scispace - formally typeset
Search or ask a question

Showing papers by "Christian V. Stevens published in 2014"


Journal ArticleDOI
TL;DR: Phosphines are an important class of ligands in the field of metal-catalysis and their development has spurred the development of new routes toward functionalized phosphines.
Abstract: Phosphines are an important class of ligands in the field of metal-catalysis. This has spurred the development of new routes toward functionalized phosphines. Some of the most important C–P bond formation strategies were reviewed and organized according to the hybridization of carbon in the newly formed C–P bond.

141 citations


Journal ArticleDOI
24 Apr 2014-eLife
TL;DR: The results suggest that an ancient horizontal transfer of a gene originally involved in sulfur amino acid biosynthesis in bacteria was co-opted by herbivorous arthropods to detoxify plant produced cyanide.
Abstract: Cyanogenic glucosides are among the most widespread defense chemicals of plants. Upon plant tissue disruption, these glucosides are hydrolyzed to a reactive hydroxynitrile that releases toxic hydrogen cyanide (HCN). Yet many mite and lepidopteran species can thrive on plants defended by cyanogenic glucosides. The nature of the enzyme known to detoxify HCN to β-cyanoalanine in arthropods has remained enigmatic. Here we identify this enzyme by transcriptome analysis and functional expression. Phylogenetic analysis showed that the gene is a member of the cysteine synthase family horizontally transferred from bacteria to phytophagous mites and Lepidoptera. The recombinant mite enzyme had both β-cyanoalanine synthase and cysteine synthase activity but enzyme kinetics showed that cyanide detoxification activity was strongly favored. Our results therefore suggest that an ancient horizontal transfer of a gene originally involved in sulfur amino acid biosynthesis in bacteria was co-opted by herbivorous arthropods to detoxify plant produced cyanide.

134 citations


Journal ArticleDOI
12 Aug 2014
TL;DR: In this paper, an overview of stability issues, both chemical and electrochemical, and the underlying degradation mechanisms that are known are presented, with a focus on the stability of ionic liquids.
Abstract: The stability of ionic liquids is of paramount importance in selecting the appropriate ionic liquid for a well-defined application. This Review provides an overview of stability issues, both chemical and electrochemical, and the underlying degradation mechanisms that are known. The influence of various functionalities on the stability of the ionic liquid, influencing both the cationic as the anionic parts of the ionic liquid, still requires several careful studies.

130 citations


Journal ArticleDOI
TL;DR: A pipeline to extract and upgrade short-chain carboxylates to esters via membrane electrolysis and biphasic esterification enables direct production of fine chemicals following mixed culture fermentation, embedding carbon in industrial chemicals rather than returning them to the atmosphere as carbon dioxide.
Abstract: Short-chain carboxylates such as acetate are easily produced through mixed culture fermentation of many biological waste streams, although routinely digested to biogas and combusted rather than harvested. We developed a pipeline to extract and upgrade short-chain carboxylates to esters via membrane electrolysis and biphasic esterification. Carboxylate-rich broths are electrolyzed in a cathodic chamber from which anions flux across an anion exchange membrane into an anodic chamber, resulting in a clean acid concentrate with neither solids nor biomass. Next, the aqueous carboxylic acid concentrate reacts with added alcohol in a water-excluding phase to generate volatile esters. In a batch extraction, 96 ± 1.6% of the total acetate was extracted in 48 h from biorefinery thin stillage (5 g L(-1) acetate) at 379 g m(-2) d(-1) (36% Coulombic efficiency). With continuously regenerated thin stillage, the anolyte was concentrated to 14 g/L acetic acid, and converted at 2.64 g (acetate) L(-1) h(-1) in the first hour to ethyl acetate by the addition of excess ethanol and heating to 70 °C, with a final total conversion of 58 ± 3%. This processing pipeline enables direct production of fine chemicals following undefined mixed culture fermentation, embedding carbon in industrial chemicals rather than returning them to the atmosphere as carbon dioxide.

106 citations


Journal ArticleDOI
TL;DR: Three new strigolactones with different structures are presented, biologically compared with the well-known GR24 and the recently identified CISA-1, and their structure varies in the ABC part of the molecules: 23 has the same ABC part as GR24, while 31 and AR36 carry, respectively, an aromatic ring and an acyclic carbon chain.

85 citations


Journal ArticleDOI
TL;DR: It is shown that the saturated form of acidic sophorolipid, a family of industrially scaled bolaform microbial glycolipids, unexpectedly forms chiral nanofibers only at pH below 7.5 and derives from a subtle cooperative effect of molecular chirality, hydrogen bonding, van der Waals forces and steric hindrance.
Abstract: In the present paper, we show that the saturated form of acidic sophorolipids, a family of industrially scaled bolaform microbial glycolipids, unexpectedly forms chiral nanofibers only at pH below 7.5. In particular, we illustrate that this phenomenon derives from a subtle cooperative effect of molecular chirality, hydrogen bonding, van der Waals forces and steric hindrance. The pH-responsive behaviour was shown by Dynamic Light Scattering (DLS), pH-titration and Field Emission Scanning Electron Microscopy (FE-SEM) while the nanoscale chirality was evidenced by Circular Dichroism (CD) and cryo Transmission Electron Microscopy (cryo-TEM). The packing of sophorolipids within the ribbons was studied using Small Angle Neutron Scattering (SANS), Wide Angle X-ray Scattering (WAXS) and 2D 1H–1H through-space correlations via Nuclear Magnetic Resonance under very fast (67 kHz) Magic Angle Spinning (MAS-NMR).

63 citations


Journal ArticleDOI
TL;DR: In this article, the effect of type and amount of bleaching earth (BE) on the final quality of refined palm oils, especially on the oxidative state and color, was investigated.
Abstract: Although studies indicate chemical changes during bleaching such as carotene and unsaturated fatty acids oxidation, which are probably responsible for the color fixation of palm oil, this process is not very clear. The objective of this study was to investigate the effect of type and amount of bleaching earth (BE) on the final quality of refined palm oils, especially on the oxidative state and color. Two types of bleaching earth were tested, one natural (NBE) and one acid-activated (ABE) (0.5–3.0% w/w). Crude palm oils were bleached at 105 °C, during 30 min at 50 mmHg pressure. Afterwards, a deodorization step was performed at 260 °C, 3 mbar, 1.5% steam during 60 min. These refining procedures were evaluated after each step by measuring β-carotene, color, peroxide (PV) and p-anisidine (pAV) values. It was observed that both BE can decompose peroxides. However, a maximum pAV followed by a decrease was observed for ABE while the pAV remains approximately constant at a maximum for NBE, suggesting only ABE catalytically decomposes secondary oxidation products. The color after deodorization was inversely proportional to pAV when bleaching was performed with ABE, even though the oil has a lighter color after deodorization.

57 citations


Journal ArticleDOI
TL;DR: In this article, the authors show that benzotriazole surrogates showing higher stabilities than the corresponding chlorophosphates, allow phosphonylation of a variety of N-, O-, and S-nucleophiles in good yields.

55 citations


17 Sep 2014
TL;DR: In this paper, the effect of type and amount of bleaching earth (BE) on the final quality of refined palm oils, especially on the oxidative state and color, was investigated.
Abstract: Abstract Although studies indicate chemical changes during bleaching such as carotene and unsaturated fatty acids oxidation, which are probably responsible for the color fixation of palm oil, this process is not very clear. The objective of this study was to investigate the effect of type and amount of bleaching earth (BE) on the final quality of refined palm oils, especially on the oxidative state and color. Two types of bleaching earth were tested, one natural (NBE) and one acid-activated (ABE) (0.5–3.0% w/w). Crude palm oils were bleached at 105 °C, during 30 min at 50 mmHg pressure. Afterwards, a deodorization step was performed at 260 °C, 3 mbar, 1.5% steam during 60 min. These refining procedures were evaluated after each step by measuring β-carotene, color, peroxide (PV) and p-anisidine (pAV) values. It was observed that both BE can decompose peroxides. However, a maximum pAV followed by a decrease was observed for ABE while the pAV remains approximately constant at a maximum for NBE, suggesting only ABE catalytically decomposes secondary oxidation products. The color after deodorization was inversely proportional to pAV when bleaching was performed with ABE, even though the oil has a lighter color after deodorization.

34 citations


Journal ArticleDOI
TL;DR: Phosphonylated pyrroles were obtained by a ZnCl2-catalyzed 5-exo-dig hydroamination of propargylic enamines by tolerating a wide variety of substituents at the 1,2- and 5-position of the pyrrole, while further derivatization allows for the introduction of substitution at the 4-position via lithiation or halogenation.
Abstract: Phosphonylated pyrroles were obtained by a ZnCl2-catalyzed 5-exo-dig hydroamination of propargylic enamines. These starting compounds were obtained in two steps from commercially available β-ketophosphonates. The method tolerates a wide variety of substituents at the 1,2- and 5-position of the pyrrole, while further derivatization allows for the introduction of substituents at the 4-position via lithiation or halogenation.

29 citations


Journal ArticleDOI
TL;DR: In this article, the main aim was to estimate the biodegradability of newly synthesized tetra- and completely substituted imidazolium ionic liquids and the kinetic parameters for the biological treatment of wastewater containing one of these ionic liquid were determined.
Abstract: BACKGROUND Ionic liquids are regarded as potential substitutes for volatile organic solvents. Thus, gaining knowledge about their biological properties is an important task. The main aim of this work was to estimate the biodegradability of newly synthesized tetra- and completely substituted imidazolium ionic liquids. Additionally, the kinetic parameters for the biological treatment of wastewater containing one of these ionic liquids were determined. RESULTS The results of OECD tests showed that none of the ionic liquids studied can be classified as readily or inherently biodegradable. The tetra-substituted ionic liquid with the longest alkyl side chain consisting of six carbon atoms was more susceptible to biodegradation than the other ionic liquids tested. The values of Monod kinetic parameters estimated for the biological treatment of wastewater containing one of these ionic liquids were usually in the range of the values determined for municipal wastewater. CONCLUSION Newly synthesized tetra- and completely substituted imidazolium ionic liquids are not susceptible to microbial decomposition. At the same time their presence in wastewater neither reduces the growth rate of activated sludge biomass nor decreases the affinity of substrate to biomass. © 2013 Society of Chemical Industry

Journal ArticleDOI
TL;DR: In this paper, an efficient continuous-flow procedure for the synthesis of tribromomethylsulfones and tribrommethanesulfonates has been developed starting from the corresponding methylsulfone or methanesulfone and potassium hypobromite using a biphasic reaction.
Abstract: An efficient continuous-flow procedure for the synthesis of tribromomethylsulfones and tribromomethanesulfonates has been developed starting from the corresponding methylsulfones or methanesulfonates and potassium hypobromite using a biphasic reaction. Two different continuous-flow systems were used and compared for the bromination reaction. Different derivatives were synthesized in excellent isolated yields in very short reaction times using a small excess of potassium hypobromite. Hypobromite can be synthesized continuously leading to the continuous production of the brominated derivates. With the optimized flow conditions, a throughput of up to 53 g/day was obtained. The bromination reaction in flow has significant advantages compared to the corresponding batch process.

Journal ArticleDOI
TL;DR: The structural diversity of these pyrido[2,3-d]pyrimidine-2,4(1H,3H)-diones resulted in significant variation in the biopharmaceutical properties, reflected by the broad range in fasted state simulated intestinal fluid solubility values, Caco-2 permeability coefficients and in vitro-predicted human in vivo intrinsic clearance values.

Journal ArticleDOI
TL;DR: Novel N-α-haloacylated homoserine lactones, in which a halogen atom was introduced at the α-position of the carbonyl function of the N-acyl chain, have been studied as quorum sensing (QS) modulators and compared with a library of natural N-ACYlated homogeneous lactones (AHLs).
Abstract: Novel N-α-haloacylated homoserine lactones, in which a halogen atom was introduced at the α-position of the carbonyl function of the N-acyl chain, have been studied as quorum sensing (QS) modulators and compared with a library of natural N-acylated homoserine lactones (AHLs). The series of novel analogues consists of α-chloro, α-bromo and α-iodo AHL analogues. Furthermore, the biological QS activity of the synthetic AHL analogues compared to the natural AHLs was evaluated. Halogenated analogues demonstrated a reduced activity in the Escherichia coli JB523 bioassay, with the α-iodo lactones being the less active ones and the α-chloro AHLs the most potent QS agonists. Most of the α-haloacylated analogues did not exhibit a significant reduction when tested in the QS inhibition test. Therefore, these novel analogues could be utilized as chemical probes for QS structure–activity studies.

Book ChapterDOI
TL;DR: Embryonic chick heart fragments in organ culture maintain many histological features of their tissue of origin: They are composed of myocytes, fibroblasts, and endothelial cells, and their ECM contains fibronectin, laminin, and several collagen types, which allows the monitoring of their functional integrity during organ culture.
Abstract: Tumors are microecosystems in which a continuous cross talk between cancer cells and host cells decides on the invasive behavior of the tumor cell population as a whole (Mareel et al., Encyclopedia of cancer, San Diego, CA, Academic Press, 1997). Both compartments secrete activating and inhibitory factors that modulate activities such as cell-extracellular matrix (ECM) interaction, cell-cell adhesion, remodeling of the ECM, and cell motility. For this reason, confrontations of cancer cells with a living normal host tissue in organ culture have been introduced by several groups: Wolff and Schneider in France (Wolff and Schneider, C R S Soc Biol (Paris) 151:1291-1292, 1957), Easty and Easty in the United Kingdom (Easty and Easty, Nature 199:1104-1105, 1963), and Schleich in Germany (Schleich et al., J Natl Cancer Inst 56:221-237, 1976). Embryonic chick heart fragments in organ culture maintain many histological features of their tissue of origin: They are composed of myocytes, fibroblasts, and endothelial cells, and their ECM contains fibronectin, laminin, and several collagen types. Moreover, the fragments remain contractile, and this activity allows the monitoring of their functional integrity during organ culture.

Journal ArticleDOI
02 Jun 2014-Arkivoc
TL;DR: In this paper, a one-step protocol for the synthesis of 3-phosphonylated aminophosphonates from α,β-unsaturated imines through tandem 1,4-1,2 -phosphite addition is presented.
Abstract: Over the past 15 years we have developed a one-step protocol for the synthesis of 3-phosphonylated aminophosphonates from α,β-unsaturated imines through tandem 1,4-1,2-phosphite addition. This account covers the initial development, mechanistic implications of using different phosphite nucleophiles and the expansion towards oximes, hydrazones and unsaturated imines included in aromatic sextets, e.g. quinolines, phenanthrolines and napthyridines.

Journal ArticleDOI
TL;DR: The synthesis of 1-cyano-2-aza-[ 2.2.2]bicyclooctanes has been studied using the dynamic cyanide addition to cyclohexanone derivatives and was further elaborated into a new class of epibatidine derivatives from which a number of examples were fully deprotected to give the potentially active compounds.

Journal ArticleDOI
TL;DR: In this paper, the compatibility of a number of protection and activation strategies with the 1,2-addition of a variety of O-, N-, S-, and C-nucleophiles to ferulic acid is evaluated.

Journal ArticleDOI
TL;DR: An expansion of the previously reported synthesis of epibatidine analogues, and five synthetic alkaloids characterized by a symmetric, 1-substituted 7-azabicyclo[2.2.1]heptane skeleton, were evaluated for their biological activity and did not show antinociceptive effects.
Abstract: The highly potent natural alkaloid epibatidine remains a source of inspiration in the search for new analgesic drugs. In this paper, we describe an expansion of our previously reported synthesis of epibatidine analogues, and five synthetic alkaloids characterized by a symmetric, 1-substituted 7-azabicyclo[2.2.1]heptane skeleton, were evaluated for their biological activity. Two of these are binding selectively to the α4β2 subtype of the nicotinic acetylcholine receptor. Their Ki values were determined to be 40 and 290 nM. After a favourable evaluation of these compounds' cytotoxicity and metabolic stability, they were submitted to a rat tail flick test. The compounds did not show antinociceptive effects, which may be caused by a combination of insufficient potency and poor brain penetration.

Journal ArticleDOI
12 May 2014-Synlett
TL;DR: In this article, a ring expansion of 4-(trifluoromethyl)-7,8-dihydroquinolin-5(6H)-ones via a Beckmann rearrangement is presented, which opens up possibilities to access novel unexplored scaffolds for medicinal chemistry.
Abstract: The synthesis and preliminary ADME evaluation of ­novel 4-(trifluoromethyl)-5,7,8,9-tetrahydro-6H-pyrido[3,2-b]azepin-6-ones is presented. The key step is a ring expansion of 4-(trifluoromethyl)-7,8-dihydroquinolin-5(6H)-ones via a Beckmann rearrangement. The rearrangement opens up possibilities to access novel unexplored scaffolds for medicinal chemistry. The biopharmaceutical profiling revealed a strong structural dependency of the druglike properties.


Journal ArticleDOI
TL;DR: In this paper, 3-azabicyclo[3.1.0]hex-2-en-1-yl phosphonates were prepared in a five-step reaction route from β-ketophosphonates.
Abstract: 3-Azabicyclo[3.1.0]hex-2-en-1-yl phosphonates were prepared in a five-step reaction route from β-ketophosphonates. The key steps in this sequence are an atom-transfer radical cyclization and an unforeseen lithium-halogen exchange with n-BuLi. The cyclization reaction proceeds with excellent diastereoselectivity. The resulting cyclic imines were reduced, and 3-azabicyclo[3.1.0]hexan-1-yl phosphonates were obtained.

Journal ArticleDOI
12 Dec 2014-Arkivoc
TL;DR: The synthesis of novel 7-aryl-7,8-dihydropyrido-5(6H)-ones is described including a one-step Mannich-type reaction followed by intramolecular ring closure of ethyl 3-methylpyridazine-4- carboxylate and aldimines catalysed by the Lewis acid Cu(OTf)2 under microwave heating.
Abstract: The synthesis of novel 7-aryl-7,8-dihydropyrido[4,3-c]pyridazin-5(6H)-ones is described including a one-step Mannich-type reaction followed by intramolecular ring closure of ethyl 3-methylpyridazine-4- carboxylate and aldimines, catalysed by the Lewis acid Cu(OTf)2 under microwave heating. This synthesis opens up possibilities to access this unexplored scaffold for medicinal chemistry.

Book ChapterDOI
01 Jan 2014
TL;DR: An overview of the existing entries to alkenes, geminally substituted with both a halogen and a heteroatom other than a chalcogen, can be found in this article.
Abstract: An overview is presented of the hitherto reported entries to alkenes, geminally substituted with both a halogen and a heteroatom other than a halogen or a chalcogen. The covered methodologies have been categorized according to the chemical class of the precursor molecule and the nature of the transformation yielding the gem-difunctionalized alkene. This work discusses primary literature reports up to the end of 2012.

Journal ArticleDOI
TL;DR: In this article, the synthesis of the title compounds was achieved via ZnCl2-mediated cyclization of propargylic enamines of type (VI) using a Zn-Cl 2-based cyclization algorithm.
Abstract: The synthesis of the title compounds is achieved via ZnCl2-mediated cyclization of propargylic enamines of type (VI).

Journal ArticleDOI
TL;DR: In this article, a one-step protocol for the synthesis of 3-phosphonylated aminophosphonates from α,β-unsaturated imines through tandem 1,4-1,2 -phosphite addition is presented.
Abstract: Over the past 15 years we have developed a one-step protocol for the synthesis of 3-phosphonylated aminophosphonates from α,β-unsaturated imines through tandem 1,4-1,2-phosphite addition. This account covers the initial development, mechanistic implications of using different phosphite nucleophiles and the expansion towards oximes, hydrazones and unsaturated imines included in aromatic sextets, e.g. quinolines, phenanthrolines and napthyridines.