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Organic & Biomolecular Chemistry

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https://www.readbyqxmd.com/read/28650499/silver-catalyzed-3-2-domino-reaction-an-efficient-strategy-to-synthesize-imidazole-5-carbaldehydes
#1
Changcheng Wang, Hangqi Jiang, Weifeng Chen, Jun Dong, Zhengwang Chen, Hua Cao
An unprecedented regioselective silver-catalyzed [3 + 2] domino reaction of amidines and ynals for the formation of C-N bonds has been developed. The reaction provided a new route to prepare imidazole-5-carbaldehydes which are important intermediates for the construction of fine chemicals. The reaction proceeds smoothly with a broad range of substrates to give imidazoles in good yields.
June 26, 2017: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/28650492/exploiting-the-biosynthetic-machinery-of-streptomyces-pilosus-to-engineer-a-water-soluble-zirconium-iv-chelator
#2
Tomas Richardson-Sanchez, William Tieu, Michael P Gotsbacher, Thomas J Telfer, Rachel Codd
The water solubility of a natural product-inspired octadentate hydroxamic acid chelator designed to coordinate Zr(iv)-89 has been improved by using a combined microbiological-chemical approach to engineer four ether oxygen atoms into the main-chain region of a methylene-containing analogue. First, an analogue of the trimeric hydroxamic acid desferrioxamine B (DFOB) that contained three main-chain ether oxygen atoms (DFOB-O3) was generated from cultures of the native DFOB-producer Streptomyces pilosus supplemented with oxybis(ethanamine) (OBEA), which competed against the native 1,5-diaminopentane (DP) substrate during DFOB assembly...
June 26, 2017: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/28650489/1-2-arylalkylation-of-n-arylsulfonyl-acrylamides-using-aliphatic-aldehydes-as-the-alkyl-source
#3
Jin-Tao Yu, Rongzhen Chen, Jiawei Zhu, Jiang Cheng
A metal-free decarbonylative arylalkylation of N-(arylsulfonyl)acrylamides using aliphatic aldehydes as the alkyl radical source was developed, providing a series of α-aryl-β-alkylamides in moderate to good yields. In this reaction, concomitant alkylation, aryl migration and desulfonylation were involved.
June 26, 2017: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/28650044/one-pot-asymmetric-synthesis-of-a-spiro-dihydrofurocoumarin-pyrazolone-scaffold-by-a-michael-addition-i2-mediated-cyclization-sequence
#4
Ai-Bao Xia, Xiao-Long Zhang, Cheng-Ke Tang, Kai-Xiang Feng, Xiao-Hua Du, Dan-Qian Xu
An asymmetric formal one-pot reaction of 4-hydroxycoumarins with unsaturated pyrazolones has been developed by merging a chiral bifunctional organocatalyst with molecular iodine, which furnished a series of optically active spiro[dihydrofurocoumarin/pyrazolone] heterocycles with spiro quaternary stereogenic centers in moderate to excellent yields (up to 99%) with excellent diastereoselectivities (up to >99 : 1 dr) and good to excellent enantioselectivities (up to 99% ee). The application in the gram-scale synthesis of chiral spiro[dihydrofurocoumarin/pyrazolone] compounds was also successfully realized...
June 26, 2017: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/28649690/enzymatic-conjugation-using-branched-linkers-for-constructing-homogeneous-antibody-drug-conjugates-with-high-potency
#5
Yasuaki Anami, Wei Xiong, Xun Gui, Mi Deng, Cheng Cheng Zhang, Ningyan Zhang, Zhiqiang An, Kyoji Tsuchikama
Antibody-drug conjugates (ADCs) are emerging therapeutic agents in the treatment of cancer, and various conjugation strategies and chemical linkers have been developed to efficiently construct ADCs. Despite previous extensive efforts for improving conjugation efficiency and ADC homogeneity, most ADC linkers developed to date load only single payloads. Branched linkers that can load multiple payload molecules have yet to be fully explored. It is logical to envisage that a multi-loading strategy allows for increase in drug-to-antibody ratio (DAR) with less chemical or enzymatic modification to the antibody structure compared to traditional linear linkers, leading to efficient ADC construction, minimal destabilization of the antibody structure, and enhanced ADC efficacy...
June 26, 2017: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/28649682/rhodium-catalyzed-redox-neutral-coupling-of-phenidones-with-alkynes
#6
Zhoulong Fan, Heng Lu, Wei Li, Kaijun Geng, Ao Zhang
A switchable synthesis of N-substituted indole derivatives from phenidones via rhodium-catalyzed redox-neutral C-H activation has been achieved. In this protocol, we firstly disclosed that the reactivity of Rh(iii) catalysis could be enhanced through employing palladium acetate as an additive. Some representative features include external oxidant-free, applicable to terminal alkynes, short reaction time and operational simplicity. The utility of this method is further showcased by the economical synthesis of potent anticancer PARP-1 inhibitors...
June 26, 2017: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/28649680/enzymatic-competition-and-cooperation-branch-the-caerulomycin-biosynthetic-pathway-toward-different-2-2-bipyridine-members
#7
Ming Chen, Yipeng Zhang, Yanan Du, Qunfei Zhao, Qinglin Zhang, Jiequn Wu, Wen Liu
In this study, we characterized CaeB6 as a selective hydroxylase and CaeG1 as an O-methyltransferase in the biosynthesis of the 2,2'-bipyridine natural products caerulomycins (CAEs). The C3-hydroxylation activity of CaeB6 competes with the C4-O-methylation activity of CaeG1 and thereby branches the CAE pathway from a common C4-O-demethylated 2,2'-bipyridine intermediate. CaeG1-catalyzed C4-O-methylation leads to a main route that produces the major product CAE-A in Actinoalloteichus cyanogriseus NRRL B-2194...
June 26, 2017: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/28640318/k2co3-catalyzed-regioselective-synthesis-of-thieno-2-3-b-thiochromen-4-one-oximes-access-to-the-corresponding-amine-and-nitroso-derivatives
#8
Karuna Mahato, Prasanta Ray Bagdi, Abu T Khan
An unprecedented and efficient method for the synthesis of useful thieno[2,3-b]thiochromen-4-one oximes is accomplished via a thio[3 + 2] cyclization reaction of 4-hydroxydithiocoumarins and trans-β-nitrostyrenes in the presence of 10 mol% K2CO3 in ethanol under reflux conditions. Furthermore, hitherto, these precursors were converted into the corresponding 2-amino thieno[2,3-b]thiochromen-4-one and 2-nitroso thieno[2,3-b]thiochromen-4-one derivatives respectively. The salient features of the present protocol are mild reaction conditions, shorter reaction times, good yields and unexpected formation of C-C and C-S bonds in a regioselective manner...
June 22, 2017: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/28639676/diastereoselective-3-2-cycloaddition-of-3-ylideneoxindoles-with-in-situ-generated-cf2hchn2-syntheses-of-cf2h-containing-spirooxindoles
#9
Wen-Yong Han, Jia Zhao, Jian-Shu Wang, Guang-Yan Xiang, Ding-Lei Zhang, Mei Bai, Bao-Dong Cui, Nan-Wei Wan, Yong-Zheng Chen
An efficient [3 + 2] cycloaddition of 3-ylideneoxindoles with in situ generated CF2HCHN2 for the syntheses of spirooxindoles has been developed. This methodology gives access to a range of relatively complex spirooxindoles featuring a CF2H group and three contiguous stereogenic centers in up to 84% yield and 99 : 1 trans/cis.
June 22, 2017: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/28639674/transition-from-disordered-aggregates-to-ordered-lattices-kinetic-control-of-the-assembly-of-a-computationally-designed-peptide
#10
Yu Tian, Huixi Violet Zhang, Kristi L Kiick, Jeffery G Saven, Darrin J Pochan
Natural biomolecular self-assembly typically occurs under a narrow range of solution conditions, and the design of sequences that can form prescribed structures under a range of such conditions would be valuable in the bottom-up assembly of predetermined nanostructures. We present a computationally designed peptide that robustly self-assembles into regular arrays under a wide range of solution pH and temperature conditions. Controling the solution conditions provides the opportunity to exploit a simple and reproducible approach for altering the pathway of peptide solution self-assembly...
June 22, 2017: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/28639665/isolation-and-identification-of-l-d-lactate-conjugated-bufadienolides-from-toad-eggs-revealing-lactate-racemization-in-amphibians
#11
Shiwen Zhou, Qingfei Zheng, Xiuyong Huang, Yong Wang, Sifan Luo, Renwang Jiang, Lei Wang, Wencai Ye, Haiyan Tian
Three pairs of bufadienolide l/d-lactate epimers (1-6) were isolated from the eggs of the toad Bufo bufo gargarizans. The structures were elucidated by using spectroscopic methods, X-ray diffraction analysis and a modified Mosher's method. Compounds 1-6 represent the first occurrence of lactate-conjugated bufadienolides in nature, and illustrate the existence of an enzyme-controlled epimerization from l- to d-lactate in amphibians. The biosynthetic pathways, in which two key enzymes might be involved (i.e., lactate racemase and acyltransferase), were proposed...
June 22, 2017: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/28639662/recent-progress-in-the-catalytic-carbene-insertion-reactions-into-the-silicon-hydrogen-bond
#12
REVIEW
Hoda Keipour, Virginie Carreras, Thierry Ollevier
The following review will explore the historical development of Si-H bond insertion reactions, giving an up-to-date account on the metal catalysts often employed, in addition to an assessment of their strengths and weaknesses. Diazo compounds have great synthetic potential as versatile reagents for the formation of metal carbenes, allowing the selective formation of C-C and C-heteroatom bonds and thus the introduction of functional groups into organic molecules. C-Si bond-forming methods, that introduce silicon motifs into organic molecules, rely on catalysts derived from metals such as rhodium, copper, iridium, silver, ruthenium, and iron to achieve the desired activities and selectivities...
June 22, 2017: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/28639657/exploring-the-catalytic-mechanism-of-dihydropteroate-synthase-elucidating-the-differences-between-the-substrate-and-inhibitor
#13
Warot Chotpatiwetchkul, Kanokthip Boonyarattanakalin, Duangkamol Gleeson, M Paul Gleeson
Dihydropteroate synthase (DHPS) catalyzes the condensation of 6-hydroxymethyl-7,8-dihydropterin pyrophosphate (DHPPP) with p-aminobenzoic acid (pABA) and is a well validated target for anti-malarial and anti-bacterial drugs. However, in recent years its utility as a therapeutic target has diminished considerably due to multiple mutations. As such, considerable structural biology and medicinal chemistry effort has been expended to understand and overcome this issue. To date no detailed computational analysis of the protein mechanism has been made despite the detailed crystal structures and multiple mechanistic proposals being made...
June 22, 2017: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/28639654/fast-easy-preparation-of-3d-scaffolds-from-methyl-benzoate-by-a-diversity-oriented-synthesis-strategy-based-on-diels-alder-and-ene-reactions
#14
Dominique Brossard, Pascal Retailleau, Vincent Dumontet, Philippe Breton, Sandy Desrat, Fanny Roussi
Thermic dimerization of methyl 1,3-cyclohexadiene 2-carboxylate gave original 3D-shape compounds by Diels-Alder cycloaddition and original [6 + 4]-ene reaction. Further selective modifications on an endo [4 + 2] cycloadduct via a diversity oriented synthesis (DOS) strategy quickly led to the preparation of a small library of original 3D scaffolds, providing access to a larger and unexplored chemical space for drug discovery processes.
June 22, 2017: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/28639651/ru-catalyzed-highly-diastereoselective-hydrogenation-of-n-tert-butylsulfinyl-ketimines-for-the-synthesis-of-aryl-glycine-derivatives
#15
Qiaoling Wei, Feng Zhang, Xiaofang Zhao, Chao Wang, Jianliang Xiao, Weijun Tang
A ruthenium pincer catalyst has been shown to be highly efficient for the hydrogenation of a wide range of α-ketimino esters derived from α-keto esters and chiral 2-methylpropyl-2-sulfinamide, affording chiral aryl glycine derivatives with high yields and diasteroselectivities (20 examples, dr values up to 99 : 1).
June 22, 2017: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/28639643/palladium-catalyzed-c-h-alkylation-of-2-phenylpyridines-with-alkyl-iodides
#16
Xiaoling Wang, Xiaoming Ji, Changdong Shao, Yu Zhang, Yanghui Zhang
Palladium-catalyzed C-H alkylation reaction of 2-phenylpyridines with alkyl iodides has been successfully developed. The palladacycles obtained from 2-phenylpyridines should act as the key intermediates in the alkylation reaction.
June 22, 2017: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/28639642/cleavage-of-ethers-in-an-ionic-liquid-enhancement-selectivity-and-potential-application
#17
William E S Hart, Leigh Aldous, Jason B Harper
The cleavage of a series of ethers was examined in an ionic liquid containing hydrogen bromide. Reactions that did not proceed in either water or DMSO were found to proceed readily in this system, with notable selectivity between the cleavage of the different ether types examined herein. Increasing the proportion of water in the reaction mixture dramatically decreased the rate constant of ether cleavage; this could, in part, be attributed to a decrease in the solvent stabilisation of the transition state. Through analysis of the electronic requirements of the reaction (using substrates containing substituents with different Hammett parameters) and observation of rate enhancements for an ortho substituted system, the importance of the extent of protonation of the ether prior to nucleophilic attack was demonstrated...
June 22, 2017: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/28639641/incorporation-of-click-chemistry-glycomimetics-dramatically-alters-triple-helix-stability-in-an-adiponectin-model-peptide
#18
Katherine R Lutteroth, Paul W R Harris, Tom H Wright, Harveen Kaur, Kevin Sparrow, Sung-Hyun Yang, Garth J S Cooper, Margaret A Brimble
Adiponectin (Adpn) has been shown to be a possible therapeutic for Type II diabetes, however the production of a therapeutic version of Adpn has proved to be challenging. Biological studies have highlighted the importance of the glycosylated lysine residues for the formation of bioactive high molecular weight oligomers of Adpn. Through the use of 'click' glycopeptide mimetics, we investigated the role of glycosylated lysine and serine residues for the formation of triple helical structures of the collagenous domain of Adpn, in the context of a collagen model peptide scaffold...
June 22, 2017: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/28639639/a-coherent-study-on-the-z-enoate-assisted-meyer-schuster-rearrangement
#19
Prabhakararao Tharra, Beeraiah Baire
A systematic study has been performed on the Z-enoate assisted Meyer-Schuster rearrangement of propargylic alcohols. The impact of various factors such as temperature, solvent, concentration of a counter ion of an acid, and the nature of the arene nucleophile was studied. The relative nucleophilicity of various arenes estimated in this study is in good agreement with that of Herbert Mayr's nucleophilicity scale.
June 22, 2017: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/28639634/copper-ii-catalyzed-iodine-promoted-oxidative-cyclization-of-2-amino-1-3-5-triazines-and-chalcones-synthesis-of-aroylimidazo-1-2-a-1-3-5-triazines
#20
Jin Jing Li, Chan Song, Dong-Mei Cui, Chen Zhang
An efficient copper(ii) catalyzed iodine-promoted synthesis of aroylimidazo[1,2-a][1,3,5]triazines from 2-amino-1,3,5-triazines and chalcones under mild conditions has been developed. The reaction occurred with good yields and excellent regioselectivities, and tolerated chalcone containing functionalities such as ethers, halogens, and nitro groups. The successful application of this methodology for a gram-scale reaction indicates its potential for bulk synthesis.
June 22, 2017: Organic & Biomolecular Chemistry
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