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The use of sodium salts of aqueous solutions of different amino acids (glycinate and prolinate) for carbon dioxide (CO2) separation by chemical absorption is analyzed in a bubble-column reactor under different experimental conditions of solvent concentration and gas flow rate. The differences in absorption rate and reaction mechanism caused by the presence of carboxylic groups in comparison to the case without (monoethanolamine and pirrolidine) are evaluated. Glycinate solvent reaches a similar behavior than monoethanolamine aqueous solutions but with a higher destabilization of carbamate that allows to increase CO2 loading. Prolinate exhibits a similar behavior than pirrolidine at low CO2 loadings. Both solvents show a significant reduction in absorption capacity when stripping regeneration is carried out.

Present work analyses the behavior of aqueous solutions of N,N-dimethylethylenediamine as chemical solvent for carbon dioxide separation by gas–liquid absorption. The interest of this molecule is centered on the presence of different types of amino centers that confer it the capability to act as a solvent based on amines blend. For this reason, a comparison between diamine and amines blend solvent has been carried out in order to understand the differences between these solvents using absorption and nuclear magnetic resonance studies. This experimental work analyses the influence of amine type, concentration, and ratio between different amines. Also, the effect of gas flow rate used in the bubble column reactor upon the absorption kinetics has been analyzed.

The present research work analyzes the behavior of aqueous solutions of hexamethylenetetramine, determining several physical properties such as density, speed of sound, viscosity, and surface tension. Besides the importance of these properties, they allow the type of interactions between solute and solvent molecules to be analyzed. The study consisted of the evaluation of the influence of amine concentration and temperature upon these properties. An increase in amine concentration causes an increase in density, viscosity, and speed of sound and a decrease in isentropic compressibility and surface tension. On the basis of experimental data of isentropic compressibility and surface tension the presence of temperature resistant structure has been determined.

The development of new solvents for carbon dioxide separation by chemical absorption has increased its importance during last years. Present work develops a series of studies using biphasic solvents (two liquid phases) in which amine is transferred from organic to aqueous phase during carbon dioxide chemical absorption. This type of solvents gets to reduce the amount of solvent that must be regenerated by stripping and this fact allows to reduce significantly the cost associated to this operation. The experimental results corresponding to the proposed solvent (based on the use of N-ethylpiperidine) have shown a suitable behavior when high ratios of organic phase/aqueous phase are used that allows to reduce the energy penalty. This behavior has been confirmed using bubbling and packed columns. Solvent regeneration studies showed suitable results avoiding losses in absorption rate and absorption capacity.

Present work analyzes the overall carbon dioxide chemical absorption process using tertiary amines in aqueous solution, taking into account absorption rate experimental data and 13C and 1H nuclear magnetic resonance. These studies try to detect the causes because different behaviors are obtained for absorption curves at different carbon dioxide loadings. The combined use of these techniques allows to evaluate the weight of different variables (chemical kinetics, mechanism, hydrodynamics, etc) upon the absorption overall process.

The present paper analyzes the overall carbon dioxide absorption process in aqueous solutions of 3-amino-1-propanol using a bubble column reactor (BCR). These studies focus on the absorption rate, the reactor hydrodynamics, the speciation during the experiments, the changes in liquid phase temperature and the solvent regeneration to be used in new absorption cycles. Some of these studies have allowed knowing the importance of each involved reaction in the mechanism, while others allow evaluating the potential use of this amine for carbon dioxide capture in an industrial process.

The present study aims to analyze the carbon dioxide absorption process in a chemical solvent based on 2-(ethylamino)ethanol, which is not commonly used in industry for this purpose, but it allows extracting interesting conclusions about the influence of absorption regime, physical properties or reagent chemical structure upon both hydrodynamic and mass transfer behavior in a bubble reactor. The influence of gas flow-rate upon bubble size distribution or gas hold-up allows understanding how the behavior of this type of reactors is and how they can influence the overall process. In this way, in analyzing the predominant reaction mechanism, the behavior of mass transfer coefficient can be known and understood as to why, for this kind of chemical solvent, a dramatic decrease of this coefficient is produced only with the presence of a small amount of amine.

This paper deals with the study of carbon dioxide capture using 2-(methylamino)ethanol (MAE) aqueous solutions. The reaction was studied in a bubble column reactor (BCR), and the most important asp...

A new carbon dioxide capture process by means of gas–liquid absorption using pyrrolidine aqueous solutions in a bubble column reactor obtaining suitable results in comparison with other commonly used amines is analyzed. The influence of several operation variables such as amine concentration and gas flow rate has been studied. Carbon dioxide mass-transfer rate data have shown a different behavior than other amine-based systems because a constant value in absorption rate was observed in the middle of batch experiments. 13C and 1H NMR spectroscopy studies were performed to analyze the species present during the experiments. These data and the carbon dioxide loading allowed to explain the reaction mechanism existed between these reagents. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1098–1106, 2014

The present work analyzes and compares the carbon dioxide absorption process in aqueous solutions of different amines (MEA, monoethanolamine; DEA, diethanolamine; TEA, triethanolamine). This study evaluates the influence of the reagents nature upon absorption using a semicontinuous regime in a bubble contactor. 13C and 1H nuclear magnetic resonance (NMR) spectroscopy has been used to analyze species (reagents and/or products) in the reaction medium. In this way, the influence of the amino group substitution degree and carbon dioxide loading upon the chemical absorption mechanism were analyzed.

Structure-guided optimization was used to design new analogues of 1α,25-dihydroxyvitamin D3 bearing the main side chain at C12 and a shorter second hydroxylated chain at C17. The new compounds 5a–c were efficiently synthesized from ketone 9 (which is readily accessible from the Inhoffen–Lythgoe diol) with overall yields of 15%, 6%, and 3% for 5a, 5b, and 5c, respectively. The triene system was introduced by the Pd-catalyzed tandem cyclization–Suzuki coupling method. The new analogues were assayed against human colon and breast cancer cell lines and in mice. All new vitamin D3 analogues bound less strongly to the VDR than 1α,25-dihydroxyvitamin D3 but had similar antiproliferative, pro-differentiating, and transcriptional activity as the native hormone. In vivo, the three analogues had markedly low calcemic effects. © 2012 American Chemical Society., We thank the Spanish Ministry of Education and Innovation (SAF2007-67205 and SAF2010-15291 to A. Mouriño, SAF2010-18302 to A. Muñoz, and SAF2009-07631 to RPF) for financial support.

A convergent synthesis of an analogue of (1α)-1,25-dihydroxyvitamin D 3 (1b) with a C 7 side chain at C(12), i.e., of 5 (Fig.), is described. A key step of the synthesis is the assembly of the triene system by a Pd II-catalyzed ring closure of an enol triflate ('bottom' fragment) followed by coupling of the resulting Pd II intermediate with an alkenylboronate ('upper' fragment) (Scheme 2). The synthetic strategy allows isotopic labelling at the end of the synthesis. Copyright © 2012 Verlag Helvetica Chimica Acta AG, Zurich, Switzerland.

© 2015 American Chemical Society.Density, speed of sound, and viscosity of the binary mixtures N-ethyl-2-pyrrolidone (EP) + 2-(methylamino)ethanol [or 2-(ethylamino)ethanol] were measured at different temperatures from (293.15 to 323.15) K and over the entire range of concentrations. The excess isentropic compressibility, excess molar volumes, and viscosity deviations were calculated. Beside, the excess molar volumes were fitted using a Redlich-Kister equation, and the viscosity data were fitted by the Grunberg-Nissan model.

The synthesis of the clinically important drug calcipotriol (2, MC903) is described as an example of a new and efficient approach to C24-hydroxylated analogs and metabolites of vitamin D3 (1). The key step of the process is the generation of the C24 stereocenter by DAIB [(-)-3-exo-(dimethylamino)isoborneol]-catalyzed addition of the alkenylzinc derivative of alkyne 3 to cyclopropylcarboxaldehyde.

Previously unknown ring closing metathesis reactions of diynes are described which open an efficient and stereoselective entry into macrocyclic (Z)-alkenes if the resulting cycloalkyne products are subjected to Lindlar reduction. This new two-step strategy offers significant advantages in stereochemical terms over conventional RCM of dienes which usually leads to (E,Z)-mixtures when applied to the formation of large rings. The tungsten alkylidyne complex (tBuO)3W⋮CCMe3(1a) and analogues thereof as well as a structurally unknown species formed in situ from Mo(CO)6 and p-chlorophenol effect the crucial alkyne metathesis reactions in a highly efficient manner, with the former catalyst being more tolerant toward structural variations of the substrates and polar functional groups. Applications to the stereoselective synthesis of the olfactory compounds ambrettolide 23 and yuzu lactone 24, the insect repellent azamacrolides epilachnene 31 and homoepilachnene 33, as well as to the fully functional building block...

3-Hydroxy-4-pyridones, which are easily prepared from commercially available 3-hydroxy-4-pyrones, can be readily transformed into 4-methoxy-3-oxidopyridinium ylides by treatment with methyl trifluoromethanesulfonate and subsequent deprotonation with a non-nucleophilic base. These ylides are capable of undergoing cycloaddition to several electron-deficient alkenes, thus allowing the synthesis of highly functionalized azabicyclo[3.2.1]octane moieties. The rich substitution patterns of these frameworks might allow their divergent conversion to a variety of natural and non-natural tropane alkaloids.

Structure-guided optimization was used to design new analogues of 1α,25-dihydroxyvitamin D₃ bearing the main side chain at C12 and a shorter second hydroxylated chain at C17. The new compounds 5a-c were efficiently synthesized from ketone 9 (which is readily accessible from the Inhoffen-Lythgoe diol) with overall yields of 15%, 6%, and 3% for 5a, 5b, and 5c, respectively. The triene system was introduced by the Pd-catalyzed tandem cyclization-Suzuki coupling method. The new analogues were assayed against human colon and breast cancer cell lines and in mice. All new vitamin D₃ analogues bound less strongly to the VDR than 1α,25-dihydroxyvitamin D₃ but had similar antiproliferative, pro-differentiating, and transcriptional activity as the native hormone. In vivo, the three analogues had markedly low calcemic effects.

Temporary connection of alkenes to 3-alkoxy-4-pyrones via sulfur or silicon tethers allows their thermal [5 + 2] cycloaddition and ensures complete regio- and stereochemical control. © 1993, American Chemical Society. All rights reserved.

3-Hydroxy-4-pyridones, which are easily prepared from commercially available 3-hydroxy-4-pyrones, can be readily transformed into 4-methoxy-3-oxidopyridinium ylides by treatment with methyl trifluoromethanesulfonate and subsequent deprotonation with a non-nucleophilic base. These ylides are capable of undergoing cycloaddition to several electron-deficient alkenes, thus allowing the synthesis of highly functionalized azabicyclo[3.2.1]octane moieties. The rich substitution patterns of these frameworks might allow their divergent conversion to a variety of natural and non-natural tropane alkaloids.

The incorporation of a sulfoxide on the tether connecting an alkene to a 5-silyloxy-4-pyrone diminishes the temperature needed for inducing their thermal [5C+2C] cycloaddition in relation to that required for annulating the homologous sulfide, and allows for attaining modest levels of diastereofacial selectivity.

One-pot coupling of an intramolecular thermal [5C + 2C] pyrone−alkene cycloaddition to a [4C + 2C] Diels−Alder reaction provides immediate access to 6,7,5-tricarbocyclic systems bearing a 1,4-oxa-b...

Six new calcitriol analogues, conformationally restricted at their side chain by the introduction of both a cyclopropane ring at C17−C20 and a double or triple bond at C22, were synthesized using the Wittig−Horner approach to construct the triene system. The six CD-ring and side-chain bearing fragments were prepared from ketone 14 by a divergent route to generate both series of epimers at C20, followed by stereoselective cyclopropanation. The (E)-alkenyl side chain was synthesized by means of a Wittig reaction. The alkynyl side chain was prepared by Corey−Fuchs homologation, followed by alkylation. The (Z)-alkenyl side chain was prepared from the previous alkyne by partial hydrogenation. The 20-epi analogues bind more strongly to VDR than the corresponding analogues with the C20 natural stereochemistry. These results can be reasoned by conformational analysis and hydrophobic interactions with the VDR ligand-binding domain.

The crystal structures of vitamin D nuclear receptor (VDR) have revealed that all compounds are anchored by the same residues to the ligand binding pocket (LBP). Based on this observation, a synthetic analog with a locked side chain (21-nor-calcitriol-20(22),23-diyne) has been synthesized in order to gain in entropy energy with a predefined active side chain conformation. The crystal structure of VDR LBD bound to this locked side chain analogue while confirming the docking provides a structural basis for the activity of this compound.

We present a receptor-based protocol for the prediction of the cell differentiation activities of a series of side chain analogues of 1 alpha,25-dihydroxyvitamin D(3), a compound that exhibits a very large variety of biological functions. Our protocol is able to reproduce the activity of the compounds studied here. It also sheds light on the relative importance of binding site residues in the biological activity and on the mechanism behind it.

We describe the synthesis of the first locked side-chain analogues of the natural hormone 1α,25-(OH)2-D 3 and their effects on gene transcription in human colon cancer cells. Analogue 2 was more potent than 1α.25-(OH)2-D 3 at inducing vitamin D receptor (VDR) transcriptional activity. Analogues 3a and 3b show potency similar to that of 1α,25-(OH) 2-D3, whereas 3c was less active. The novel analogues efficiently bind VDR in vivo to induce transcription from a consensus vitamin D responsive element (VDRE)., Generous financial support for this research was provided by the DIGICYT (Spain, Projects SAF2001-3187 and SAF2001-2291).

The first total synthesis of three naturally occurring cyclophane derivatives belonging to the turriane family of natural products is described. Their sterically hindered biaryl entity is formed by reaction of the Grignard reagent derived from aryl bromide 10 with the oxazoline derivative 18, and the macrocyclic tether of the targets is efficiently forged by ring closing metathesis. While conventional RCM catalyzed by the ruthenium-carbene complexes 33 or 34 invariably leads to the formation of mixtures of both stereoisomers with the undesirable (E)-alkene prevailing, ring closing alkyne metathesis (RCAM) followed by Lindlar reduction of the resulting cycloalkynes 37 and 38 opens a convenient and stereoselective entry into this class of compounds. RCAM can either be accomplished by using the tungsten alkylidyne complex [(tBuO)3 [triple bond] WCCMe3] or by means of a catalyst formed in situ from [Mo(CO)6] and para-trifluoromethylphenol. The latter method is significantly accelerated when carried out under microwave heating. Furthermore, the judicious choice of the protecting groups for the phenolic -OH functions turned out to be crucial. PMB-ethers were found to be compatible with the diverse reaction conditions en route to 3-5; their cleavage, however, had to be carried out under carefully optimized conditions to minimize competing O-C PMB migration. Turrianes 3-5 are shown to be potent DNA cleaving agents under oxidative conditions when administered in the presence of copper ions.

The incorporation of a sulfoxide on the tether connecting an alkene to a 5-silyloxy-4-pyrone diminishes the temperature needed for inducing their thermal [5C+2C] cycloaddition in relation to that required for annulating the homologous sulfide, and allows for attaining modest levels of diastereofacial selectivity.

The first total synthesis of three naturally occurring cyclophane derivatives belonging to the turriane family of natural products is described. Their sterically hindered biaryl entity is formed by reaction of the Grignard reagent derived from aryl bromide 10 with the oxazoline derivative 18, and the macrocyclic tether of the targets is efficiently forged by ring closing metathesis. While conventional RCM catalyzed by the ruthenium-carbene complexes 33 or 34 invariably leads to the formation of mixtures of both stereoisomers with the undesirable (E)-alkene prevailing, ring closing alkyne metathesis (RCAM) followed by Lindlar reduction of the resulting cycloalkynes 37 and 38 opens a convenient and stereoselective entry into this class of compounds. RCAM can either be accomplished by using the tungsten alkylidyne complex [(tBuO)3 [triple bond] WCCMe3] or by means of a catalyst formed in situ from [Mo(CO)6] and para-trifluoromethylphenol. The latter method is significantly accelerated when carried out under microwave heating. Furthermore, the judicious choice of the protecting groups for the phenolic -OH functions turned out to be crucial. PMB-ethers were found to be compatible with the diverse reaction conditions en route to 3-5; their cleavage, however, had to be carried out under carefully optimized conditions to minimize competing O-C PMB migration. Turrianes 3-5 are shown to be potent DNA cleaving agents under oxidative conditions when administered in the presence of copper ions.

Temporary connection of alkenes to 3-alkoxy-4-pyrones via sulfur or silicon tethers allows their thermal [5 + 2] cycloaddition and ensures complete regio- and stereochemical control. © 1993, American Chemical Society. All rights reserved.

The reaction products from the CO2 capture process by chemical absorption was studied using different amines (pyrrolidine, bezylamine and 1,2-diaminepropane) in aqueous solution. Pyrrolidine aqueous solutions showed the best CO2 loading as compared with the others amine-based systems. For CO2-pyrrolidine systems, the CO2 loading was > 1 mole of CO2/mole of amine while for the other systems, values obtained were between 0.55 and 0.35 for 1,2-diaminopropane and benzylamine, respectively. Only the CO2-1,2-diaminopropane system yielded a stable carbamate at the end of the experiment. The amines used showed a high reaction rate for this kind of capture, and this characteristic indicated that these solutes can be a suitable option for the optimization of CO2 capture. This is an abstract of a paper presented at the CHISA 2012 - 20th International Congress of Chemical and Process Engineering and PRES 2012 - 15th Conference PRES (Prague, Czech Republic 8/25-29/2012).

One-pot coupling of an intramolecular thermal [5C + 2C] pyrone-alkene cycloaddition to a [4C + 2C] Diels-Alder reaction provides immediate access to 6,7,5-tricarbocyclic systems bearing a 1,4-oxa-bridge in the seven-membered carbocycle. The transformation entails the net formation of four carbon-carbon bonds and creates three new cycles and a minimum of five new stereocenters. Preliminary attempts to open the oxa-bridge by reaction of the adducts with samarium diiodide and trimethylsilyl triflate led to relatively unexpected deoxygenated and aromatized products.