence, this technique yields complex 3D geometries with thin cross sections that can enable lightweight, structured carbides. The importance of the work presented here is furthering our understanding on how different processing variables affect the composition of the resultant material. The carbide materials from paper are synthesized by the carbothermal reduction of metallic ethyl esters which have been embedded into a pure cellulosic paper matrix. In this work we use a porous matrix of cellulosic fibers and infiltrate them with solutions of either Tetraethylorthosilicate (TEOS) or Tyzor to form SiC or TiC respectively. The manner of infiltration used was capillary action through the cellulose matrix after exposing one side of the paper to the metallic solution. With the paper fully saturated, we allowed the samples to dry before placing them in a tube furnace for pyrolization in an inert N2 environment. Around 900 OC, cellulosic fibers decompose to a carbon fiber matrix and the metal ethers reduce to metal oxides. Our work currently focuses on determining the impact of different processing variables on the composition of the final material. These variables include the synthesis temperature, heating rate, and ratio of carbon to silicon or titanium. We expect that the variability in the ratio of the carbon to metallic precursors will influence the concentrations of the resultant materials while the changes in synthesis temperature and heating rate will influence the growth of the carbides once the reaction is initiated. We are testing these parameters using the Taguchi method of design to increase the efficiency of investigation. We have already had success in the synthesis of metallic carbides using this procedure with a titanium precursor and are now attempting to expand on our work by controlling the carbide growth and testing with additional metallic precursors. Future work is needed to test the impact of using different synthesis environments (such as Argon and vacuum instead of Nitrogen) and the use of alternative metal ethyl ethers on the final quantity and morphology of the resultant carbides. Figure 1

Nrf2-Mediated Antioxidant Defense and Peroxiredoxin 6 Are Linked to Biosynthesis of Palmitic Acid Ester of 9-Hydroxystearic Acid.

Fatty acid esters of hydroxy fatty acids (FAHFAs) are lipid mediators with promising antidiabetic and anti-inflammatory properties that are formed in white adipose tissue (WAT) via de novo lipogenesis, but their biosynthetic enzymes are unknown. Using a combination of lipidomics in WAT, quantitative trait locus mapping, and correlation analyses in rat BXH/HXB recombinant inbred strains, as well as response to oxidative stress in murine models, we elucidated the potential pathway of biosynthesis of several FAHFAs. Comprehensive analysis of WAT samples identified ∼160 regioisomers, documenting the complexity of this lipid class. The linkage analysis highlighted several members of the nuclear factor, erythroid 2 like 2 (Nrf2)-mediated antioxidant defense system (Prdx6, Mgst1, Mgst3), lipid-handling proteins (Cd36, Scd6, Acnat1, Acnat2, Baat), and the family of flavin containing monooxygenases (Fmo) as the positional candidate genes. Transgenic expression of Nrf2 and deletion of Prdx6 genes resulted in reduction of palmitic acid ester of 9-hydroxystearic acid (9-PAHSA) and 11-PAHSA levels, while oxidative stress induced by an inhibitor of glutathione synthesis increased PAHSA levels nonspecifically. Our results indicate that the synthesis of FAHFAs via carbohydrate-responsive element-binding protein-driven de novo lipogenesis depends on the adaptive antioxidant system and suggest that FAHFAs may link activity of this system with insulin sensitivity in peripheral tissues.

Catalytic Silane‐Reduction of Carboxylic Esters and Lactones: Selective Synthetic Methods to Aldehydes, Lactols, and Ethers via Silyl Acetal Intermediates

AbstractPractical procedures for the production of aldehydes, lactols, and ethers are offered by the palladium‐catalyzed silane‐reduction of carboxylic esters and lactones. The partial reduction of carboxylic esters or lactones with 1,1,3,3‐tetramethyldisiloxane in the presence of commercially available palladium on carbon (Pd/C) and some copper compounds as a co‐catalyst smoothly proceeds under mild conditions to afford the silyl acetal derivatives in high yields, which are easily converted to the corresponding aldehydes or lactols by hydrolysis of silyloxy group. On the other hand, deoxygenated ethers are obtained with high selectivity by treatment of silyl acetals with catalytic amounts of Me3SiOTf at –78 °C or stoichiometric amounts of BF3•OEt2 at ambient temperature.

Volatile profile of white wines fermented with sequential inoculation of Starmerella bacillaris and Saccharomyces cerevisiae

Mixed fermentations with Starmerella bacillaris and Saccharomyces cerevisiae affect the chemical composition of wines, by modulating various metabolites of oenological interest. The current study was carried out to elucidate the effect of sequential inoculation of the above mentioned species on the production of white wines, especially on the chemical and aromatic characteristics of Chardonnay, Muscat, Riesling and Sauvignon blanc wines. Titratable acidity and glycerol content exhibited evident differences among the wines after fermentation. For volatile compounds, mixed fermentations led to a reduction of the total esters, including ethyl acetate, which is a compound responsible for wine deterioration. However, Sauvignon blanc wines fermented by mixed cultures contained significantly higher levels of esters and thiols, both associated with positive sensory attributes. These findings suggest that sequential inoculations possess great potential in affecting and modulating the chemical and aromatic profile of white wines, especially those produced from Sauvignon blanc grapes.