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European Journal of Organic Chemistry

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https://www.readbyqxmd.com/read/27917069/stereochemical-control-of-enzymatic-carbon-carbon-bond-forming-michael-type-additions-by-substrate-engineering
#1
Yufeng Miao, Pieter G Tepper, Edzard M Geertsema, Gerrit J Poelarends
The enzyme 4-oxalocrotonate tautomerase (4-OT) promiscuously catalyzes the Michael-type addition of acetaldehyde to β-nitrostyrene derivatives to yield chiral γ-nitroaldehydes, which are important precursors for pharmaceutically active γ-aminobutyric acids. In this study, we investigated the effect of different substituents at the aromatic ring of the Michael acceptor on the catalytic efficiency and stereoselectivity of the 4-OT-catalyzed acetaldehyde addition reactions. Highly enantioenriched (R)- and (S)-γ-nitroaldehydes and 4-substituted chroman-2-ol could be obtained in good to excellent yields by applying different substituents at appropriate positions of the aromatic substrate...
November 2016: European Journal of Organic Chemistry
https://www.readbyqxmd.com/read/27840588/the-amadori-rearrangement-for-carbohydrate-conjugation-scope-and-limitations
#2
Cornelia Hojnik, Anne Müller, Tobias-Elias Gloe, Thisbe K Lindhorst, Tanja M Wrodnigg
The Amadori rearrangement was investigated for the synthesis of C-glycosyl-type neoglycoconjugates. Various amines including diamines, amino-functionalized glycosides, lysine derivatives, and peptides were conjugated with two different heptoses to generate non-natural C-glycosyl-type glycoconjugates of the d-gluco and d-manno series. With these studies, the scope and limitations of the Amadori rearrangement as a conjugation method have been exemplified with respect to the carbohydrate substrate, as well as the amino components...
September 2016: European Journal of Organic Chemistry
https://www.readbyqxmd.com/read/27840587/efficient-o-acylation-of-alcohols-and-phenol-using-cp2ticl-as-a-reaction-promoter
#3
María Jesús Durán-Peña, José Manuel Botubol-Ares, James R Hanson, Rosario Hernández-Galán, Isidro G Collado
A method has been developed for the conversion of primary, secondary, and tertiary alcohols, and phenol, into the corresponding esters at room temperature. The method uses a titanium(III) species generated from a substoichiometric amount of titanocene dichloride together with manganese(0) as a reductant, as well as methylene diiodide. It involves a transesterification from an ethyl ester, or a reaction with an acyl chloride. A radical mechanism is proposed for these transformations.
July 2016: European Journal of Organic Chemistry
https://www.readbyqxmd.com/read/27840586/strigolactone-analogues-with-a-d-ring-modified-at-c-2
#4
Alinanuswe S Mwakaboko, Binne Zwanenburg
Strigolactones (SLs) are important new plant hormones that receive much attention in current plant science. SLs are produced by many plants and are exuded by the root system. SLs are, amongst others, germination stimulants for seed of parasitic weeds. Naturally occurring SLs invariably contain three annelated rings, the ABC-scaffold, connected to a butenolide (the D-ring) via an enol ether unit. The synthesis of natural SLs requires many steps, therefore there is a continuous search for SL analogues with a simpler structure but with retention of bioactivity...
July 2016: European Journal of Organic Chemistry
https://www.readbyqxmd.com/read/27774038/synthesis-of-a-crushed-fullerene-c60h24-through-sixfold-palladium-catalyzed-arylation
#5
Ruth Dorel, Paula de Mendoza, Pilar Calleja, Sergio Pascual, Esther González-Cantalapiedra, Noemí Cabello, Antonio M Echavarren
The synthesis of a new C3v -symmetric crushed fullerene C60H24 (5) has been accomplished in three steps from truxene through sixfold palladium-catalyzed intramolecular arylation of a syn-trialkylated truxene precursor. Laser irradiation of 5 induces cyclodehydrogenation processes that result in the formation of C60, as detected by LDI-MS.
July 2016: European Journal of Organic Chemistry
https://www.readbyqxmd.com/read/27790071/macrosteres-the-deltic-guanidinium-ion
#6
Kenji Mishiro, Fanghao Hu, Daniel W Paley, Wei Min, Tristan H Lambert
The "deltic guanidinium" ion is described here as a "macrostere" of the guanidinium ion. The use of the 2,4-dimethoxybenzyl protecting group allows for the synthesis of the fully unsubstituted parent compound and a variety of derivatives bearing multiple N-H functions for the first time. Deltic urea, deltic thiourea, and deltic benzamidine are also synthesized. A comparison of the physical properties of guanidinium and deltic guanidinium ions is provided. The use of a deltic guanidinium dendrimer for cell transport is demonstrated...
March 2016: European Journal of Organic Chemistry
https://www.readbyqxmd.com/read/26877706/palladium-catalyzed-directed-c-sp-3-h-arylation-of-saturated-heterocycles-at-c-3-using-a-concise-optimization-approach
#7
Dominic P Affron, James A Bull
Saturated heterocycles, such as THFs, pyrrolidines, piperidines and THPs, are essential components of many biologically active compounds. Examples of C-H functionalization on these important ring systems remain scarce, especially at unactivated positions. Here we report the development of conditions for the palladium-catalyzed stereoselective C(sp(3))-H arylation at unactivated 3-positions of 5- and 6-membered N- and O-heterocycles with aminoquinoline directing groups. Subtle differences in substrate structures altered their reactivity significantly; and different conditions were required to achieve high yields in each case...
January 2016: European Journal of Organic Chemistry
https://www.readbyqxmd.com/read/26693210/hbf4-catalysed-nucleophilic-substitutions-of-propargylic-alcohols
#8
Elena Barreiro, Alvaro Sanz-Vidal, Eric Tan, Shing-Hing Lau, Tom D Sheppard, Silvia Díez-González
The activity of HBF4 (aqueous solution) as a catalyst in propargylation reactions is presented. Diverse types of nucleophiles were employed in order to form new C-O, C-N and C-C bonds in technical acetone and in air. Good to excellent yields and good chemoselectivities were obtained using low acid loading (typically 1 mol-%) under simple reaction conditions.
December 2015: European Journal of Organic Chemistry
https://www.readbyqxmd.com/read/26693209/ether-cleavage-re-investigated-elucidating-the-mechanism-of-bbr3-facilitated-demethylation-of-aryl-methyl-ethers
#9
Talon M Kosak, Heidi A Conrad, Andrew L Korich, Richard L Lord
One of the most well-known, highly utilized reagents for ether cleavage is boron tribromide (BBr3), and this reagent is frequently employed in a 1:1 stoichiometric ratio with ethers. Density functional theory calculations predict a new mechanistic pathway involving charged intermediates for ether cleavage in aryl methyl ethers. Moreover, these calculations predict that one equivalent of BBr3 can cleave up to three equivalents of anisole, producing triphenoxyborane [B(OPh)3] prior to hydrolysis. These predictions were validated by gas chromatography analysis of reactions where the BBr3:anisole ratio was varied...
December 2015: European Journal of Organic Chemistry
https://www.readbyqxmd.com/read/26726292/the-industrial-age-of-biocatalytic-transamination
#10
Michael Fuchs, Judith E Farnberger, Wolfgang Kroutil
During the last decade the use of ω-transaminases has been identified as a very powerful method for the preparation of optically pure amines from the corresponding ketones. Their immense potential for the preparation of chiral amines, together with their ease of use in combination with existing biocatalytic methods, have made these biocatalysts a competitor to any chemical methodology for (asymmetric) amination. An increasing number of examples, especially from industry, shows that this biocatalytic technology outmaneuvers existing chemical processes by its simple and flexible nature...
November 2015: European Journal of Organic Chemistry
https://www.readbyqxmd.com/read/27047257/azadioxatriangulenium-synthesis-and-photophysical-properties-of-reactive-dyes-for-bioconjugation
#11
Ilkay Bora, Sidsel A Bogh, Marco Santella, Martin Rosenberg, Thomas Just Sørensen, Bo W Laursen
Azadioxatriangulenium (ADOTA) is a fluorescent triangulenium dye with a long fluorescence lifetime, highly polarized transitions and emission in the red part of the visible spectrum. These properties make the chromophore suited for application in fluorescence polarization/anisotropy assay. To be useful for these applications, reactive forms of the dyes must be available in significant quantities. Here, the synthesis and photophysical properties of amine-reactive NHS esters and a thiol-reactive maleimide derivate of ADOTA are reported...
October 2015: European Journal of Organic Chemistry
https://www.readbyqxmd.com/read/27065751/a-mild-and-general-one-pot-synthesis-of-densely-functionalized-diaryliodonium-salts
#12
Linlin Qin, Bao Hu, Kiel D Neumann, Ethan J Linstad, Katelyenn McCauley, Jordan Veness, Jayson J Kempinger, Stephen G DiMagno
Diaryliodonium salts are powerful and widely used arylating agents in organic chemistry. Here we report a scalable, synthesis of densely functionalized diaryliodonium salts from aryl iodides under mild conditions. This two-step, one-pot process has remarkable functional group tolerance, is compatible with commonly employed acid-labile protective group strategies, avoids heavy metal and transition metal reagents, and provides a direct route to stable precursors to PET imaging agents.
September 1, 2015: European Journal of Organic Chemistry
https://www.readbyqxmd.com/read/26962300/functionalized-metallated-cavitands-via-imidation-and-late-stage-elaboration
#13
Yanchuan Zhao, Timothy M Swager
Efficient methods for the preparation of functionalized metallated cavitands are described. Functional groups can be either introduced by an imidation of metal-oxo complexes or by a late-stage elaboration of the imido ligands. By using diversified iminophosphorane (PPh3=NR) reagents, π-conjugated pyrene, redox active ferrocene and polymerizable norbornene moieties were successfully introduced. Furthermore, the iodo and alkynyl groups on the imido ligands are capable of undergoing efficient Sonogashira cross-coupling and copper-catalyzed azide alkyne cycloaddition reactions, thereby providing facile access to complex architectures containing metallated cavitands...
July 1, 2015: European Journal of Organic Chemistry
https://www.readbyqxmd.com/read/26257578/chlorin-e6-13-1-15-2-anhydride-a-key-intermediate-in-conjugation-reactions-of-chlorin-e6
#14
Hui Chen, R G Waruna Jinadasa, Lijuan Jiao, Frank R Fronczek, Alex L Nguyen, Kevin M Smith
Since the patent for the photodynamic therapy agent Talaporfin (mono-L-aspartylchlorin e6) was issued in 1987, confusion has existed regarding which of the three carboxylic acid groups in the chlorophyll degradation product, chlorin e6 (1), is modified in standard amino acid type conjugations (using DCC or EDC and an organic base) with amino acids and other biomolecules. Here it is shown that the site of conjugation is the central 15(2)-carboxylic acid, such reactions proceeding in numerous examples via a 13(1),15(2)-anhydride for which a high resolution X-ray structure is reported...
June 2015: European Journal of Organic Chemistry
https://www.readbyqxmd.com/read/26213484/crossed-mcmurry-coupling-reactions-for-porphycenic-macrocycles-non-statistical-selectivity-and-rationalisation
#15
Thomas Y Cowie, Lorna Kennedy, Justyna M Żurek, Martin J Paterson, Magnus W P Bebbington
Crossed McMurry reactions of bifuran- or bithiophenedicarbaldehydes with bipyrroledicarbaldehydes have been studied for the first time. Only those porphycenic macrocycles derived from homocoupled McMurry products were formed. The results are explained by using both density functional theory and electron propagator computations to model the electron affinity of the dialdehyde starting materials. It was predicted that bifuran\bithiophene cross-coupling would indeed occur, and this was demonstrated by the first synthesis of a novel dioxa,dithio hetero-porphycenoid annulene...
June 2015: European Journal of Organic Chemistry
https://www.readbyqxmd.com/read/26257577/a-convergent-synthesis-of-6-o-branched-%C3%AE-glucan-oligosaccharides
#16
Guochao Liao, Srinivas Burgula, Zhifang Zhou, Zhongwu Guo
β-Glucans are important carbohydrate antigens on the surface of fungal cells useful for antifungal vaccine development. This paper has described a highly convergent and efficient strategy for the synthesis of structurally defined branched β-glucan oligosaccharides that can be used for detailed studies of β-glucans and for the design of β-glucan-based vaccines. The strategy was highlighted by assembling the title compounds via preactivation-based glycosylation with thioglycosides as glycosyl donors. It was used to successfully prepare β-glucan oligosaccharides that had a β-1,3-linked nonaglucan backbone with β-1,6-glucotetraose, β-1,3-glucodiose and β-1,3-glucotetraose branches at the 6-O-position of the nonaglucan central sugar unit...
May 1, 2015: European Journal of Organic Chemistry
https://www.readbyqxmd.com/read/26279638/coordinating-chiral-ionic-liquids-design-synthesis-and-application-in-asymmetric-transfer-hydrogenation-under-aqueous-conditions
#17
Maria Vasiloiu, Peter Gaertner, Ronald Zirbs, Katharina Bica
Hydrophilic coordinating chiral ionic liquids with an amino alcohol substructure were developed and efficiently applied to the asymmetric reduction of ketones. Their careful design and adaptability to the desired reaction conditions allow for these chiral ionic liquids to be used as the sole source of chirality in a ruthenium-catalyzed transfer hydrogenation reaction of aromatic ketones. When used in this reaction system, these chiral ionic liquids afforded excellent yields and high enantioselectivities.
April 2015: European Journal of Organic Chemistry
https://www.readbyqxmd.com/read/26257576/studies-towards-the-leucetta-derived-alkaloids-spirocalcaridine-a-and-b-possible-biosynthetic-implications
#18
Panduka B Koswatta, Jayanta Das, Muhammed Yousufuddin, Carl J Lovely
An exploration of an abiotic approach to spirocalcaridines A and B is described centered on electrophile-induced dearomatizing spirocyclization of aryl enyne derivatives. Elaboration of the α-iodoenone via an Ullmann-like, copper-catalyzed amidation provided a formamide which upon treatment with methylamine undergoes a dienol-arene rearrangement, providing the corresponding kealiinine-like framework. This observation suggests a possible biosynthetic links between the spirocalcaridines and the naphthimidazole group of Leucetta alkaloids...
April 2015: European Journal of Organic Chemistry
https://www.readbyqxmd.com/read/26257575/conformationally-constrained-penta-hetero-cyclic-molecular-architectures-via-photoassisted-diversity-oriented-synthesis
#19
Weston J Umstead, Olga A Mukhina, Dr Andrei G Kutateladze
Intramolecular cycloadditions of photogenerated azaxylylenes provide access to unprecedented polyheterocyclic scaffolds, suitable for subsequent postphotochemical modifications to further grow molecular complexity. Here we explore approaches to rapid "assembly" of novel photoprecursors with nitrogen/oxygen-rich tethers capable of producing potential pharmacophores and also compatible with subsequent 1,3-dipolar cycloadditions to furnish pentacyclic heterocycles with new structural cores, minimal number of rotatable bonds, and a high content of sp(3) hybridized carbons...
April 1, 2015: European Journal of Organic Chemistry
https://www.readbyqxmd.com/read/26161035/calixarene-mediated-liquid-membrane-transport-of-choline-conjugates-2-transport-of-drug-choline-conjugates-and-neurotransmitters
#20
Birendra Babu Adhikari, Sahar Roshandel, Ayu Fujii, Michael P Schramm
Lower rim carboxylic acid calix[n]arenes and upper rim phosphonic acid functionalized calix[4]arenes effect selective transport of distinct molecular payloads through a liquid membrane. The secret to this success lies in the attachment of a receptor-complementary handle. We find that the trimethylammonium ethylene group present in choline is a general handle for the transport of drug and drug-like species. Furthermore, neurotransmitters possessing ionizable amine termini are also transported. Some limitations to this strategy have been uncovered as payloads become increasingly lipophilic...
April 1, 2015: European Journal of Organic Chemistry
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