- Selective Hydrogenation of Aldehydes Using a Well-Defined Fe(II) PNP Pincer Complex in Biphasic Medium
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A biphasic process for the hydrogenation of aldehydes was developed using a well-defined iron (II) PNP pincer complex as model system to investigate the performance of various ionic liquids. A number of suitable hydrophobic ionic liquids based on the N(Tf)2? anion were identified, allowing to immobilize the iron (II) catalyst in the ionic liquid layer and to facilitate the separation of the desired alcohols. Further studies showed that targeted Br?nsted basic ionic liquids can eliminate the need of an external base to activate the catalyst.
- Weber, Stefan,Brünig, Julian,Zeindlhofer, Veronika,Schr?der, Christian,St?ger, Berthold,Limbeck, Andreas,Kirchner, Karl,Bica, Katharina
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- Characterization of the Rv3378c gene product, a new diterpene synthasefor producing tuberculosinol and (13R, S)-isotuberculosinol (nosyberkol), from the mycobacterium tuberculosis H37Rv genome
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The Rv3377c and Rv3378c genes from Mycobacterium tuberculosis are specifically found in the virulent Mycobacterium species, but not in the avirulent species. The Rv3378c-encoded enzyme produced tuberculosinol 2 (5(6), 13(14)-halimadiene-15-ol), 13R-5a and 13Sisotuberculosinol 5b (5(6), 14(15)-halimadiene-13-ol) as its enzymatic products from tuberculosinyl diphosphate 3, indicating that the Rv3378c enzyme catalyzed the nucleophilic addition of a water molecule after the release of a diphosphate moiety. The three enzymatic products 2, 5a, and 5b were produced irrespective of the N- and C-terminal His-tagged Rv3378c enzymes, and of the maltose-binding protein fusion enzyme; the product distribution ratio was identical between the enzymes as 1:1 for 2:5, and 1:3 for 5a:5b. The successful separation of 5a and 5b by a chiral HPLC column provided the first complete assignments of 1H- and 13C-NMR data for 5a and 5b. The enzymatic mechanism for producing 2, 5a, and 5b is proposed here, and the optimal catalytic conditions and kinetic parameters, in addition to the divalent metal effects, are described. Site-directed mutagenesis of Asp into Asn, targeted at the DDXXD motif, resulted in significantly decreased enzymatic activity.
- Nakano, Chiaki,Ootsuka, Takahiro,Takayama, Kazutoshi,Mitsui, Toshiaki,Sato, Tsutomu,Hoshino, Tsutomu
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- Labeling of polyprenylated macromolecules using mild Ene reactions
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Protein posttranslational modifications play pivotal roles in a wide range of functions such as gene expression regulation, differentiation, cell migration, various human diseases and so on. Polyprenylated group are a lipid modification only found in the Ras super family protein. It was demonstrated that farnesyl, geranylgeranyl groups are covalently attached into sulfur atom on cysteine of Caxx motif, playing essential roles in anchoring on plasma membrane and signal transduction etc. We first reported a straightforward chemical approach to labelling of polyprenylated macromolecules. Our method mainly relied on a novel fluorination/Ene reaction, exhibiting application potential in the study of proteome-wide mapping of protein prenylation target.
- Zhang, Jingwen,Zhao, Jizhong,Wang, Li,Hu, Hongmei,Wang, Sheng,Yu, Ping,Wang, Rui
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- Large Pore Bifunctional Titanium-Aluminosilicates: the Inorganic Non-enzymatic Version of the Epoxidase Conversion of Linalool to Cyclic Ethers
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Bifunctional aluminosilicate catalysts containing framework Ti are prepared, with two different topologies and pore sizes; these samples contain both acid and oxidizing catalytic sites and are highly selective for carrying out multistep reactions with selectivities close to those obtained with epoxidases, this is shown to occur for the oxidation of linalool to cyclic hydroxy ethers.
- Corma, A.,Iglesias, M.,Sanchez, F.
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- Gold catalysis for selective hydrogenation of aldehydes and valorization of bio-based chemical building blocks
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Gold catalysts are best known for their selectivity in oxidation reactions, however, there is a promising future for gold in selective hydrogenations. Herein, the hydrogenation of several aldehydes and important bio-based chemical building blocks, namely 5-hydroxymethylfurfural (5-HMF), furfural and vanillin, was performed throughout the combination of Au nanoparticles with Lewis bases. The Au-amine ligand (e.g., 2,4,6-trimethylpyridine) catalytic system could reduce the aldehyde carbonyl group selectively, without reducing alkene moieties or opening the furanic ring that occur on most traditional catalysts. Otherwise, the reduction of nitro group is preferential and the catalytic system was used for the synthesis of furfurylamines, important intermediates in the synthesis of different pharmaceuticals (e.g., furosemide), through the selective reductive amination of furfural starting from nitro-compounds. Moreover, a fully heterogeneous gold catalyst embedded in N-doped carbon (Au@N-doped carbon / TiO2) was able to perform these reactions in successive recycles without the addition of ligands, with impact in the development of a continuous flow process for biomass valorization.
- Silva, Rerison J. M.,Fiorio, Jhonatan L.,Vidinha, Pedro,Rossi, Liane M.
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- Tris(2,4,6-trimethoxyphenyl)phosphine (TTMPP): A novel catalyst for selective deacetylation
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Chemo-and stereoselective deacetylation was achieved by the use of a catalytic amount of tris(2,4,6-trimethoxyphenyl)phosphine (TTMPP).
- Yoshimoto, Kazuya,Kawabata, Hirotoshi,Nakamichi, Natsuki,Hayashi, Masahiko
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- Cloning and characterization of Pfl-1841, a 2-methylenebornane synthase in Pseudomonas fluorescens PfO-1
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The pfl-1841 gene from Pseudomonas fluorescens PfO-1 is the only gene in any of the three sequenced genomes of the Gram-negative bacterium P. fluorescens, that is, annotated as a putative terpene synthase. The predicted Pfl-1841 protein, which harbors the two strictly conserved divalent metal binding domains found in all terpene cyclases, is closely related to several known or presumed 2-methylisoborneol synthases, with the closest match being to the MOL protein of Micromonaspora olivasterospora KY11048 that has been implicated as a 2-methylenebornane synthase. A synthetic gene encoding P. fluorescens Pfl-1841 and optimized for expression in Escherichia coli was expressed and purified as an N-terminal His6-tagged protein. Incubation of recombinant Pfl-1841 with 2-methylgeranyl diphosphate produced 2-methylenebornane as the major product accompanied by 1-methylcamphene as well as other minor, monomethyl-homomonoterpene hydrocarbons and alcohols. The steady-state kinetic parameters for the Pfl-1841-catalyzed reaction were K M=110±13 nM and kcat=2.4±0.1×10 -2 s-1. Attempts to identify the P. fluorescens SAM-dependent 2-methylgeranyl diphosphate synthase have so far been unsuccessful.
- Chou, Wayne K.W.,Ikeda, Haruo,Cane, David E.
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- Asymmetric bioreduction of activated alkenes using cloned 12-oxophytodienoate reductase isoenzymes OPR-1 and OPR-3 from Lycopersicon esculentum (tomato): A striking change of stereoselectivity
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(Chemical Equation Presented) Tomato source: 12-Oxophytodienoate reductase isoenzymes OPR1 and OPR3 from tomato possess a broad substrate spectrum for the asymmetric bioreduction of α,β-unsaturated enals, enones, dicarboxylic acids, and N-substituted male-imides (see scheme). Stereocomplementary behavior of both isoenzymes was observed in the reduction of a nitroalkene that led to the formation of opposite stereoisomers in high enantiomeric excess.
- Hall, Melanie,Stueckler, Clemens,Kroutil, Wolfgang,Macheroux, Peter,Faber, Kurt
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- Diisopropoxytitanium(III) Tetrahydroborate: A Highly Useful Reagent for the Remarkably Selective 1,2-Reduction of α,β-Unsaturated Carbonyl Compounds
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Diisopropoxytitanium(III) tetrahydroborate formed by the reaction of diisopropoxytitanium dichloride and benzyltriethylammonium borohydride (1:2) reacts with a variety of α,β-unsaturated carbonyl compounds in dichloromethane (-20 deg C) very readily to yield exclusively the corresponding allylic alcohols in excellent yields.
- Ravikumar, K. S.,Baskaran, Sundarababu,Chandrasekaran, Srinivasan
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- SELECTIVE REDUCTION OF ALDEHYDES IN PRESENCE OF A KETONE WITH CHLOROTRIMETHYLSILANE AND NICKEL BORIDE
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It has been shown that a combination of chlorotrimethylsilane and nickel boride effects the chemoselective reduction of an aldehyde in presence of a ketonic carbonyl group.
- Borbaruah, M.,Barua, N. C.,Sharma, R. P.
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- The biosynthetic origin of irregular monoterpenes in lavandula: Isolation and biochemical characterization of a novel cis-prenyl diphosphate synthase gene, lavandulyl diphosphate synthase
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Lavender essential oils are constituted predominantly of regular monoterpenes, for example linalool, 1,8-cineole, and camphor. However, they also contain irregular monoterpenes including lavandulol and lavandulyl acetate. Although the majority of genes responsible for the production of regular monoterpenes in lavenders are now known, enzymes (including lavandulyl diphosphate synthase (LPPS)) catalyzing the biosynthesis of irregular monoterpenes in these plants have not been described. Here, we report the isolation and functional characterization of a novel cis-prenyl diphosphate synthase cDNA, termed Lavandula x intermedia lavandulyl diphosphate synthase (LiLPPS), through a homology-based cloning strategy. The LiLPPS ORF, encoding for a 305-amino acid long protein, was expressed in Escherichia coli, and the recombinant protein was purified by nickel-nitrilotriacetic acid affinity chromatography. The approximately 34.5-kDa bacterially produced protein specifically catalyzed the head-to-middle condensation of two dimethylallyl diphosphate units to LPP in vitro with apparent Km and k cat values of 208 ± 12 μM and 0.1 s-1, respectively. LiLPPS is a homodimeric enzyme with a sigmoidal saturation curve and Hill coefficient of 2.7, suggesting a positive co-operative interaction among its catalytic sites. LiLPPS could be used to modulate the production of lavandulol and its derivatives in plants through metabolic engineering.
- Demissie, Zerihun A.,Erland, Lauren A.E.,Rheault, Mark R.,Mahmoud, Soheil S.
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- Manganese-Catalyzed Hydrogenation of Ketones under Mild and Base-free Conditions
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In this paper, several Mn(I) complexes were applied as catalysts for the homogeneous hydrogenation of ketones. The most active precatalyst is the bench-stable alkyl bisphosphine Mn(I) complex fac-[Mn(dippe) (CO)3(CH2CH2CH3)]. The reaction proceeds at room temperature under base-free conditions with a catalyst loading of 3 mol % and a hydrogen pressure of 10 bar. A temperature-dependent selectivity for the reduction of α,β-unsaturated carbonyls was observed. At room temperature, the carbonyl group was selectively hydrogenated, while the C=C bond stayed intact. At 60 °C, fully saturated systems were obtained. A plausible mechanism based on DFT calculations which involves an inner-sphere hydride transfer is proposed.
- Brünig, Julian,Kirchner, Karl,Veiros, Luis F.,Weber, Stefan
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- Lipase-catalyzed separation of geometrical isomers: Geraniol-nerol
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The substrate/lipase ratio as well as pH of the buffer medium played important roles in the resolution of geometrical isomeric mixture of geraniol-nerol. Based on the results, an immobilized lipase from Pseudomonas fluorescens (PFL) was found effective in selective transesterifications whereas Pseudomonas sp. Lipase (PSL) was found to be useful in hydrolyzing the esters. Copyright
- Gupta, Pankaj,Taneja, Subhash C.,Shah, Bhahwal A.,Sethi, Vijay K.,Qazi, Ghulam N.
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- SYNTHESE A L'AIDE DE SULFONES-XXVI. SYNTHESE D'ALCOOLS ALLYLIQUES ET DE POLYPRENOLS PAR ATTACHEMENT D'UN SYNTHON PRENOL EN POSITION 4 E
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The E-hydroxyalkylsulphone PhSO2CH2C(CH3)=CHCH2OH is regioselectively and stereoselectively substituted by Grignard reagents in the presence of copper(II) acetylacetonate, giving E allylic alcohols in high yield.A recurrent synthesis of polyprenols and an efficient preparation of the African Monarch pheromone are described.
- Julia, Marc,Verpeaux, Jean-Noel
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- Functional investigation and applications of the acetylesterase activity of the Citrus sinensis (L.) Osbeck peel
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The hydrolysis of acetyl moieties on a set of commercially relevant substrates was performed by employing the whole tissue of Citrus sinensis (L.) Osbeck peel as an efficient biocatalyst in mild reaction conditions with high degree of regioselectivity. The reaction is done in aqueous media and the product is easily recovered. Optimal reaction conditions were deduced and two practical applications were investigated: the elaboration of acetylglicerols and the preparation of vitamin K1 precursor. Peel waste (flavedo and albedo) from orange juice manufacturing was successfully employed as a biocatalyst.
- Fontana, Gianfranco,Bruno, Maurizio,Maggio, Antonella,Rosselli, Sergio
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- Biosynthesis of monoterpene scent compounds in roses
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The scent of roses (Rosa x hybrida) is composed of hundreds of volatile molecules. Monoterpenes represent up to 70% percent of the scent content in some cultivars, such as the Papa Meilland rose. Monoterpene biosynthesis in plants relies on plastid-localized terpene synthases. Combining transcriptomic and genetic approaches, we show that the Nudix hydrolase RhNUDX1, localized in the cytoplasm, is part of a pathway for the biosynthesis of free monoterpene alcohols that contribute to fragrance in roses. The RhNUDX1 protein shows geranyl diphosphate diphosphohydrolase activity in vitro and supports geraniol biosynthesis in planta.
- Magnard, Jean-Louis,Roccia, Aymeric,Caissard, Jean-Claude,Vergne, Philippe,Sun, Pulu,Hecquet, Romain,Dubois, Annick,Oyant, Laurence Hibrand-Saint,Jullien, Frédéric,Nicolè, Florence,Raymond, Olivier,Huguet, Stéphanie,Baltenweck, Raymonde,Meyer, Sophie,Claudel, Patricia,Jeauffre, Julien,Rohmer, Michel,Foucher, Fabrice,Hugueney, Philippe,Bendahmane, Mohammed,Baudino, Sylvie
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- A mild and selective deprotection of p-methoxybenzyl (PMB) ether by magnesium bromide diethyl etherate-methyl sulfide
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The magnesium bromide diethyl etherate (MgBr2 · OEt2)-methyl sulfide (Me2S) system is useful for the mild and chemo-selective deprotection of p-methoxybenzyl (PMB) ether in the presence of 1,3-diene, t-butyldimethylsilyl (TBDMS) ether, benzoate, benzyl ether and acetonide.
- Onoda, Toshihiko,Shirai, Ryuichi,Iwasaki, Shigeo
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- Speedy and regioselective 1,2-reduction of conjugated α,β-unsaturated aldehydes and ketones using NaBH4/I2
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Synthesis of allylic alcohols from α,β-unsaturated aldehydes/ketones has been achieved in excellent yields utilizing NaBH4 and iodine. This reducing agent is mild and tolerant to a number of functional groups.
- Singh, Jasvinder,Kaur, Irvinder,Kaur, Jasamrit,Bhalla, Aman,Kad, Goverdhan L.
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- Hydrolysis of isoprenyl diphosphates with the acid phosphatase from Cinnamomum camphora
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Direct observations of the enzymatic hydrolysis of C10 acyclic allylic isoprenyl diphosphates by an acid phosphatase from the leaves of Cinnamomum camphora (camphor tree) were made using 1H and 31P NMR spectrometers. The measurements indicated that the allylic primary diphosphates, geranyl diphosphate and neryl diphosphate, were hydrolysed to their corresponding alcohols in a sequential manner via their corresponding monophosphates, whereas the allylic tertiary diphosphate, linalyl diphosphate, was hydrolysed only to its corresponding monophosphate.
- Izumi,Ashida,Yamamitsu,Hirata
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- Rearrangement of Linalool, Geraniol, and Nerol and Their Derivatives
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Acid-catalyzed conversion of linalool into geraniol, nerol, and α-terpineol is slower than the corresponding reactions of geraniol and nerol, because the tertriary linalyl carbocation reverts to linalool rather than going forward to rearranged products.The linalyl carbocation does not lose its stereochemical identity, and oxygen exchange of linalool is faster than rearrangement or cyclization.Solvolyses of linalyl esters and chloride are faster than those of the geranyl and neryl derivatives.These solvolyses are different from acid heterolysis of linalool in that there is extensive racemization of linalool, but cyclization to α-terpineol goes with considerable retention of configuration.Participation by the 6,7-double bond controls the stereochemistry of linalool heterolysis and solvolysis of linalyl esters, but it does not markedly affect the reaction rates.
- Cori, Osvaldo,Chayet, Liliana,Perez, Luz Maria,Bunton, Clifford A.,Hachey, David
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- Syntheses of α,β-Epoxy Silyl Ketones
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The synthesis of the α,β-epoxy-acylsilanes 1 and 2 starting from the allylic silyl alcohols (E)- and (Z)-3, respectively, by epoxidation with t-BuOOH/VO(acac)2 followed by oxidation with Collins reagent (CrO3/pyridine) in up to 70percent overall yields, is described.The acid-catalyzed rearrangement of the epoxy-silyl alcohols 4A+B and 5A+B led to the novel unstable diastereomeric α-silyl-β-hydroxy-aldehydes 9 and 10, respectively.The structure of 10 was established by X-ray crystal-structure analysis of the corresponding alcohol 11.
- Scheller, Markus E.,Schweizer, W. Bernd,Frei, Bruno
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- ISOMERIZATION OF PRIMARY ALLYLIC ALCOHOLS TO TERTIARY ONES BY MEANS OF Me3SiOOSiMe3-VO(acac)2 CATALYST
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The title rearrangement proceeds in dichloromethane at 25 oC in the presence of the catalyst prepared in situ to give tertiary isomers in good yields.Other rearrangements of sec. -> tert. or sec. -> sec. have been examined.
- Matsubara, Seijiro,Takai, Kazuhiko,Nozaki, Hitosi
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- ISOMERIZATION OF ALLYLIC ALCOHOLS CATALYZED BY VANADIUM OR MOLYBDENUM COMPLEXES.
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Isomerization of primary allylic alcohols proceeds in dichloromethane at 25 degree C in the presence of the catalyst prepared in situ from VO(acac)//2 or MoO//2(acac)//2, and Me//3SiOOSiMe//3 to give tertiary isomers in good yields. The catalysts are also effective for the rearrangements of sec. yields tert. allylic alcohols. The isomerization of an allenyl allylic alcohol, 6-methyl-1,2,5-heptatrien-4-ol, gives either (E)-2-methyl-3,5,6-heptarien-2-ol or (E)-6-methyl-3,5-heptadien-2-one selectively depending on the reaction conditions.
- Matsubara,Okazoe,Oshima,Takai,Nozaki
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- A mild, efficient, and inexpensive protocol for the selective deprotection of TBDMS ethers using KHSO4
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Potassium hydrogensulfate in 30% aq. methanol deprotects a variety of tert-butyldimethylsilyl ethers at room temperature in excellent yields.
- Arumugam, Pandurangan,Karthikeyan, Ganesan,Perumal, Paramasivan T.
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- Electrogenerated Acid as an Efficient Catalyst for the Protection and Deprotection of Alcohols with Dihydropyran and Transesterification of Glyceride
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Protection of alcohols with 3,4-dihydro-2H-pyran and hydrolysis of the resulting tetrahydropyranyl ethers are cleanly performed by using an electrogenerated acid (EG acid) as a catalyst.Transesterification of glyceride was also achieved with EG acid.
- Torii, Sigeru,Inokuchi, Tsutomu,Kondo, Kazumi,Ito, Hiroshi
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- Titanyl acetylacetonate as an efficient catalyst for regioselective 1,2-reduction of α,β-unsaturated carbonyl compounds and conversion of α-diketones & acyloins to vicinal diols with sodium borohydride
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α,β-Unsaturated aldehydes and ketones were reduced readily and exclusively to their corresponding allylic alcohols with NaBH4 and catalytic amounts of titanyl acetylacetonate at room temperature. Reduction reactions were carried out in CH3CN or THF. This reducing system was also efficient for the reduction of α-diketones and acyloins to their corresponding vicinal diols in CH3CN.
- Zeynizadeh, Behzad
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- Microwave assisted catalytic protection and deprotection of alcohols with 3,4-dihydro-2h-pyran
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Protection of alcohols as their 2-tetrahydropyranyl ethers and their subsequent hydrolysis can be easily achieved through a microwave irradiated reaction catalysed by iodine.
- Deka,Sarma
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- Linalool dehydratase-isomerase, a bifunctional enzyme in the anaerobic degradation of monoterpenes
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Castellaniella (ex Alcaligenes) defragrans strain 65Phen mineralizes monoterpenes in the absence of oxygen. Soluble cell extracts anaerobically catalyzed the isomerization of geraniol to linalool and the dehydration of linalool to myrcene. The linalool dehydratase was present in cells grown on monoterpenes, but not if grown on acetate. We purified the novel enzyme ～1800-fold to complete homogeneity. The native enzyme had a molecular mass of 160 kDa. Denaturing gel electrophoresis revealed one single protein band with a molecular mass of 40 kDa, which indicated a homotetramer as native conformation. The aerobically purified enzyme was anaerobically activated in the presence of 2 mM DTT. The linalool dehydratase catalyzed in vitro two reactions in both directions depending on the thermodynamic driving forces: a water secession from the tertiary alcohol linalool to the corresponding acyclic monoterpene myrcene and an isomerization of the primary allylalcohol geraniol in its stereoisomer linalool. The specific activities (Vmax) were 140 nanokatals mg-1 for the linalool dehydratase and 410 nanokatals mg-1 for the geraniol isomerase, with apparent Km values of 750 μM and 500 μM, respectively. The corresponding open reading frame was identified and revealed a precursor protein with a signal peptide for a periplasmatic location. The amino acid sequence did not affiliate with any described enzymes. We suggest naming the enzyme linalool dehydratase-isomerase according to its bifunctionality and placing it as a member of a new protein family within the hydrolyases (EC 4.2.1.X).
- Brodkorb, Danny,Gottschall, Matthias,Marmulla, Robert,Lueddeke, Frauke,Harder, Jens
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- Remarkable support effects of gallium compounds on the activity and selectivity of Ru metal catalyst for liquid-phase citral hydrogenation
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Various types of p-block metal oxides and nitrides were employed as catalyst supports for Ru metal in liquid-phase citral hydrogenation. Compounds containing Ga3+ ions, in particular GaOOH, were found to exhibit remarkable support effects on the enhancement of catalytic activity and reaction selectivity for the production of α, β-unsaturated alcohols (nerol and geraniol). Copyright
- Nishiyama, Hiroshi,Takeuchi, Junichi,Hayase, Hiroshi,Saito, Nobuo,Inoue, Yasunobu
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- Three-Dimensionally Hierarchical Pt/C Nanocomposite with Ultra-High Dispersion of Pt Nanoparticles as a Highly Efficient Catalyst for Chemoselective Cinnamaldehyde Hydrogenation
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A monolithic carbon-supported Pt nanocomposite with an interconnected three-dimensionally hierarchical porous carbon framework and ultra-high dispersion of Pt nanoparticles (Pt/3DHPC) is synthesized by using an effective “liquid phase impregnation template” strategy. The obtained Pt/3DHPC possesses rich mesoporosity and a low amount of oxygen-containing functional groups, which notably improve the accessible internal surface area of macropores, number of active Pt sites, and electron transfer ability. When used as a catalyst for the selective cinnamaldehyde (CMA) hydrogenation towards cinnamyl alcohol (CMO), Pt/3DHPC exhibits high CMA conversion (92.7 %) and CMO selectivity (91.1 %) at 1 h reaction time, and the corresponding activity (1553.7 h?1) greatly surpasses not only the single-sized mesoporous carbon and microporous activated carbon-supported counterparts but also the previously reported Pt catalysts dispersed on other forms of carbon. Furthermore, Pt/3DHPC can be reused at least fifteen times without pronounced decay owing to the strong interaction between Pt and carbon. The present work demonstrates the validity of multiscale control in carbon-supported Pt catalysts by overall consideration of the mass transportation, and the accessibility, quantity, and capability of active sites towards chemoselective hydrogenation of CMA, which is expected to be extended to other catalysis-related processes.
- Hu, Duo,Fan, Wenqian,Liu, Zhi,Li, Ling
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- Surface-Plasmon-Mediated Hydrogenation of Carbonyls Catalyzed by Silver Nanocubes under Visible Light
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Plasmonic nanoparticles are exciting and promising candidates for light-activated catalysis. We report herein the use of plasmonic nanocubes for the activation of molecular hydrogen and the hydrogenation of ketones and aldehydes via visible light irradiation at 405 nm, corresponding to the position of the plasmon band of the nanocubes, at 80 °C. Only 1 atm of molecular hydrogen is required to access, using catalytic amounts of silver, primary, and secondary alcohols, with complete chemoselectivty for C=O over C=C reduction. The resulting catalytic system was studied over a scope of 12 compounds. Exposure to other wavelengths, or absence of light failed to provide activity, thus proving a direct positive impact of the plasmonic excitation to the catalytic activity. By varying the irradiation intensity, we studied the relationship between plasmon band excitation and catalytic activity and propose a potential reaction mechanism involving plasmon-activated hot electrons. This study expands the scope of reactions catalyzed by free-standing plasmonic particles and sheds light on H2 activation by silver surfaces.
- Landry, Michael J.,Gellé, Alexandra,Meng, Beryl Y.,Barrett, Christopher J.,Moores, Audrey
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- Regioselective Hydroxylations of 1,3-Dienes via Hydrocobaltation Reactions. Facile Conversion of Myrcene to Geraniol and to (+/-)-Linalool
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Regioselective (1,4-) hydrocobaltation of myrcene (1) leads to a 2:1 mixture of (E)- and (Z)-allylcobaloximes (2) which can be converted via the corresponding hydroxylamines (5) to geraniol (6a) and nerol (6b); by contrast, in the presence of molecular oxygen, (2) is converted into the peroxyallylcobalt complex (7), a precursor to linalool (8) and to linalool oxide (10).
- Howell, Amy R.,Pattenden, Gerald
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- Exploring castellaniella defragrans linalool (De)hydratase-isomerase for enzymatic hydration of alkenes
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Acyclic monoterpenes constitute a large and highly abundant class of secondary plant metabolites and are, therefore, attractive low-cost raw materials for the chemical industry. To date, numerous biocatalysts for their transformation are known, giving access to highly sought-after monoterpenoids. In view of the high selectivity associated with many of these reactions, the demand for enzymes generating commercially important target molecules is unabated. Here, linalool (de)hydratase-isomerase (Ldi, EC 4.2.1.127) from Castellaniella defragrans was examined for the regio- and stereoselective hydration of the acyclic monoterpene β-myrcene to (S)-(+)-linalool. Expression of the native enzyme in Escherichia coli allowed for identification of bottlenecks limiting enzyme activity, which were investigated by mutating selected residues implied in enzyme assembly and function. Combining these analyses with the recently published 3D structures of Ldi highlighted the precisely coordinated reduction–oxidation state of two cysteine pairs in correct oligomeric assembly and the catalytic mechanism, respectively. Subcellular targeting studies upon fusion of Ldi to different signal sequences revealed the significance of periplasmic localization of the mature enzyme in the heterologous expression host. This study provides biochemical and mechanistic insight into the hydration of β-myrcene, a nonfunctionalized terpene, and emphasizes its potential for access to scarcely available but commercially interesting tertiary alcohols.
- Engleder, Matthias,Müller, Monika,Kaluzna, Iwona,Mink, Daniel,Schürmann, Martin,Leitner, Erich,Pichler, Harald,Emmerstorfer-Augustin, Anita
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- A domain swapping approach to elucidate differential regiospecific hydroxylation by geraniol and linalool synthases from perilla
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Geraniol and linalool are acyclic monoterpenes found in plant essential oils that have attracted much attention for their commercial use and in pharmaceutical studies. They are synthesized from geranyl diphosphate (GDP) by geraniol and linalool synthases, respectively. Both synthases are very similar at the amino acid level and share the same substrate; however, the position of the GDP to which they introduce hydroxyl groups is different. In this study, the mechanisms underlying the regiospecific hydroxylation of geraniol and linalool synthases were investigated using a domain swapping approach and sitedirected mutagenesis in perilla. Sequences of the synthases were divided into ten domains (domains I to IV-4), and each corresponding domain was exchanged between both enzymes. It was shown that different regions were important for the formation of geraniol and linalool, namely, domains IV-1 and -4 for geraniol, and domains III-b, III-d, and IV-4 for linalool. These results suggested that the conformation of carbocation intermediates and their electron localization were seemingly to be different between geraniol and linalool synthases. Further, five amino acids in domain IV-4 were apparently indispensable for the formation of geraniol and linalool. According to three-dimensional structural models of the synthases, these five residues seemed to be responsible for the different spatial arrangement of the amino acid at H524 in the case of geraniol synthase, while N526 is the corresponding residue in linalool synthase. These results suggested that the side-chains of these five amino acids, in combination with several relevant domains, localized the positive charge in the carbocation intermediate to determine the position of the introduced hydroxyl group.
- Sato-Masumoto, Naoko,Ito, Michiho
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- Chemoselective Reduction of Complex α,β-Unsaturated Ketones to Allylic Alcohols over Ir-Metal Particles on β Zeolites
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The combination of Ir, which has a strong affinity for carbonyl groups, with an acid H-β zeolite as a support and promotor, provides an effective catalyst for the chemoselective hydrogenation of α,β-unsaturated aldehydes and ketones to the corresponding allylic alcohols. Steroidal enones are suitable substrates for this transformation (see scheme). R = CH (Me)(CH2)3CH(Me)2.
- De Bruyn, Mario,Coman, Simona,Bota, Roxana,Parvulescu, Vasile I.,De Vos, Dirk E.,Jacobs, Pierre A.
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- Metal-doped mesoporous ZrO2catalyzed chemoselective synthesis of allylic alcohols from Meerwein-Ponndorf-Verley reduction of α,β-unsaturated aldehydes
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Meerwein-Ponndorf-Verley reduction (MPVr) is a sustainable route for the chemoselective transformation of α,β-unsaturated aldehydes. However, tailoring ZrO2 catalysts for improved surface-active sites and maximum performance in the MPV reaction is still a challenge. Here, we synthesized mesoporous zirconia (ZrO2) and metal-doped zirconia (M_ZrO2, M = Cr, Mn, Fe, and Ni). The incorporation of metal dopants into zirconia's crystal framework alters its physico-chemical properties such as surface area and total acidity-basicity. The prepared catalysts were evaluated in the MPVr using 2-propanol as a hydrogen donor under mild reaction conditions. The catalysts' remarkable reactivity depends mainly on their surface mesostructure's intrinsic properties rather than the specific surface area. Cr_ZrO2, which is stable and sustainable, presented superior activity and 100% selectivity to unsaturated alcohols. The synergistic effect between Cr and Zr species in the binary oxide facilitated the Lewis acidity-induced performance of the Cr_ZrO2 catalyst. Our work presents the first innovative application of a well-designed mesoporous Cr_ZrO2 in the green synthesis of unsaturated alcohols with exceptional reactivity. This journal is
- Akinnawo, Christianah Aarinola,Bingwa, Ndzondelelo,Meijboom, Reinout
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- TOTAL SYNTHESIS OF DIHYDROTELEOCIDIN B-4 (DIHYDROTELEOCIDIN B)
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A potent tumor promoter, dihydroteleocidin B-4 (= dihydroteleocidin B) (1) was synthesized from L-valine derivative 8 using an acid-catalyzed cyclization of 15 to 16a to construct the teleocidin B structure unit.
- Muratake, Hideaki,Okabe, Kazuaki,Natsume, Mitsutaka
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- Use of short time-on-stream attenuated total internal reflection infrared spectroscopy to probe changes in adsorption geometry for determination of selectivity in the hydrogenation of citral
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A new experimental procedure based on attenuated total reflection infrared spectroscopy has been developed to investigate surface species under liquid phase reaction conditions. The technique has been tested by investigating the enhanced selectivity in the hydrogenation of α,β-unsaturated aldehyde citral over a 5% Pt/SiO2 catalyst toward unsaturated alcohols geraniol/nerol, which occurs when citronellal is added to the reaction. The change in selectivity is proposed to be the result of a change in the citral adsorption mode in the presence of citronellal. Short time on stream attenuated total internal reflection infrared spectroscopy has allowed identification of the adsorption modes of citral. With ssno citronellal, citral adsorbs through both the C = C and C = O groups; however, in the presence of citronellal, citral adsorption occurs through the C = O group only, which is proposed to be the cause of the altered reaction selectivity.
- Daly,Manyar,Morgan,Thompson,Delgado,Burch,Hardacre
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- BIOTRANSFORMATION OF LINALYL ACETATE BY SUSPENSION CULTURES OF PAPAVER BRACTEATUM
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Suspension cultures of Papaver bracteatum biotransform the acyclic monoterpene, linalyl acetate, into linalool, geraniol and the monocyclic alcohol, α-terpineol.Total metabolism of linalyl acetate occurs within eight days of substrate addition, with 40percent of the substrate being transformed within the first 36hr.No regiospecific hydroxylation of the 3-methyl-2-butenyl group is observed.
- Hook, Ingrid,Lecky, Rhonda,McKenna, Brian,Sheridan, Helen
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- Me3SI-promoted chemoselective deacetylation: a general and mild protocol
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A Me3SI-mediated simple and efficient protocol for the chemoselective deprotection of acetyl groups has been developedviaemploying KMnO4as an additive. This chemoselective deacetylation is amenable to a wide range of substrates, tolerating diverse and sensitive functional groups in carbohydrates, amino acids, natural products, heterocycles, and general scaffolds. The protocol is attractive because it uses an environmentally benign reagent system to perform quantitative and clean transformations under ambient conditions.
- Gurawa, Aakanksha,Kashyap, Sudhir,Kumar, Manoj
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p. 19310 - 19315
(2021/06/03)
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- Regiospecific Synthesis of Calcium-Independent Daptomycin Antibiotics using a Chemoenzymatic Method
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Daptomycin (DAP) is a calcium (Ca2+)-dependent FDA-approved antibiotic drug for the treatment of Gram-positive infections. It possesses a complex pharmacophore hampering derivatization and/or synthesis of analogues. To mimic the Ca2+-binding effect, we used a chemoenzymatic approach to modify the tryptophan (Trp) residue of DAP and synthesize kinetically characterized and structurally elucidated regiospecific Trp-modified DAP analogues. We demonstrated that the modified DAPs are several times more active than the parent molecule against antibiotic-susceptible and antibiotic-resistant Gram-positive bacteria. Strikingly, and in contrast to the parent molecule, the DAP derivatives do not rely on calcium or any additional elements for activity.
- Mupparapu, Nagaraju,Lin, Yu-Hsin Cindy,Kim, Tae Ho,Elshahawi, Sherif I.
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supporting information
p. 4176 - 4182
(2021/02/01)
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- Redox-active ligand based Mn(i)-catalyst for hydrosilylative ester reduction
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Herein a Mn(i) catalyst bearing a redox-active phenalenyl (PLY) based ligand is reported for the efficient hydrosilylation of esters to alcohols using the inexpensive silane source polymethylhydrosiloxane (PMHS) under mild conditions. Mechanistic investigations suggest a strong ligand-metal cooperation where a ligand-based single electron transfer (SET) process initiates the reaction through Si-H bond activation.
- Chakraborty, Soumi,Das, Arpan,Mandal, Swadhin K.
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supporting information
p. 12671 - 12674
(2021/12/04)
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- 3'-KETOGLYCOSIDE COMPOUND FOR THE SLOW RELEASE OF A VOLATILE ALCOHOL
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The present invention relates to a 3'-ketoglycoside compound defined by formula (I) and its use for controlled release of alcohols, in particular alcohols showing an insect repellent effect. It relates also to a process for preparing the 3'-ketoglycoside compound of formula (I). It further relates to a composition comprising a 3'- ketoglycoside compound of formula (I). It relates also to the use of a 3'-ketoglycoside compound of formula (I) for the controlled release of alcohols. It related also to a method of use of such composition.
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Page/Page column 63-64
(2021/08/20)
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- A new catalytic approach for aerobic oxidation of primary alcohols based on a Copper(I)-thiophene carbaldimines
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We report here novel Cu(I) thiophene carbaldimine catalysts for the selective aerobic oxidation of primary alcohols to their corresponding aldehydes and various diols to lactones or lactols. In the presence of the in situ generated Cu(I) species, a persistent radical (2,2,6,6-tetramethylpiperdine-N-oxyl (TEMPO)) and N-methylimidazole (NMI) as an auxiliary ligand, the reaction proceeds under aerobic conditions and at ambient temperature. Especially the catalytic system of 1-(thiophen-2-yl)-N-(4-(trifluoromethoxy)phenyl)methanimine (ligand L2) with copper(I)-iodide showed high reactivity for all kind of alcohols (benzylic, allylic and aliphatic). In the case of benzyl alcohol even 2.5 mol% of copper loading gave quantitative yield. Beside high activity under aerobic conditions, the catalysts ability to oxidize 1,5-pentadiol to the corresponding lactol (86% in 4 h) and N-phenyldiethanolamine to the corresponding morpholine derivate lactol (86% in 24 h) is particularly noteworthy.
- Lagerspets, Emi,Valbonetti, Evelyn,Eronen, Aleksi,Repo, Timo
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- A Bifunctional Copper Catalyst Enables Ester Reduction with H2: Expanding the Reactivity Space of Nucleophilic Copper Hydrides
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Employing a bifunctional catalyst based on a copper(I)/NHC complex and a guanidine organocatalyst, catalytic ester reductions to alcohols with H2 as terminal reducing agent are facilitated. The approach taken here enables the simultaneous activation of esters through hydrogen bonding and formation of nucleophilic copper(I) hydrides from H2, resulting in a catalytic hydride transfer to esters. The reduction step is further facilitated by a proton shuttle mediated by the guanidinium subunit. This bifunctional approach to ester reductions for the first time shifts the reactivity of generally considered "soft"copper(I) hydrides to previously unreactive "hard"ester electrophiles and paves the way for a replacement of stoichiometric reducing agents by a catalyst and H2.
- Kaicharla, Trinadh,Ngoc, Trung Tran,Teichert, Johannes F.,Tzaras, Dimitrios-Ioannis,Zimmermann, Birte M.
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supporting information
p. 16865 - 16873
(2021/10/20)
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- KMnO4-catalyzed chemoselective deprotection of acetate and controllable deacetylation-oxidation in one pot
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A novel and efficient protocol for chemoselective deacetylation under ambient conditions was developed using catalytic KMnO4. The stoichiometric use of KMnO4 highlighted the dual role of a heterogeneous oxidant enabling direct access to aromatic aldehydes in one-pot sequential deacetylation-oxidation. The reaction employed an alternative solvent system and allowed the clean transformation of benzyl acetate to sensitive aldehyde in a single step while preventing over-oxidation to acids. Use of inexpensive and readily accessible KMnO4 as an environmentally benign reagent and the ease of the reaction operation were particularly attractive, and enabled the controlled oxidation and facile cleavage of acetate in a preceding step. This journal is
- Gurawa, Aakanksha,Kumar, Manoj,Rao, Dodla S.,Kashyap, Sudhir
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supporting information
p. 16702 - 16707
(2020/10/27)
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- Iridium-Catalyzed Asymmetric Isomerization of Primary Allylic Alcohols Using MaxPHOX Ligands: Experimental and Theoretical Study
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The asymmetric isomerization of primary allylic alcohols to chiral aldehydes using iridium-catalysts bearing P,N-MaxPHOX ligands has been studied. These catalysts can be fine-tuned as they present three different stereogenic centers to modulate both the reactivity and enantioselectivity of a family of different substrates. The experimental part is supported by a DFT study of the reaction mechanism, which provides new insights into the key steps of this transformation.
- Cabré, Albert,Gar?on, Martí,Gallen, Albert,Grisoni, Lorenzo,Grabulosa, Arnald,Verdaguer, Xavier,Riera, Antoni
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p. 4112 - 4120
(2020/07/04)
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- Improved method for preparation of nerol and geraniol and catalytic system thereof
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The invention relates to a method for preparing nerol and geraniol through selective hydrogenation by taking citral as a raw material and a catalytic system for the method. The method comprises the following step: carrying out selective hydrogenation reaction on initial compound citral under the catalytic action of a homogeneous catalyst and an auxiliary agent to prepare nerol and geraniol. According to the method and the catalytic system provided by the invention, by-products citronellol and nerol isomers I-III in the reaction process are remarkably reduced, and the method has a relatively good industrial prospect.
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Paragraph 0054-0055; 0058-0059
(2020/05/01)
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- Layered double hydroxide derived NiAl-oxide hollow nanospheres for selective transfer hydrogenation with improved stability
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Selective transfer hydrogenation (STH) is an efficient strategy in biomass upgradation, especially for the production of unsaturated alcohols from biomass-derived α,β-unsaturated aldehydes. Design of effective catalysts with excellent stability for the STH is highly desired. Here, we report the synthesis of Ni3Al1-oxide hollow nanospheres (h-Ni3Al1-800) derived from Ni3Al1 layered double hydroxide grafted on hollow polymer spheres (HPS?Ni3Al1-LDH) by calcination at 800 °C in air. h-Ni3Al1-800 is an efficient catalyst for the STH of α,β-unsaturated aldehydes with selectivities towards α,β-unsaturated alcohols >99% at almost full conversions. More importantly, h-Ni3Al1-800 can be recycled at least 12 times without loss of activity. Experimental results and DFT calculations prove that the Al dopant in h-Ni3Al1-800 provides much stable Niδ+-type (2 δ 3) acid-base pairs which can efficiently catalyze the STH with improved stability. This work provides a promising direction for the design of STH catalysts that have potential for industrial applications. This journal is
- Gong, Bingbing,Jiang, Haibin,Luo, Rong,Pan, Zhengyi,Wang, Guang-Hui,Zhang, Wenhua
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supporting information
p. 23376 - 23384
(2020/11/25)
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- A highly efficient Cu/AlOOH catalyst obtained by in situ reduction: Catalytic transfer hydrogenation of ML into Γ-GVL
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Catalytic transfer hydrogenation (CTH) of carbonyl compounds is considered as one of the most promising processes in the synthesis of fuels and chemicals. In this work, we propose a one-step strategy for catalyst preparation and CTH. Using the strategy, the production of γ-valerolactone (γ-GVL) was performed with isopropanol (2-PrOH) as solvent over in situ reduced nano-Cu/AlOOH catalyst from Cu2(OH)2CO3/AlOOH and the optimal reaction conditions for γ-GVL are 180 °C for 5 h using the in situ reduced catalyst with Cu/Al molar ratio 3/1 (90.51% yields of γ-GVL). Furthermore, it has been confirmed by different characterization methods (such as: SEM, TEM, XPS, etc.) that the catalyst is heterogeneous and exhibits high catalytic activity and stability which is attributed to the stability of the zero-valent copper in the catalyst and the nanosized particles of the catalyst. In addition, the catalysts also show general applicability to other carbonyl compounds.
- Ma, Mingwei,Liu, Hui,Cao, Jingjie,Hou, Pan,Huang, Jiahui,Xu, Xingliang,Yue, Huijuan,Tian, Ge,Feng, Shouhua
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- Selective Hydrogenation of Citral on Pt-Containing Catalysts at Room Temperature and Atmospheric Pressure
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Abstract: It is shown that the 1% Pt/CeO2–ZrO2 (1% Pt/CZ) catalytic system allows selective hydrogenation of citral with a 94% conversion and a selectivity towards unsaturated alcohols of 59% at room temperature and atmospheric pressure. The effect of addition of alkali to the reaction mixture on the yield of the target products is studied, and the optimum conditions of the reaction are determined.
- Vikanova,Redina
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p. 2566 - 2569
(2019/12/30)
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- Flat and Efficient H CNN and CNN Pincer Ruthenium Catalysts for Carbonyl Compound Reduction
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The bidentate HCNN dicarbonyl ruthenium complexes trans,cis-[RuCl2(HCNN)(CO)2] (1-3) and trans,cis-[RuCl2(ampy)(CO)2] (1a) were prepared by reaction of [RuCl2(CO)2]n with 1-[6-(4′-methylphenyl)pyridin-2-yl]methanamine, benzo[h]quinoline (HCNN), and 2-(aminomethyl)pyridine (ampy) ligands. Alternatively, the derivatives 1-3 were obtained from the reaction of RuCl3 hydrate with HCO2H and HCNN. The pincer CNN cis-[RuCl(CNN)(CO)2] (4) was isolated from 1 by reaction with NEt3. The monocarbonyl complexes trans-[RuCl2(HCNN)(PPh3)(CO)] (5-7) were synthesized from [RuCl2(dmf)(PPh3)2(CO)] and HCNN ligands, while the diacetate trans-[Ru(OAc)2(HCNN)(PPh3)(CO)] (8) was obtained from [Ru(OAc)2(PPh3)2(CO)]. Carbonylation of cis-[RuCl(CNN)(PPh3)2] with CO afforded the pincer derivatives [RuCl(CNN)(PPh3)(CO)] (9-11). Treatment of 9 with Na[BArf]4 and PPh3 gave the cationic complex trans-[Ru(CNN)(PPh3)2(CO)][BArf4] (12). The dicarbonyl derivatives 1-4, in the presence of PPh3 or PCy3, and the monocarbonyl complexes 5-12 catalyzed the transfer hydrogenation (TH) of acetophenone (a) in 2-propanol at reflux (S/C = 1000-100000 and TOF up to 100000 h-1). Compounds 1-3, with PCy3, and 6 and 8-10 were proven to catalyze the TH of carbonyl compounds, including α,β-unsaturated aldehydes and bulky ketones (S/C and TOF up to 10000 and 100000 h-1, respectively). The derivatives 1-3 with PCy3 and 5 and 6 catalyzed the hydrogenation (HY) of a (H2, 30 bar) at 70 °C (S/C = 2000-10000). Complex 5 was active in the HY of diaryl ketones and aryl methyl ketones, leading to complete conversion at S/C = 10000.
- Giboulot, Steven,Baldino, Salvatore,Ballico, Maurizio,Figliolia, Rosario,P?thig, Alexander,Zhang, Shuanming,Zuccaccia, Daniele,Baratta, Walter
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p. 1127 - 1142
(2019/03/14)
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- Supported Co–Re Bimetallic Catalysts with Different Structures as Efficient Catalysts for Hydrogenation of Citral
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Bimetallic Co–Re/TiO2 catalysts were developed for efficient citral hydrogenation. Bimetallic catalysts were prepared by co-impregnation (CI), successive-impregnation (SI), and surface redox method (SR). The arrangement between the Co and Re species on these systems was fully characterized using several techniques (TEM–energy-dispersive X-ray spectroscopy, H2 temperature-programmed reduction, temperature-programmed desorption, XRD, CO FTIR spectroscopy, model reaction of cyclohexane dehydrogenation), and their catalytic performances were evaluated for the selective hydrogenation of citral towards unsaturated alcohols. The Re and Co species are completely isolated in the CI sample, presenting a very limited Co–Re interaction. In SI samples, the metals coexist in a Janus-type structure with a concentration of Re around Co. Decoration/core–shell structures are observed for SR samples resulting from the redox exchange between the metallic surface of the parent Co/TiO2 catalyst and the Re7+ species of the modifier precursor salt. The contact degree between the two metals gradually increases as follows: Isolated structure (CI)a disadvantage for the hydrogenation reaction. For SR samples, the increase of Re loading contributes to the electron transfer from Re to Co that is consistent with a change of structure from decoration to core–shell. The lack of directly accessible Co atoms for SR catalysts with fully coated structure decreases the efficiency of Re reduction. The presence of Co–Re interaction resulting from the close contact between metals plays a dominant role in the hydrogenation of citral. Nevertheless, an excessively high contact degree is unnecessary for citral hydrogenation once Co–Re interaction has formed.
- Di, Xin,Lafaye, Gwendoline,Especel, Catherine,Epron, Florence,Qi, Ji,Li, Chuang,Liang, Changhai
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p. 807 - 823
(2019/02/19)
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- Catalytic removal of tert-butyldimethylsilyl (TBS) ether by PVP-I
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A mild, efficient and rapid protocol the deprotection of alcoholic TBDMS ethers using PVP-1 as catalyst in methanol, the procedure of deprotection of various TBDMS ethers were found to be very convenient, easy work-up, high yielding.
- Ke, Yanxiong,Lu, Guangying,Ren, Jiangmeng,Wang, Di,Zeng, Bu-Bing
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- Transfer Hydrogenation of Aldehydes and Ketones with Isopropanol under Neutral Conditions Catalyzed by a Metal-Ligand Bifunctional Catalyst [Cp?Ir(2,2′-bpyO)(H2O)]
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A Cp?Ir complex bearing a functional bipyridonate ligand [Cp?Ir(2,2′-bpyO)(H2O)] was found to be a highly efficient and general catalyst for transfer hydrogenation of aldehydes and chemoselective transfer hydrogenation of unsaturated aldehydes with isopropanol under neutral conditions. It was noteworthy that many readily reducible or labile functional groups such as nitro, cyano, ester, and halide did not undergo any change under the reaction conditions. Furthermore, this catalytic system exhibited high activity for transfer hydrogenation of ketones with isopropanol. Notably, this research exhibited new potential of metal-ligand bifunctional catalysts for transfer hydrogenation.
- Wang, Rongzhou,Tang, Yawen,Xu, Meng,Meng, Chong,Li, Feng
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p. 2274 - 2281
(2018/02/23)
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- Selective hydrogenation of unsaturated aldehydes over Pt nanoparticles promoted by the cooperation of steric and electronic effects
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The selective hydrogenation of α,β-unsaturated aldehydes to unsaturated alcohols can reach high selectivity and activity at room temperature using Pt nanoparticles immobilized on a non-porous Al2O3 support stabilized by aspartic acid. Aspartic acid molecules had a significant steric effect on CC hydrogenation and could modify the electronic state of metal particles.
- Liu, Hangyu,Mei, Qingqing,Li, Shaopeng,Yang, Youdi,Wang, Yanyan,Liu, Huizhen,Zheng, Lirong,An, Pengfei,Zhang, Jing,Han, Buxing
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supporting information
p. 908 - 911
(2018/02/07)
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- Nerol and geraniol preparation method
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The invention discloses a nerol and geraniol solid-phase method production technology. The technology adopts citral, paraformaldehyde and sodium hydroxide as raw materials, adds quaternary phosphoniumsalt as an auxiliary agent, and performs a solid-phase reaction in a ball mill reactor. After completion of the reaction, the obtained slurry is subjected to sieving, centrifugation, washing, and finally distilled to obtain nerol and geraniol products. The process is the green and solid-phase synthesis process, the product is easy to separate and purify, and the by-product sodium formate is highin purity and can be directly sold. The process overcomes the disadvantages of more step, low yield, large amount of three wastes, and many impurities in products in a traditional process route, and has industrial value.
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Paragraph 0032-0046
(2019/01/08)
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- Transition-Metal-Free Formylation of Allylzinc Reagents Leading to α-Quaternary Aldehydes
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The first example of formylation of allylzinc reagents using S-phenyl thioformate is presented. The reaction proceeded under mild conditions without any transition-metal catalyst, forming quaternary carbon centers with reactive functionalities, such as formyl and vinyl groups. Moreover, Barbier-type formylation of an allylic bromide with a sterically demanding thioformate was achieved. As a preliminary result, asymmetric formylation was conducted using a menthol-derived chiral thioformate.
- Haraguchi, Ryosuke,Kusakabe, Akinori,Mizutani, Nakaba,Fukuzawa, Shin-Ichi
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supporting information
p. 1613 - 1616
(2018/03/23)
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- Mechanistic Investigation of Bis(imino)pyridine Manganese Catalyzed Carbonyl and Carboxylate Hydrosilylation
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We recently reported a bis(imino)pyridine (or pyridine diimine, PDI) manganese precatalyst, (Ph2PPrPDI)Mn (1), that is active for the hydrosilylation of ketones and dihydrosilylation of esters. In this contribution, we reveal an expanded scope for 1-mediated hydrosilylation and propose two different mechanisms through which catalysis is achieved. Aldehyde hydrosilylation turnover frequencies (TOFs) of up to 4900 min-1 have been realized, the highest reported for first row metal-catalyzed carbonyl hydrosilylation. Additionally, 1 has been shown to mediate formate dihydrosilylation with leading TOFs of up to 330 min-1. Under stoichiometric and catalytic conditions, addition of PhSiH3 to (Ph2PPrPDI)Mn was found to result in partial conversion to a new diamagnetic hydride compound. Independent preparation of (Ph2PPrPDI)MnH (2) was achieved upon adding NaEt3BH to (Ph2PPrPDI)MnCl2 and single-crystal X-ray diffraction analysis revealed this complex to possess a capped trigonal bipyramidal solid-state geometry. When 2,2,2-trifluoroacetophenone was added to 1, radical transfer yielded (Ph2PPrPDI·)Mn(OC·(Ph)(CF3)) (3), which undergoes intermolecular C-C bond formation to produce the respective Mn(II) dimer, [(μ-O,Npy-4-OC(CF3)(Ph)-4-H-Ph2PPrPDI)Mn]2 (4). Upon finding 3 to be inefficient and 4 to be inactive, kinetic trials were conducted to elucidate the mechanisms of 1- and 2-mediated hydrosilylation. Varying the concentration of 1, substrate, and PhSiH3 revealed a first order dependence on each reagent. Furthermore, a kinetic isotope effect (KIE) of 2.2 ± 0.1 was observed for 1-catalyzed hydrosilylation of diisopropyl ketone, while a KIE of 4.2 ± 0.6 was determined using 2, suggesting 1 and 2 operate through different mechanisms. Although kinetic trials reveal 1 to be the more active precatalyst for carbonyl hydrosilylation, a concurrent 2-mediated pathway is more efficient for carboxylate hydrosilylation. Considering these observations, 1-catalyzed hydrosilylation is believed to proceed through a modified Ojima mechanism, while 2-mediated hydrosilylation occurs via insertion.
- Mukhopadhyay, Tufan K.,Rock, Christopher L.,Hong, Mannkyu,Ashley, Daniel C.,Groy, Thomas L.,Baik, Mu-Hyun,Trovitch, Ryan J.
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p. 4901 - 4915
(2017/04/11)
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- Structure-Function Studies of Artemisia tridentata Farnesyl Diphosphate Synthase and Chrysanthemyl Diphosphate Synthase by Site-Directed Mutagenesis and Morphogenesis
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The amino acid sequences of farnesyl diphosphate synthase (FPPase) and chrysanthemyl diphosphate synthase (CPPase) from Artemisia tridentata ssp. Spiciformis, minus their chloroplast targeting regions, are 71% identical and 90% similar. FPPase efficiently and selectively synthesizes the "regular" sesquiterpenoid farnesyl diphosphate (FPP) by coupling isopentenyl diphosphate (IPP) to dimethylallyl diphosphate (DMAPP) and then to geranyl diphosphate (GPP). In contrast, CPPase is an inefficient promiscuous enzyme, which synthesizes the "irregular" monoterpenes chrysanthemyl diphosphate (CPP), lavandulyl diphosphate (LPP), and trace quantities of maconelliyl diphosphate (MPP) from two molecules of DMAPP, and couples IPP to DMAPP to give GPP. A. tridentata FPPase and CPPase belong to the chain elongation protein family (PF00348), a subgroup of the terpenoid synthase superfamily (CL0613) whose members have a characteristic α terpene synthase α-helical fold. The active sites of A. tridentata FPPase and CPPase are located within a six-helix bundle containing amino acids 53 to 241. The two enzymes were metamorphosed into one another by sequentially replacing the loops and helices of the six-helix bundle from enzyme with those from the other. Chain elongation was the dominant activity during the N-terminal to C-terminal metamorphosis of FPPase to CPPase, with product selectivity gradually switching from FPP to GPP, until replacement of the final α-helix, whereupon cyclopropanation and branching activity competed with chain elongation. During the corresponding metamorphosis of CPPase to FPPase, cyclopropanation and branching activities were lost upon replacement of the first helix in the six-helix bundle. Mutations of active site residues in CPPase to the corresponding amino acids in FPPase enhanced chain-elongation activity, while similar mutations in the active site of FPPase failed to significantly promote formation of significant amounts of irregular monoterpenes. Our results indicate that CPPase, a promiscuous enzyme, is more plastic toward acquiring new activities, whereas FPPase is more resistant. Mutations of residues outside of the α terpene synthase fold are important for acquisition of FPPase activity for synthesis of CPP, LPP, and MPP.
- Lee, J. Scott,Pan, Jian-Jung,Ramamoorthy, Gurusankar,Poulter, C. Dale
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supporting information
p. 14556 - 14567
(2017/10/24)
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- New In(OiPr)3-MCM-41 heterogeneous catalyst in MPV reductions of unsaturated carbonyl compounds: effect of mesoporous SBA-15 and MCM-41 as supporting surfaces on catalytic activity of In(OiPr)3
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Indium tri-isopropoxide, In(OiPr)3, was immobilized on mesoporous material, MCM-41, and denoted as “In(OiPr)3-MCM-41”. This new heterogeneous catalyst was characterized by XRD, 29Si NMR-, N2 adsorption–desorption isotherms and ICP-OES techniques. The new heterogeneous catalyst, In(OiPr)3-MCM-41, was tested for the capable of catalyzed Meerwein–Ponndorf–Verley (MPV) reduction of unsaturated aldehydes and ketones with low catalyst loadings under mild conditions and showed good to excellent catalytic activities. Also, effect of supporting surfaces, both of SBA-15 and MCM-41, on catalytic activity of In(OiPr)3 were examined. In(OiPr)3-SBA-15 heterogeneous catalyst in comparison with the In(OiPr)3-MCM-41 catalyst, display comparatively higher catalytic activity in the MPV reduction of unsaturated aldehydes and ketones. Also, similiar reaction times and selectivities for the unsaturated alcohols were obtained with the In(OiPr)3-SBA-15 catalyst compared with the In(OiPr)3-MCM-41 catalyst. The reason for the lower activity observed for MCM-41 sample may be due to smaller pore size of the In(OiPr)3-MCM-41 catalyst as compared with In(OiPr)3-SBA-15 catalyst can creat restrict site accessibility for the carbonyl compounds. Eventually, effect of supporting surfaces, SBA-15 and MCM-41, on catalytic activity of In(OiPr)3 insignificant for MPV reduction of unsaturated carbonyl compounds.
- Karatas, Burcu Uysal,Oksal, Birsen S.,Karatas, Erhan
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- Catalytic activity of nanoscale borides: Co2B and Ni7B3 in the liquid-phase hydrogenation of citral
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Metal borides are unconventional heterogeneous catalysts. Now, two compounds – the new phase Ni7B3 and well-known Co2B – were synthesized as well-defined, nanoscale material. After characterization (X-ray diffraction, scanning electron microscopy, nitrogen physisorption) they were tested for the liquid phase hydrogenation of citral (3,7-dimethyl-2,6-octadienal) in n-hexane at different temperatures. Hydrogenation products such as geraniol, nerol, citronellal and citronellol were analyzed. The Ni-free catalyst Co2B results in the formation of nerol and geraniol or citronellol selectively, depending on the reaction time. The new compound Ni7B3 yields citronellal or citronellol, depending on the temperature. Thus, the hydrogenation potential of borides – obtained as well-characterized, unsupported heterogeneous catalysts by a one-pot synthesis procedure and post-synthetic annealing – is demonstrated. The cobalt boride preferentially hydrogenates C[dbnd]O bonds, while the nickel boride is selective for C[dbnd]C double bonds.
- Kalyon,Hofmann,Malter,Lucas,Claus,Albert
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p. 436 - 441
(2017/07/05)
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- Asymmetric Traceless Petasis Borono-Mannich Reactions of Enals: Reductive Transposition of Allylic Diazenes
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The traceless Petasis borono-Mannich reaction of enals, sulfonylhydrazines, and allylboronates, catalyzed by chiral biphenols, results in an asymmetric reductive transposition of the in situ generated allylic diazene. Acyclic 1,4-diene products bearing either alkyl- or aryl-substituted benzylic stereocenters are afforded in excellent yields and enantiomeric ratios of up to 99:1. The use of crotylboronates in the reaction results in concomitant formation of two stereocenters in either a 1,4-syn or anti relationship from the corresponding E- or Z-crotylboronate used in the reaction. The use of β-monosubstituted enals in the asymmetric traceless Petasis borono-Mannich reaction of crotylboronates installs tertiary methyl-bearing stereocenters in good yields and high enantioselectivities.
- Jiang, Yao,Thomson, Regan J.,Schaus, Scott E.
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supporting information
p. 16631 - 16635
(2017/12/13)
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- Manufacture of Citronellal by the Rhodium-Catalyzed Homogeneous Hydrogenation of Neral
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The highly chemoselective hydrogenation of neral affording citronellal is described. The reaction has been conducted with homogeneous rhodium complexes. Among the set of ancillary diphosphane ligands tested, Xantphos was found to be superior. The relevant precatalyst has been generated from neutral metal sources such as Rh(acac)(CO)2 or the carbon monoxide-free rhodium source Rh(acac)(cod) in the absence of any base. A high activity and chemoselectivity in favor of the desired citronellal is achieved at 0.1 MPa and room temperature. Under the same conditions, geranial is also reduced to citronellal. The addition of carbon monoxide to the hydrogen stream as used in an industrial process is not necessary. (Figure presented.).
- Holz, Jens,Doerfelt, Stephan,B?rner, Armin
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p. 4379 - 4387
(2017/12/26)
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- Ionic liquids that form adducts with alcohols
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A class of ionic liquids with a built-in active ketone functionality is shown to form adducts with structurally diverse alcohols. The positions of the equilibria for adduct formation are shown to be dependent on the structure of the alcohols. How these functionalised ionic liquids could be applied in altering vapour phase compositions of alcohols and in separations of perfumery alcohols are demonstrated, here.
- Gunaratne, H. Q. Nimal,McCarron, Philip,Seddon, Kenneth R.
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p. 614 - 618
(2017/08/18)
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- Indium-mediated cleavage of the trityl group from protected alcohols and diols
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The reaction of primary, secondary, allylic and benzylic trityl ethers with indium powder in MeOH/NH4Cl led to reductive cleavage of the trityl-oxygen bond, affording the corresponding alcohols in good to excellent yield under very mild reaction conditions. The detritylation process could successfully be extended to mono and detritylated diols. This methodology represents a new and efficient detritylation procedure under mild reaction conditions.
- Behloul, Cherif,Chouti, Aicha,Guijarro, David,Foubelo, Francisco,Nájera, Carmen,Yus, Miguel
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p. 7937 - 7941
(2016/11/19)
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- Transesterification Reactions Catalyzed by a Recyclable Heterogeneous Zinc/Imidazole Catalyst
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We report the development of a universal and recyclable heterogeneous zinc/imidazole catalyst. The catalyst is recoverable through simple filtration and can be reused at least five times, retaining its catalytic activity. Leached zinc species were not responsible for the observed catalysis based on the hot filtration test and ICP-MS analysis. The heterogeneous zinc catalyst also promotes chemoselective transesterification over amidation. (Figure presented.).
- Nakatake, Daiki,Yazaki, Ryo,Matsushima, Yoshimasa,Ohshima, Takashi
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supporting information
p. 2569 - 2574
(2016/08/16)
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- A detailed view on 1,8-cineol biosynthesis by Streptomyces clavuligerus
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The stereochemical course of the cyclisation reaction catalysed by the bacterial 1,8-cineol synthase from Streptomyces clavuligerus was investigated using stereospecifically deuterated substrates. In contrast to the well investigated plant enzyme from Salvia officinalis, the reaction proceeds via (S)-linalyl diphosphate and the (S)-terpinyl cation, while the final cyclisation reaction is in both cases a syn addition, as could be shown by incubation of (2-13C)geranyl diphosphate in deuterium oxide.
- Rinkel, Jan,Rabe, Patrick,Zur Horst, Laura,Dickschat, Jeroen S.
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supporting information
p. 2317 - 2324
(2016/11/17)
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- Highly efficient reduction of carbonyls, azides, and benzyl halides by NaBH4 in water catalyzed by PANF-immobilized quaternary ammonium salts
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A series of polyacrylonitrile fiber-supported quaternary ammonium salts (PANF-QAS) were prepared and applied to the catalytic reduction of aldehydes, ketones, azides, and benzyl halides in water using NaBH4 as the reducing reagent in a highly efficient, economic, and environmentally benign way. The structure-activity relationships were investigated, which showed that the catalysts made up of quaternary ammonium salts with longer alkyl chains, larger cationic radii and better lipophilicity speed up the reduction reaction to afford the products in excellent yield. Moreover, the optimized catalyst can be applied to the reduction of 1-naphthaldehyde in a continuous flow process with outstanding reactivity and recyclability.
- Du, Jianguo,Xu, Gang,Lin, Huikun,Wang, Guangwei,Tao, Minli,Zhang, Wenqin
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supporting information
p. 2726 - 2735
(2016/05/24)
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- Surface Lewis acid-promoted copper-based nanocatalysts for highly efficient and chemoselective hydrogenation of citral to unsaturated allylic alcohols
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Chemoselective hydrogenation of α,β-unsaturated aldehydes or ketones to unsaturated alcohols (UAs) is one of the key processes for the production of various important intermediate chemicals. In the present work, well-dispersed ZnO-promoted supported copper nanocatalysts were generated from Cu-Zn-Al layered double hydroxide (CuZnAl-LDH) precursors for liquid-phase chemoselective hydrogenation of citral to allylic alcohols (geraniol and nerol isomers). A series of characterizations including XRD, TEM, STEM, XPS, H2-TPR, and Py-IR demonstrated that the microstructure and catalytic performance of as-formed Cu-based nanocatalysts were significantly affected by the incorporation of Zn into catalyst precursors. It was found that the addition of more ZnO to catalysts could result in better metal dispersion and an increase in the surface Cu+/(Cu+ + Cu0) ratio and surface Lewis acid sites. In liquid-phase chemoselective hydrogenation of citral, a high selectivity toward allylic alcohols (>75%) at complete citral conversion was achieved successfully on as-formed non-noble-metal Cu-based nanocatalysts with a Cu/Zn molar ratio of 2:1 under mild reaction conditions (e.g. 80°C, 1.0 MPa). The high efficiency of the catalysts was attributed mainly to both the synergism between Cu0 and Cu+ species and the promotion of surface Lewis acid sites, thereby improving the dissociation of hydrogen and facilitating the adsorption of the citral molecule and the following activation of the carbonyl group during the citral hydrogenation.
- Li, Wei,Fan, Guoli,Yang, Lan,Li, Feng
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p. 2337 - 2348
(2016/04/26)
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- Chemoselective Pt-catalysts supported on carbon-TiO2 composites for the direct hydrogenation of citral to unsaturated alcohols
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A series of carbon xerogels-TiO2 composites with different TiO2 contents were prepared, exhaustively characterized and used as a Pt-support to develop selective hydrogenation catalysts. The carbon phase in the composite hinders the TiO2 crystal growth and the transformation to rutile during thermal treatments. Textural, chemical and catalytic properties are determined by the TiO2 content, with an optimum around 40 wt.% of TiO2 content. The mesoporosity of the supports, the Pt-dispersion and Pt-support interactions are favoured in this sense. During the H2-pretreatment, the Pt and TiO2 phases were simultaneously reduced and the formation of oxygen vacancies leads to the mobility of Pt-species inside the TiO2 structure, avoiding sintering in surface and strongly improving both catalytic activity and selectivity. The catalytic performance was discussed on the basis of the sample characteristics. Unsaturated alcohols were obtained as main reaction products in all cases, being the only product in the case of the optimized catalyst.
- Bailón-García, Esther,Carrasco-Marín, Francisco,Pérez-Cadenas, Agustín F.,Maldonado-Hódar, Francisco J.
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p. 701 - 711
(2016/12/09)
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- Synthesis of Co-Sn intermetallic nanocatalysts toward selective hydrogenation of citral
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In this work, three supported Co-Sn intermetallic compound (IMC) catalysts (Co2.9Sn2, CoSn and CoSn2) with a particle size of ～20 nm were prepared via a facile hydrotalcite approach, and their catalytic performances were evaluated in the selective hydrogenation of citral to unsaturated alcohols (geraniol and nerol). EXAFS, in situ CO-FTIR and DFT calculation results reveal that the introduction of Sn in Co-Sn IMCs dramatically optimizes the geometric and electronic structures of active Co, in which Sn isolates the Co active-site and electron transfer occurs from Sn to the Co atom. H2-TPD measurements indicate the presence of four different Co sites (labeled as α, β, γ and σ) on the surface of these IMCs; the sample of CoSn IMC shows the largest β/(γ + σ) ratio, which results in the highest selectivity toward unsaturated alcohols (SUA: 67.6%). DFT studies prove that the geometric and electronic effects of the CoSn IMC weaken the hydrogenation of the CC group, accounting for the largely enhanced hydrogenation selectivity of citral to unsaturated alcohols.
- Zhou, Junyao,Yang, Yusen,Li, Changming,Zhang, Shitong,Chen, Yudi,Shi, Shuxian,Wei, Min
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p. 12825 - 12832
(2018/06/26)
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- Chemoselective transfer hydrogenation of α,β-unsaturated carbonyl compounds using potassium formate over amine-grafted Ru/AlO(OH) catalysts
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Grafting of 3-(2-aminoethylamino)propyltrimethoxysilane onto Ru/AlO(OH) resulted in an active and highly chemoselective heterogeneous catalyst for the transfer hydrogenation of α,β-unsaturated carbonyl compounds to the corresponding allylic alcohols. Potassium formate was used as a sustainable hydrogen donor. A range of substrates including cinnamaldehyde, α-amylcinnamaldehyde, citral, 3-methyl-2-butenal, trans-2-pentenal, and trans-hexenal were selectively hydrogenated at the CO moiety with >96% selectivity. In comparison, the unmodified 1 wt% Ru/AlO(OH) catalyzed hydrogenation of cinnamaldehyde at the CC bond, yielding 3-phenylpropanal as the product. Higher loaded samples with 2-10 wt% Ru exhibited 20-25% selectivity to cinnamyl alcohol. The results show that low coordination sites were more selective to hydrogenation of the internal CC than the terminal CO bond. Immobilization of the amine via chemical bonding with hydroxyl groups of the AlO(OH) support blocks adjacent exposed metal sites, increasing the chemoselective reduction of CO. Optimum results were achieved at an amine/Ru ratio of 6. The catalyst maintained high activity and chemoselectivity even after five cycles.
- Gao, Yanxiu,Wang, Jie,Han, Aijuan,Jaenicke, Stephan,Chuah, Gaik Khuan
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p. 3806 - 3813
(2016/06/13)
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- Chemoselective hydrogenation of α,β-unsaturated aldehydes on hydrogenated MoOx nanorods supported iridium nanoparticles
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As reducible supports, metal oxides present the varied charge effect after hydrogen doping and partial reduction, accomplishing the tunable metal-support interactions and the promoted catalytic turnover in heterogeneous catalysis. Herein, the one-pot fabrication of hydrogenated MoOx (H-MoOx) nanorods supported Ir (Ir/H-MoOx) was developed, which simultaneously combined the generation of active centers (Ir) and the hydrogen doping on supports (H-MoOx). Because of the accumulated electrons around MoO6 octahedras after hydrogen doping, the electronic perturbations arising from H-MoOx supports led to the negatively charge Irδ? species being beneficial for the selective hydrogenation of C[dbnd]O moiety in α,β-unsaturated aldehydes. In the hydrogenation of cinnamaldehyde to cinnamyl alcohol, Ir/H-MoOx delivered selectivity as high as ～93%, performing among the best of current metal-based catalysts. Additionally, the efficacy for various substrates with multiple groups further verified our Ir/H-MoOx system to be competitive for chemoselective hydrogenation.
- He, Sina,Xie, Lifang,Che, Minwei,Chan, Hang Cheong,Yang, Lichun,Shi, Zhangping,Tang, Yi,Gao, Qingsheng
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p. 248 - 254
(2016/10/30)
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- Green, Multi-Gram One-Step Synthesis of Core–Shell Nanocomposites in Water and Their Catalytic Application to Chemoselective Hydrogenations
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We devise a new and green route for the multi-gram synthesis of core–shell nanoparticles (NPs) in one step under organic-free and pH-neutral conditions. Simply mixing core and shell metal precursors in the presence of solid metal oxides in water allowed for the facile fabrication of small CeO2-covered Au and Ag nanoparticles dispersed on metal oxides in one step. The CeO2-covered Au nanoparticles acted as a highly efficient and reusable catalyst for a series of chemoselective hydrogenations, while retaining C=C bonds in diverse substrates. Consequently, higher environmental compatibility and more efficient energy savings were achieved across the entire process, including catalyst preparation, reaction, separation, and reuse.
- Urayama, Teppei,Mitsudome, Takato,Maeno, Zen,Mizugaki, Tomoo,Jitsukawa, Koichiro,Kaneda, Kiyotomi
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supporting information
p. 17962 - 17966
(2016/12/16)
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- Vanadium-Catalyzed Oxidative Debenzylation of O-Benzyl Ethers at ppm Level
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An advantageous methodology for the oxidative debenzylation of ethers has been developed. Very low amounts of a catalyst system based on vanadyl acetylacetonate and a triazole type pincer ligand allow the selective oxidative cleavage of a number of O-benzyl ethers in the presence of oxygen as the sole oxidant. The methodology tolerates a number of functional groups such as halo-, alkoxy-, or trifluoromethylarenes, alkyne, alkene, ether, and acetal units. Large-scale deprotections can be also carried out by the optimized procedure, which is amenable to enantioenriched reactants as well. (Figure presented.).
- Urgoitia, Garazi,SanMartin, Raul,Herrero, María Teresa,Domínguez, Esther
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p. 3307 - 3312
(2016/10/21)
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- Comparison of enzymatic and acid hydrolysis of bound flavor compounds in model system and grapes
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Four synthesized terpenyl-β-D-glycopyranosides (geranyl, neryl, citronellyl, myrtenyl) were subjected to enzymatic (AR 2000, pH 5.5) and acid (citric buffer, pH 2.5) hydrolysis. Decrease of glycosides was measured by HPLC and the volatiles released - by comprehensive gas chromatography-mass spectrometry (GC x GC-ToF-MS). Enzymatic hydrolysis performed for 21 h yielded 100% degree of hydrolysis for all glycosides but citronellyl (97%). Degree of acid hydrolysis was highly dependent on type of aglycone and the conditions. The highest degree was achieved for geraniol, followed by citronellol and nerol. Myrtenylo-β-D-glycopyranoside was the most resistant glycoside to hydrolysis. Acid hydrolysis degree was also related to temperature/time combination, the highest being for 100 °C and 2 h. In a result of enzymatic hydrolysis 85-91% of total peak areas was terpene aglycone, whereas for acid hydrolysis the area of released terpene aglycone did not exceed 1.3% of total peak area indicating almost complete decomposition/transformation of terpenyl aglycone.
- Dziadas, Mariusz,Jeleń, Henryk H.
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p. 412 - 418
(2015/06/17)
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- Effect of 2-propanol on the transfer hydrogenation of aldehydes by aqueous sodium formate using a rhodium(i)-sulfonated triphenylphosphine catalyst
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In water/2-propanol mixtures [RhCl(mtppms)3] (mtppms = monosulfonated triphenylphosphine) was an efficient catalyst for the selective C=C reduction of trans-3-phenyl-2-propenal (trans-cinnamaldehyde) by hydrogen transfer from formate at temperatures as low as 30 °C. An outstandingly high catalyst turnover frequency of 1214 h-1 was determined at 70 °C. A possible mechanism of the reaction is suggested on the basis of kinetic studies and 1H- and 31P-NMR spectroscopic identification of the major Rh(i) species in the reaction mixtures as cis-mer-[H2RhX(mtppms)3] (X = HCOO- or H2O). It was established that a large part but not all of the rate increase observed in water/2-propanol mixtures in comparison with systems with neat water as solvent was the consequence of complete dissolution of trans-cinnamaldehyde on the effect of the co-solvent. Nevertheless, the rate showed a significant further increase with increasing 2-propanol concentration even in homogeneous solution and this was ascribed to changes in the solvent structure. The high catalyst activity in this solvent mixture allowed the transfer hydrogenation of citral. Although good to excellent conversions were observed at 30-70 °C, a useful degree of selectivity in hydrogenation of C=C vs. C=O bonds could not be achieved.
- Kathó, ágnes,Szatmári, Imre,Papp, Gábor,Joó, Ferenc
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p. 339 - 344
(2015/11/24)
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- Unexpectedly fast catalytic transfer hydrogenation of aldehydes by formate in 2-propanol-water mixtures under mild conditions
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Unsaturated aldehydes were efficiently reduced by transfer hydrogenation from sodium formate in water-2-propanol mixtures using a water-soluble Ru(II)-tertiary phosphine catalyst. The reaction yielded unsaturated alcohols with complete selectivity and without hydrogenation or isomerization of CC bonds of the substrates. Very high reaction rate was observed in the transfer hydrogenation of cinnamaldehyde already at 30 °C with turnover frequency of 160 h-1 and this increased to 3800 h-1 at 70 °C. Consequently, the method is applicable to the synthesis of unsaturated alcohols in case of heat sensitive or highly volatile aldehydes, too. Based on multinuclear NMR investigations, trans-[RuH2(H2O)(mtppms)3] is suggested as the key catalytic species.
- Szatmári, Imre,Papp, Gábor,Joó, Ferenc,Kathó, ágnes
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