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https://www.readbyqxmd.com/read/27921333/direct-access-to-chiral-%C3%AE-fluoroamines-with-quaternary-stereogenic-center-via-cooperative-cation-binding-catalysis
#1
Venkataramasubramanian Vaithiyanathan, Mun Jong Kim, Yidong Liu, Hailong Yan, Choong Eui Song
Reported herein is a direct route for chiral β-fluoroamines possessing tetrasubstituted C-F centers through the organocatalytic Mannich reaction of α-fluoro cyclic ketones and α-amidosulfones using a chiral oligoEG as a cation binding catalyst with KF as a base. In most substrates, nearly perfect enantioselectivites were achieved even at very high temperatures (>80 ºC). The salient features of this process include (a) a transition metal free and operationally simple procedure, (b) direct use of α-amidosulfones as bench-stable precursors of sensitive imines, (c) direct enolization of racemic α-fluoro cyclic ketones and (d) excellent stereoselectivity up to 99% ee and >20:1 diastereoselectivity (anti:syn)...
December 6, 2016: Chemistry: a European Journal
https://www.readbyqxmd.com/read/27918635/nickel-catalyzed-co2-rearrangement-of-enol-metal-carbonates-for-the-efficient-synthesis-of-%C3%AE-ketocarboxylic-acids
#2
Ryo Ninokata, Tatsuya Yamahira, Gen Onodera, Masanari Kimura
4-Methylene-1,3-dioxolan-2-ones underwent oxidative addition of a Ni(0) catalyst in the presence of Me2 Al(OMe), followed by a coupling reaction with alkynes, to form δ,ϵ-unsaturated β-ketocarboxylic acids with high regio- and stereoselectivity. The reaction proceeds by [1,3] rearrangement of an enol metal carbonate intermediate and the formal reinsertion of CO2 .
December 5, 2016: Angewandte Chemie
https://www.readbyqxmd.com/read/27917069/stereochemical-control-of-enzymatic-carbon-carbon-bond-forming-michael-type-additions-by-substrate-engineering
#3
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/27911981/asymmetric-ketone-reduction-by-imine-reductases
#4
Maike Lenz, Jan Meisner, Leann Quertinmont, Stefan Lutz, Johannes Kästner, Bettina Nestl
The rapidly growing area of asymmetric imine reduction by imine reductases (IREDs) has provided alternative routes to chiral amines. Here we report the expansion of the reaction scope of IREDs by showing the stereoselective reduction of 2,2,2-trifluoroacetophenone (1). Assisted by an in silico analysis of energy barriers, we evaluated asymmetric hydrogenations of carbonyls and imines considering the influence of substrate reactivity on the chemoselectivity of this novel class of reductases. We report on the asymmetric reduction of C=N as well as C=O bonds catalyzed by members of the IRED enzyme family...
December 2, 2016: Chembiochem: a European Journal of Chemical Biology
https://www.readbyqxmd.com/read/27906488/total-synthesis-of-leupyrrins-a1-and-b1-highly-potent-antifungal-agents-from-the-myxobacterium-sorangium-cellulosum
#5
Sebastian Thiede, Paul R Wosniok, Daniel Herkommer, Thomas Debnar, Maoqun Tian, Tongtong Wang, Michael Schrempp, Dirk Menche
Full details on the design, elaboration and application of efficient strategies for the high-yielding total syntheses of leupyrrins A1 and B1, unique antifungal agents from the myxobacterium Sorangium cellulosum are reported. A sequential zirconocene-mediated diyne-cyclization and regioselective opening of the zirconacyclopentadiene intermediate enabled a concise entry into the unique dihydrofuran fragment, while another domino reaction was developed for the butyrolactone involving a one-pot lactol opening, stereoselective aldehyde addition and in situ-lactonization...
December 1, 2016: Chemistry: a European Journal
https://www.readbyqxmd.com/read/27905524/insights-into-the-competing-mechanisms-and-origin-of-enantioselectivity-for-n-heterocyclic-carbene-catalyzed-reaction-of-aldehyde-with-enamide
#6
Yan Qiao, Xinhuan Chen, Donghui Wei, Junbiao Chang
Hydroacylation reactions and aza-benzoin reactions have attracted considerable attention from experimental chemists. Recently, Wang et al. reported an interesting reaction of N-heterocyclic carbene (NHC)-catalyzed addition of aldehyde to enamide, in which both hydroacylation and aza-benzoin reactions may be involved. Thus, understanding the competing relationship between them is of great interest. Now, density functional theory (DFT) investigation was performed to elucidate this issue. Our results reveal that enamide can tautomerize to its imine isomer with the assistance of HCO3(-)...
December 1, 2016: Scientific Reports
https://www.readbyqxmd.com/read/27901144/a-highly-selective-synthesis-of-new-alkenylsilsesquioxanes-by-hydrosilylation-of-alkynes
#7
A Franczyk, K Stefanowska, M Dutkiewicz, D Frąckowiak, B Marciniec
Hydrosilylation of a wide group of mono- and disubstituted (symmetrical and nonsymmetrical) alkynes with 1-dimethylsiloxy-3,5,7,9,11,13,15-heptaisobutylpentacyclo-[9.5.1.1(3,9).1(5,15).1(7,13)]octasiloxane ((HSiMe2O)(i-Bu)7Si8O12, 1) in the presence of Karstedt's catalyst (Pt2(dvs)3) has been performed for the first time. A series of new 1,2-(E)-disubstituted and 1,1,2-(E)-trisubstituted ethenes with a silsesquioxane moiety were selectively afforded and fully characterized. On the basis of nuclear magnetic resonance (NMR) and infrared spectroscopy (in situ FT-IR and/or FT-IR), the influence of alkyne structure and reaction conditions on the stereoselectivity as well as on the progress of triple bond hydrosilylation catalyzed by Pt2(dvs)3 was explained...
November 30, 2016: Dalton Transactions: An International Journal of Inorganic Chemistry
https://www.readbyqxmd.com/read/27900780/vicinal-difluoroalkylation-and-aminosulfonylation-of-alkynes-under-photoinduced-conditions
#8
Yuanchao Xiang, Yuewen Li, Yunyan Kuang, Jie Wu
A photoinduced vicinal difluoroalkylation and aminosulfonylation of alkynes under photocatalysis is realized. The combination of ethyl 2-bromo-2,2-difluoroacetate, alkynes, DABCO*(SO2)2 with hydrazines catalyzed by 9-mes-10-methyl acridinium perchlorate in the presence of visible light affords (E)-ethyl 2,2-difluoro-4-aryl-4-sulfamoylbut-3-enoates in good yields with high stereoselectivity. This four-component reaction proceeds through radical addition with the insertion of sulfur dioxide.
November 29, 2016: Chemistry: a European Journal
https://www.readbyqxmd.com/read/27900690/a-microtiter-plate-based-assay-to-screen-for-active-and-stereoselective-hydrolytic-enzymes-in-enzyme-libraries
#9
Dominique Böttcher, Patrick Zägel, Marlen Schmidt, Uwe T Bornscheuer
A procedure for the high-throughput screening (HTS) of esterases is described. This includes a pretest for discrimination of active and inactive clones using an agar plate overlay assay, the enzyme expression in microtiter plates and the measurement of activity and enantioselectivity (E) of the esterase variants using acetates of secondary alcohols as model substrates. Acetic acid released is converted in an enzyme cascade leading to the stoichiometric formation of NADH, which is quantified in a spectrophotometer...
2017: Methods in Molecular Biology
https://www.readbyqxmd.com/read/27898188/modern-approaches-to-discovering-new-hydroxynitrile-lyases-for-biocatalysis
#10
REVIEW
Santosh Kumar Padhi
Hydroxynitrile lyases (HNLs) have grown in importance from laboratory to industry due to their potential to catalyze stereoselective C-C bond-formation reactions in the synthesis of several chiral intermediates, such as enantiopure α-cyanohydrins, β-nitro alcohols, and their derivatives with multiple functional groups. With these wide applications, the demand for finding new HNLs has increased, and this has led to exploration not only of new HNLs but also of new ways to discover them. An exclusive review article on HNLs by Asano et al...
November 29, 2016: Chembiochem: a European Journal of Chemical Biology
https://www.readbyqxmd.com/read/27897366/active-site-crowding-of-p450-3a4-as-a-strategy-to-alter-its-selectivity
#11
Paolo Schiavini, Kin J Cheong, Nicolas Moitessier, Karine Auclair
Substrate promiscuous enzymes are a promising starting point for the development of versatile biocatalysts. In this study, human cytochrome P450 3A4, known for its ability to metabolize hundreds of drugs, was engineered to alter its regio- and stereoselectivity. Rational mutagenesis was used to specifically introduce steric hindrance in the large active site of P450 3A4 and favour oxidation at a more sterically accessible position on the substrate. Hydroxylation of a synthetic precursor of (R)-lisofylline, a compound under investigation for its anti-inflammatory properties, was chosen as a first proof-of-principle application of our protein engineering strategy...
November 29, 2016: Chembiochem: a European Journal of Chemical Biology
https://www.readbyqxmd.com/read/27896351/on-chip-integration-of-organic-synthesis-and-hplc-ms-analysis-for-monitoring-stereoselective-transformations-at-the-micro-scale
#12
Josef J Heiland, Rico Warias, Carsten Lotter, Laura Mauritz, Patrick J W Fuchs, Stefan Ohla, Kirsten Zeitler, Detlev Belder
We present a microfluidic system, seamlessly integrating microflow and microbatch synthesis with a HPLC/nano-ESI-MS functionality on a single glass chip. The microfluidic approach allows to efficiently steer and dispense sample streams down to the nanoliter-range for studying reactions in quasi real-time. In a proof-of-concept study, the system was applied to explore amino-catalyzed reactions, including asymmetric iminium-catalyzed Friedel-Crafts alkylations in microflow and micro confined reaction vessels.
November 29, 2016: Lab on a Chip
https://www.readbyqxmd.com/read/27893812/solid-phase-synthesis-of-%C3%A9-lactone-and-1-2-oxazine-derivatives-and-their-efficient-chiral-analysis
#13
Sona Krupkova, Gonzalo Pazos Aguete, Leona Kocmanova, Tereza Volna, Martin Grepl, Lucie Novakova, Marvin John Miller, Jan Hlavac
Derivatives of 3-methyl-3,6-dihydro-2H-1,2-oxazine-6-carboxylic acid prepared by regioselective hetero Diels-Alder reaction of arylnitroso compounds with sorbic acid were used for solid-phase synthesis of a library of derivatives that included modification of carboxylic group, dihydroxylation of double bond and cleavage of N-O bond. Derivatives of 2,3,4-trihydroxyhexanoic acid obtained from 3,6-dihydro-2H-1,2-oxazines after double bond dihydroxylation and N-O cleavage were used for simple and stereoselective formation of chiral lactones derived from 3,4-dihydroxydihydrofuran-2(3H)-one...
2016: PloS One
https://www.readbyqxmd.com/read/27891825/iridium-catalyzed-stereoselective-allylic-alkylation-reactions-with-crotyl-chloride
#14
J Caleb Hethcox, Samantha E Shockley, Brian M Stoltz
The development of the first enantio-, diastereo-, and regioselective iridium-catalyzed allylic alkylation reaction of prochiral enolates to form an all-carbon quaternary stereogenic center with an aliphatic-substituted allylic electrophile is disclosed. The reaction proceeds with good to excellent selectivity with a range of substituted tetralone-derived nucleophiles furnishing products bearing a newly formed vicinal tertiary and all-carbon quaternary stereodyad. The utility of this protocol is further demonstrated via a number of synthetically diverse product transformations...
November 28, 2016: Angewandte Chemie
https://www.readbyqxmd.com/read/27885768/gram-scale-synthesis-of-chiral-cyclopropane-containing-drugs-and-drug-precursors-with-engineered-myoglobin-catalysts-featuring-complementary-stereoselectivity
#15
Priyanka Bajaj, Gopeekrishnan Sreenilayam, Vikas Tyagi, Rudi Fasan
Engineered hemoproteins have recently emerged as promising systems for promoting asymmetric cyclopropanations, but variants featuring predictable, complementary stereoselectivity in these reactions have remained elusive. In this study, a rationally driven strategy was implemented and applied to engineer myoglobin variants capable of providing access to 1-carboxy-2-aryl-cyclopropanes with high trans-(1R,2R) selectivity and catalytic activity. The stereoselectivity of these cyclopropanation biocatalysts complements that of trans-(1S,2S)-selective variants developed here and previously...
November 25, 2016: Angewandte Chemie
https://www.readbyqxmd.com/read/27883156/synthesis-of-the-biological-repeating-unit-of-streptococcus-pneumoniae-serotype-23f-capsular-polysaccharide
#16
Kang Yu, Yin Qiao, Guofeng Gu, Jian Gao, Shuihong Cai, Zhongzhu Long, Zhongwu Guo
An efficient synthesis of the 3-aminopropyl glycoside of the biological repeating unit of Streptococcus pneumoniae serotype 23F capsular polysaccharide (CPS) was accomplished. The synthetic target contained a tetrasaccharide with a phosphoglycerol branch. Its oligosaccharide backbone was assembled via linear glycosylation, and the challenging β-rhamnosyl linkage in its structure was achieved stereospecifically through naphthylmethyl-assisted intramolecular aglycon delivery (IAD). The remaining 1,2-trans glycosylation reactions were executed in excellent yields and stereoselectivity based on neighboring group participation...
November 24, 2016: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/27879680/stereoselective-alkane-oxidation-with-meta-chloroperoxybenzoic-acid-mcpba-catalyzed-by-organometallic-cobalt-complexes
#17
Georgiy B Shul'pin, Dmitriy A Loginov, Lidia S Shul'pina, Nikolay S Ikonnikov, Vladislav O Idrisov, Mikhail M Vinogradov, Sergey N Osipov, Yulia V Nelyubina, Polina M Tyubaeva
Cobalt pi-complexes, previously described in the literature and specially synthesized and characterized in this work, were used as catalysts in homogeneous oxidation of organic compounds with peroxides. These complexes contain pi-butadienyl and pi-cyclopentadienyl ligands: [(tetramethylcyclobutadiene)(benzene)cobalt] hexafluorophosphate, [(C₄Me₄)Co(C₆H₆)]PF₆ (1); diiodo(carbonyl)(pentamethylcyclopentadienyl)cobalt, Cp*Co(CO)I₂ (2); diiodo(carbonyl)(cyclopentadienyl)cobalt, CpCo(CO)I₂ (3); (tetramethylcyclobutadiene)(dicarbonyl)(iodo)cobalt, (C₄Me₄)Co(CO)₂I (4); [(tetramethylcyclobutadiene)(acetonitrile)(2,2'-bipyridyl)cobalt] hexafluorophosphate, [(C₄Me₄)Co(bipy)(MeCN)]PF₆ (5); bis[dicarbonyl(B-cyclohexylborole)]cobalt, [(C₄H₄BCy)Co(CO)₂]₂ (6); [(pentamethylcyclopentadienyl)(iodo)(1,10-phenanthroline)cobalt] hexafluorophosphate, [Cp*Co(phen)I]PF₆ (7); diiodo(cyclopentadienyl)cobalt, [CpCoI₂]₂ (8); [(cyclopentadienyl)(iodo)(2,2'-bipyridyl)cobalt] hexafluorophosphate, [CpCo(bipy)I]PF₆ (9); and [(pentamethylcyclopentadienyl)(iodo)(2,2'-bipyridyl)cobalt] hexafluorophosphate, [Cp*Co(bipy)I]PF₆ (10)...
November 22, 2016: Molecules: a Journal of Synthetic Chemistry and Natural Product Chemistry
https://www.readbyqxmd.com/read/27879039/stereoselective-carbonyl-olefination-with-fluorosulfoximines-facile-access-to-z-or-e-terminal-monofluoroalkenes
#18
Qinghe Liu, Xiao Shen, Chuanfa Ni, Jinbo Hu
Terminal monofluoroalkenes are important structural motifs in the design of bioactive compounds, such as homeostasis regulators and mechanism-based enzyme inhibitors. However, it is difficult to control the stereoselectivity of known carbonyl olefination reactions, and olefin metathesis is limited to disubstituted terminal monofluoroalkenes. Although sulfoximines have been used extensively in organic synthesis, reports on their use in carbonyl olefination reactions have not appeared to date. Herein, we report highly stereoselective carbonyl monofluoroolefination with a fluorosulfoximine reagent...
November 23, 2016: Angewandte Chemie
https://www.readbyqxmd.com/read/27879031/combining-organocatalysis-and-lanthanide-catalysis-a-sequential-one-pot-quadruple-reaction-sequence-hetero-diels-alder-asymmetric-synthesis-of-functionalized-tricycles
#19
Simon Dochain, Fabrizio Vetica, Rakesh Puttreddy, Kari Rissanen, Dieter Enders
A stereoselective one-pot synthesis of functionalized complex tricyclic polyethers has been achieved using the combination of secondary amine and lanthanide catalysis. This one-pot quadruple reaction/Hetero-Diels-Alder sequence gave good yields (per step) as well as excellent diastereo- and enantioselectivities. Furthermore, the particular combination of lanthanide complexes with organocatalysis is one of the first examples described for sequential catalysis.
November 23, 2016: Angewandte Chemie
https://www.readbyqxmd.com/read/27874143/total-synthesis-of-natural-derivatives-and-artificial-analogs-of-13-oxyingenol-and-their-biological-evaluation
#20
Takayuki Ohyoshi, Yuki Tamura, Ichiro Hayakawa, Go Hirai, Yamato Miyazawa, Shota Funakubo, Mikiko Sodeoka, Hideo Kigoshi
We have established an efficient synthetic methodology for the 13-oxyingenol natural derivative (13-oxyingenol-13-dodecanoate-20-hexanoate), featuring a ring-closing olefin metathesis reaction for the "direct" construction of a highly strained inside-outside framework and a Mislow-Evans-type [2,3]-sigmatropic rearrangement for the stereoselective introduction of the hydroxy group at C5. We also synthesized artificial analogs of 13-oxyingenol and ingenol by using our synthetic strategy. In vitro activation assays of protein kinase C (PKC) α and δ revealed that the dodecanoyl group at O13 on 13-oxyingenol analogs had a significant role in PKCδ activation...
November 22, 2016: Organic & Biomolecular Chemistry
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