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Organic & Biomolecular Chemistry

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https://www.readbyqxmd.com/read/30226509/synthesis-of-macrocyclic-precursors-of-the-vioprolides
#1
Eibhlin Butler, Lucia Florentino, Damien Cornut, Gonzalo Gomez-Campillos, Hao Liu, Andrew C Regan, Eric J Thomas
The vioprolides are novel depsipeptides that have not been synthesized. However, they have been identified as important targets for synthesis because of their novel biological activities and challenging chemical structures. Following early work on the synthesis of a modified tetrapeptide that contained both the (E)-dehydrobutyrine and thiazoline components of vioprolide D, problems were encountered in taking an (E)-dehydrobutyrine containing intermediate further into the synthesis. A second approach to vioprolides and analogues was therefore investigated in which (E)- and (Z)-dehydrobutyrines were to be introduced by selenoxide elimination very late in the synthesis...
September 18, 2018: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/30226258/robust-buchwald-hartwig-amination-enabled-by-ball-milling
#2
Qun Cao, William I Nicholson, Andrew C Jones, Duncan L Browne
An operationally simple mechanochemical method for the Pd catalysed Buchwald-Hartwig amination of arylhalides with secondary amines has been developed using a Pd PEPPSI catalyst system. The system is demonstrated on 30 substrates and applied in the context of a target synthesis. Furthermore, the performance of the reaction under aerobic conditions has been probed under traditional solution and mechanochemical conditions, the observations are discussed herein.
September 18, 2018: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/30226256/catalytic-enantioselective-one-pot-approach-to-cis-and-trans-2-3-diaryl-substituted-1-5-benzothiazepines
#3
Sara Meninno, Ilaria Quaratesi, Chiara Volpe, Andrea Mazzanti, Alessandra Lattanzi
The first enantioselective catalytic approach to cis- and trans-2,3-diaryl substituted 1,5-benzothiazepines has been conveniently developed in a one-pot fashion, starting from α,β-unsaturated acyl pyrazoles and 2-aminothiophenol. The organocatalytic two-step sulfa-Michael/lactamization sequence is promoted by a readily available bifunctional thiourea and p-toluenesulfonic acid, respectively. The protocol enables access to both N-unprotected cis- and trans-diastereoisomers in moderate to satisfactory overall yields (up to 84%) and good to excellent ee values (up to 99%)...
September 18, 2018: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/30226251/syntheses-of-the-plant-auxin-conjugate-2-o-indole-3-acetyl-myo-inositol-iainos
#4
Saúl Silva, Osvaldo S Ascenso, Eva C Lourenço, Margarida Archer, Christopher D Maycock, M Rita Ventura
The plant hormone conjugate 2-O-(indole-3-acetyl)-myo-inositol (IAInos) has been selectively prepared for the first time by two routes from myo-inositol. One of the syntheses depended upon the construction of the 3-indoleacetyl group by a Fischer indole synthesis on an unreactive axial hydroxyl group, while the other via a direct acylation of the equatorially orientated hydroxy group created by conformational constraint of the cyclohexane ring. The latter synthesis produced IAInos in 5 steps and 29% overall yield...
September 18, 2018: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/30225511/synthesis-of-difluoromethylated-enynes-by-the-reaction-of-%C3%AE-trifluoromethyl-styrenes-with-terminal-alkynes
#5
Mingsheng Wu, Xianghu Zhao, Yisen Liu, Song Cao
A novel and efficient method for the synthesis of difluoromethylated enynes by the reaction of α-(trifluoromethyl)styrenes with terminal alkynes with the assistance of NaOtBu was described. The mechanism of the reaction might involve the SN2' reaction of α-(trifluoromethyl)styrenes and a subsequent 1,3-H shift. Isomerization (E → Z) of 1-difluoromethyl-1,3-enynes in the presence of ZrCl4 was also developed.
September 18, 2018: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/30225506/synthesis-of-%C3%AE-amino-ketones-through-aminations-of-umpoled-enolates
#6
Xiaowen Xia, Bocheng Chen, Xiaojun Zeng, Bo Xu
An efficient synthesis of α-amino ketones is developed using the umpolung strategy. Umpoled enolates such as N-alkenoxypyridinium salts react smoothly with diverse amines to give α-amino ketones via an SN2' pathway. This umpolung strategy overcomes the drawbacks of traditional methods such as the need for prefunctionalized ketone derivatives. Our method also offers good chemical yields and high functional group tolerance.
September 18, 2018: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/30225495/dimericursones-a-and-b-two-unprecedented-hexacyclic-dimeric-diterpenoids-from-the-root-barks-of-jatropha-curcas
#7
Jie-Qing Liu, Ying Xu, Qin Xiao, Jin-Di Huang, Jun-Jie Ma, Chen-Lei Lian, Mei-Ying Huang, Zhen-Bo Du, Cui-Fang Wang
Dimericursones A and B (1 and 2), two unprecedented hexacyclic dimeric diterpenoids, were obtained from the root barks of Jatropha curcas. Their structures were elucidated by extensive spectroscopic analysis, electronic circular dichroism calculations, and single-crystal X-ray diffraction. Dimericursone B (2) showed significant inhibition on nitric oxide production of lipopolysaccharide-induced RAW264.7 macrophages with IC50 values of 5.65 μM.
September 18, 2018: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/30225481/glycodendron-rhenium-complexes-as-luminescent-probes-for-lectin-sensing
#8
Alessandro Palmioli, Monica Panigati, Anna Bernardi
The design, synthesis and characterization of novel glycoconjugate luminescent probes based on dinuclear rhenium(i) complexes are reported. A multivalent platform bearing different carbohydrate moieties (Glc, Gal and Man) was used to target carbohydrate-binding proteins (lectins), exploiting the unique photophysical characteristics of a Re(i) luminophore for protein sensing. Our results show that these glycoconjugates, non-luminescent in aqueous medium, are able to specifically bind different lectins (ConA and PNA) with a consequent enhancement of emission intensity...
September 18, 2018: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/30222171/recent-advances-in-homogeneous-borrowing-hydrogen-catalysis-using-earth-abundant-first-row-transition-metals
#9
REVIEW
Benjamin G Reed-Berendt, Kurt Polidano, Louis C Morrill
The review highlights the recent advances (2013-present) in the use of earth-abundant first row transition metals in homogeneous borrowing hydrogen catalysis. The utility of catalysts based on Mn, Fe, Co, Ni and Cu to promote a diverse array of important C-C and C-N bond forming reactions is described, including discussion on reaction mechanisms, scope and limitations, and future challenges in this burgeoning area of sustainable catalysis.
September 17, 2018: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/30221304/first-catalyst-free-co-2-trapping-of-n-acyliminium-ions-under-ambient-conditions-sustainable-multicomponent-synthesis-of-thia-and-oxazolidinyl-carbamates
#10
Max Franz, Timo Stalling, Henning Steinert, Jürgen Martens
The first trapping of N-acyliminium ions by in situ generated carbaminic acid (product of carbon dioxide (CO2) and amine) is reported. This catalyst-free reaction provides a convenient and feasible approach to prepare N-acyl thia- and oxazolidinyl carbamates with good functional-group compatibility and high efficiency under green conditions. Furthermore, the multicomponent method features a broad substrate scope, facile product diversification, smooth scale-up and notable potential for polymer applications.
September 17, 2018: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/30221279/xylopsides-a-d-four-rare-guaiane-dimers-with-two-unique-bridged-pentacyclic-skeletons-from-xylopia-vielana
#11
Yang-Guo Xie, Yi-Gong Guo, Guo-Jing Wu, Sheng-Lan Zhu, Tao-Fang Cheng, Yu Zhang, Shi-Kai Yan, Hui-Zi Jin, Wei-Dong Zhang
Four unprecedented guaiane dimers, xylopsides A-D (1-4), were isolated and identified from the roots of Xylopia vielana. The structures of 1-4 were elucidated by spectroscopic analysis, Cu Kα X-ray crystallography and CD spectra. 1-4 showed two bridged pentacyclic skeletons between two guaiane-type sesquiterpenes, which were characterized as two different bridged ring systems. Among these compounds, 4 exhibited a moderate inhibitory activity against the production of nitric oxide with an IC50 value of 25.7 μM in RAW264...
September 17, 2018: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/30215653/cyclic-arylopeptoid-oligomers-synthesis-and-conformational-propensities-of-peptide-mimetic-aromatic-macrocycles
#12
Masahide Hayakawa, Ayaka Ohsawa, Kumi Takeda, Ryo Torii, Yoshiaki Kitamura, Hiroshi Katagiri, Masato Ikeda
Macrocyclic peptide-mimetic molecules are attracting renewed attention and have found widespread application in research fields ranging from biochemical science to materials science. Herein, we describe the synthesis and structural elucidation of cyclo[n]-p-arylopeptoids (classified into cyclic aromatic ε-amino acids) bearing various side chains, namely, C[n]pAP(Rn) (where n inside brackets denotes the number of main chain units and R inside parentheses represents side chains). We investigate the influence of n and R on the macrocyclization efficiency of linear p-arylopeptoid oligomers (n = 3, 4, 5) under high-dilution conditions with or without slow addition...
September 14, 2018: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/30215652/copper-catalyzed-synthesis-of-2-aminophenyl-benzothiazoles-a-novel-approach
#13
S N Murthy Boddapati, Chandra Mohan Kurmarayuni, Baby Ramana Mutchu, Ramana Tamminana, Hari Babu Bollikolla
A novel, convenient and efficient protocol for the construction of various 2-aminophenyl benzothiazoles by domino intra- and intermolecular C-N cross-coupling reactions of arylisothioureas with aryl iodides using an inexpensive, air stable and readily available copper catalyst is described. The arylisothioureas were obtained from thiourea via copper promoted desulfurization followed by nucleophilic substitution. In addition, the reactivity of arylhalides and the reaction mechanism have also been studied. The protocol features operational simplicity and a broad substrate scope...
September 14, 2018: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/30215651/organocatalytic-asymmetric-michael-hemiketalization-acyl-transfer-reaction-of-1-3-propanediones-with-e-2-2-nitrovinyl-phenols
#14
Nimisha Bania, Subhas Chandra Pan
An organocatalytic asymmetric cascade Michael/hemiketalization/acyl transfer reaction between (E)-2-(2-nitrovinyl)phenols and 1,3-propanediones is disclosed. A cinchona alkaloid derived bifunctional thiourea catalyst was found to be the most effective for this reaction and provided the desired products in moderate to good yields with good to high enantioselectivities.
September 14, 2018: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/30215086/molecular-iodine-mediated-synthesis-of-thiocarbamates-from-thiols-isocyanides-and-water-under-metal-free-conditions
#15
Wen-Hu Bao, Chao Wu, Jing-Ting Wang, Wen Xia, Ping Chen, Zilong Tang, Xinhua Xu, Wei-Min He
A simple and practical molecular iodine-mediated method for the efficient construction of thiocarbamates from isocyanides, thiols and water under metal-free and mild conditions has been developed. A variety of thiocarbamates were easily synthesized through this methodology, which has the advantages of simple operation, eco-friendly conditions, good functional group tolerance, and readily accessible raw materials.
September 14, 2018: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/30209510/rhodium-catalyzed-cyclization-of-acceptor-substituted-biphenyl-%C3%AE-diazoketones-a-study-of-the-substitution-effect-on-chemoselectivity
#16
Kuo-Hsin Chen, Yi-Jung Chiang, Jia-Liang Zhu
A range of biphenyl α-diazoketones containing various electron-withdrawing groups (EWG = COCH3, CN, CO2Et, COPh, SO2CH3, SO2Ph) on diazo carbon has been investigated for rhodium(ii)-catalyzed intramolecular cyclization. Among which, the α-acetyl, carboxylate and cyano substituted substrates show markedly different selectivity between aromatic substitution and aromatic cycloaddition processes, affording phenanthrol and/or benz[α]azulenone products in varying ratios. The selectivity is mainly directed by α-substitutions, and is also possibly influenced by the substituents on the biphenyl ring...
September 13, 2018: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/30209506/the-4-2-cyclization-retro-mannich-reaction-cascade-of-para-quinone-methide-derivatives-with-pd-containing-1-4-dipoles
#17
Xiao-Li Jiang, Shu-Fang Wu, Jin-Rong Wang, Han Lu, Guang-Jian Mei, Feng Shi
The first [4 + 2] cyclization/retro-Mannich reaction cascade of para-quinone methides with Pd-containing 1,4-dipoles generated in situ from vinyl benzoxazinanones has been established. The corresponding rearrangement products were obtained in generally good to excellent yields (up to 92% yield). This reaction represents the first example of C[double bond, length as m-dash]C double bond cleavage of para-quinone methides, which will greatly enrich the chemistry of quinone methides.
September 13, 2018: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/30209503/cobalt-catalyzed-cyclization-of-benzamides-with-alkynes-a-facile-route-to-isoquinolones-with-hydrogen-evolution
#18
Ramasamy Manoharan, Masilamani Jeganmohan
The reaction of benzamides with alkynes assisted by an 8-aminoquinoline ligand in the presence of Co(OAc)2·4H2O and pivalic acid under an air atmosphere provided isoquinolone derivatives in good to excellent yields. In this reaction, the active Co(iii) species is regenerated by the reaction of Co(i) species with pivalic acid under an air atmosphere with hydrogen evolution. The proposed mechanism was supported by competition experiments, deuterium labelling studies, radical scavenger experiments and kinetic studies...
September 13, 2018: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/30209495/highly-regioselective-%C3%AE-alkylation-of-%C3%AE-%C3%AE-%C3%AE-%C3%AE-unsaturated-aldehydes
#19
Venkata M D Padmaja, Sachin Jangra, Chandrakumar Appayee
The first α-alkylation of α,β,γ,δ-unsaturated aldehydes is achieved under mild reaction conditions. Several α,β,γ,δ-unsaturated aldehydes and diarylcarbinols are successfully tested for the synthesis of MBH-type α-alkylated products with an excellent regioselectivity. Simple pyrrolidine is efficiently used as a catalyst to achieve a perfect E/Z selectivity of the α-alkylated products.
September 13, 2018: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/30209482/tert-butyl-nitrite-mediated-nitrogen-transfer-reactions-synthesis-of-benzotriazoles-and-azides-at-room-temperature
#20
Sadaf Azeez, Priyanka Chaudhary, Popuri Sureshbabu, Shahulhameed Sabiah, Jeyakumar Kandasamy
A conversion of o-phenylenediamines into benzotriazoles was achieved at room temperature using tert-butyl nitrite. The optimized conditions are also well suited for the transformation of sulfonyl and acyl hydrazines into corresponding azides. This protocol does not require any catalyst or acidic medium. The desired products were obtained in excellent yields in a short span of time.
September 13, 2018: Organic & Biomolecular Chemistry
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