- Selective methoxylation of limonene over ion-exchanged and acid-activated clays
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In this study, we report the use of clay-based catalysts in the methoxylation of limonene, for the selective synthesis of α-terpinyl methyl ether. Na-SAz-1, Ca-SWy-2 and Sap-Ca source clays and a montmorillonite (SD) from Porto Santo, Madeira Archipelago, Portugal were modified by (i) ion-exchange with Al, Fe, Ni and Na and (ii) acid activation, to produce catalysts with markedly different acidic and textural properties. The lack of activity of Ni2+-SAz-1 (with Lewis acidity maximized), provided evidence that the process occurs preferentially on Bro?nsted acid sites. The catalysts based on the high layer-charge SAz-1 montmorillonite proved to be the most active. Ion-exchange with Al3+, followed by thermal activation at 150°C, afforded the highest number of Br?nsted acid sites located in the clay gallery and this coincided with the maximum catalytic activity. The influence of various reaction conditions, to maximize limonene conversion and selectivity, was studied over Al-SAz-1. When the reaction was performed for 20 h at 40°C, the conversion reached 71% with 91% selectivity to the mono-ether. Mild acid activation (1 M HCl, 30 min, reflux) of the raw SAz-1 clay leads to a material with a good catalytic behaviour (slightly inferior to Al-SAz-1), while any increase in the severity of the acid-treatment (6 M HCl, 30 min, reflux), caused a marked decrease in catalytic activity.
- Catrinescu,Fernandes,Castilho,Breen,Carrott, M.M.L. Ribeiro,Cansado
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Read Online
- Hydroalkoxylation of non-activated olefins catalysed by Lewis superacids in alcoholic solvents: an eco-friendly reaction
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Lewis superacids such as tin(IV) triflate catalyse the intermolecular addition of primary alcohols to non-activated olefins under mild conditions.
- Lemechko, Pierre,Grau, Fanny,Antoniotti, Sylvain,Du?ach, Elisabet
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Read Online
- Monoterpenes etherification reactions with alkyl alcohols over cesium partially exchanged Keggin heteropoly salts: effects of catalyst composition
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In this work, cesium partially exchanged Keggin heteropolyacid (HPA) salts were prepared, characterized, and evaluated as solid catalysts in monoterpenes etherification reactions with alkyl alcohols. A comparison of the activity of soluble HPAs and their insoluble cesium salts showed that among three different Keggin anions the phosphotungstate was the most efficient catalyst. Assessments on the effects of the level of the protons exchange by cesium cations demonstrated that Cs2.5H0.5PW12O40 solid salt was the most active and selective phosphotungstate catalyst, converting β-pinene to α-terpinyl methyl ether. The influences of the main reaction parameters such as reaction temperature, time, catalyst load, substrate nature (i.e., alcohols and monoterpenes) were investigated. We have demonstrated that the simultaneous presence of the cesium ions and protons in the catalyst plays an essential role, being the 2.5–0.5 the optimum molar ratio. The Cs2.5H0.5PW12O40 salt was efficiently recovered and reused without loss of catalytic activity. Graphic abstract: [Figure not available: see fulltext.]
- da Silva, Márcio José,Lopes, Neide Paloma Goncalves,Ferreira, Sukarno Olavo,da Silva, Rene Chagas,Natalino, Ricardo,Chaves, Diego Morais,Texeira, Milena Galdino
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p. 153 - 168
(2020/07/21)
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- Exploring the Keggin-Type Heteropolyacid-Catalyzed Reaction Pathways of the Β-Pinene with Alkyl Alcohols
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Abstract: In this work, we investigated the activity of Keggin heteropolyacid catalysts (i.e., H3PW12O40, H3PMo12O40 and H4SiW12O40) in β-pinene reactions with alkyl alcohols (i.e. methyl, ethyl, propyl, sec-propyl, butyl and sec-butyl alcohols), and exploring the different aspects that drive the selectivity of this process. We have found that carbon skeletal rearrangements and isomerization providing intermediate carbocations that controlling the reaction selectivity. β-pinene was preferentially converted to α-terpinyl ion which undergoes a nucleophilic attack of alcohol providing alkyl alcohol. Bornyl ion was converted to bornyl and fenchyl ethers. The other secondary products were β-pinene isomers obtained from bornyl and α-terpinyl carbocations. Phosphotungstic acid (i.e., H3PW12O40) was the most active catalyst and selective toward the main product (α-terpinyl alkyl ether); the highest conversion (ca. 96%) and ether selectivity (ca. 61%) was achieved in the reactions with β-pinene. Although having also been alkoxylate, α-pinene was less reactive (ca. 40%), while camphene and limonene remained unreactive under reaction conditions studied. An increase of temperature resulted in an improvement on conversion of β-pinene and selectivity toward α-terpinyl methyl ether. Similarly, the H3PW12O40 concentration played a crucial role on reaction selectivity. This work presents positive features such as a short reaction time, high atom economy, mild reaction conditions (i.e., low temperature and room pressure). Even though soluble the catalyst was easily recovered by liquid -liquid extraction and efficiently reused. Graphical Abstract: [Figure not available: see fulltext.].
- Polo, Henrique Priori,Lopes, Neide Paloma Goncalves,da Silva, Márcio José
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p. 2844 - 2853
(2019/05/28)
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- Oxidation of imidazole- and pyrazole-derived aldehydes by plant aldehyde dehydrogenases from the family 2 and 10
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Plant cytosolic aldehyde dehydrogenases from family 2 (ALDH2s, EC 1.2.1.3) are non-specific enzymes and participate for example in the metabolism of acetaldehyde or biosynthesis of phenylpropanoids. Plant aminoaldehyde dehydrogenases (AMADHs, ALDH10 family, EC 1.2.1.19) are broadly specific and play an important role in polyamine degradation or production of osmoprotectants. We have tested imidazole and pyrazole carbaldehydes and their alkyl-, allyl-, benzyl-, phenyl-, pyrimidinyl- or thienyl-derivatives as possible substrates of plant ALDH2 and ALDH10 enzymes. Imidazole represents a building block of histidine, histamine as well as certain alkaloids. It also appears in synthetic pharmaceuticals such as imidazole antifungals. Biological compounds containing pyrazole are rare (e.g. pyrazole-1-alanine and pyrazofurin antibiotics) but the ring is often found as a constituent of many synthetic drugs and pesticides. The aim was to evaluate whether aldehyde compounds based on azole heterocycles are oxidized by the enzymes, which would further support their expected role as detoxifying aldehyde scavengers. The analyzed imidazole and pyrazole carbaldehydes were only slowly converted by ALDH10s but well oxidized by cytosolic maize ALDH2 isoforms (particularly by ALDH2C1). In the latter case, the respective Km values were in the range of 10–2000 μmol l?1; the kcat values appeared mostly between 0.1 and 1.0 s?1. The carbaldehyde group at the position 4 of imidazole was oxidized faster than that at the position 2. Such a difference was not observed for pyrazole carbaldehydes. Aldehydes with an aromatic substituent on their heterocyclic ring were oxidized faster than those with an aliphatic substituent. The most efficient of the tested substrates were comparable to benzaldehyde and p-anisaldehyde known as the best aromatic aldehyde substrates of plant cytosolic ALDH2s in vitro.
- Fr?mmel, Jan,Kon?itíková, Radka,Kope?ny, David,Soural, Miroslav,?ebela, Marek
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p. 194 - 201
(2019/03/06)
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- Rapid probing of the reactivity of P450 monooxygenases from the CYP116B subfamily using a substrate-based method
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Developing a detailed understanding of the reactivity of self-sufficient Type IV P450 monooxygenases, four types of O-methylated substrates were designed as probes, including monoterpenes, cycloalkanes, aromatic compounds and steroids, and the efficiency of their oxyfunction was determined using a colorimetric assay which was based on the reaction between the enzymatic demethylation product, formaldehyde, and Purpald dye. The activity-based fingerprints of new P450RpMO, P450ArMO and P450CtMO (CYP116B members) indicated that CYP116B P450s preferentially oxidize substrates with aromatic components. Moreover, the hydroxylated products were detected based on the preference results. This rapid and efficient strategy, when coupled with GCMS, enables the exploration of the reactivity of other CYP116B members.
- Li, Ren-Jie,Xu, Jian-He,Yin, Yue-Cai,Wirth, Nicolas,Ren, Jiang-Meng,Zeng, Bu-Bing,Yu, Hui-Lei
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supporting information
p. 8928 - 8934
(2016/10/13)
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- Selective methoxylation of α-pinene to α-terpinyl methyl ether over Al3+ ion-exchanged clays
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In this study, we report the use of clay-based catalysts in the methoxylation of α-pinene, for the selective synthesis of α-terpinyl methyl ether, TME. The main reaction products and intermediates were identified by GC-MS. The reaction conditions (stirring rate and catalyst load) that afford a kinetic regime were established. SAz-1 (Cheto, Arizona, USA) source clay and a montmorillonite (SD) from Porto Santo, Madeira Archipelago, Portugal, were modified by ion-exchange with Al3+ to produce catalysts with markedly different acidities and textural properties. The catalysts based on the high layer-charge SAz-1 montmorillonite proved to be the most active. Ion-exchange with Al3+, followed by thermal activation at 150°C, afforded the highest number of Br?nsted acid sites - a significant proportion of which were located in the clay gallery - and this coincided with the maximum catalytic activity. The influence of various reaction conditions, to maximize α-pinene conversion and selectivity, was studied over AlSAz-1. When the reaction was performed for 1 h at 60°C, the conversion reached 65% with 65% selectivity towards the mono-ether, TME. Similar conversions and selectivities required up to 50 h over zeolites and other solid acid catalysts. The kinetic dependencies of this reaction on temperature and reagent concentration, over the selected clays were also investigated. It was established that, in the temperature and reagent concentration regime studied, the reaction was first order with respect to α-pinene. The apparent activation energies over the two catalysts, calculated from Arrhenius plots, were almost identical at 72 kJ mol-1.
- Catrinescu,Fernandes,Castilho,Breen
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p. 171 - 179
(2015/05/05)
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- Fe(III)-catalyzed α-terpinyl derivatives synthesis from β-pinene via reactions with hydrogen peroxide in alcoholic solutions
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In this study, a novel and environmentally benign Fe(iii)-catalyzed terpinyl derivatives synthesis using hydrogen peroxide in alcohol solutions (i.e. methyl, ethyl, propyl, isopropyl and butyl alcohols) was investigated. The use of Bronsted acid catalysts was avoided and β-pinene was used as the starting reactant. High conversions (ca. 90%) and combined selectivities for the α-terpineol and terpinyl alkyl ethers (ca. 70-73%) were obtained when Fe(NO3)3 was used as the catalyst. The role of each component catalyst system was studied with special focus on the solvent. The use of a biodegradable and renewable origin solvent (ethyl alcohol), which was added to an inexpensive and mildly toxic catalyst and a green oxidant are the main positive features of this process.
- Da Silva,Carari,Manoel Da Silva, Adalberto
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p. 10529 - 10536
(2015/01/30)
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- LXR MODULATORS
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The present invention provides compounds of Formula I: and pharmaceutically acceptable salts or solvates thereof, as modulators of liver X receptors (LXR), compositions comprising any of such novel compounds, methods of using these compounds or compositions as medicaments for prevention or treatment of diseases or disorders related to liver X receptor (LXR), as well as methods of preparing these LXR modulators and using them in the manufacture of medicaments.
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Page/Page column 185
(2014/09/29)
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- Methoxylation of α-pinene over heteropolyacids immobilized in silica
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The methoxylation of α-pinene was studied using heteropolyacids immobilized on silica as catalysts, at 60 °C, being the α-terpinyl methyl ether the main product. Tungstophosphoric acid (PW), molybdophosphoric acid (PMo), tungstosilicic acid (SiW) and molybdosilicic acid (SiMo) were immobilized on silica by sol-gel method. It was observed that the catalytic activity of the silica-supported heteropolyacids decreases in the series: PW2_S > SiW_S > PMo_S > SiMo_S. A series of PW immobilized on silica with different PW loading were prepared. It was observed that the catalytic activity increases with the amount of PW immobilized on silica. However, at high amount of PW on silica, a decrease of the catalytic activity was observed. Good values of selectivity to α-terpinyl methyl ether (about 60% near complete conversion) were obtained with all catalysts. Catalytic stability of the PW2_S was evaluated by performing consecutive batch runs with the same catalyst sample. After the third batch it was observed a stabilisation of the initial activity. A kinetic model was developed assuming that the α-pinene is consumed according to the parallel reaction network. It was observed that the kinetic model fits the experimental concentration data quite well.
- Pito,Matos,Fonseca,Ramos,Vital,Castanheiro
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body text
p. 140 - 146
(2010/10/01)
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- FeCl3-catalyzed functionalization of monoterpenes via hydroalkylation of unactivated alkenes
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Monoterpenes such as α-pinene, β-pinene, limonene and isolimonene undergo smooth hydroalkoxylation in the presence of 20 mol % of FeCl3 under mild reaction conditions to produce a wide range of the corresponding ethers in excellent yields and with high selectivity.
- Yadav,Subba Reddy,Narasimhulu,Purnima
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experimental part
p. 5783 - 5785
(2009/12/26)
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- Utilization of alternate substrates by the first three modules of the epothilone synthetase assembly line
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The epothilones, a family of macrolactone natural products produced by the myxobacterial species Sorangium cellulosum, are of current clinical interest as antitumor agents. Inspection of the structure of the epothilones suggests a hybrid polyketide/nonribosomal peptide biosynthetic origin, and the recent sequencing of the epothilone biosynthetic gene cluster has validated this proposal. Here we have examined unnatural substrates with the first two enzymes of the biosynthetic pathway, EpoA and EpoB, to investigate the enzymatic construction of alternate heterocyclic structures and the subsequent elongation of these products by the third enzyme of the pathway, EpoC. The epothilone biosynthetic machinery can utilize serine to install an oxazole in place of a thiazole in the epothilone structure and will tolerate functionalized donor groups from the EpoA-ACP domain to produce epothilone fragments modified at the C21 position. These studies with the early enzymes of the epothilone biosynthesis cluster suggest that combinatorial biosynthesis may be a viable means for producing a variety of epothilone analogues that incorporate diversity into the heterocycle starter unit. Copyright
- Schneider, Tanya L.,Walsh, Christopher T.,O'Connor, Sarah E.
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p. 11272 - 11273
(2007/10/03)
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- A convenient methodology for demercuration of organomercurials by Na/MeOH - Synthesis of ethers
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Monoenes and dienes upon treatment with mercuric acetate in dry methanol, followed by demercuration with Na in methanol at 0°C, give ethers in good yields. The coagulation of mercury makes this a simple and convenient work-up process for such reactions.
- Kaur, Navdeep,Dhillon, Ranjit S.
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p. 327 - 328
(2007/10/03)
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- Carbon monoxide as a building block in organic synthesis. Part V. Involvement of palladium-hydride species in carbonylation reactions of monoterpenes. X-ray crystal structure of 4
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A palladium precursor and SnCl2 as cocatalyst were used under 4 MPa of carbon monoxide for the catalytic alkoxycarbonylation of several monoterpenes into C11 esters.The active catalyst involves a palladium-hydride species whose formation was investigated.In the case of the model substrate 3-phenylpropene, the source of the hydrido ligand was determined to be the alkene itself.Allylic hydrogen abstraction seems to be a general way to produce the active hydridopalladium species since monoterpenes having labile allylic hydrogens were converted under exceptional mild conditions.An X-ray crystal structure analysis was carried out on . Key words: Palladium; X-ray structure; Terpenes; Carbonylation; Hydroesterification
- Naigre, Ruth,Chenal, Thomas,Cipres, Isabelle,Kalck, Philippe,Daran, Jean-Claude,Vaissermann, Jacqueline
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- SOLVOLYTIC DISPLACEMENT OF ALKYL HALIDES BY METAL SALTS. PREPARATIVE PROCEDURES FOR ALLYL-, BENZYL- AND TERTIARY ALKYL-OXY DERIVATIVES USING THE ZINC SALTS
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Reaction of allylic, benzylic and tertiary alkyl halides with zinc oxide in protic solvents leads to the formation of the corresponding alcohols, ethers and esters in good yields.The scope and limitations of this reaction have been examined.The possible involvement of ion quadruplets in the reaction is suggested.
- Gurudutt, K. N.,Ravindranath, B.,Srinivas, P.
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p. 1843 - 1846
(2007/10/02)
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- PHOTOCHEMISTRY OF AZOLES, PART VII. PHOTOSOLVOLYSIS OF ALKYLMERCAPTOAZOLES. AN APPLICATION TO SOME ACYCLIC MONOTERPENE DERIVATIVES
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Salts derived from 2-alkylmercapto-1-methylimidazoles 1b-e and 3-alkylmercapto-4-methyl-1,2,4-triazoles 2b-d have been found to undergo photochemical heterolytic fission of the S-alkyl bond in aqueous or methanolic solution to give solvolysis-type products.
- Iwasaki, Shigeo
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p. 125 - 138
(2007/10/02)
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- Rearrangement of Pinane Derivatives. Part 8. Deamination of 2αH-Pinan-3α-ylamine
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Solvolysis of 2αH-pinan-3α-yl toluene-p-sulphonate has been shown to proceed with concomitant 1,2-hydride shift to give the pinan-2-yl carbocation.Contrary to earlier reports, this species reacts normally to give, in good yield, pinan-2-yl substitution products.In contrast the pinan-3-ylamines react via a similar route, but give much smaller amounts of pinan-2-yl products.The usual reasons for differences between solvolysis and deamination (i.e. the intermediacy of diazonium ions and/or high-energy ions) can be discounted, and possible reasons for the differences in behaviour are discussed.
- Giddings, Rodney M.,Jones-Parry, Richard,Salmon, J. Roger,Whittaker, David
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p. 725 - 728
(2007/10/02)
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- Oxidation of Δ3-Carene and α-Pinene with Thallium(III) Nitrate
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The reaction of thallium((III) nitrate with Δ3-carene in methanol involves oxidative rearrangement giving exclusively 3-acetyl-6,6-dimethylbicyclohexane (3) in high yield.A similar reaction with α-pinene results in a regioselective cleavage of cyclobutane ring to furnish a mixture of cis-trans isomers of sobrerol dimethyl ethers.
- Pol, A. V.,Naik, V. G.,Sonawane, H. R.
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p. 603 - 604
(2007/10/02)
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- Cyclobutane Ring Opening of Pin-2(10)-ene with Mercury(II) Salts. A New, High-yield Synthesis of p-Mentha-1,8-dien-7-ol
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The nucleophilic attack of pin-2(10)-ene-mercury(II) complex systems by water results in the opening of the four-membered ring leading to an allylic organomercury(II) derivative (11) with the p-menthane skeleton.This intermediate can be reduced by hydride to p-menth-1(2)-en-8-ol (6a) or can undergo an in situ SE2' elimination yielding p-menth-1(7)-en-8-ol (9a), in high yields. (-)-2,10-Epoxypinane (15) reacts with mercury(II) salts at room temperature, giving the diol (16) in a quantitative yield.Compound (16) is a suitable intermediate for convenient preparation of p-mentha-1,8-dien-7-ol (17) and its derivatives.
- Bluthe, Norbert,Ecoto, Jules,Fetizon, Marcel,Lazare, Sylvain
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p. 1747 - 1751
(2007/10/02)
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